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BUMPUS IN THE SNAKE DEN: EFFECTS OF SEX, SIZE, AND BODY CONDITION ON MORTALITY OF RED‐SIDED GARTER SNAKES
Abstract
Abstract Huge breeding aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) at overwintering dens in Manitoba provide a unique opportunity to identify sources of mortality and to clarify factors that influence a snake's vulnerability to these factors. Comparisons of sexes, body sizes, and body condition of more than 1000 dead snakes versus live animals sampled at the same time reveal significant biases. Three primary sources of mortality were identified. Predation by crows, Corvus brachyrhynchos (590 snakes killed), was focussed mostly on small snakes of both sexes. Crows generally removed the snake's liver and left the carcass, but very small snakes were sometimes brought back to the nest. Suffocation beneath massive piles of other snakes within the den (301 dead animals) involved mostly small males and (to a lesser extent) large females; snakes in poor body condition were particularly vulnerable. Many emaciated snakes (in= 142, mostly females) also died without overt injuries, probably due to depleted energy reserves. These biases in vulnerability are readily interpretable from information on behavioral ecology of the snakes. For example, sex biases in mortality reflect differences in postemergence behavior and locomotor capacity, the greater attractiveness of larger females to males, and the high energy costs of reproduction for females.
... These waves push anoxic air from the female's avascular lung anteriorly to her respiratory surfaces, thus impeding breathing and inducing the stress response of cloacal gaping and thereby allowing intromission of the male's hemipenis (Shine et al. 2003a). Thus, males obtain matings by forcible insemination via induction of hypoxic stress in females (Shine et al. 2003a); indeed, some females die from suffocation within large mating balls (Shine et al. 2001a). However, sexual conflict is less intense as soon as the females disperse into the woodland surrounding the den. ...
... Rapid dispersal from the den may enhance female fitness via multiple pathways. For example, it reduces the female's vulnerability to crow predation (which is concentrated near the den; Shine et al. 2001a; R. Shine, personal observation) and provides more time for the female to feed on her summer range prior to reproduction. Food is scarce near the dens but abundant in the surrounding woodland: snakes begin to feed almost as soon as they begin dispersing (O'Donnell et al. 2004). ...
... Food is scarce near the dens but abundant in the surrounding woodland: snakes begin to feed almost as soon as they begin dispersing (O'Donnell et al. 2004). Lastly, sexual conflict imposes costs per se: females that remain near the den risk injury or death if they are trapped beneath piles of vigorously courting males (Shine et al. 2001a). ...
Females of many species behave in ways that make it difficult for males to locate, court, and inseminate them. Two hypotheses have been advanced to explain such behavior: either a female thereby minimizes costs of harassment (sexual conflict model) or by playing “hard to get” she discourages inferior suitors (indirect mate choice model). Our studies of garter snakes (Thamnophis sirtalis parietalis) at a communal den in Manitoba support an interpretation of sexual conflict rather than indirect mate choice. Female snakes dispersed rapidly from the den through areas with relatively few males rather than waiting for additional courtship. Many females dispersed without mating. Experimental (pheromonal) manipulation of the intensity of courtship accelerated rates of female dispersal rather than delaying dispersal, as would be predicted if females wait to obtain matings. The behaviors of females escaping from courting groups were maximally effective in losing their suitors regardless of the number of courting males or whether or not the female was capable of mating (recently mated females cannot mate again because of a mating plug). In total, our data are most consistent with the hypothesis that female garter snakes at communal dens evade males to escape harassment rather than to enhance mate quality.
... His data are often cited as an example of both directional and stabilizing selection (Buttemer 1992;Pugesek and Tomer 1996;Janzen and Stern 1998). A few researchers have been as fortunate as Bumpus to witness viability selection in action (Grant and Grant 1993;Brown and Brown 1998;Nolan et al. 1998;Brown and Brown 1999;Shine et al. 2001), but catastrophic events are rare. For many taxa, it is extremely unusual to recover large numbers of dead individuals. ...
... Sixty-six percent of birds examined showed signs of hemorrhage in either the gastrointestinal tract or major organs (Table 1), a finding consistent with the action of an infectious agent (Samour 2000), suggesting death by enteritis. Prior work supporting this conclusion comes from a geographically adjacent population in which enteritis was documented as a cause of death in western bluebirds (Thompson-Cowley et al. 1979;Bildfell et al. 2001). ...
... Second, the finding that 66% of birds necropsied suffered internal bleeding without external trauma (i.e. impact) strongly suggested that illness was responsible (Samour 2000). ...
Hypothesis: Variation in ornamental traits, such as plumage coloration, is maintained by the opposing forces of sexual selection (increased ornamentation) and natural selection (decreased ornamentation). Organisms: A wild population of western bluebirds (Sialia mexicana) in northwestern Oregon which has been the subject of longitudinal population studies since 1988. Methods: We necropsied 47 adult birds recovered dead in 2002. We measured their plumage coloration with an Ocean Optics S2000 reflectance spectrophotometer. Using Mann-Whitney U-tests with Bonferroni correction, we compared these data to measurements collected from 43 adults recaptured alive. Results: Necropsies suggested that birds died of an epidemic during 2002. Dead females did not differ from survivors in morphology or plumage. Dead males were significantly more highly ornamented (darker, redder breast patch) than males that survived the epidemic.
... Smaller snakes may be more at risk, because they are slower than adults 25 and are ingestible by a wider range of gape-limited predators 26 . In terrestrial snakes, predators sometimes target smaller individuals 27 . Consistent with the hypothesis that small body size increases the vulnerability of a sea snake, the offspring of most marine snakes are larger than those of terrestrial snakes because (a) offspring size increases with mean adult body size, and adult sea snakes are larger than most terrestrial species 28 ; and (b) the offspring of marine snakes are larger relative to adult body size 29 . ...
... Although thermal factors have often been implicated as critical determinants of viability for terrestrial snakes 12,27 , temperatures are buffered by the ocean at our study sites, and vary less from one year to the next than between winter and summer in any given year (annual means 27°C in summer; 23°C in winter; also see 30 ). Our preliminary analyses revealed no significant effects of annual thermal variation on snake population densities or other parameters. ...
For sea snakes as for many types of animals, long-term studies on population biology are rare and hence, we do not understand the degree to which annual variation in population sizes is driven by density-dependent regulation versus by stochastic abiotic factors. We monitored three populations of turtle-headed sea snakes ( Emydocephalus annulatus ) in New Caledonia over an 18-year period. Annual recruitment (% change in numbers) showed negative density-dependence: that is, recruitment increased when population densities were low, and decreased when densities were high. Windy weather during winter increased survival of neonates, perhaps by shielding them from predation; but those same weather conditions reduced body condition and the reproductive output of adult snakes. The role for density-dependence in annual dynamics of these populations is consistent with the slow, K-selected life-history attributes of the species; and the influence of weather conditions on reproductive output suggests that females adjust their allocation to reproduction based on food availability during vitellogenesis.
... However, there are many examples of (temporary) aggregated living in squamates. Most common are group formations in hibernacula or in nocturnal or diurnal retreat sites, aggregations of basking individuals, and gatherings for egg-laying [e.g., (Wikelski 1994;Graves and Duvall 1995;Shine et al. 2001;Shah et al. 2003;Mouton 2011;Rabosky et al. 2012;Doody et al. 2013)]. These are most often transient associations restricted to certain phases of the life cycle and are typically formed when the conditions that are suitable or required for a particular activity are spatially limited and thereby attract numerous animals (Graves and Duvall 1995;Mouton 2011;Gardner et al. 2016). ...
... A first possibility is that predators can be deterred by the sighting of two or more intertwined basking snakes (Graves and Duvall 1995). However, it may also be argued that aggregations can actually attract predators (Shine et al. 2001). Specifically, basking of both solitary and aggregated adders increases their visibility toward human predators (Bauwens and Claus 2019b). ...
Snakes live a predominantly solitary and secretive life, and are most often considered to be “non-social”. We here provide quantitative information on the occurrence of basking aggregations, i.e., gatherings of two or more adders having clear physical contact with each other, in the adder (Vipera berus). Overall, approximately 1 out of 10 observed adders was seen in groups that consisted predominantly of two individuals and rarely of 3 up to 7 adders. The incidence of aggregations was higher in the adults than in the younger age classes, and in the adult males than in the adult females. Males and especially females were found much more than expected in single-sex clusters, whereas male–female groups were seen much less frequently. Aggregations of adult males were seen almost exclusively during early spring, and groups with only adult females were mainly noticed during mid-summer. For both sexes, aggregated adders were seen most often during periods when the observation frequency of solitary adders was also highest. Hence, the seasonal variation of adder groupings is not induced by varying levels of the tendency to actively associate with conspecifics. There were no indications that adders actively aggregate in large groups and individual snakes did not exhibit a stronger tendency toward gregariousness than others. Overall, our analyses indicate that the observed aggregations are mainly non-social, but rather reflect the tendency of individual adders to simultaneously select scarce thermally suitable microhabitats.
... Male traits that facilitate coercive matings have the potential to harm females [4]. Indeed, male-induced injury has been documented in a wide range of taxa, including mammals [4,47], birds [49], reptiles [35,50,51], insects [29,30,34,37,38] and molluscs [31,52]. Harmful coercion also occurs in sexual cannibals, but is rare. ...
... While the damage incurred by females was quite severe, including substantial haemolymph loss and scar tissue formation, injury was not a universal outcome. This contrasts with the high prevalence of adaptive harm by spiked genitalia in seed beetles [53], but is similar to the sporadic incidence of non-adaptive harm observed in other taxa [39,40,51]. This suggests that injury is not the primary function of males' fore-tibial claws but a negative pleiotropic side-effect [1,40] of coercive mating behaviour and foraging morphology, although future work on the economics of harm will be necessary to confirm this. ...
Sexual conflict can generate coercive traits in males that enhance mating success at the expense of female fitness. Pre-copulatory sexual cannibalism—where females consume males without mating—typically favours cautious rather than coercive mating tactics, and few examples of the latter are known. Here, we show that males of the highly cannibalistic springbok mantis, Miomantis caffra , wrestle females during pre-mating interactions. We find that most initial contacts between males and females involve a violent struggle whereby each sex tries be the first to grasp hold of the other with their raptorial forelegs. When females win the struggle, they always cannibalize males. However, when males grasp females first, they dramatically increase the chance of mating. We also find striking evidence that, on some occasions, males wound females with their fore-tibial claws during struggles, resulting in haemolymph loss and scar tissue formation. Taken together, our results show how males can overcome the threat of cannibalism by coercively wrestling females. We argue that pre-copulatory injury in this species is likely to be a negative pleiotropic side-effect of coercive mating behaviour and foraging morphology.
... On the other hand, aggregation has some unique costs for snakes: snakes cannot share food and, among communally housed neonate and juvenile snakes, food fights can be both common and deadly (Yeager and Burghardt 1991). Furthermore, predators may be attracted to aggregations of snakes (Shine et al. 2001), and heat kleptoparasitism from other male snakes is a purported strategy used by shemale red-sided garter snakes (T. sirtalis parietalis) to warm up after emerging from hibernation (Shine et al. 2012). ...
... Despite this, snakes left their shelters, potentially exposing themselves to danger, explored alternative shelters, and were more likely to remain for longer in shelters that already housed larger groups. This effect disappeared in the oldest snakes, suggesting that social aggregation in garter snakes may be an exclusively juvenile phenomenon, possibly due to larger (and older) snakes being less vulnerable to predation (Shine et al. 2001) or more sensitive to competition. However, age was confounded with parentage in our data, limiting our ability to answer this question. ...
Previous research has shown that competition, familiarity, diet, and relatedness can all influence aggregation patterns in garter snakes. We controlled for these factors and examined social aggregation patterns in juvenile Eastern garter snakes (Thamnophis sirtalis sirtalis). We assayed snakes individually for consistent individual differences in boldness and sociability. We then placed snakes in groups of 10 in an enclosure with four shelters and observed their social interactions over a period of 8 days. We demonstrate that the snakes actively seek social interaction, prefer to remain with larger aggregates, and associate nonrandomly with specific individuals or groups. We show that their social interaction patterns are influenced by individual boldness, sociability, and age. The snakes’ social networks were perturbed twice a day by “shuffling” their locations. Despite these disturbances, the snakes eventually re-formed their preferred social environment. Aggregation and exploration patterns also varied across time, with most activity occurring later in the day. These results highlight the complexity of snake sociality and may have important implications for conservation efforts.
Significance statement
Snakes are often considered nonsocial animals, but this is inaccurate. We used social network analyses to compare juvenile Eastern garter snakes’ group behaviors to their individual personalities. Our research demonstrates that these snakes actively seek out social interaction and prefer to join and remain with larger groups and that their social interaction patterns are influenced by consistent individual differences in boldness and sociability. Our work contributes to a sparse but growing body of literature on sociability in reptiles. This work is important for changing perceptions among the scientific community and the public as a whole. As a consequence, it may aid efforts in developing appropriate conservation techniques that consider sociability patterns in relocated reptiles.
... In the lab, snout-to-vent (SVL), and mass (g) measurements of each snake were taken. Sex of each individual was determined by manual eversion of hemipenes in juveniles, and visual inspection of tail shape and size in adults (Shine et al., 2001). Individuals that could not be reliably sexed were omitted from sex comparisons. ...
... For example, Roe et al. (2006) suggested that larger body size (SVL) contributed to increased risk of road mortality in snakes due to the increased " kill width " which the authors of that study calculated as two times tire width plus SVL of the individual snake. Presumably, large body size of some species leads to decreased risk from predators, particularly avian predators (Shine et al., 2001). Large body size in males is associated with successful mating particularly for those species that perform ritualized combat for mating opportunities such as A. piscivorus, and P. obsoletus (Shine, 1978 ), and larger body size in female snakes is associated with higher reproductive success (Brown and Weatherhead, 2000; Barron and Andraso, 2001). ...
... Still, the energetic costs to females can be mitigated because they actively forage during vitellogenesis and through most of pregnancy (Gregory, 2006; Gregory and Stewart, 1975), whereas males are aphagous during breeding (O'Donnell et al., 2004). Therefore, energy usage during breeding explains the significant decrease in a male's body condition found in other studies of this species, which in turn increases the risk of mortality and places a limit on male reproductive effort (Shine et al., 2001b; Mason, 2004, 2005). Although previous work in this system demonstrated that body condition is a factor that predicts mating success (Shine et al., 2004a), neither courtship nor ejaculate costs depended on body condition, as has been found in other species (e.g. ...
... These allocation strategies are likely to shift through ontogeny (Pianka and Parker, 1975). Greater energetic investment by smaller males is risky, as it may leave them in poor body condition that then increases their chances of mortality in the dens (Shine et al., 2001b) and further reduces their chances of remating (Shine and Mason, 2005). However, this strategy makes sense if the prospect for future matings is low and the costs of attaining a mating are high, as they seem to be for small males who have considerably high RMR after courtship. ...
The non-sperm components of an ejaculate, such as copulatory plugs, can be essential to male reproductive success. But the costs of these ejaculate components are often considered trivial. In polyandrous species, males are predicted to increase energy allocation to the production of non-sperm components, but this allocation is often condition dependent and the energetic costs of their production have never been quantified. Red-sided garter snakes (Thamnophis sirtalis parietalis) are an excellent model with which to quantify the energetic costs of non-sperm components of the ejaculate as they exhibit a dissociated reproductive pattern in which sperm production is temporally disjunct from copulatory plug production, mating and plug deposition. We estimated the daily energy expenditure and resting metabolic rate of males after courtship and mating, and used bomb calorimetry to estimate the energy content of copulatory plugs. We found that both daily energy expenditure and resting metabolic rate were significantly higher in small mating males than in courting males, and a single copulatory plug without sperm constitutes 5-18% of daily energy expenditure. To our knowledge, this is the first study to quantify the energetic expense of size-dependent ejaculate strategies in any species.
© 2015. Published by The Company of Biologists Ltd.
... Consequently, some studies are conducted in controlled settings (Trexler, Tempe & Travis 1994) that may not fully represent natural conditions, and others can only subsample and approximate the distributions of the survivors and mortalities (Britton & Moser 1982). As Shine et al. (2001) noted, 'The problem involves logistics: It is simpler to quantify differential mortality by assessing phenotype distributions in living animals before and after the mortality event than it is to directly observe mortality or measure the attributes of dying vs. living animals'. In addition, directional selection is often either inconsistent over time (Grant & Grant 2002;Seamons, Bentzen & Quinn 2007) or opposed by other forms of selection. ...
... Given the logistic problems in field studies (Shine et al. 2001), trade-offs associated with age, size and reproductive success can be quantified more easily in semelparous as opposed to iteroparous species. The life history and reproductive biology of Pacific salmon, Oncorhynchus spp., is well-documented (Fleming & Reynolds 2004;Quinn 2005), facilitating studies of reproductive success and life-history trade-offs. ...
Selection drives evolutionary changes but is often difficult to quantify and tightly link to phenotypic trait distributions in wild populations.
Sampling a single population of sockeye salmon ( O ncorhynchus nerka ) for over a decade, we calculated the expected spawning success for females resulting from: (i) increased fecundity with body length, (ii) the mortality cost of prolonged marine residency necessary to achieve large size, (iii) size‐selective natural mortality on the spawning grounds from biotic (bear and gull predation) and abiotic (stranding) processes and (iv) exploitation by a size‐selective commercial fishery. We quantified the size‐specific probability of different modes of death and the resultant potential for successful spawning, and then modelled the theoretical relationship between female length and fitness (spawning success) in the population.
This optimal distribution closely matched the observed length distribution of the focal population, when removals by the size‐selective commercial fishery were included. We then used a likelihood‐based approach to compare competing model predictions to length distributions from other populations in the watershed with different levels of size‐selective freshwater mortality, as determined by the physical characteristics of the spawning grounds.
This study provides a quantitative framework for assessing female spawning success in wild populations, as represented by the expected number of eggs deposited per spawning female. These results advance previous analyses of natural selection in that predictions for phenotypic distributions were generated and then compared to those observed in situ , rather than assuming the adaptive nature of observed distributions.
... We confirmed sightings of these potential predators within our long term field notes. Guthrie (1932) provided a list of invaluable references for avian snake predation reports prior to 1932, and Sherrod (1978) provided a very thorough and detailed list of references describing falconiform birds consuming snakes. Identities of avian predator species and references for predation reports—divided into those that involve predation particularly on Thamnophis sp. and those that involve predation on other snake species—are given inTable 1. ...
... It is likely that the majority of wounds were due to predatory encounters because the highest incidence of wounds by far was in the mid-body region (Fig. 5). This result suggests that wounds were inflicted by predators that preferentially targeted the mid-body, as is known to occur with corvid predation on T. sirtalis (Shine et al., 2001). We found a higher incidence of individuals with wounds in slow living meadow populations than in fast living lakeshore populations (Table 4). ...
Predation pressure has often been postulated as a major selective force for the evolution of life histories, with high predation (particularly on small sizes) resulting in a fast-living strategy characterized by fast growth, early maturation, and short lifespan. However, due to the difficulty of assessing actual predation pressure in the wild, evidence for a role of predation in life-history evolution is rare. We examined the relationship between avian predation and life-history strategy in replicate populations of fast and slow-living garter snake ecotypes. To assess avian predation, we first compiled a list of known and suspected predators based on direct observations of predation events recorded in our long term detailed field notes from 1978-present. Furthermore, we added to this list with published records of snake predation involving avian species known to occur in our study site, and a novel method of inferring predator identity via analysis of bill marks on live snakes. Using this list of candidate predators, we conducted surveys quantifying predator incidence in replicate habitats of both ecotypes. We found that known and suspected predators are more abundant in habitats of the fast-living ecotype than in those of the slow-living ecotype. We also show a higher incidence of bill marks on slow-living snakes, which may indicate an increased effectiveness at escaping predation attempts. In general, we provide evidence to suggest that predation pressure may indeed have been an important selective force in the evolution of fast growth and early maturation in the fast-living ecotype and may continue to constitute an important source of extrinsic mortality leading to differences in lifespan between the two ecotypes.
... T HE body condition of an animal reflects its energetic state such that an animal in good condition has greater energy reserves than one that is in poor condition (Hayes and Shonkwiler, 2001;Schulte-Hostedde et al., 2001, 2005. Variation in body condition has been associated with male and female fitness components, such as survival and reproductive success, in a variety of taxa including mammals (Schulte-Hostedde et al., 2005;Toïgo et al., 2006), amphibians (Lowe et al., 2006), birds (O'Dwyer et al., 2006), and snakes (Shine et al., 2001). Maternal body condition has a substantial effect on both offspring size and offspring number and therefore is positively correlated with reproductive fitness (Chastel et al., 1995;Dobson and Michener, 1995). ...
... Body condition (as measured by residual mass) has been used in studies of squamates and turtles in a number of contexts. In the case of squamates, body condition is assumed to represent fat reserves and thus affect survival (Shine et al., 2001;Husak, 2006) and reproductive success (Blouin-Demers et al., 2005). In the case of turtles, direct measurements of energy reserves through lipid extractions have been conducted in hatchling Painted Turtles (Chrysemys picta; Packard and Packard, 2001), but this approach requires destructive sampling, an approach incompatible with long-term mark-recapture studies. ...
The body condition of an animal reflects its energetic state such that an animal in good condition has greater energy reserves than one that is in poor condition. Body condition in turn should be positively correlated with fitness because energetic reserves limit the amount of energy that can be allocated to reproduction. Using Spotted Turtles (Clemmys guttata) as a model system, and three years of field data from a South Carolina, USA population, we tested the prediction that reproductive output increases with maternal body condition. The effect of body condition on the reproductive output of female turtles was examined at three temporal scales (among clutches, among nesting seasons, and among females) using several variables including clutch frequency, clutch size, and multiple measures of egg size. We predicted that females in good condition will have a higher clutch frequency than those in poor condition; that females in good condition will have larger clutch sizes than those in poor condition; and that females in good condition will have larger eggs than those in poor condition. Among clutches and nesting seasons, we found no relationship between female body condition and reproductive output. Among females over the entirety of the three-year study, we found a positive relationship between body condition and clutch mass and egg size. In addition, females in poor condition and females in good condition both produced larger clutch sizes than females in intermediate condition. Our findings suggest that within a given reproductive bout and within a given reproductive season, energy reserves do not affect immediate reproductive investment. However, over the longer-term, females in good condition have greater reproductive output, which supports the idea of a bet-hedging life history strategy in turtles.
... Although many snakes (e.g., vipers) are venomous (differentiated by an active delivery of toxin, as in biting or stinging), Rhabdophis is the only documented (Akizawa et al., 1985 ) poisonous snake (passive delivery of toxin, usually by ingestion ). Known garter snake predators include herons (Ardea, Butorides; Hancock and Kushlan, 1984), ravens and crows (Corvus; Shine et al., 2001), hawks (Buteo; Fitch, 1965; Richardson et al., 2001), raccoons (Procyon), minks (Mustela), foxes (Vulpes), and badgers (Taxidea; Fitch, 1965; and see Rossman et al., 1996). American Bitterns (Botaurus; Rapp, 1954; Hancock and Kushlan, 1984) are known to eat Thamnophis up to 2 ft in length. ...
... Had the snake been able to completely digest the newt, the concentration of TTX in the liver may have been higher. Regardless, the occurrence of large quantities of TTX in wild snakes was verified. The literature, combined with our data, suggests that snakes may harbor TTX in the approximate range, or just below a lethal dose for certain predators. Shine et al. (2001) found that crows were the main predators of T. sirtalis emerging from dens in Manitoba (outside the geographic range of T. granulosa). Remarkably, the crows excised the garter snake livers preferentially (an easily located, highly nutritional source in snakes), and consumed several in quick succession. Notably, live snakes were observed ...
... A measure that reflects acquired resources is the body mass relatively to body size, or body condition (e.g., Jackson 1980). Body condition may correlate to rainfall and primary production (Hailey 2000), and may affect growth, survival (Shine et al. 2001) and reproduction (Henen 1997;. Body condition may also be affected by ectoparasite infestations, because parasites use host resources. ...
... Several studies have shown that body condition indices, based on body mass, correlate with fitness parameters such as survival (Shine et al. 2001) and reproduction (Dobson & Michener 1995). Body condition is associated with the reproductive output of several arid-zone tortoises (Henen 2004;, and good body condition is critical for reproductive success of desert tortoises (Henen 1997(Henen , 2002a. ...
... Wild juvenile Eastern Box Turtles have numerous potential predators, and their primary anti-predator strategy entails exhibiting secretive behavior or crypsis (Dodd, 2001). Remaining in close proximity to conspecifics may therefore increase predation risk by enhancing visual and olfactory cues to predators (Shine et al., 2001;Tetzlaff et al., 2020). ...
Behavioral interactions between conspecific animals can be influenced by relatedness and familiarity. Compared to other vertebrate taxa, considering such aspects of social behavior when housing captive reptiles has received less attention, despite the implications this could have for informing husbandry practices, enhancing welfare, and influencing outcomes of conservation translocations. To test how kinship and familiarity influenced social behavior in juvenile Eastern Box Turtles (Terrapene carolina), we reared 16 captive-born individuals under semi-natural conditions in four equally sized groups, where each group comprised pairs of siblings and non-siblings. Using separation distance between pairs of turtles in rearing enclosures as a measure of gregariousness, we found no evidence suggesting siblings more frequently interacted with one another compared to non-relatives over the first five months of life (β = -0.016, 95% CI: -0.117 to 0.084). Average pair separation distance decreased during this time (β = -0.146, 95% CI: -0.228 to -0.063) but may have been due to turtles aggregating around concentrated resources like heat and moist retreat areas as cold winter temperatures approached. When subjects were eight months old, we measured repeated separation distances between unique pair combinations in an experimental environment and similarly found no support for gregariousness (associations) being influenced by kinship or familiarity (β = -1.554, 95% CI: -9.956 to 6.848). Additionally, neither differences in body size between pairs of turtles (β = -22.289, 95% CI: -68.448 to 23.870) nor the five-minute time interval during the 90-minute trial (P ≥ 0.18) had any apparent effect on associations. Agonistic interactions between individuals were never observed. Encouragingly, based on our results, group housing and rearing of juvenile box turtles did not appear to negatively impact their welfare. Unlike findings for other taxa, including some reptiles, our results suggest strategically housing groups of juvenile T. carolina to maintain social stability may not be an important husbandry consideration or necessary when planning releases of captive-reared individuals for conservation purposes.
... For instance, wading birds and raptors are a large source of tail injury to T. elegans (Sparkman et al. 2013) and Nerodia spp. (Mushinsky and Miller 1993), and corvids (e.g., crows and ravens) are major predators on T. sirtalis (Shine et al. 2001). At BP it is common to see numerous wading birds that are known snake predators such as Great Blue Herons (Ardea herodias), Green Herons (Butorides virescens), Snowy Egrets (Egretta thula), and Cattle Egrets (Bubulcus ibis) foraging along the edges of the hatchery ponds, as well. ...
Once widespread and abundant in riparian areas and wetlands throughout central and southern Arizona, Northern Mexican Gartersnakes (Thamnophis eques megalops) have declined and now persist in only a fraction of their former distribution. Because of their declines the species was listed as Threatened under the Endangered Species Act of 1973 in 2014. Mexican Gartersnakes are also Tier 1A Species of Greatest Conservation Need in Arizona’s State Wildlife Action Plan. There are currently only a few isolated populations where the species is still commonly found in the middle/upper Verde River drainage, middle/lower Tonto Creek, the Bill Williams River drainage, upper Santa Cruz River drainages, and Ciénega Creek drainage. The Arizona Game and Fish Department fish hatcheries at Page Springs and Bubbling Ponds, in the Verde River drainage, support one of the largest known Northern Mexican Gartersnake populations in Arizona. Understanding the population dynamics of this population is important to shed light on the species ecology and to inform how hatchery management can benefit the species. From 2009–2011 the Department conducted a five-year mark-recapture study to assess relative abundance, detection, population dynamics, and the natural history of the Northern Mexican Gartersnake at the Page Springs and Bubbling Ponds hatcheries. In 9,510 trap days over five-years a total of 237 were captured and 188 marked in annual surveys done from May–September. Annual relative abundance, detection, and size class distribution exhibited little variation suggesting a stable population. We found snakes to be most abundant around ponds from June to August and didn’t vary between fallow and unlined ponds. Sex ratios were strongly female biased and few young and subadult snakes were captured, but these biases are suspected to be related to the trapping technique and not an inherent aspect of the population structure. Despite coexisting with a large population of the non-native and predatory America Bullfrog (Rana catesbeiana) we found no evidence that tail injuries in this population are higher than populations without American Bullfrogs. This study provides a baseline on the Northern Mexican Gartersnake population at the Page Springs and Bubbling Ponds hatcheries to assess future trends and changes and guide the timing of maintenance around ponds.
... For example, in many garter snake populations, males congregate around hibernacula and compete by scramble competition for emerging females. The males stay at the hibernaculum for up to several weeks, while the females disperse in a few days (e.g., Shine et al. 2001b). ...
Many animal species exhibit multiple paternity, defined as multiple males genetically contributing to a single female reproductive event, such as a clutch or litter. While this phenomenon is well-documented across a broad range of taxa, the underlying causes and consequences remain poorly understood. For example, it is unclear how multiple paternity correlates with life-history strategies. Furthermore, males and females may differ in mating strategies and these patterns may shift with ecological context and life history variation. Here, we take advantage of natural life-history variation in garter snakes (Thamnophis elegans) to address these questions in a robust field setting where populations have diverged along a slow-to-fast life-history continuum. We determine both female (observed) and male (using molecular markers) reproductive success in replicate populations of two life-history strategies. We find that despite dramatic differences in annual female reproductive output: (1) females of both life-history ecotypes average 1.5 sires per litter and equivalent proportions of multiply sired litters; whereas (2) males from the slow-living ecotype experience greater reproductive skew and greater variance in reproductive success relative to males from the fast-living ecotype males despite having equivalent average reproductive success. Together, these results indicate strong intrasexual competition among males, particularly in the fast-paced life-history ecotype. We discuss these results in the context of competing hypotheses for multiple paternity related to population density, resource variability, and life-history strategy.
... The ability to track demographic changes in snake populations is important not only in the conservation of snakes (Böhm et al., 2013), but also because snakes are indicators of ecological change (Beaupre and Douglas, 2009). Population-specific survival rates in snakes are influenced by individual factors such as body condition (Beaupre, 2008;Hyslop et al., 2012), sex (Shine, 1980;Shine et al., 2001), and age to maturity (Adolph and Porter, 1996), as well as stochastic environmental variation (Andrewartha and Birch, 1986;Brown et al., 2007), resource availability (Beaupre and Douglas, 2012), and the current demographic composition of the population (Altwegg et al., 2005;Clark et al., 2008). Although it is likely a combination of factors influence survival rates in snake populations, comparing the importance of these different factors is critical to developing life history models (Diller and Wallace, 2002;Brown et al., 2007) to inform conservation efforts. ...
... Commonly, the term is used to designate the energy reserves of an individual (Labocha et al., 2014;Peig and Green, 2009). For example, animals with a better body condition are predicted to have more energy reserves (i.e., fat and protein), enabling them to endure longer periods of food shortage and present higher survival and reproductive success compared to animals with a poor body condition (Peig andGreen, 2009, 2010;Schulte-Hostedde et al., 2001, Shine et al., 2001. Body condition indices thus inform on the quantity of energy extracted from the environment and can give for instance important insights on foraging behavior or prey distribution (Lloret et al., 2013). ...
Aspects of reproduction and population structure were investigated between June 2017 to May 2018 in sardines, Sardina pilchardus (Walbaum, 1792) from the Safi fishing area. The sex ratio was generally in favor of males (χ2=19.50). Out of 3252 total specimens sampled, 1404 were females (46.00%), 1648 males 50.68%) and 200 immatures (6.15%). The immatures were best represented in the small size classes, between 8 and 12 cm. This study showed that sardines can breed throughout the year with a peak breeding season between November and February. The gonado-somatic index (GSI) and the condition coefficient (CC) evolved almost invariably. The volumetric absolute body condition index [kv= Fresh total body mass (g)/total body volume (cm3)] showed two peaks, which are discriminately sex dependent. For females, the peaks are concomitantly observed in September and April while for males, these are shown in June and February. Moreover, the morphometric index (kn) showed a single peak in January and September for reproductive males and females, respectively. As regards the non-reproductive individuals the males have two peaks in June and December or females, they have one peak in November. Additionally, the GSI showed a single peak in February. The size at first sexual maturity in males and females was 16.1 cm and 16.5 cm, respectively.
... Female bias could also result from higher mortality in males, although females experienced higher levels of injury (see next section). Skewed sex ratios resulting from differential mortality have been reported in several species of snakes (Shine et al. 2001;Wang and Tu 2003;Patten et al. 2009). Skewed sex ratios favoring females can also occur when inbreeding is frequent (Shine and Bull 1977), in which case we would expect the skew to be greater on smaller islands (e.g., Allen Cay), which we did not see. ...
Sexual dimorphism in animals exists in many forms, including overall size difference between the sexes (sexual size dimorphism, SSD) and size and structural differences in body components (sexual body component dimor-phism, SBCD). Studies of sexual dimorphism seek to determine whether dimorphic traits result from sexual selection, natural selection, or non-adaptive processes. Characterizing sexual dimorphism depends on identifying an unbiased character for overall body size, which can then be used to assess both SSD and SBCD. Most studies of snakes use snout-vent length (SVL) for this purpose, but SVL may itself be dimorphic. In this study, we examined SSD and SBCD in three island populations of the Bahamian Racer (Cubophis vudii vudii). Discriminant function analysis (DFA) showed that head width (females wider) and tail length (males longer) best discriminated between the sexes, and total length provided the least discrimination. Linear models using total length as the least-biased measure for overall size revealed an absence of SSD, but SBCD existed for head size (width 8.9% greater in females, length similar), trunk length (4.3% longer in females), and tail length (9.8% longer in males). Linear models also revealed differences among island populations for total length (New Providence < Eleuthera = Allen Cay) and head length (Allen Cay < Eleuthera < New Providence), but not head width or tail length. Extent of SBCD varied depending on choice of character to control for overall body size, with total length yielding the most female-biased values, and geometric mean, principal component 1 (PC1) of a principal components analysis, and SVL providing increasingly more male-biased values, respectively. Body condition was statistically similar for the two sexes and three seasons (spring, summer-fall, winter), but the moderate and large effect sizes, respectively, suggest that females were heavier than males, and both sexes were heaviest in spring. Females, which represented 64.9 of all snakes, suffered injuries disproportionately to males (19.7% and 3.1%, respectively), but no differences in sex ratio or frequency of injury existed among the island populations. Collectively, these findings illustrate the utility of using DFA and other approaches (geometric mean, PC1) to identify a relatively unbiased reference character for overall body size and suggest that sexual and natural selection interact to shape the morphology of these snakes.
... Thus, the monitoring of metrics like body condition and shell hardness within head-start studies would provide a comprehensive assessment of robustness of captivereared tortoises. Body condition (BC) is expressed as the mass of an animal relative to an appropriate size metric (approximated volume in our case) and can reflect nutritional condition, stored fat, and water balance (Shine et al. 2001;Nagy et al. 2002;Loehr et al. 2007;Nagy et al. 2015a). Shell hardness increases with body size and age in juvenile desert tortoises (Nagy et al. 2011), and the hardness of the shell of a turtle likely plays a major role in its protection against predators. ...
Head-starting is a management tool used to augment recruitment in depleted turtle populations. The approach protects animals during the first part of their life, when they are most vulnerable to predation, before they are released into the wild at a larger, less vulnerable size. In 2015 we initiated a comparative study on desert tortoises to evaluate the potential for indoor-rearing—as opposed to standard outdoor-rearing—to reduce the time animals are captive. We obtained 74 neonate tortoises by temporarily moving gravid females to semi-natural predator-proof pens and allowing them to nest inside the enclosures. We assigned 70 of these neonates to three treatment groups: 1) indoor-reared (n = 30), 2) outdoor-reared (n = 20), and 3) directly released (control group; n = 20). In September 2015, we began housing the indoor treatment group in indoor vivaria and offering them food five times weekly. Concurrently, we placed the outdoor treatment
group in predator-proof pens and began providing them with artificial rain and food weekly. On 28 September, we released the 20 hatchlings into the wild, and began monitoring them with radio-telemetry. From September 2015 to March 2016 (≈6 months), growth in midline carapace length was 70.7% (1 SE = 2.7%) for indoor-reared headstarts, 8.3% (SE = 0.6%) for outdoor-reared headstarts, and 4.3% (SE = 0.5 %) for directly released hatchlings. Indoor-reared headstarts grew over 8.5 times faster than outdoor-reared headstarts and 16.4 times faster than directly released hatchlings. Survivorship during the same period was 100% for both the indoor- and outdoor-reared treatment groups and 75% (15/20) for the directly released treatment group. In our study, indoor- and outdoor-rearing were effective in increasing survivorship relative to direct-release hatchlings and indoor-rearing produced the fastest growth. We will monitor growth, survivorship, microhabitat use, and movement of each treatment group post-release in Spring 2016.
... Body condition varies with temporal fluctuations in the environment (Piersma and van Gils, 2011), habitat quality (Oliva-Paterna et al., 2003), maternal effects (Litzgus et al., 2008), animal life-history characteristics (Reed et al., 2008), and genotype (Blanckenhorn and Hosken, 2003). All of the above contribute to individual fitness parameters, and the impact of body condition on fitness parameters has been documented in a variety of taxa including mammals (Schulte-Hostedde et al., 2005), amphibians (Lowe et al., 2006), birds (O'Dwyer et al., 2006), and reptiles (Shine et al., 2001). Generally, individuals with greater energy reserves and better body condition experience higher survival and reproductive success than do individuals with lower body condition (Litzgus et al., 2008). ...
Body composition is a measure of an animal's energetic state that can inform many research fields, yet the analysis traditionally requires individuals to be killed, and chemical analysis is labor intensive. Quantitative magnetic resonance (QMR) measures body composition noninvasively in live and nonanesthetized animals. Our aim was to validate QMR analysis for snakes by comparing it with gravimetric chemical analysis. We collected Northern Watersnakes (Nerodia sipedon sipedon) and Eastern Massasaugas (Sistrurus catenatus catenatus) that were found dead on roads, analyzed their body composition using the QMR scanner, and then by gravimetric chemical analysis. We compared fat mass, wet lean mass, and total water mass between the two methods, and then calculated bias, absolute error (g), and relative error (%) of the QMR analysis. Body composition values from the QMR analyses were highly correlated with the values obtained by gravimetric chemical analysis. Bias and errors were reasonable for wet lean and total water mass values, but the raw QMR data overestimated fat mass. When we calibrated the QMR using the chemical extraction data, it nearly eliminated bias and greatly reduced absolute and relative error. Therefore, following calibration, QMR analysis is an effective method to measure body composition of snakes. QMR very accurately measures wet lean and total water masses and can be used to detect changes in fat mass particularly in longitudinal studies of individuals across seasons.
... We have one confirmed case of avian predation (Eastern Screech Owl, Megascops asio) at Carlyle Lake, although many other avian species capable of killing Eastern Massasaugas inhabit the site. Predation by American Crows (Corvus brachyrhynchos) has been identified as the largest source of mortality in a population of Redsided Gartersnakes (Thamnophis sirtalis parietalis) in Manitoba, and predation by hawks has also been observed at the same site (Shine et al. 2001). Management related activities around Carlyle Lake include mowing along roadsides and other man-made structures, prescribed burns for woody vegetation control, and chemical and mechanical treatments of invasive plant species. ...
The identification and management of threats to endangered species are imperative for conservation. Reptile populations are declining globally, yet their secretive nature and a lack of demographic data often make the implementation of conservation strategies difficult. The Eastern Massasauga (Sistrurus catenatus) has been recommended for listing as threatened under the federal endangered species act and listed in Illinois as endangered since 1994. As part of a long-term population monitoring project, we quantified sources of mortality in a population of the Eastern Massasauga using data collected from 2000–2011. Using mortality data amassed during both observational and radio-telemetry studies (2001–2003 and 2009–2011), we classified each mortality event into one of eleven categories. We used Poisson regression to evaluate the impacts of sex, stage-class, season, and study type on mortality. Our results indicate automobiles and predation are the leading sources of mortality, together accounting for over 50% of observed mortalities. We found season and mortality category significantly affected the number of observed mortalities. Most mortalities occur in the summer and fall when snakes are most active. Observational studies detected nearly all the automobile mortality while radio-telemetric studies detected nearly all the predation events. We offer conservation and management recommendations to reduce Eastern Massasauga mortality at Carlyle Lake, which are applicable throughout the range.
... On a finer temporal scale, determining whether peaks in adult mortality occur on a seasonal basis can highlight behaviors or times of year when individuals are most vulnerable to mortality, and thus help identify threatening processes. For instance, snakes may be particularly susceptible during reproductive behaviors and while overwintering, as the energy expenditure and risk of exposure to predators and unsuitable environmental conditions can result in higher mortality (Brown and Weatherhead 1997;Bonnet et al. 1999;Shine et al. 2001). In the presence of additional stressors that are already threatening populations, we might expect imperiled species to be even more vulnerable at these times. ...
Many snake populations have experienced significant declines, including the Copper-bellied Watersnake (Nerodia erythrogaster neglecta), a species listed as threatened under the federal endangered species act. here, we assess aspects of population biology and vital rates in N. e. neglecta to help elucidate potential mechanisms of their decline and inform more targeted recovery efforts. We use the common Watersnake (Nerodia sipedon sipedon) as a benchmark for comparison. survey results indicate that the N. e. neglecta population may have experienced a 70% decline in abundance from 2001-2006, whereas the N. s. sipedon population remained relatively stable. annual survivorship rates did not differ appreciably between N. e. neglecta (0.67) and N. s. sipedon (0.63). surprisingly, N. e. neglecta grew three times faster than N. s. sipedon, regardless of sex, with evidence of high growth rates across the entire size-range of the population, suggesting that food resource limitations or excess energy expenditures are not likely constraining N. e. neglecta. Frequency of mating encounters, sex ratios, and proportion of juveniles in the sampled population of N. e. neglecta showed little evidence of deviation from that of N. s. sipedon. While broad scale threats such as habitat fragmentation, the loss of shallow ephemeral wetlands, mining, road mortality, or declines in amphibian prey have likely driven range-wide declines of N. e. neglecta, the proximate mechanisms (i.e., fitness consequences) behind the decline of our study population remain unresolved. nevertheless, the vital rates presented here provide useful information for more informed management and recovery efforts.
... This pattern of body mass loss under mild wintering conditions can have very strong implications. First, reduced body condition has been identified as a direct cause of mortality in wintering and emerging snakes (Hirth, 1966;Shine et al., 2001). Emergence involves a need to revive basic organismal functions, and emaciated organisms may not be able to sustain such an energy demand (Irwin and Lee, 2003;Zani et al., 2012). ...
... In this study, we tested the effects of illegal harvesting on changes in tusk size by comparing tusks from elephants captured in southern Kenya between 2005 and 2013 with tusks of elephants culled between 1966 and 1968 from the same region. Comparative analysis of morphological traits of survivors with traits of the original populations to provide evidence of selection in different vertebrate species has a rich history (e.g., Bumpus 1899;Endler 1986;Shine et al. 2001;Garel et al. 2007;Festa-Bianchet et al. 2014). We take advantage of this approach to detect selection for large tusks by illegal harvesting in our analyses. ...
Harvesting of wild populations can cause the evolution of morphological, behavioral, and life history traits that may compromise natural or sexual selection. Despite the vulnerability of large mammals to rapid population decline from harvesting, the evolutionary effects of harvesting on mega-fauna have received limited attention. In elephants, illegal ivory harvesting disproportionately affects older age classes and males because they carry large tusks, but its' effects on tusk size for age or tusk size for stature are less understood. We tested whether severe historical elephant harvests eliminated large tuskers among survivors and whether elephants born thereafter had smaller tusks. Adjusting for the influence of shoulder height – a metric strongly correlated with body size and age and often used as a proxy for age – we compared tusk size for elephants sampled in 1966–1968, prior to severe ivory harvesting in the late 1970s and early 1980s, with tusk size of survivors and elephants born during population recovery in the mid-1990s. In a regional population, tusk length declined by ˜21% in male and by ˜27% in female elephants born during population recovery, while tusk length declined by 22% in males and 37% in females among survivors. Tusk circumference at lip declined by 5% in males but not in females born during population recovery, whereas tusk circumference reduced by 8% in male and by 11% in female survivors. In a single subpopulation, mean tusk length at mean basal tusk circumference declined by 12.4% in males and 21% in females. Tusk size varied between elephant social groups. Tusk homogeneity within social groups and the often high genetic similarity within social groups suggest that tusk size may be heritable. Our findings support a hypothesis of selection of large tuskers by poachers as a driver of the decline in tusk size for age proxy and contemporary tusk evolution in African elephants.
... Here, we discuss the relationship between various measures of energy reserves and animal performance, highlighting studies in which detailed knowledge of energy stores has been crucial. Body condition indices have been shown to correlate with various fitness measures−individuals in better body condition survive better (e.g., Naef-Daenzer et al., 2001;Shine et al., 2001;Murray, 2002;Morrison et al., 2007) and have overall higher reproductive success (e.g., Chastel et al., 1995;Dobson and Michener, 1995;Otronen, 1995;Wauters and Dhondt, 1995). Direct links between available carbohydrates and animal performance have also been documented. ...
Animal signals are commonly found to be condition-dependent, recognized as a positive correlation between signal expression and a proxy of individual condition. The term 'condition' encompasses the acquisition and allocation of resources throughout an individual's lifespan and is assumed to relate to health, vigor, and viability. Despite its widespread use and sizeable literature base, the term condition remains somewhat enigmatic and challenging to quantify. Condition encompasses the resources used during development to create structures; the resources used in survival and reproductive functions; as well as the resources currently available as energy stores. Since the pool of available resources is constantly changing, scientists typically focus on current energy reserves and estimate these using proxies-the most common of which is body condition. More detailed estimates of energy reserves are sometimes acquired through direct measures of carbohydrates, fats, and/or proteins. Numerous studies, incorporating a range of taxonomic groups, have demonstrated links between body condition and animal performance, with several examples relating to reproductive performance (e.g. courtship displays). Yet few of these studies examine either the details of available energy reserves or the genetic basis of body condition. Females paying attention to the level of condition-dependent signal expression can gain information on the male's ability to acquire and allocate resources, and significant evidence exists demonstrating that in systems with condition-dependent signaling, females prefer males with higher levels of signal expression. However, the link between these mate-choice decisions and female fitness benefits frequently remain elusive. We suggest that a more proximate approach will ultimately facilitate our understanding of the relevant sources of selection influencing the evolution and maintenance of condition-dependent signaling. Specifically, we advocate for more of a focus on (i) the specifics of available energy reserves (i.e. carbohydrates, fats, and proteins), with a concentration on how they are utilized throughout an individual's life in relevant reproductive-related tasks, (ii) the genetic basis of resource acquisition and allocation, and (iii) the direct and indirect benefits females receive from mate decisions based upon condition-dependent signal expression.
... Further studies manipulating only one factor at a time will give a clearer indication of whether they warrant incorporation into conservation programs. A rigorous examination of how sex and reproductive status influence the responses of released animals would also be important, as these demographic differences often have a strong influence on snake behavior and vital rates (Brown and Weatherhead 1999;Shine et al. 2001). Snakes can reach high abundances (Godley 1980) and play important roles in aquatic ecosystems (Dorcas et al. 2012), yet numerous snake species and/or populations are in decline and in need of immediate conservation action (Reading et al. 2010). ...
The use of captive animals for population re-establishment or augmentation can be an important part of conservation efforts, but practitioners need experimentally derived evidence to guide the best strategies and inform whether such practices could be successful. Here, we examined how several manipulations to captive-rearing practices influence the performance of the Common Watersnake, Nerodia sipedon sipedon, during their first year in the wild. Following release, snakes that had experienced a period of enrichment during captivity to better simulate natural environments did not differ from conspecifics reared in more simplistic conditions on any measure of post-release behavior or performance. Moreover, captive snakes in both treatments exhibited habitat use, movement, thermoregulatory, and seasonal activity behaviors largely indistinguishable from resident conspecifics at the release site, and ultimately performed similarly in maintenance of body condition and survivorship. These results are in contrast to earlier releases and suggest that using older and larger individuals that have undergone a period of simulated winter dormancy may improve success during the early phase of establishment. However, captive snakes grew only one third as fast as wild native snakes, suggesting they experienced difficulties foraging in the wild. Further studies testing the effectiveness of translocation programs using captive animals as a management tool are urgently needed, but our findings do point to some success.
... The ecological mechanisms that may affect fitness, such as fluctuations in body condition influenced by food availability and habitat quality, are not well understood for many free-ranging snake species. Intraspecific variation in body condition, whether naturally observed or experimentally determined, may affect life history traits such as reproductive success (Naulleau and Bonnet 1996;Taylor et al. 2005), as well as survival (Shine et al. 2001). ...
Fitness is affected by resource needs driving behavior of cryptic ectotherms and
requires trade-offs in activities such as foraging, locomotion and thermoregulation. However,
the allocation of time and energy into such activities are often not well understood. Due to low
energy demands and infrequent feeding, little is known about potential fitness trade-offs for
temperate pitvipers which must balance remaining stationary to acquire and digest food while
traversing large areas, particularly to procure mating opportunities. I radio-tracked 16 male
Massasaugas (Sistrurus catenatus), an imperiled rattlesnake, from May to August 2014 in
northern Michigan, half of which were fed a supplement diet of mice. I compared body
condition as well as space and habitat use between the two treatments. Although open habitats
were the highest in thermal quality, operative environmental temperatures that allowed
Massasaugas to thermoregulate within their preferred range (30-33.6 oC) were uncommon
overall in all habitats. Temperatures exceeding their challenging lower limit (19.9 oC), where
they can still perform reasonably well, were much more typical. Relative to their availability
across the study site, both fed and naturally foraging (control) snakes predominately used
wetlands. Within the areas utilized by individual snakes, both groups used edges more than
other habitats. Fed snakes were in better body condition than controls at the end of the study.
Movement patterns and microhabitat selection of fed snakes did not differ from controls during
the breeding season. Controls maintained higher diurnal body temperatures during the breeding
season than fed snakes, but groups did not differ in their accuracy or effectiveness of
thermoregulation during that time. Fed snakes did not increase body temperatures after
feeding, perhaps because all of the snakes are already trying to maintain elevated temperatures
in a thermally challenging environment. My results suggest movements associated with finding
mates exert a significant pressure on male Massasaugas, causing them to forgo stationary
digestion in exchange for increasing the prospect of reproducing. Given the infrequent
reproductive rates of female Massasaugas in northern latitudes, intense mate searching by
males may be a fixed behavior in these populations, regardless of food intake.
... We removed snakes with discernible food items in their stomachs from analyses, and if a snake was captured more than once in the same year, we used only one set of measurements (drawn at random) in the analysis to avoid pseudoreplication (Coates et al., 2009). For the body condition analysis, we followed Parent & Weatherhead (2000), Shine et al. (2001) and Brown et al. (2009 by using residuals from a regression between weight and SVL as an index of body condition. Differences and interactions in the body condition scores between disturbance categories and years were tested using analysis of variance (ANOVA). ...
Species may remain present on developed landscapes over extended periods, suggesting viability, while in reality, populations may be indirectly affected in subtle and significant ways. We investigated indirect effects of human disturbance and habitat development on a population of the threatened Northern Pacific Rattlesnake Crotalus oreganus oreganus in British Columbia, Canada. We used mark-recapture (n = 623 males and non-gravid females, 2002–2011) and radio-telemetry (n = 100 males, n = 4 non-gravid females, 2004–2011) to examine weight, length, body condition, ecdysis and exposure risk in habitats of varying disturbance levels. Snakes in the most disturbed areas (<10 m to the nearest source of human activity or development) had lower weights and body condition, and they lost significantly more weight during the active season. Mean body condition of all snakes was stable or even increasing up to 2008 whereafter declines occurred in all categories, but particularly so for animals using disturbed habitat. Although there was some indication that ecdysis rates were affected by disturbance, we found no evidence that animals in disturbed habitat tended to be more exposed (i.e. distant from cover). Our findings indicate that there are consequences of occupying disturbed habitats, even though outward changes in behaviour or declines in density on the landscape are not detected.
... Fitness metrics such as growth rates, fecundity and survivorship have all been used to estimate an organism's long term fitness (Schmidt and Levin, 1985;Stearns et al., 2000). The Body Condition Index (BCI) is a method that has been used to estimate short-term shifts in an organism's health status and to infer instantaneous fitness levels throughout different stages of an organism's life (Litzgus et al., 2008;Shine et al., 2001;Wallis et al., 1999). The effects of resource limitations on fitness are demonstrated when fitness metrics are different between high and low resource environments. ...
... We tested the prediction that above-ground and woodensided cages would experience lower hatching success and longer incubation durations. Also, we predicted that above-ground and wooden-sided cages would have a negative effect on proxies of hatchling fitness, measured as a higher frequency of deformities (Mast and Carr 1989;Türkozan et al. 2001), reduced body condition (Shine et al. 2001) and reduced locomotor performance (Freedberg et al. 2004;Delmas et al. 2007). Nest predators may use research markers as visual cues for predation (Burke et al. 2005;Rollinson and Brooks 2007;Spotila 2011); thus, the third objective was to determine whether predators preferentially interacted with, and depredated nests with protective cages. ...
Context A main goal of conservation is to mitigate anthropogenic impacts on natural ecosystems, thus conservation tools themselves should not negatively affect target species. Predator-exclusion cages are effectively used to reduce predation of turtle nests; however, their effects on nest environment and developing hatchlings have not been examined. Aims Our study had the following four goals: (1) to examine effects of cages on the nest environment, (2) determine whether nest caging affects proxies for hatchling fitness, (3) evaluate whether nest predators preferentially interact with certain cage types, and (4) assess the cost-effectiveness of different nest caging designs. Methods In 2010 and 2011 in Algonquin Provincial Park, Ontario, painted turtle (Chrysemys picta; n≤93) and snapping turtle (Chelydra serpentina; n≤91) nests were assigned to one of three treatments (wooden-sided cages, above- and below-ground wire cages) or a control (no nest cage) and outfitted with a data logger to record incubation temperature. After emergence, hatching success and proxies of hatchling fitness were measured. Key results Nest temperature, hatching success, frequency of hatchling deformities and locomotor performance did not differ among cage treatments. However, hatchling body condition differed among treatments; wooden-sided and below-ground cages had the most positive influence on body condition in painted and snapping turtles, respectively. Predator interactions did not differ among treatments, and wooden-sided cages were the most inexpensive to construct. Conclusions Nest cages did not alter the nest environment from natural conditions but did alter hatchling body condition, and nest caging affected species differently. Implications Nest cages are known to reduce nest depredation, and our data indicated that, in general, nest cages also do not affect the nest environment or proxies for hatchling fitness. Thus, our findings indicated that cages are effective conservation tools that do not present secondary deleterious effects on potential recruitment.
... Thus, the two studied pesticides increased invertebrate mortality through both direct and indirect effects. Further, as reported elsewhere (Peig and Green, 2009;Shine et al., 2001), mortality was significantly correlated with body condition of invertebrates, implying that an energetic imbalance led to increased mortality. Zubrod et al. (2011) also reported lower growth rates and energy reserves for Gammarus pulex exposed to the fungicide tebuconazole even though food assimilation was higher under pesticide exposure. ...
The intensification of agriculture has promoted the use of pesticides such as fungicides and insecticides. Many pesticides readily leach into natural water bodies and affect both organisms and ecosystem processes such as leaf breakdown, a crucial process in headwater streams. As leaf breakdown in streams involves sequential steps by different groups of organisms (first microbial conditioning, then invertebrate shredding), pesticides targeting different organisms are likely to affect one or the other step, and a mixture of contaminants might have interactive effects. Our objective was to evaluate the effect of a fungicide (imazalil) and an insecticide (diazinon) on stream fungal and invertebrate activities, and their effects on leaf consumption. After an initial assay to define 'effective concentration' of both pesticides in a laboratory experiment, we manipulated pesticide presence/absence during the conditioning and shredding phases. Both pesticides affected fungal community and reduced the performance of the shredding amphipod Echinogammarus berilloni, and leaf consumption. The impact of pesticides on fungal sporulation depended on the length of the exposure period. In addition, pesticides seemed to cause an energetic imbalance in the amphipod, affecting body condition and mortality. The combined effect of both pesticides was similar to those of the fungicide. Overall, our results show that the effects of pesticide mixtures on leaf breakdown are hard to predict from those observed in either fungi or macroinvertebrate performance.
... However, the structure of the mating system and the spatial distribution of females therein may facilitate this endeavour. For example, females that are spatially predicable during the mating period (e.g., T. s. parietalis) may move to reduce sexual conflict (Shine et al., 2001) whereas females which are wide-ranging and spatially unpredictable during the mating period, such as Pantherophis obsoletus and C. viridis (Blouin-Demers & Weatherhead, 2002;Duvall et al., 1992, respectively), may move to facilitate location by males. ...
To facilitate location of mating partners, females of many taxa emit chemical signals (i.e., sex pheromones) to inform male conspecifics of their location and reproductive status. Males subse-quently alter their movements to increase their likelihood of encountering females and this move-ment has been historically viewed as a primary determinant of mate location. However, because of the method of female sex pheromone release, particularly via terrestrial trails, female movement likely contributes to mate location; however, information on this topic is lacking. We monitored the movements of 27 free-ranging radio-equipped adult female northern watersnakes (Nerodia sipedon) during the 2007–2009 mating seasons to determine if females employed movement tac-tics to facilitate location by males. For a limited period following shedding, female movement increased. During this period, they were approximately five times more likely to be located by a male than during the remainder of the mating period. Further, females experienced maximum male mate location following shedding. Because increased movement is associated with increased costs, females may minimise these costs by restricting this risky behavior to a limited period of time when their attractiveness and/or receptiveness is presumed to peak.
... In some cases, scramble competition among males for mating opportunities can have detrimental effects on females in terms of dispersal (Shine et al. 2000(Shine et al. , 2004, survival (Davies and Halliday 1979;McKinney et al. 1983;Shine et al. 2001) and fecundity (Byrne and Roberts 1999;Johnson and Brockmann 2010). In this study, scramble competition was associated with disruption of mating events. ...
Intense male–male competition driven by high male density during mating can result in the evolution of alternative mating tactics that increase male fertilization success. The effects of alternative male mating tactics on females can range from increased fertilization and genetic benefits to decreased fertilization and loss of paternal care. However, the influence of male competitive behavior and alternative mating tactics on female behavior and reproductive success has seldom been addressed. In this work, I investigated the occurrence of alternative male mating tactics and their potential influence on female behavior and fertilization success in Japanese medaka (Oryzias latipes). Groups of one, two, or four males competed for access to a female in a repeated-measures experiment. Male density had a significant influence on female reproductive output as a result of a change in competitive mode from contest to scramble competition that coincided with more disruption during mating when more than one male attempted to mate. By contrast, sneaking during mating was beneficial to males, as more than one male sired offspring in most spawnings involving sneaker males. These results suggest that there may be conflict between males and females over mating, such that females are detrimentally affected by the occurrence of alternative mating tactics, whereas males may benefit from sneak mating. The occurrence of conflict between the sexes can be related to ecological factors, such as male density, which cause behavioral change in both males and females.
... Predation is a major source of mortality and, hence, a potential selective pressure for garter snakes in Manitoba. Crows (Corvus brachyrhynchos) kill many snakes each year and, thus, impose strong selection on traits such as size, morphology, and antipredator tactics (Shine et al., 2001b). In keeping with this idea, the snakes display complex antipredator behaviors and possess bright red markings visible only during these displays (Passek and Gillingham, 1997;Shine et al., 2000). ...
Garter snakes (Thamnophis sirtalis parietalis) in Manitoba court and mate at communal overwintering dens and then disperse to feeding ranges in summer. The restriction of mating activities to (tell areas may reduce gene flow between populations from adjacent dens, in turn allowing divergence in traits such as antipredator behavior. We quantified responses of adult male snakes to the approach of human observers at four (lens, prior to dispersal in late spring. Larger snakes bit us more frequently than did smaller individuals, at all four (lens. Although some of the dens were <20 km apart (and hence, individuals from each would likely encounter each other during summer), we found strong geographic differences in antipredator tactics (approach distance and propensity to bite). These differences may reflect genetic isolation Of den populations, due in turn to den-based mating and philopatry. However, to rule out alternative explanations such as learned responses to different predation exposure, studies are needed on naive snakes.
... where Mi and Li are the body mass and body length of the individual, respectively, i, L0 is the arithmetic mean of body length for each species and bSMA is a scaling exponent derived from the standardized major-axis (SMA) regression of body mass on body length. This index has been validated in several small-mammal species and, contrary to other condition indices (e.g., OLS, mass/body length ratios, e.g., Shine et al., 2001;Schulte-Hostedde et al., 2005) it accounts for the scaling between body components and body size, removing the covariation between body size and body components, and recognizes that the scaling relationships between body metrics may have interspecies variation (Peig and Green, 2009). ...
The present study aims at assessing allometric relationships in the Sigmodontinae rodents (Calomys tener, Akodon cf. montensis, Necromys lasiurus, Oligoryzomys flavescens, and Oligoryzomys nigripes), and morphological variation among different habitats in human-dominated environments in Southeastern Brazil. We captured rodents using pitfall traps placed in Eucalyptus plantations, abandoned pastures, and remnants of secondary native vegetation, and took the following measurements: body mass, total length, body length, left hind foot length, and left ear length. Males were usually larger than females, except in N. lasiurus. There was no intraspecific difference in body condition among habitats, suggesting that Eucalyptus may not have a deleterious effect upon its residents. However, A. cf montensis from Eucalyptus plantations had longer feet than those from other vegetation associations, suggesting a possible adaptive response to the lower cover in the plantation environment, and its consequent higher predation risk, or alternatively that only individuals with greater dispersal ability are found in Eucalyptus plantations. Future studies should investigate a possible co-evolutionary predator-prey relationship, including rapid evolution by Sigmodontinae rodents in anthropogenic landscapes.
... Among ectotherms, squamate reptiles (e.g., lizards and snakes) also tend to become smaller at higher altitudes and latitudes (Ashton and Feldman, 2003). In the Redsided Garter Snakes (Thamnophis sirtalis parietalis), poor body condition (i.e., depletion of energy reserves below certain thresholds) was found to be the most significant factor responsible for mortality (Shine et al., 2001). The trade-off between growth and storage may vary depending on altitudes and latitudes, and animals at high elevations likely allocate more resources into storage presumably because they need to survive longer non-growing seasons. ...
Ecologists have long studied extrinsic factors to explain intraspecific variation in phenotypic expression, yet assessment of intrinsic factors may also be important in understanding intraspecific phenotypic variation. Resources are allocated among the competing life history traits of growth, reproduction and storage. Thus, assessment of the suite of these traits may be critical to better understand phenotypic expression of life history traits. We examined growth (body size), reproduction (reproductive frequency) and storage (tail fat) of museum specimens of Red-backed Salamanders, Plethodon cinereus, at low and high elevations to test how altitudinal differences affected resource allocation among these life history traits. Based on the findings from previous studies, we hypothesized that animals at high elevations would be smaller in body size, reproduce less frequently and have less fat storage. We found that adult animals at high elevations were smaller in body size, reproduced less frequently (only females), but had greater tail fat storage relative to their body size than their counterparts at low elevations. The stored fat on tails can be used when salamanders are short of food. It may be more crucial for animals at high elevations to store more fuel for survival because longer and colder winters prevent them from actively foraging for longer periods. Our results suggest that resource allocation to growth and reproduction may be more constrained at high elevations because of the shorter growing season and greater allocation of energy into storage.
Ecosystem disturbance is increasing in extent, severity and frequency across the globe. To date, research has largely focussed on the impacts of disturbance on animal population size, extinction risk and species richness. However, individual responses, such as changes in body condition, can act as more sensitive metrics and may provide early warning signs of reduced fitness and population declines. We conducted the first global systematic review and meta-analysis investigating the impacts of ecosystem disturbance on reptile and amphibian body condition. We collated 384 effect sizes representing 137 species from 133 studies. We tested how disturbance type, species traits, biome and taxon moderate the impacts of disturbance on body condition. We found an overall negative effect of disturbance on herpetofauna body condition (Hedges' g = -0.37, 95% CI: -0.57, -0.18). Disturbance type was an influential predictor of body condition response and all disturbance types had a negative mean effect. Drought, invasive species and agriculture had the largest effects. The impact of disturbance varied in strength and direction across biomes, with the largest negative effects found within Mediterranean and temperate biomes. In contrast, taxon, body size, habitat specialisation and conservation status were not influential predictors of disturbance effects. Our findings reveal the widespread effects of disturbance on herpetofauna body condition and highlight the potential role of individual-level response metrics in enhancing wildlife monitoring. The use of individual response metrics alongside population and community metrics would deepen our understanding of disturbance impacts by revealing both early impacts and chronic effects within affected populations. This could enable early and more informed conservation management.
A bstract
The severity of the impacts of pathogens on hosts may be driven by environmental factors like resource availability that create tradeoffs on energetic demands for immune responses and basal metabolic activity within the host. These responses can vary among species from sublethal to lethal effects, which can have consequences for the host population trajectories within a community. Chytridiomycosis, caused by the pathogen Batrachochytrium dendrobatidis (or Bd), has been associated with global amphibian population declines. However, it also occurs in populations without appearing to cause mass mortality; the effect of Bd in these situations is not well understood and environmental factors like food abundance that impact host conditions could play an important role in the magnitude of the pathogen’s impact. In the present study, we exposed American toad ( Anaxyrus americanus ), northern leopard frog ( Lithobates pipiens ), and Blanchard’s cricket frog ( Acris blanchardi ) metamorphs to Bd and then reared them in the terrestrial habitat under low or high food environments. We found additive effects of Bd and reduced food abundance on host growth and survival that varied according to species. For instance, Bd-induced reductions in American toad survival were greater under low food conditions compared to high food conditions but survival of northern leopard frogs and Blanchard’s cricket frogs was not affected by Bd. For northern leopard frogs and Blanchard’s cricket frogs, low food abundance resulted in the lower growth rates under Bd exposure compared to high food abundance. Additionally, we developed stage-structured population models for American toads to assess if reduced survival of metamorphs exposed to Bd under conditions of low and high food abundance could influence population trajectories; models indicated that Bd exposure would reduce annual population growth rates by 14% under conditions of high food abundance and 21% under conditions of low food abundance. Our results suggest that environmental conditions that influence resource availability for species that are sensitive or tolerant to Bd may increase the negative effects of Bd on host growth and survival, which could have important implications for how populations and communities with infected members respond over time.
A bstract
Development of infectious diseases within hosts may be shaped by environmental conditions that cause tradeoffs in energetic demands for immune responses against demands for host growth and survival. Environmental conditions may influence these tradeoffs by affecting size of hosts, or tradeoffs may change across seasons, thereby altering the impacts of diseases on hosts. In the present study, we exposed northern leopard frog ( Lithobates pipiens ) tadpoles to varying larval environments (low leaf litter, high density of conspecifics, 40 µg/L atrazine, caged fish, or control) that influenced size at metamorphosis, a measure of host quality. Subsequently, we exposed these metamorphs of to Batrachochytrium dendrobatidis (Bd), a fungal pathogen linked to worldwide host population declines, at metamorphosis and/or 12 weeks later, prior to overwintering. Bd exposure dramatically reduced survival during overwintering and the effect was strongest when frogs were exposed both at metamorphosis and before overwintering. Larval environments, which determined host size, did not influence effects of Bd. Stage-structured models built to assess the impacts of Bd exposure on host populations suggest that Bd exposure at metamorphosis or before overwintering would reduce annual population growth rates by an average of 19% and 41%, respectively. Our study indicates that northern leopard frog hosts suffered little effects of Bd exposures following metamorphosis and that lower host quality did not hamper a frog’s ability to respond to Bd. Instead, we provide evidence that Bd exposure can reduce survival and result in population size reductions via reduced recruitment from overwintering mortality, providing a plausible mechanism for enigmatic declines of amphibians in temperate regions.
Predator‐based selection is ubiquitous and can be a major driver of phenotypic and life‐history evolution. However, how characteristics of individual prey species influence predation risk is unknown for many taxa. This dearth of information on what factors can drive predation risk is particularly profound for small terrestrial vertebrates. We focused our research on the rough earth snake (Haldea striatula), which is ideal for this research because they are small, abundant and subject to predation from a host of predators. We then tested for the role of sex, color morph and body size on the likelihood that a snake would experience attempted predation. This was accomplished by coupling the (1) examination of natural history specimens for evidence of predation and (2) use of clay models of rough earth snakes to test for variation in predation in a natural setting. For the natural history study, we found that scars on specimens increased in frequency with body size, but wound frequency did not differ based upon color pattern or sex. For the clay model study, we found that attack rates increased with model size. Our results suggest that predation risk increases with body size in these diminutive snakes, perhaps due to greater detection probability or different predatory assemblages for larger snakes. More broadly, our results suggest that predator‐based selection may drive smaller body size, which has implications for understanding the diversity of body size in snakes.
Relocating snakes is used to reduce potential snake-human conflict and to re-establish or augment populations. Relocation may be unsuccessful if snakes attempt to home back to their capture locations or otherwise alter their behavior in ways that reduce fitness. To better understand the conditions under which the technique is likely to be successful, we conducted two types of relocation (repatriation and short-distance translocation) using Eastern Massasaugas (Sistrurus c. catenatus) in Ontario. For the repatriation experiment, 27 snakes were captive-born, raised for four years, and released into a nature reserve previously known to host massasaugas. Other than being relatively sedentary, snakes behaved normally upon release in that they engaged in reproductive behavior. Survival (70%) was relatively high until hibernation (19 weeks). However, none of the snakes that did hibernate (n = 19) survived into the following active season. In a preliminary assessment of the effects of short-distance translocation, snakes that we moved 200 m from capture locations (n = 4) did not return, nor did they exhibit abnormal movement or basking behavior relative to non-translocated controls (n = 7). The different outcomes of our two relocations could indicate that the success of relocation depends on the extent of displacement and the source of relocated individuals, although corroborating evidence is needed before these results can be used to support management strategies.
The fundamental niche is formed as a result of evolution. In the state of evolutionary stasis, species undergo various deteriorations in the conditions of their existence, which interfere with counterbalance of the vectors of directional selection, which sustains this stasis. The unbalanced selection vectors induce the adaptations to extreme conditions of existence that are superfluous relative to the common conditions. The limits of tolerance and resistance to extreme ecological situations restrict the fundamental niche. Interspecific competition is not the cause of narrowing the obtained niche relative to the fundamental niche. In the cases when the competition intensity is sufficient to redistribute resources between competitors, it can restrict one or two parameters of the obtained niche according to the limited resources, but does not cover the overall multidimensional space of the obtained niche. The obtained niche is a part of fundamental niche, since populations of a species live under conditions that provide for their existence in a particular habitat. The achievement of only part of the adaptive potential of a species and its fundamental niche is sufficient for existence of this species under more or less suitable conditions.
Colours influence numerous aspects of an animal's ecology. One possibility is that colour helps make an animal cryptic against the background on which it is resting. We test this hypothesis for two different, geographically separated colour forms (dark forms and light forms) of the Western Terrestrial Garter Snake, Thamnophis elegans. We quantified crypsis of snakes, in terms of colour (chromatic crypsis) and brightness (achromatic crypsis), by using objective measures of spectral reflectance of snakes and the surrounding habitat. These data were visually modelled from the perspective of potential snake predators and human researchers. Overall, snakes of both colour forms selected basking sites that increased chromatic crypsis over that which would have been achievable on random backgrounds. Both colour forms of T.elegans appear to exhibit similar achromatic and chromatic crypsis when viewed by potential predators, such as mammals and birds. From the perspective of the human visual model, dark T.elegans were generally more chromatically cryptic than light T.elegans, contrary to our a priori subjective impression. The main contribution of the present study is that we provide one of the first objective comparisons of snakes and their backgrounds as a measure of crypsis. Although we found some evidence for crypsis as a factor in choice of basking sites for snakes, other factors (e.g. thermoregulatory opportunities) undoubtedly play important roles as well. We also have not addressed whether snakes involved in other activities are cryptic or whether there are differences between the sexes or between reproductive and nonreproductive females. The adaptive significance of colour variation has been studied in diverse taxonomic groups. Although the mechanisms are not straightforward, the opportunities to carry out further work in this area are enhanced by the availability of objective approaches.
During courtship interactions, the courted individual may not always be prepared to mate. For example, mating or courtship may be detrimental to its fitness and resistance is expected under these circumstances. As such, various resistance strategies have evolved, from physically fending off courting individuals to producing behavioural signals of unreceptivity. In the parasitoid wasp Spalangia endius, females rarely re-mate and mated females are avoided by males in favour of virgin females. Further, mated females appear to advertise their mating status by the release of a pheromone component (methyl 6-methylsalicylate), but direct evidence of the nature of this release is lacking. Here we used real-time chemical analysis to track the emission of the pheromone component during courtship interactions between virgin males and either virgin or mated females. We found that females actively release methyl 6-methylsalicylate when courted and that significantly greater concentrations are released by previously mated females. Further, high concentrations of this component are associated with both the prevention and termination of courtship.
Body condition indices (CI) are useful tools as indicators of the health, nutrition, and life history of the individuals in a population. Healthy individuals with high energy reserves have more probabilities to breed; therefore, good body conditions are essential in order to preserve populations and the ecosystem functioning. Morelet’s crocodile (Crocodylus moreletii) is a key species for the stability of the ecosystem. However, studies about the health of its populations are quite scarce. The aim of this research was to determine the CI of the population of C. moreletii in the Hondo River, through the application of Fulton’s “K” condition factor (CF). During two survey periods (April-September 2002, and June 2009 to February 2010), we conducted spotlight counts aboard a 4.5 m-long aluminum boat in six sections of the river. We analyzed 200 crocodiles, most of which (n=177) had a good body condition (mean K = 41.63), which denotes a healthy population. ANOVA tests applied to mean CF values revealed significant differences (P<0.05) between survey sections, and age classes, but no significant differences between males and females (P>0.05) in both periods. Monitoring of CF in the C. moreletii population is important for the improvement of the conservation and management actions for the species and its habitat, and must be considered in future research.
We studied the ecology of Psammobates oculifer over 13 months near Kimberley, South Africa, to ascertain if the population's life history traits conform to chelonian patterns in arid environments. Capture rates were highest in spring and lowest in winter when environmental conditions were respectively most and least favourable for tortoise activity. Body condition did not change from autumn to spring, but reached lower values during the summer drought. Capture effort averaged 5 hours/tortoise, which corresponds closely to that of species with low population densities in arid regions. Population size structure was skewed towards adults, indicative of low recruitment and/or low juvenile survivorship. Females were larger and heavier than males, confirming sexual dimorphism in this species. Body size of cohorts scaled to annuli counts, indicating a close correspondence between body size and age. Telemetered adults deposited one or no growth ring in the year of study; consequently, annuli counts could underestimate adult age. Regression analyses showed that male and female growth rates did not differ, but males matured at a smaller size and younger age than females. The smallest male showing reproductive behaviour had 12 annuli and a shell volume of 157 cm3, while similar measures for females were 14 annuli and 185 cm3. The sex ratio of the population did not differ from 1:1 but the bias towards males in spring, and towards females in autumn, indicates that studies limited to particular seasons can misrepresent life history traits of populations. We concluded that the life history of P. oculifer conforms to chelonian patterns in arid regions.
An archaeological excavation site among ancient ruins in Histria, south-eastern Romania, that harbours several thousand dice snakes (Natrix tessellata), is the focus of various ongoing studies. The current work evaluates seasonal variation of gender specific movements. Seasonal movements were estimated from captures of adult snakes over four years. Visible abundance of snakes among the ruins was largest in early spring and autumn. Summed over one entire season, the capture rates were similar for both sexes. During April males were more frequently captured than females. However, the proportion of males decreased later during the mating period in spring and until the end of June, only to rise again in August. Capture rates of gravid females continued to remain high in the vicinity of the ruins throughout vitellogenesis until ovulation, for which they mainly stayed near the hibernation area, which is also favoured for ovipositing. At the onset of hibernation in October, the ratio of males to females was consistently 0.4 across all years of study. We suggest that the skewed sex ratio among captures is due to gender-specific behaviours rather than to a naturally uneven sex ratio or capture artefacts. Males generally emerge earlier from hibernation in order to maximize their chances to reproduce. Consistent with our data, we suggest that in autumn males may be entering hibernation dens over a longer period than do females. Arguably, males do not have the same energy re-quirements as females, which could be expected to exploit the feeding season maximally, due to their higher-energy reproductive investment.
Decisions affecting wildlife management and conservation policy of imperiled species are often aided by population models. Reliable population models require accurate estimates of vital rates and an understanding of how vital rates vary geographically. The eastern massasauga (Sistrurus catenatus catenatus) is a rattlesnake species found in the Great Lakes region of North America. Populations of the eastern massasauga are fragmented and only a few areas harbor multiple, sizable populations. Eastern massasauga research has typically focused on single populations or local metapopulations but results suggest that demographic parameters vary geographically. We used 21 radiotelemetry datasets comprising 499 telemetered snakes from 16 distinct locations throughout the range of the eastern massasauga to characterize geographic patterns of adult survival using the known-fate model in Program MARK. Annual adult survival ranged from 0.35 to 0.95 (mean ¼ 0.67) and increased along a southwest to northeast geographic axis. Further analysis of 6 datasets indicated no consistent difference in survival between males and females. Our results provide a better understanding of the relationship between survivorship and geography for the eastern massasauga and suggest that such variation should be incorporated into population models as well as local and regional management plans.
We took advantage of unique aspects of the red-sided garter snake's breeding biology at northern latitudes to investigate whether mating was correlated with a reduced risk of predation. We scored the number of mated vs. unmated and predated vs. surviving female snakes at four dens in Manitoba, Canada. Predation intensity did not significantly vary through time during the course of the study, nor did it vary among dens. Female mating significantly decreased the odds that a female would be the victim of predation. This is likely a result of reduced courtship of females after mating, which reduces female conspicuousness and facilitates the ability to escape. These results provide support for the hypothesis that the copulatory pheromone, which communicates female mating status to males and thus reduces male courtship, benefits females by indirectly reducing their risk of predation after mating.
Extreme climatic disturbances provide excellent opportunities to study natural selection in wild populations because they may cause measurable directional shifts in character traits. Insectivorous cliff swallows (Petrochelidon pyrrhonota) in the northern Great Plains must often endure periods of cold weather in late spring that reduce food availability, and if cold spells last four or more days, mortality due to starvation may result. We analyzed morphological shifts associated with viability selection, and how patterns of bilateral symmetry were affected by survival selection, during a four-day period of cold weather in 1992 and a six-day period in 1996 in southwestern Nebraska. Birds that died during the cold were compared to those still alive when the severe weather ended. The event in 1992 killed relatively few birds, but the cold spell in 1996 killed thousands of cliff swallows and reduced their population by about 53%. Climatological records suggest that mortality events comparable to that of 1996 have occurred in only one other year since 1875. Larger birds were favored in the 1996 event. Selection was more intense in 1996 than in 1992 because of more stressful conditions in 1996. Directional selection gradient analysis showed that measures of skeletal body size (tarsus length, culmen width and length) and wing length were targets of selection in 1996. Survivors had lower wing and outer tail asymmetry, and wing and tail asymmetry were targets of selection in both events. Mortality patterns did not differ by sex, but older birds suffered heavier mortality; morphological traits generally did not vary with age. Nonsurvivors were not in poorer apparent condition prior to the weather event than survivors, suggesting that selection acted directly on morphology independent of condition. Selection on body size in cliff swallows was more intense than in studies of body size evolution in other bird species. Larger swallows were probably favored in cold weather due to the thermal advantages of large size and the ability to store more fat. Swallows with low asymmetry were favored probably because low asymmetry in wing and tail made foraging more efficient and less costly, conferring survival advantages during cold weather. This population of cliff swallows may have undergone relatively recent body size evolution.
Female mimicry is found in many diverse taxa including insects and most vertebrate classes (Weldon and Burghardt, 1984) and occurs in two forms. In several species, males assume a female-like morphology or color pattern (Dominey, 1980; Gross, 1979), whereas in others, males mimic female behavior patterns (Arnold, 1976; Thornhill, 1979). In some species males mimic both female morphology and behavior (Gross, 1983).
Most grass snakes have a yellow black bordered collar just behind the head. In neonates the contrast between the collar and the body colour is more distinct than in adults which makes the young snakes particularly conspicuous. Seventy-five normal (with a yellow collar) and 75 melanistic models of neonate grass snakes were manufactured from black plasticine and exposed in the study area. Ten experiments were carried out. The melanistic models were more subjected to avian predation than the normal models. I suggest that the yellow head collar could be a form of mimicry of aposematically coloured unpalatable insects. The lower bird predation on the normal models could thus be due to the birds interpreting these as being unpalatable.
The allocation of mammals, lizards, and insects captured by a nesting Great Grey Shrike and a nesting Kestrel hunting in the same clear-cut was recorded. Both predators carried most mammals (large prey) to the nest, and consumed all insects (small prey) at the capture site. The small predator (Great Grey Shrike) carried most lizards (medium-sized prey) to the nest, whereas the large predator (Kestrel) consumed most lizards at the capture site, although the distance from lizard capture sites to the nest did not differ between the two predators. If the allocation pattern found applies in general, traditional nest-based food analyses overstimate the proportion of lizards in the overall diet of the Great Grey Shrike and underestimate it in the Kestrel.
Predators of small mammals may selectively kill either large individuals, usually male or the old, or small individuals, often females and young. We studied the prey choice of breeding male Tengmalm's owls (Aegolius, funereus) in western Finland. The owls fed mainly on sibling voles (Microtus rossiaemeridionalis), field voles (M. agrestis), bank voles (Clethrionomys glareolus) and common shrews (Sorex araneus). We identified, sexed and weighed prey items cached by the owls in their nest-boxes, and compared characteristics of these prey to small mammals trapped in the same study area during 1985-1992. For each of the three vole species, owls captured more males than females, but we did not find that owls preferred one sex of common shrews. Our long term data indicated that male-bias of two Microtus species in the diet of owls was highest in the low phase of the vole cycle, and decreased through the increase and peak phases. This suggests that the two sexes of voles behave differently, but that these differences change over the course of the 3-yr cycle. The proportion of prey individuals with a small body mass was greater in owl caches compared to trapping censuses, irrespective of species or sex. Large dominant individuals may occupy safe habitats with dense vegetation cover, where avian predation risk is minimal.
We studied the spring emergence of red-sided gartersnakes (Thamnophis sirtalis parietalis) from a large communal den in Manitoba to clarify the context in which courtship and mating occur. In particular, is the mating system in such a massive aggregation ( 20,000 snakes) substantially different from that at smaller dens? Radio-tracked female snakes stayed near the den for a few days postemergence, apparently waiting until they recovered locomotor ability after the long hibernation period, before setting out for their summer ranges. Females dispersed from the den in all directions, rather than following distinct migration corridors. Male snakes moved frequently and spent much of their time far from the den in surrounding woodland. Most males remained near the den for only a small proportion of the entire mating season, apparently because of high rates of energy expenditure during mate-searching and courtship. Courting groups contained from 1-62 males and were largest close to the den. Most courting and mating occurred in groups of less than five males, often more than 20 m from the den. These small group sizes resulted from the females' dispersal prior to mating. Larger groups did not induce female cooperation (mating) more quickly than small groups. Despite the spectacular ag- gregations of courting snakes within the den, most reproductive activity in this pop- ulation (as in other gartersnake populations) occurs in small groups, widely dis- persed over a broad area.
The purpose of this study was to document the extent of variation in indi- vidual growth rates and its fitness consequences among several populations of an indeter- minate grower, the western terrestrial garter snake Thamnophis elegans. Twenty years of mark-recapture data and six years of laboratory breeding data provided evidence of large differences among six populations in individual growth rates and subsequent reproductive maturation, fecundity, and survival. Weather, diet composition, and prey availability were examined for their effects on individual growth. Two ecotypes were revealed whose dis- tribution coincided with differences in prey availability. Individuals from populations that had continuous access to prey and water across years exhibited fast growth, early maturation, high fecundity, and low adult survival. In contrast, individuals from populations that ex- perienced variable prey availability exhibited slow growth, late maturation, low fecundity, and high adult survival. This growth rate variation was examined in the context of two competing explanations: the maximization and optimization hypotheses. Food availability may be a primary limiting factor to growth and subsequent life history traits, which is consistent with the maximization hypothesis. However, negative phenotypic correlations between growth and survival and between growth and reproduction may indicate an un- derlying negative genetic correlation, consistent with the trade-off hypothesis. Field studies such as this one are useful for documenting the patterns of life history variation that occur in nature, identifying possible causes of such variation, and generating testable hypotheses for controlled experiments.
Human land uses have resulted in landscape mosaics with habitat patches that vary in quality. Patch quality (including the abundance of food and the risk of predation) can affect the survival of animals that are sequestered in remnant patches of habitat. Recent investigations of the demography of New England cottontails (Sylvilagus transitionalis) have shown that cottontails on small (resource poor) patches were in poor physical condition (based on body mass) and often foraged at sites with limited cover. This resulted in a higher mortality rate than among rabbits occupying large (resource rich) patches. To gain additional insight into the consequences of habitat fragmentation, we tracked the physiological condition of rabbits occupying small and large patches during winter. The physiological condition of rabbits was determined using the urinary urea nitrogen:creatinine ratio, and the results were compared with similar indices obtained from captive rabbits. Consistent with our expectations, the nitrogen:creatinine ratios indicated that rabbits on small patches were nutrient limited for a longer period than rabbits on large patches. Transmitter-equipped rabbits on small patches had a lower survival rate and died earlier than rabbits on large patches. All mortalities were predator related. Using these data, we developed a simple model that supports the role of "condition-sensitive predation" as a major factor limiting populations of New England cottontails. Our results also demonstrate the utility of sampling physiological condition to provide an index of quality of lagomorph habitat in human-dominated landscapes.
Although garter snake populations in northern areas have been shown to undergo annual migrations, no detailed information has been available on these movements. Through biotelemetry and, to a lesser extent, mark–recapture methods, the migration of an extreme northern population of Thamnophis sirtalis was documented. Snakes emerging from a hibernaculum moved towards the closest freshwater marsh, which was approximately 3.75 km away. Radio-tracked individuals moved along a constant bearing; once they reached the proximal regions of the marsh, they continued to move away from the den, but circled back during the later part of the summer. One individual completed a round trip of over 15 km during one active season. Snakes routinely exhibited a distinct behavioral sequence during the daily travels, and five rather lengthy searches for overnight retreats were observed. The extensive migration documented in this study may be quite costly for the northern snakes, for (i) it may significantly decrease the time available for other important activities, such as feeding, and (ii) it increases the snakes' exposure to the adverse spring and fall weather conditions, which in turn may subject them to predation or lethal temperatures.
Functional appraisal of the differential survival pattern reported by Bumpus (1899) for House Sparrows (Passer domesticus) prompted this study of morphometric and energy relations of birds collected at a winter roost in Ann Arbor. There was no relation between overall size (mass or Principal Component I score) and total body length of males, but PC-I scores and body mass were correlated significantly in Ann Arbor males and females. Female Ann Arbor sparrows had higher proportionate energy reserves than males and, overall, were predicted to have greater fasting endurance. When body masses of Bumpus' male and female birds were evaluated as a function of their PC-I scores (based on six skeletal measures), survivors of a given gender had the same slope but significantly lower elevation than non-survivors. The consistently higher body mass of non-survivors for a given PC-I score in Bumpus' sample suggests that these birds died of exposure soon after the storm's onset and, consequently, used far less of their energy stores than their surviving counterparts. If the birds classed as survivors by Bumpus were fully representative of House Sparrows enduring the storm of 1898, then larger males and intermediate-sized females were more likely to secure and remain at protected roost sites during the 1898 storm than their less fortunate roostmates. On the other hand, because Bumpus' sample was collected by hand and had a disproportionately low female composition, conclusions about gender differences in pattern of selection in Bumpus' birds must be questioned.
A 5-year mark-recapture study of smooth snakes (Coronella austriaca) in the Carnic Alps (1100 m above sea level) of north-eastern Italy provided extensive information on the biology and life-history of these small viviparous snakes. Offspring were relatively large (mean=15 cm total length, 2.9 g) when they were born in late summer, and females grew to maturity (44 cm, 50 g) in approximately 4 years. Larger neonates retained their size advantage for at least 12 months, but did not have a higher probability of survival. Although sexual size dimorphism (at birth and at mean adult body sizes) was minor, the sexes differed significantly in several respects. Females grew faster than males during juvenile life, and adult females diverged in dietary habits from the rest of the population. Whereas juveniles (of both sexes) and adult males fed primarily on lizards, larger females shifted to feeding less frequently, but taking larger prey (mammals and snakes). Reproductive output increased strongly with maternal body size: larger females reproduced more frequently, produced larger litters of larger neonates, had higher relative clutch masses (RCMs), and had a lower proportion of stillborn off-spring. Most females produced a litter every 2nd or 3rd year. We did not detect significant year-to-year variation in reproductive traits over the 5 years of our study. Females were consistent from one litter to the next in several traits (e.g., litter sizes, offspring sizes and shapes, proportions of stillborn neonates, RCMs), but this consistency was due to differences in body size among females rather than to size-independent maternal effects. Overall litter sex ratios averaged 50/50, but sex ratios tended to be more male-biased in litters that were unusually large relative to maternal body size, and in litters containing a high proportion of stillborn offspring. Costs of reproduction appear to be high in this population, in terms of both energy allocation and risk. Reproduction reduced growth rates, and females that recovered condition more quickly in the year after reproduction were able to reproduce again after a briefer delay. Mortality was highest in reproducing females with high RCMs, and in females that were very emaciated after parturition. The marked increase in reproductive output with increasing maternal body size in C. austriaca may reflect a reduction in costs as females grow larger, and the dietary shift to larger prey may enhance the rate that females can accumulate energy for reproduction.
During the month of February 1979, several hundred hatchling land iguanas (Conolophus pallidus) were observed emerging from their natal burrows in a 2 ha communal nesting area on Isla Santa Fe, Galapagos Islands. During this emergence, as many as nine Galapagos hawks were observed to patrol the nesting area and attack hatchling iguanas.The hypothesis that the ability of hatchling land iguanas to escape predation could be influenced by the interaction of the physiological state of the lizards and the thermal environment was analyzed using (1) empirical data on the effect of body temperature (T
b) on locomotory ability of iguanas and (2) biophysical modeling of the T
b's of hatchlings under natural conditions. This hypothesis was tested by assessing the success of natural hawk attacks on lizards exposed to different thermal environments.During those periods when predicted T
b's of hatchlings were always T
b's of hatchlings were always 32 C, hawks were successful on only 19% of observed attacks. During periods when hatchling T
b's could be These data indicate that the physical environment, as mediated through the physiological state of the lizards and to correlated locomotary abilities, significantly affects the ability of hatchling land iguanas to escape predation.
Eleven years of data on a small population of adders (Vipera berus) in southern Sweden provide quantitative information on the nature and degree of costs faced by reproducing animals. Reproduction
imposes both an energy cost (measured by loss in body mass) and a mortality cost on adders of both sexes. The extent of the
energy cost is broadly independent of levels of reproductive activity in males, but mortality costs are highest for large
males, perhaps because they are more obvious to predators. In females, energy costs include a high ‘fixed’ (fecundity-independent)
component, such that a large litter may cost little more to produce than would a small litter. Energy costs and mortality
costs are separate in males, but inter-related in females. Mortality of reproducing females is high (40% per year), primarily
because post-parturient females are emaciated and must forage actively, hence increasing their vulnerability to predators.
Females producing relatively large litters (high Relative Clutch Mass) lose more body mass, and are less likely to survive
after reproducing. The observed low reproductive frequencies of female adders may result from the presence of high fecundity-independent
costs of reproduction.
Mating aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) in Manitoba provide a unique opportunity to identify the cues that attract a male snake and induce him to court. The snakes are abundant, tolerate human presence, and males direct courtship to a subset of other males ("she-males") as well as to females. Previous work has emphasised the role of pheromonal cues (skin lipid profiles) as sexual attractants in snakes. However, pheromones are so widely distributed throughout the den area that these chemical cues may be difficult for males to use to localise females. Our field studies show that males and females differ in several other attributes such as size (females are larger than males), body temperature (very cold snakes are often females), muddiness (females are often covered in mud) and whether or not they are solitary (most females are surrounded by courting males). Experiments show that males use all of these cues to identify possible sexual partners. Visual and thermal cues are particularly important for solitary mate-searching males; but after a mating ball forms around a female, pheromones may be most important. Our study also reveals substantial variation among individuals: females vary in attractiveness, and males vary in their intensity of courtship as well as in the magnitude of their preference for one potential partner versus another. Thus, a male snake's "decision" whom to court depends not only on visual and thermal as well as chemical cues, but also on the male's own preferences and on subtle differences among potential sexual "targets".
We analysed the data of H.C. Bumpus on the survival of house sparrows (Passer domesticus) using structural equation modelling techniques. Using data on seven morphological variables measured by Bumpus, we tested and confirmed a three-factor model that characterized physical attributes for general size, leg size and head size. Although males were physically larger than females, we found no difference between males and females in the physical attributes as measured by the three factors. Survival increased significantly with increasing general size and was unrelated to leg size and head size. Wing length, independent of its relationship to the general size factor, was also significantly related to survival. Higher survival was found among birds with short wings. Males had a higher survival compared to females. Their higher survival was mediated, to a lesser extent indirectly, through greater size and, to a greater extent directly, through effects of unknown origin. We favour the use of structural equation modelling methods in studies of selection because of their ability to test and confirm or disconfirm hypotheses related to selection events.
Empirical studies of mimicry have rarely been conducted under natural conditions. Field investigations of some lepidopteran systems have provided a bridge between experiments examining artificial situations and the mimicry process in nature, but these systems do not include all types of mimicry. The presence of dangerous or deadly models is thought to alter the usual rules for mimicry complexes. In particular, a deadly model is expected to protect a wide variety of mimics. Avoidance of different types of mimics should vary according to how closely they resemble the model. Coral snake mimicry complexes in the neotropics may provide natural systems in which these ideas can be examined, but there is no direct evidence that the patterns of venomous coral snakes or potential mimics are avoided in the wild. Plasticine replicas of snakes were used to assess the frequency of avian predation attempts as a function of color pattern. Avian predators left identifiable marks on the replicas, the position of which indicated that replicas were perceived as potentially dangerous prey items by birds. The number of attacks on unmarked brown replicas was greater than that on tricolor coral snake banded replicas. This result was true whether replicas were placed on natural or plain white backgrounds, suggesting that coral snake banded patterns function aposematically. In a separate experiment, replicas representing all six patterns of proposed coral mimics at the study site were attacked less often than unmarked brown replicas. Within these six banded patterns, some were attacked significantly more often than others. This study provides direct field evidence that coral snake banded patterns are avoided by free-ranging avian predators and supports theoretical predictions about mimicry systems involving deadly models.
Understanding the mechanics of adaptive evolution requires not only knowing the quantitative genetic bases of the traits of interest but also obtaining accurate measures of the strengths and modes of selection acting on these traits. Most recent empirical studies of multivariate selection have employed multiple linear regression to obtain estimates of the strength of selection. We reconsider the motivation for this approach, paying special attention to the effects of nonnormal traits and fitness measures. We apply an alternative statistical method, logistic regression, to estimate the strength of selection on multiple phenotypic traits. First, we argue that the logistic regression model is more suitable than linear regression for analyzing data from selection studies with dichotomous fitness outcomes. Subsequently, we show that estimates of selection obtained from the logistic regression analyses can be transformed easily to values that directly plug into equations describing adaptive microevolutionary change. Finally, we apply this methodology to two published datasets to demonstrate its utility. Because most statistical packages now provide options to conduct logistic regression analyses, we suggest that this approach should be widely adopted as an analytical tool for empirical studies of multivariate selection.
Selection on locomotor performance was determined for a series of marked and recaptured individuals from a population of garter snakes (Thamnophis sirtalis fitchi) in Northern California. We measured snake length and mass, burst speed, endurance on a treadmill, and the distance crawled around a stationary circular track. Size-corrected values (residuals) of mass and locomotor performance were generated from the scaling equations of S-V length (SVL). Randomization tests and regressions were used to determine the probability that a trait was a significant predictor of survivorship, and a nonparametric, cubic spline estimate of the fitness function was used to facilitate detection of the patterns of selection. From 275 ("cohort") snakes measured and tested within 8 days of birth in 1985, 79 were recaptured in the spring-summer of 1986 and subsequent years. Birth SVL was the only significant (randomization P = 0.022) predictor of neonatal survival from 1985 to 1986 with directional selection favoring larger individuals. In addition to the lab-born cohort, 382 field-born snakes from all ages in the population were captured, tested, and released during spring-summer 1986. Similar to the 1985 cohort, the survivorship of 37 of 86 neonates from 1986 to 1987 showed no significant relationship with any residual value using any statistical test. Survivorship from 1986 to 1987 for 127 of 250 yearlings (including 32 lab-born cohort snakes) analyzed with the randomization test showed that greater values of both speed (P = 0.007) and distance residual (P = 0.008) significantly favored survival, whereas intermediate values of mass residual (P = 0.006) were significantly more likely to survive. Univariate regressions predicting the survival of yearlings from 1986 to 1987 gave similar results to the randomization test, but in a multiple regression with yearling burst speed residual, distance capacity residual, and a quadratic term of mass residual, distance capacity residual was the least important predictor variable. For the survivorship of 37 of the 113 older snakes, greater burst speed residual significantly favored survival (randomization P = 0.001).
Examined Lirceus fontinalis in relation to differences in predation risk from green sunfish Lepomis cyanellus. Isopods of all sizes were far more dense in Cladophora, a filamentous green algae, than in open silt/sand substrates in fish pools. Densities of each size did not increase in open silt/sand substrates in fish pools. Densities of each size did not increase in open areas at night in fish pools when risk of predation presumably decreases. Few individuals of any size class occurred in open silt/sand areas in fish pools, but habitat use did not depend on fish presence. Densities and relative abundances of all sizes were similar between algal and open habitats in fishless pools both day and night, except for mature males which were more abundant in open areas during daylight. All sizes of isopods were significantly more dense in fishless versus fish pools, and density of a size class was influenced by fish presence. Green sunfish are size selective feeders on isopods, thus demography of isopods within pools may be partially influenced by the size structure of the fish population. -from Authors
At northern latitudes the garter snake (Thamnophis sirtalis parietalis) undergoes a prolonged period of hibernation and has access to food only from mid-May to mid-September. An examination of seasonal changes in the body composition of this organism revealed that protein and ash, expressed as percentage of total body weight, remain essentially constant throughout the year. Lipids are low in the spring, increase during the summer, and decrease during the autumn and winter. Percentage water content exhibits a pattern which is the reverse of that of lipids, with the exceptions of a dehydration in the autumn and a rehydration in the spring. Expressed in absolute terms, for an animal of fixed body length, ash remains relatively constant throughout the year, while all other components show a seasonal pattern similar to that of lipids. The data suggest that the animals are near starvation in May, at the end of an 8-month aphagic period. The period of aphagia and low winter temperatures appear to be the most important factors causing seasonal changes in body composition.
Extreme climatic disturbances provide excellent opportunities to study natural selection in wild populations because they may cause measurable directional shifts in character traits. Insectivorous cliff swallows (Petrochelidon pyrrhonota) in the northern Great Plains must often endure periods of cold weather in late spring that reduce food availability, and if cold spells last four or more days, mortality due to starvation may result. We analyzed morphological shifts associated with viability selection, and how patterns of bilateral symmetry were affected by survival selection, during a four-day period of cold weather in 1992 and a six-day period in 1996 in southwestern Nebraska. Birds that died during the cold were compared to those still alive when the severe weather ended. The event in 1992 killed relatively few birds, but the cold spell in 1996 killed thousands of cliff swallows and reduced their population by about 53%. Climatological records suggest that mortality events comparable to that of 1996 have occurred in only one other year since 1875. Larger birds were favored in the 1996 event. Selection was more intense in 1996 than in 1992 because of more stressful conditions in 1996. Directional selection gradient analysis showed that measures of skeletal body size (tarsus length, culmen width and length) and wing length were targets of selection in 1996. Survivors had lower wing and outer tail asymmetry, and wing and tail asymmetry were targets of selection in both events. Mortality patterns did not differ by sex, but older birds suffered heavier mortality; morphological traits generally did not vary with age. Nonsurvivors were not in poorer apparent condition prior to the weather event than survivors, suggesting that selection acted directly on morphology independent of condition. Selection on body size in cliff swallows was more intense than in studies of body size evolution in other bird species. Larger swallows were probably favored in cold weather due to the thermal advantages of large size and the ability to store more fat. Swallows with low asymmetry were favored probably because low asymmetry in wing and tail made foraging more efficient and less costly, conferring survival advantages during cold weather. This population of cliff swallows may have undergone relatively recent body size evolution.
Empirical studies of mimicry have rarely been conducted under natural conditions. Field investigations of some lepidopteran systems have provided a bridge between experiments examining artificial situations and the mimicry process in nature, but these systems do not include all types of mimicry. The presence of dangerous or deadly models is thought to alter the usual rules for mimicry complexes. In particular, a deadly model is expected to protect a wide variety of mimics. Avoidance of different types of mimics should vary according to how closely they resemble the model. Coral snake mimicry complexes in the neotropics may provide natural systems in which these ideas can be examined, but there is no direct evidence that the patterns of venomous coral snakes or potential mimics are avoided in the wild. Plasticine replicas of snakes were used to assess the frequency of avian predation attempts as a function of color pattern. Avian predators left identifiable marks on the replicas, the position of which indicated that replicas were perceived as potentially dangerous prey items by birds. The number of attacks on unmarked brown replicas was greater than that on tricolor coral snake banded replicas. This result was true whether replicas were placed on natural or plain white backgrounds, suggesting that coral snake banded patterns function aposematically. In a separate experiment, replicas representing all six patterns of proposed coral mimics at the study site were attacked less often than unmarked brown replicas. Within these six banded patterns, some were attacked significantly more often than others. This study provides direct field evidence that coral snake banded patterns are avoided by free-ranging avian predators and supports theoretical predictions about mimicry systems involving deadly models.
We examined ontogenetic changes in diel patterns of habitat use and activity of the lotic isopod Lirceus fontinalis in relation to differences in predation risk from green sunfish, Lepomis cyanellus. Juveniles are ≤5 mm total length (TL), individuals 6-9 mm TL are mature females (c. 90%) and immature males, and mature males are ≥10 mm TL. Isopods of all sizes were far more dense in Cladophora, a filamentous green algae, than in open silt/sand substrates in fish pools. Densities of each size did not increase in open areas at night in fish pools when risk of predation presumably decreases. Few individuals of any size class occurred in open silt/sand areas in fish pools. However, habitat use did not depend on fish presence. Densities and relative abundances of all sizes were similar between algal and open habitats in fishless pools both day and night, except for mature males which were more abundant in open areas during daylight. All sizes of isopods were significantly more dense in fishless versus fish pools, and density of a size class was influenced by fish presence. Densities of size classes were typically juveniles > individuals 6-9 mm TL > mature males. Green sunfish are size selective feeders on isopods, thus demography of isopods within pools may be partially influenced by the size structure of the fish population.
Isopods reduced their activity, as measured by captures in benthic traps, in the presence of caged green sunfish only at night. This behavior coupled with relatively high activity levels during daylight regardless of fish presence suggests other predators or factors may influence diel activity. Mature males were overrepresented in traps relative to their occurrence in fish runs, indicating high activity levels. Mature males were also more active than gravid and nongravid females and juveniles in the presence of fish in laboratory aquaria. Number of male encounters with nongravid females depended on activity level.
Between 1980 and 1990, 176 adult Merriam's kangaroo rats were subcutaneously implanted with radio transmitters and tracked for a total of 6316 animal-days at a California site, prior to and during reproductive seasons. Thirty-six animals are known to have been killed by predators, and 14 who disappeared abruptly are also presumed victims. These 50 cases permit various analyses of differential predation risk. Males incurred a predation rate (4·22 deaths per animal-year) more than twice that of females (2·01); this sex difference in mortality was apparently absent or reversed after the breeding season. Both male and female victims travelled significantly greater distances between successive radio-locations shortly before their deaths than surviving same-sex animals tracked contemporaneously. Rather than being selective for the feeble, predation on kangaroo rats is selective for the mobile.
Abstrad-Selection on locomotor performance was determined for a series of marked and recap- tured individuals from a population of garter snakes (Thamnophis sirtalis &hi) in Northern California. We measured snake length and mass, burst speed, endurance on a treadmill, and the distance crawled around a stationary circular track. Size-corrected values (residuals) of mass and locomotor performance were generated from the scaling equations of S-V length (SVL). Random- ization tests and regressions were used to determine the probability that a trait was a significant predictor of survivorship, and a nonparametric, cubic spline estimate of the fitness function was used to facilitate detection of the patterns of selection. From 275 ("cohort") snakes measured and tested within 8 days of birth in 1985, 79 were recaptured in the spring-summer of 1986 and subsequent years. Birth SVL was the only significant (randomization P = 0.022) predictor of neonatal survival from 1985 to 1986 with directional selection favoring larger individuals. In addition to the lab-born cohort, 382 field-born snakes from a11 ages in the population were captured, tested, and released during spring-summer 1986. Similar to the 1985 cohort, the survivorship of 37 of 86 neonates from 1986 to I987 showed no significant relationship with any residual value using any statistical test. Survivorship from 1986 to 1987 for 127 of 250 yearling (including 32 lab-born cohort snakes) analyzed with the randomization test showed that greater values of both speed (P = 0.007) and distance residual (P = 0.008) significantly favored survival, whereas inter- mediate values of mass residual (P = 0.006) were significantly more likely to survive. Univariate regressions predicting the survival of yearlings from 1986 to 1987 gave similar results to the randomization test, but in a multiple regression with yearling burst speed residual, distance capacity residual, and a quadratic term of mass residual, distance capacity residual was the least important predictor variable. For the survivorship of 37 of the 1 13 older snakes, greater burst speed residual significantly favored survival (randomization P = 0.001).
The impact of occasional severe events on the individuals comprising a study population has been the subject of some classic studies, for differential mortality is the essence of natural selection. For ornithology, the prime example is that of House Sparrows Passer domesticus killed by a snow storm in the U.S.A. (Bumpus, 1899; O'Donald, 1973). More recent examples include Grant (1983) demonstrating that larger Geospiza fortis in the Galapagos survived better through a drought, and Jones (1987) showing, conversely, that smaller Sand Martins Riparia riparia were favoured during a population crash.
Exposure of Thamnophis sirtalis parietalis to elevated temperatures immediately after emergence from hibernation induced intense mating behavior. The thermal threshold for courtship varied widely among individuals, and ranged from below 5 °C to between 20° and 25 °C. The lowest temperature at which copulation occurred was 10 °C. Both courtship and copulation increased with increasing temperature, and reached maximal levels at 25° and 30 °C respectively. The existence of low thermal thresholds for mating behavior and the marked stimulating effect of temperature on mating behavior explain the rapid onset of courtship and copulation after emergence from hibernation. A possible mechanism for thermal induction of mating behavior is discussed.
Previous ecological studies of Thamnophis sirtalis in the Interlake region of Manitoba have concentrated on the spring and fall phases of the annual cycle. This study is an investigation of two aspects of the summer activity of these populations: summer dispersal and feeding habits. Summer dispersal in these animals is highly directional; snakes move south in spring and return north to their hibernation sites in late summer and fall. Large distances are also involved; movements of as much as 17.7 km have been recorded. No explanation of this pattern of dispersal is apparent. Feeding takes place in the summer range only, during June, July, and August. The wood frog (Rana sylvatica) is the most frequently eaten prey species. It is suggested that the short feeding period is the result of a life history strategy which maximizes the efficiency of reproductive activities at the expense of non-reproductive activities.
The author incubated eggs from 17 clutches of common snapping turtles Chelydra serpentina on wet and dry substrates, producing "large' and "small' hatchlings, respectively. Hatchlings were individually marked, measured, and released in a National Wildlife Refuge area, Whiteside County, Illinois from which the eggs were collected originally. Subsequently, hatchlings were recaptured. Survivorship was not related to clutch, incubation conditions, or locomotor performance, but was significantly size dependence. However, larger body size of hatchling turtles may not evolve rapidly because the strength of selection was moderate in magnitude and the heritability was relatively low. -from Author
Simultaneous studies on an insular population of house mice Mus domesticus and an avian predator, the barn owl Tyto alba, showed that owls differentially take small female mice from the population. Owls hunted at night over open vegetation, when mice were also active. Fluorescent pigment tracking and trapping showed that juvenile mice, especially females, used open vegetation more than adults, and hence were potentially most at risk of predation. On an hourly basis, observations of hunting owls were correlated strongly with the numbers of juvenile females using open vegetation, and less strongly with the numbers of juvenile males. A removal experiment showed that adults partially confine juveniles to open vegetation by interference. These findings suggest that fitness of adults is probably increased by foraging in dense vegetation where resources are abundant and risk of predation from owls is low. In contrast, the foraging decisions of juveniles are balanced both against the risk of predation in open vegetation and interference from adults where cover is dense.
In a population of adders (Vipera berus) in Southwest Sweden, melanistic males were heavier than normal coloured males of the same length. Victory in male-male sexual combats was positively related to size. Higher risk of predation in the black morph was inferred from experiments showing a high predator attack rate on models of the black morph. Even the bright colour in newly moulted basking males of the normal morph gives cryptic protection. In females, melanism probably also affects body size and risk of predation by visually searching predators. The thermoregulatory influence of black colour, the reproductive success and the maintenance of two colour morphs in the population are discussed.
We show evidence of differential predation on snowshoe hares (Lepus americanus) by great horned owls (Bubo virginianus) and ask whether predation mortality is related to antipredator behaviour in prey. We predicted higher predation on (1) young and inexperienced hares, (2) hares in open habitats lacking cover to protect from owl predation, and (3) hares in above average condition assuming that rich food patches are under highest risk of predation. Information on killed hares was obtained at nest sites of owls and by monitoring hares using radio-telemetry. The availability of age classes within the hare population was established from live-trapping and field data on reproduction and survival. Great horned owls preferred juvenile over adult hares. Juveniles were more vulnerable to owl predation before rather than after dispersal, suggesting that displacement or increased mobility were not causes for this increased mortality. Owls killed ratio-collared hares more often in open than in closed forest types, and they avoided or had less hunting success in habitats with dense shrub cover. Also, owls took hares in above average condition, although it is unclear whether samples from early spring are representative for other seasons. In conclusion, these results are consistent with the hypothesis that variation in antipredator behaviours of snowshoe hares leads to differential predation by great horned owls.
In large mating aggregations of red-sided garter snakes, Thamnophis sirtalis parietalis, in Manitoba, male courtship is directed not only to females, but also to other males with female-like skin lipids (‘she-males’). We show that ‘she-maleness’ is an intrinsic property of a male rather than an artefact of lipid transfer from females, and that male–male courtship is very common in the field. She-males were distinctive in terms of appearance (they were heavier than other males and more often covered with mud), behaviour (they were inactive and rarely courted females) and performance (they were slow crawlers, ineffective courters and easily outcompeted by other males in mating trials). ‘She-maleness’ was not a characteristic of a particular subset of males, as envisaged in previous work; instead, it was a transitory phase that most (perhaps all) male snakes passed through soon after they first emerged from the winter den. Recently emerged males spent their first day or two relatively inactive, while restoring physiological functions (including locomotor performance and courtship ability). Experimental application of female skin lipids on to males dramatically decreased courtship levels of the recipient snakes. Thus, recently emerged males may derive two kinds of benefit from mimicking female skin lipids. First, female mimicry ‘switches off’ the male's own (energetically expensive) courtship at a time when that courtship would be unproductive. Second, it may disadvantage his rivals by distracting them from females, and increasing their energy expenditure.
Data on over 950 natural matings of red-sided garter snakes,Thamnophissirtalisparietalis , in Manitoba revealed size-assortative pairing: large males tended to mate with large females, and small males with small females. Unlike previously reported cases of size-assortative mating, the causal mechanism in these snakes involved a size-related shift in active mate selection by males. In the field, courtship as well as mating was size assortative (albeit, with considerable scatter around the trend line). Staged trials in outdoor arenas showed that males of all sizes preferred to court large rather than small females, but this preference was stronger in large males. Males adjusted their courtship intensity in response to the numbers and sizes of females and competing males, but did not change their preferences with respect to female body size. Thus, size-assortative mating was not a direct consequence of large males excluding their smaller rivals from large females. Males may be selective courters in this species because they have a limited supply of sperm and mating plugs, and hence can copulate effectively only a few times within the mating season. Given intense competition from large males (which primarily court large females), small males may benefit from focusing on small females. Alternatively, small males may be less capable of inducing sexual receptivity from large females. Mark–recapture data confirmed that males grow rapidly from one year to the next. Thus, the size-related shift in male mate choice was due to an ontogenetic change rather than the existence of multiple male morphs differing in both body size and courtship preference.
Two species of insectivorous bats, Lasiurus cinereus and L. borealis, ate significantly more male than female moths in the wild. The observed bias was likely to be a consequence of sexual dimorphism in moth flight activity associated with sexual differences in mate acquiring mechanisms. Female moths flew less than males and their activity peaks occurred at different times. The peak of male activity coincided with a peak in bat activity in the middle of the night, while female activity peaked earlier in the night when bat activity was relatively low. The results of this study are interpreted in a sexual selection framework, and the conclusions about predation risk from bats that hunt airborne prey are applicable to all nocturnally flying insects that exhibit sexual dimorphism in flight activity.
Understanding the mechanics of adaptive evolution requires not only knowing the quantitative genetic bases of the traits of interest but also obtaining accurate measures of the strengths and modes of selection acting on these traits. Most recent empirical studies of multivariate selection have employed multiple linear regression to obtain estimates of the strength of selection. We reconsider the motivation for this approach, paying special attention to the effects of nonnormal traits and fitness measures. We apply an alternative statistical method, logistic regression, to estimate the strength of selection on multiple phenotypic traits. First, we argue that the logistic regression model is more suitable than linear regression for analyzing data from selection studies with dichotomous fitness outcomes. Subsequently, we show that estimates of selection obtained from the logistic regression analyses can be transformed easily to values that directly plug into equations describing adaptive microevolutionary change. Finally, we apply this methodology to two published datasets to demonstrate its utility. Because most statistical packages now provide options to conduct logistic regression analyses, we suggest that this approach should be widely adopted as an analytical tool for empirical studies of multivariate selection.