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Bumpus in the snake den: effects of sex, size, and body condition on mortality of red-sided garter snakes
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 (n = 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.
... A snake's body size can affect its vulnerability to predation, with smaller snakes often attacked by a wider size range of predators in terrestrial habitats (reviewed by [22]). Also, some predators actively target smaller snakes as prey [23]. A study using snake-shaped clay models reported higher rates of predator attack to smaller models, reinforcing the importance of body size (rather than behavioural shifts associated with ontogeny) as the determinant of size-related prey vulnerability [24]. ...
... Demonstrations of differential predation relative to phenotype (colour) using clay models of snakes have been criticized on the grounds that disturbance to models may be due to curiosity or scavenging rather than predation [46]. In a few natural systems rates of predation may be high enough that observers can quantify selection on traits such as size and colour [23]. Ethical and logistical constraints are less stringent for studies on invertebrates with field and laboratory evidence of non-random predation on several insect species [47]. ...
... Open Sci. 10: 231429 over the course of prolonged deployment (typically, several days [23]). These are orders of magnitude lower than recorded in our own study (38 attacks in 25 trials, each lasting only a few minutes), but comparison is weakened by the difference in stimuli used. ...
Evolutionary shifts from one habitat type to another can clarify selective forces that affect life-history attributes. Four lineages of snakes (acrochordids and three clades within the Elapidae) have invaded marine habitats, and all have larger offspring than do terrestrial snakes. Predation by fishes on small neonates offers a plausible selective mechanism for that shift, because ascending to breathe at the ocean surface exposes a marine snake to midwater predation whereas juvenile snakes in terrestrial habitats can remain hidden. Consistent with this hypothesis, snake-shaped models moving through a coral-reef habitat in New Caledonia attracted high rates of attack by predatory fishes, and small models (the size of neonatal terrestrial snakes) were attacked more frequently than were large models (the size of neonatal sea snakes). Vulnerability to predatory fishes may have imposed strong selection for increased offspring size in marine snakes.
... Body condition is a key indicator of health at the individual or population level (e.g., Froese, 2006;Jakob et al., 1996;Labocha et al., 2014;Le Cren, 1951;Peig & Green, 2009) since it is closely related to important fitness variables, such as growth (Lloret et al., 2002), reproduction (Bachman & Widemo, 1999;Dobson & Michener, 1995), behavior (Bachman & Widemo, 1999), and survival (Jakob et al., 1996;Peig & Green, 2009;2010;Shine et al., 2001). The term "body condition" has been used in different manners, and it can mean different things. ...
... Commonly, the term is used to designate the energy reserves of an individual (Labocha et al., 2014;Peig & 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 & Green, 2009, 2010Schulte-Hostedde et al., 2001Shine et al., 2001). However, in some studies, body condition has been considered a measure of the biological and physical events that happen during some anterior period in the life cycle of an individual (Lloret & Ratz, 2000) or as an indicator of habitat quality and food availability (Johnson, 2007;Lloret et al., 2002). ...
Aim
In this paper we present a scientometric analysis aimed at to assess and quantify the contribution of Le Cren’s condition factor and the main ideas advanced by ‘Le Cren, 1951’ to studies on the health of individuals or populations in aquatic environments. Specifically, we addressed the following questions: (i) what are the temporal and spatial citation trends of ‘Le Cren, 1951’?; (ii) Which journals cited ‘Le Cren, 1951’ most frequently?; (iii) In which types of aquatic environments and organisms have Le Cren’s condition factor been most commonly applied?; (iv) Which of the main applications addressed in ‘Le Cren, 1951’ have been most frequently used by fisheries scientists?; (v) Which of the methods (i.e., Quételet’s index or body mass index, Fulton’s condition factor, Le Cren’s condition factor, relative weight, residual index and scaled mass index) used to estimate condition factor identified in the papers that cited ‘Le Cren, 1951’ have been most frequently used? In addition, the main criticisms of the use of the relative condition factor are discussed.
Methods
We carried out a scientometric analysis on the papers published from 1951 to December 2015 that cited Le Cren’s article. The papers were obtained from the Thomson Reuters database (ISI Web of Knowledge, apps.isiknowledge.com) in May 2016.
Results
In total, 1128 papers were assessed. The number of citations increased significantly over time. Most citations occurred in two journals (Journal of Fish Biology and Journal of Applied Ichthyology). Most of papers were carried out in marine environments. In addition, we show that Le Cren's paper has been cited mainly in articles that estimate the condition factor or the weight-length relationship of populations. Finally, we emphasize that the relative condition factor proposed by Le Cren in 1951 is still the main method used to estimate the body condition of an individual or population.
Conclusions
Le Cren's significant contribution to animal well-being is undeniable, and we emphasize that among the methods identified in the papers that cited ‘Le Cren, 1951’ that estimated body condition, the relative condition factor proposed by Le Cren in 1951 is still the most commonly used method.
... In temperate climates, larger hosts may be better suited to sustain overwintering and pathogenic exposures because immune responses and overwinter survival are energetically costly processes. Body size can predict fitness and host condition in many vertebrates (Dobson 1992, Bachman & Widemo 1999, Shine et al. 2001. For instance, larger body size in amphibians at metamorphosis is associated with increased overwinter survival and with earlier time to first reproduction and increased fecundity (Semlitsch & Wilbur 1988, Berven 1990, Schmidt et al. 2012, Earl & Whiteman 2015. ...
... Manipulating the larval en vironment led to hosts of different size classes, and these size classes were sustained over the course of the experiment. However, even though previous studies have shown that small size is linked to reduced ability to respond to pathogens (Dobson 1992, Bachman and Widemo 1999, Shine et al. 2001, Burrow et al. 2017 Table 5. Sensitivity and elasticity values for projection matrices representing no Bd exposure, Bd exposure of recently metamorphosed northern leopard frogs Lithobates pipiens, and Bd exposure of metamorphs before overwintering. The first number listed is the sensitivity value, and the second is the elasticity value herbicide atrazine; Rohr et al. 2013), the conditions of the larval environment did not differentially alter the effect of Bd exposure. ...
The result of pathogen exposures may depend upon trade-offs in energetic demands for immune responses against host growth and survival. Environmental conditions may influence these trade-offs by affecting host size, or trade-offs may change across seasons, altering impacts of pathogens. We exposed northern leopard frog Lithobates pipiens tadpoles to different larval environments (low leaf litter, high density of conspecifics, atrazine, caged fish, or controls) that influenced size at metamorphosis. Subsequently, we exposed metamorphs to Batrachochytrium dendrobatidis (Bd), a fungal pathogen, just after metamorphosis and/or prior to overwintering 12 wk later. Bd exposure dramatically reduced survival during overwintering, with the strongest effects when hosts were exposed at both time points. Larval environments resulted in differences in host size. Those exposed to caged fish were 2.5 times larger than the smallest (those exposed to high density of conspecifics), but larval environment did not influence Bd effects on growth and survival. The largest frogs exposed to caged fish had greater survival through overwintering, but in the absence of Bd. We built stage-structured models to evaluate if overwinter mortality from Bd is capable of having effects on host populations. Our models suggest that Bd exposure after metamorphosis or before overwintering can reduce population growth rates. Our study demonstrates that hosts suffer little effects of Bd exposures following metamorphosis and that small body size did not hamper growth and survival. Instead, we provide evidence that winter mortality from Bd exposure is capable of reducing population sizes, providing a plausible mechanism for amphibian declines in temperate regions.
... Predation by other snakes has also been observed in Green Snakes (Opheodrys aestivus; Plummer 1990), and was suggested as a possible factor in the documented decline of the Eastern Kingsnake (Lampropeltis getula) at a protected site in South Carolina (Winne et al. 2007 ), indicating intraguild predation may play a more significant role in population dynamics than previously known. We have one confirmed case of avian predation (Eastern Screech Owl, 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. ...
... Predation by other snakes has also been observed in Green Snakes (Opheodrys aestivus;Plummer 1990), and was suggested as a possible factor in the documented decline of the Eastern Kingsnake (Lampropeltis getula) at a protected site in South Carolina (Winne et al. 2007), indicating intraguild predation may play a more significant role in population dynamics than previously known. We have one confirmed case of avian predation (Eastern Screech Owl,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.
... 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.
... seasonality, prey availability) can influence the body condition of the individuals (e.g. Losos 2001;Shine et al. 2001). In this way, the BCI has been recognized in natural history studies of several taxonomic groups, such as reptiles, birds and mammals (e.g. ...
The present study adds new data on the natural history of Dendrobates tinctorius. We conducted our fieldwork during the rainy season of the years 2018 and 2019 in two protected areas (Parque Natural Municipal do Cancão-PNMC and Reserva Extrativista Beija-Flor Brilho de Fogo-REBFBF) in the state of Amapá, Brazil. Through active visual searches we sampled 22 individuals of D. tinctorius, of which 10 were counted for the population of PNMC and 12 for the population of REBFBF. We calculated the Body Condition Index (BCI) for all individuals and, for dietary data, each frog's stomach was flushed. Females from the REBFBF were larger than males when compared to the PNMC population. BCI of females from the REBFBF showed higher values than males. Gravid females of both populations showed higher BCI. Retrieved stomachs revealed a total of 290 prey items divided into four main taxonomic categories of Arthropods. The Index of Relative Importance revealed that ants of the genus Solenopsis were the majority of the diet, and mites represented only 4.86%. The niche breadth for both populations was narrow, indicating a specialist diet, as expected for the species. Our study evidences the importance of integration between BCI and dietary aspects.
... Snake size is one of the main variables that interfere with strike behavior [7,10]. Being more susceptible to predation pressure, small snakes tend to have higher strike rates [29,[41][42][43][44][45], which would explain the marked defensive behavior of B. alcatraz. Another important factor is that we have no knowledge of the aerial predation frequency, although there are more potential avian predators on Alcatrazes island than on Queimada Grande island, even though far less than on the mainland [18]. ...
The reduction of predation is a potentially important factor for the evolution of the traits of an island animal species. By relaxed selection, insular animals tend to lose their antipredator behaviors. A monophyletic group of pitvipers (genus Bothrops) in southeastern Brazil, which have high genetic affinity and dwell on the mainland and adjacent islands, provide an appropriate setting to study the evolution of antipredator behavior and how different predatory stimuli can influence this behavior. The mainland Bothrops jararaca has several terrestrial and aerial predators, whereas B. insularis and B. alcatraz, restricted to two small islands, Queimada Grande and Alcatrazes, respectively, have a smaller range of aerial predators. Terrestrial predators are absent on Queimada Grande, but one potential snake predator occurs on Alcatrazes. We observed that the defensive repertoire of island snakes has not been lost, but they display different frequencies of some antipredator behaviors. The type of predatory stimuli (terrestrial and aerial) influenced the defensive response. Bothrops insularis most often used the escape strategies, especially against terrestrial predatory stimuli. Bothrops alcatraz displayed the highest rate of strike for both terrestrial and aerial stimuli. Our results indicate that even though relaxed selection may occur in island environments as compared to mainland environments, these pitvipers still retain their antipredator behaviors but with different response degrees to the two predator types.
... Beyond agonistic interactions, the act of courtship may also be stressful. Female red-sided gartersnakes (Thamnophis sirtalis parietalis) leaving a communal densite following hibernation may be harassed by males attempting to mate for several days (Shine et al., 2000c), which can expose them to predators (Shine et al., 2001b) and lead to exhaustion. Given the choice, females select areas with less male scent . ...
Understanding stress ecology in snakes is important to anticipate individual and population-level consequences of different types of stressors and plan for conservation efforts. Additionally, an understanding of stress ecology in snakes broadens the basic understanding of stress responses across vertebrates. We review a variety of metrics available to assess stress and provide context and resources where these metrics have been applied in snakes. We then explore how these metrics change as snakes respond to different types of stressors. Throughout, we highlight gaps in understanding, and summarize important future research directions to establish a more comprehensive understanding of snake stress ecology.
... For example, exposure to PFAS has been shown to magnify the impact of cadmium and lead on kidney function (Jain, 2019), but otherwise, the relationship between PFAS and metal toxicity is largely unknown and warrants further investigation. Importantly, these potential co-contributing impacts to snake body condition makes them particularly vulnerable to predation (Mattisson et al., 2016) and mortality (Shine et al., 2001), and a reduction in reproductive frequency and outputs (Madsen and Shine, 1996;Milenkaya et al., 2015) which may lead to population declines. ...
PFAS contamination of urban waters is widespread but understanding the biological impact of its accumulation is limited to humans and common ecotoxicological model organisms. Here, we combine PFAS exposure and bioaccumulation patterns with whole organism responses and omics-based ecosurveillance methods to investigate the potential impacts of PFAS on a wetland top predator, the tiger snake (Notechis scutatus). Tiger snakes (18 male and 17 female) were collected from four wetlands with varying PFAS chemical profiles and concentrations in Perth, Western Australia. Tiger snake livers were tested for 28 known PFAS compounds, and Σ28PFAS in liver tissues ranged between 322 ± 193 μg/kg at the most contaminated site to 1.31 ± 0.86 μg/kg at the least contaminated site. The dominant PFAS compound detected in liver tissues was PFOS. Lower body condition was associated with higher liver PFAS, and male snakes showed signs of high bioaccumulation whereas females showed signs of maternal offloading. Biochemical profiles of snake muscle, fat (adipose tissue), and gonads were analysed using a combination of liquid chromatography triple quadrupole (QqQ) and quadrupole time-of-flight (QToF) mass spectrometry methodologies. Elevated PFAS was associated with enriched energy production and maintenance pathways in the muscle, and had weak associations with energy-related lipids in the fat tissue, and lipids associated with cellular genesis and spermatogenesis in the gonads. These data demonstrate the bioavailability of urban wetland PFAS in higher-order reptilian predators and suggest a negative impact on snake health and metabolic processes. This research contributes to our understanding of the impact of PFAS residue on wildlife health which can be used for improved risk management and regulation. Thus, expanding the use of omics-based ecosurveillance tools for informing mechanistic toxicology.
... The specimen showed immobility at first, a few attempts to escape followed by head-hiding with no tail display. Since body size can influence predation risk (Vitt, 2000;Shine et al., 2001) the variation on defensive behaviour could reflect different selection pressures on body sizes (Roth and Johnson, 2004), therefore it is possible that body size could influence P. nigra adjustment of antipredator behaviour accordingly to the predation risk. ...
... The chief limitation in such environments is temporal: the amount of time these ectotherms can be safely active during the year is approximately six months at most (May to October). Worse, weather events during the active period of the year can be random and severe, such as a mass mortality event one spring caused by a sudden snowstorm and freeze (29). The frequency and intensity of extreme climatic events are likely to increase due to climate change, increasing the need to understand the range and limitations of phenotypic plasticity (30,31). ...
Sex steroid hormones are powerful regulators of reproductive behavior and physiology in vertebrates, and steroidogenesis has distinct sex- and season-specific patterns ultimately dictated by the expression of key enzymes. Most comparative endocrinology studies, however, focus only on circulating levels of sex steroids to determine their temporal association with life-history events in what are termed associated reproductive patterns. The red-sided garter snake (Thamnophis sirtalis parietalis) is a notable exception; this species exhibits maximal sex behavior decoupled from maximal sex steroid production and gametogenesis in what is termed a dissociated reproductive pattern. And while this is true for male red-sided garter snakes and their production of testosterone, females have maximal estradiol production during peak breeding (spring) but only immediately after mating. Here, we demonstrate that expression of ovarian aromatase (conversion of androgens to estrogens) matches the established seasonal hormone pattern in females. Additionally, steroidogenic gene expression in the ovary is broadly reduced if not suppressed compared to the testis throughout the active year. Bizarrely, male red-sided garter snakes demonstrate an unexplained pattern of steroidogenic gene expression in the testis. StAR (import of cholesterol to steroidogenesis) is maximally expressed in spring, yet Hsd17b3 expression (conversion of androstenedione to testosterone) is highest in summer, with the latter matching the established summer peak in male testosterone. The function of elevated StAR in spring is unknown, but our results suggest a decoupling between maximal StAR expression and testosterone biosynthesis (Hsd17b3 expression). We also purport that the reproductive pattern binary should be reassessed given its lack of fit for many vertebrate species that demonstrate seasonal, mixed patterns of (a)synchrony between circulating sex hormones and reproductive behavior.
... spectra (Corcobado et al., 2016). Birds are important predators of both venomous and non-venomous snakes in many ecosystems (Brodie, 1993;Shine et al., 2007;Ajtić et al., 2013;Radovics et al., 2022), and are capable of perceiving light in the near-ultraviolet (UV) part of the spectrum. Therefore, here we test whether the aposematic colours of two geographically separated elapid snakes and their proposed Batesian mimics extend into the ultraviolet region of the spectrum. ...
We explore the usefulness of UV photography in investigating putative Batesian mimicry of aposematic elapid snakes by harmless colubrids. We predicted that Batesian mimics would share similar UV reflectance patterns as their models and tested this in two likely Batesian mimicry systems. In North America, both Micruroides euryxanthus and Lampropeltis knoblochi lack any UV reflectance from any part of their dorsum. In India, Bungarus caeruleus displays strong UV reflectance from its light body rings, which is largely echoed in visually similar black and white Lycodon anamallensis, but not in reddish-brown individuals of the same species. Our results highlight the potential for UV photography to contribute to testing mimicry hypotheses. Researchers using inanimate models to test the function of animal patterns need to consider reflectance outside the human visual spectrum to maximise the resemblance of their models to the focal organisms.
... Locomotor abilities may vary with body size, with smaller or younger individuals having less stamina than adults. Many studies have shown that body size is positively related to locomotor performance (Jayne and Bennett, 1990;Carrier, 1996;Kelley et al., 1997;Roth and Johnson, 2004) and inversely related to predation risk (Mushinsky and Miller, 1993;Shine et al., 2001). Thus, smaller snakes may have exhibited NGRB more frequently because they cannot effectively depend on locomotor escape when facing predation threat. ...
Snakes have a wide range of antipredator behaviors that are often associated with unique morphological modification. Rhabdophis subminiatus (Red-Neck Keelback) is a snake with nuchal glands where toxins sequestered from prey animals are stored that work in conjunction with a set of antipredator behaviors. In this study, we investigated antipredator behavior in this species, particularly behavior that is coordinated with the presence of the nuchal glands. We tested the hypothesis that the nuchal gland-related behavior is exhibited more frequently as snake size increases because larger snakes have had more opportunities to consume toads and acquire toxins. We also examined the effects of sex and body condition on antipredator behavior. All snakes performed body flattening and neck flattening in response to a standardized stimulus, which suggests that these responses are their major antipredator behaviors. However, the results did not support our hypothesis. Snake body size was negatively correlated with the frequency of neck butt, neck flatten, and neck arch. This indicates that the tendency to perform the nuchal gland-related behavior declines as body size increases. There was no significant sexual difference except that females tended to exhibit a higher frequency of flight than males. Furthermore, we found a negative correlation between the frequency of neck butt and body condition. Overall, our study suggests that smaller snakes, particularly those in below-average body condition, depend more on nuchal glands to deter predators.
... Snakes have proven to be especially useful subjects for such studies because they serve as important prey for other vertebrate groups (Greene, 1997), often express striking color and pattern elements that might be expected to influence predator behavior (Brodie, 1993;Pfennig et al., 2001;Wüster et al., 2004), and exhibit a uniform tubular shape that simplifies model production. Birds, in particular, are well known as predators of snakes (Guthrie, 1932;Martín and López, 1990;Sparkman et al., 2013), and both terrestrial and aquatic snakes are consumed by a wide variety of avian species (e.g., common buzzards: Selås, 2001; American crows: Shine et al., 2001;American bitterns: Preuss et al., 2018). The importance of birds as snake predators is likely related to the exceptional visual acuity and color discrimination of the former, which in turn are thought to exert strong selection on snake integumentary color and patterning (Kikuchi et al., 2014). ...
Albinism is a conspicuous and distinctive phenotype arising from the absence of melanin in the integument that has been documented in all major vertebrate groups. With few exceptions, albinism is rare in natural populations, suggesting that it incurs significant fitness costs as compared to wild-type phenotypes. One possible explanation for this rarity is that albinos experience higher predation risk as compared to wild-type individuals. We tested this hypothesis by comparing rates of attack by avian predators on immobile clay model proxies that mimicked wild-type and albino eastern garter snakes (Thamnophis s. sirtalis) at Bond Swamp in central Georgia, USA; two mixed pattern treatments provided intermediate phenotypes for comparison. Surprisingly, we found no difference in attack rate across all four model treatments, nor among pairs of treatments (i.e., wild-type-like vs. albino-like models). This indicates that albino garter snakes are not subject to higher predation risk from birds due to coloration alone, and that other factors (correlated pathologies of albinism, thermoregulatory challenges, mate selection) are likely to be more important in explaining the rarity of albinism in snakes and perhaps other vertebrate groups.
... The perils of poor body condition include reduced reproductive success (Milenkaya et al., 2015), increased predation (Mattisson et al., 2016), and ultimately individual mortality (Shine et al., 2001). Therefore, despite the current abundance of tiger snakes in these sites, a population-wide reduction in body condition could be a precursor to population decline (Aubry et al., 2013;Reading, 2007). ...
Urban ecosystems and remnant habitat 'islands' therein, provide important strongholds for many wildlife species including those of conservation significance. However, the persistence of these habitats can be undermined if their structure and function are too severely disrupted. Urban wetlands, specifically, are usually degraded by a monoculture of invasive vegetation, disrupted hydrology, and chronic-contamination from a suite of anthropogenic pollutants. Top predators—as bioindicators—can be used to assess and monitor the health of these ecosystems. We measured eight health parameters (e.g., parasites, wounds and scars, tail loss and body condition) in a wetland top predator, the western tiger snake, Notechis scutatus occidentalis. For three years, snakes were sampled across four wetlands along an urban gradient. For each site, we used GIS software to measure the area of landscape variables and calculate an urbanisation–landscape score. Previously published research on snake contamination informed our calculations of a metal-pollution index for each site. We used generalised linear mixed models to assess the relationship between all health parameters and site variables. We found the metal-pollution index to have the most significant association with poor body condition. Although parasitism, tail loss and wounds differed among sites, none of these parameters influenced body condition. Additionally, the suite of health parameters suggested differing health status among sites; however, our measure of contemporary landscape urbanisation was never a significant predictor variable. Our results suggest that the health of wetland predators surrounding a rapidly growing city may be offset by higher levels of environmental pollution.
... In our study, reduced female survival is unlikely to be due to higher costs of reproduction-as no individuals had reproduced. Amongst wild snakes, size can also influence survival when mortality is driven by predation or food availability and size (Forsman, 1993;Shine et al., 2001). We are uncertain why we may have observed differences in python survival between sexes as females were generally of equivalent or greater size than males. ...
Individual identification is fundamental to the study of captive and wild animals but can have adverse impacts if the method of identification is inappropriate for the species or question of interest. We conducted a randomised controlled trial to test whether passive integrated transponder (PIT) tags reduced the growth or survival of pythons. We randomly allocated 200 captive-bred Burmese python (Python bivittatus) hatchlings into two groups, tagged versus untagged. Hatchlings were individually identified using a combination of PIT tags and unique colour patterns, and their mass, snout-vent length (SVL) and body condition measured at 9, 73, 134, 220, 292 and 385 days of age. We recorded the date of all mortalities. Python morphometrics and their rate of change increased or fluctuated non-linearly with age. The impact of PIT tagging on python body mass and body mass growth over the 376 day study period was insignificant. PIT tagging additionally had an insignificant impact on python survival. However, we found minor differences in SVL growth between tagged and untagged pythons. These differences peaked at approximately 0.5 mm/day and appeared to drive similar, but more pronounced, differences between tagged and untagged pythons in their rate of change in body condition; peaking at approximately 3-4 g/day. While we cannot be certain that these small differences are, or are not, biologically meaningful, they nonetheless appear to be short-term and readily resolved. Unsurprisingly, the strongest driver of python growth was their age, with growth rapidly increasing or highest amongst younger snakes for all measures of size. Python sex was associated with their body mass and survival, with higher mass but lower survival amongst females. Python size at hatching did not impact on their growth or survival. Our results confirm that PIT tags are a valuable and effective tool for the identification and tracking of captive pythons, and snakes generally, and meet high safety and animal welfare standards.
... 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.
... This may suggest that body scarring did not decrease the foraging success and the associated growth. Moreover, injuries did not affect body condition which, in turn, strongly influences survival (Shine et al. 2001;Bonnet et al. 2002;Bonnet et al. 2010). Severe injuries may, however, never heal, thus causing the death of the snakes without the snakes being noticed. ...
Animals can suffer injuries due to diseases, intraspecific aggression and, most of all, predation events. We present field data to provide numerical information about the injuries found in the largest Caspian Whip Snake (Dolichophis caspius) population in Hungary, near the northernmost portion of the species' distribution range.
... 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. ...
Desert Tortoise (Gopherus agassizii) populations have declined, and head-starting hatchlings in captivity until they are larger and older, and presumably more likely to survive, is one strategy being evaluated for species recovery. Previous studies have reared hatchlings in outdoor, predator-proof pens for 5-9 y before release, in efforts to produce hatchlings in excess of 100-110 mm midline carapace length that are believed to be predation-resistant. We began a comparative study to evaluate indoor-rearing to shorten this rearing period by facilitating faster initial growth. We assigned 70 neonates from the 2015 hatching season to three treatment groups: (1) indoor-reared (n = 30), (2) outdoor-reared (n = 20), and (3) direct-release (n = 20). We released direct-release hatchlings shortly after hatching in September 2015 and monitored them 1-2 times per week with radio telemetry. We head-started the indoor-and outdoor-reared treatment groups for 7 mo before releasing them in April 2016. Indoor-reared tortoises were fed five times per week (September to March). Outdoor-reared tortoises had access to native forage and we gave them supplemental water and food once per week while active before winter dormancy. Indoor-reared tortoises grew > 16 times faster than direct-release tortoises and > 8 times faster than outdoor-reared tortoises; however, indoor-reared tortoises weighed less and had softer shells than comparatively sized older (3-4 y-old) tortoises raised outdoors. Increasing the duration of the indoor-rearing period or incorporating a combination of both indoor and later outdoor husbandry may increase shell hardness among head-starts, while retaining the growth-promoting effect of indoor rearing and shortening overall captivity duration.
... Other research has found discrepancies in predation risk between cryptic and conspicuous species of insect larvae, but these trends are also highly context-dependent (Mand, Tammaru & Mappes, 2007). While research in terrestrial vertebrates is sparse, research has shown that predation risk is independent of body size in anole lizards (Calsbeek & Cox, 2010), but that garter snakes exhibit higher predator-related mortality at smaller body sizes (Shine et al., 2001). Given how complex and contextdependent size-based predation can be, there is a need for studies that determine how predation risk varies with morphology and body size in other taxa. ...
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.
... All three life history traits (growth rate, reproductive output, and survivorship), usually used as a measure of habitat quality, are dependent to varying degrees on an animal's BC (Shine et al., 2001;Litzgus et al., 2008;Harrison et al., 2011;Gallego-Carmona et al., 2016;Sasaki et al., 2016) which in turn reflects the availability of energy, in terms of food/prey abundance and quality, within the habitat. Our study shows that the BC of heathland snakes remained relatively constant whilst that of plantation snakes, which was initially similar to that of heathland snakes, declined with increasing plantation age and was negatively correlated with increasing tree canopy cover. ...
Different habitat types that support similar densities of a particular species may not be equally suitable for that species and this may impact on the ability of that species to grow, reproduce, and survive. Here we investigate the impact of habitat quality on the performance of the UK's rarest snake which inhabits both lowland heath and adjacent areas of managed conifer plantation located on former lowland heath. Annually, over an 8 year period (2009-2016), we recaptured known individual smooth snakes (Coronella austriaca) in these two habitat types and compared their survivorship, using Program MARK, and growth rates, estimated ages, reproductive outputs, emigration/immigration, and body condition, using regression analysis and GLM. When compared with snakes from plantations those inhabiting open heathland had higher growth rates, were larger for any given age, had a higher body condition and females produced more embryos for a given body size. Smooth snake survivorship rates within the two habitats were similar. Whilst the body condition of snakes in heathland did not change during the study it declined in plantations and this decline was correlated with increasing plantation age and tree canopy cover. Our data show that although smooth snakes occur in both habitat types the overall quality of open heathland is superior to that of plantations, particularly in the long term. This study has potentially important implications for the conservation of smooth snakes and other reptile and vertebrate species inhabiting coniferous plantations, where management practices aimed at reducing ground vegetation cover, such as cattle grazing and the use of herbicides, are also used. The combination of increasing canopy cover and these additional ground vegetation control measures are likely to significantly reduce further the time period over which plantations can be utilised by these taxa.
... During this period the males are very active, moving along the wetland looking for reproductive females (Lebboroni & Chelazzi 1991). This energyexpensive activity is also evident in males of Gorgo Tondo Basso, based on the significant decrease in May of the BCI, a parameter linked to nutritional and physiological status (Speakman 2001) that can correlate with fitness parameters such as survival (Shine et al. 2001) and reproduction (Dobson & Michener 1995). This is a common trait among freshwater turtles explained using a cost-benefit argument, where males disperse in search of females despite costs such as increased energy expenditure and increased predation risk (Morreale et al. 1984). ...
The lack of data relating to basic life-history and population dynamics is one of the gaps to be filled in
order to develop a proper strategy for the conservation of the Sicilian Pond Turtle (Emys trinacris). In this
study, we present the results of the first year of a multi-annual monitoring program focusing on a specific
wetland area, located within the “Lago Preola e Gorghi Tondi” Nature Reserve (Sicily, Italy). The sub-
population size was estimated with capture-recapture method at 719 ± 47 turtles, with a mean density of
239.7 ± 15.7 ind./ha. The overall sex ratio of the captured individuals was males-biased (2.9 : 1) but also a
significant differences between spring and summer was found. We discuss this finding in relation to differ-
ential reproductive strategies of the sexes, with the support of data on movements and on body condition.
The importance of a multi-year monitoring approach is underlined in order to get a better understanding
of the factors that affect the population ecology.
... Our Jacky Dragons were studied for the remainder of their lives, and those incubated at warmer temperatures were always larger than those incubated at cooler temperatures (Warner and Shine, 2008); this difference in size was not due to growth over winter. Body size has been correlated with winter survival in snakes (Shine et al., 2001;Kissner and Weatherhead, 2005) and turtles (Mitchell et al., 2015), and many authors speculate that larger lizards have a survival advantage during winter due to greater energy reserves (e.g., Congdon et al., 1979;Civantos et al., 1999), but more studies across multiple taxa are required to determine the influence of body size on overwinter survival in lizards. ...
Most temperate-climate lizards become inactive during the winter months of each year. As temperatures drop, they must find appropriate overwintering microhabitats to avoid lethal surface temperatures and/or thermoregulate. The environmental variables that characterize such microhabitats and the cues that lizards utilize to assess them are a critical but understudied component of their natural history. While many studies of overwintering site selection focus on temperature, other factors constituting microhabitats (e.g., surface structures, substrate) may play a role in site selection. We used the Jacky Dragon (Amphibolurus muricatus), an Australian agamid lizard, to test for preference of using various cover types (leaf litter, open sand, sticks, rocks) for overwintering as well as the consequences of cover type selection. Jacky Dragons preferred overwintering beneath leaves compared to other structures, and this choice was associated with growth during winter, but not with survival. Our study highlights the potential importance of cover structures in overwintering site selection, suggests that midwinter activity may be common in Jacky Dragons, and calls for further study of the winter ecology of temperate-climate lizard species. © 2017 by the American Society of Ichthyologists and Herpetologists.
... BCI was estimated as the residual from a linear regression of the fall mass against the fall SVL, where a more positive residual indicates a better body condition (i.e., greater mass than predicted for its body length; Waye and Mason 2008). We focused our analysis on fall body condition because condition of a female upon return to the den is what determines whether it has the stored tissue resources necessary to survive winter hibernation (Shine et al. 2001) and become gravid in the following season (Gregory 2006). Additionally, we assumed that a snake's fall body condition reflects its summer foraging success. ...
An individual’s migration path shape should affect its fitness, because patchily distributed features (e.g., prey) are encountered more often on straight than tortuous paths. We hypothesized that Prairie Rattlesnakes (Crotalus viridis viridis (Rafinesque, 1818)) with straighter migration paths should have better body condition, because they encounter prey patches more frequently, and higher migration mortality, because they also encounter predators and hazardous human land uses more frequently, than individuals with tortuous paths. If true, then a straighter path should be favoured when the benefit (resource acquisition) outweighs the cost (mortality risk). Humans pose a significant mortality risk for migrants; thus, the cost of straight-line movement should increase relative to the benefit in more human-dominated landscapes, favouring more tortuous movements. We tested these hypotheses using data on the body condition, mortality, and migration movements of 25 female Prairie Rattlesnakes in one human-dominated and one seminatural landscape. As hypothesized, we found better body condition and higher migration mortality for snakes with straighter migration paths, and that snakes followed more tortuous paths in the human-dominated landscape. Although selection for tortuous movements may reduce rates of migration mortality in humandominated landscapes, this may ultimately contribute to population declines if poorer body condition reduces overwinter survival or reproductive success.
... For example, a winterkill event in 1998-1999 shifted the size distribution toward smaller animals in subsequent years in both sexes, but the largest females were most strongly affected [93]. Small males, and to a lesser extent large females, are more likely to be trapped and suffocate in large mating aggregations (more than 500 animals) [94]. Such events could cull a size class or spare only old females with the longest telomeres, generating results similar to ours. ...
Life-history strategies vary dramatically between the sexes, which may drive divergence in sex-specific senescence and mortality rates. Telomeres are tandem nucleotide repeats that protect the ends of chromosomes from erosion during cell division. Telomeres have been implicated in senescence and mortality because they tend to shorten with stress, growth and age.We investigated age-specific telomere length in female and male red-sided garter snakes, Thamnophis sirtalis parietalis. We hypothesized that age-specific telomere length would differ between males and females given their divergent reproductive strategies. Male garter snakes emerge from hibernation with high levels of corticosterone, which facilitates energy mobilization to fuel mate-searching, courtship and mating behaviours during a two to four week aphagous breeding period at the den site. Conversely, females remain at the dens for only about 4 days and seem to invest more energy in growth and cellular maintenance, as they usually reproduce biennially. As male investment in reproduction involves a yearly bout of physiologically stressful activities, while females prioritize self-maintenance, we predicted male snakes would experience more age-specific telomere loss than females. We investigated this prediction using skeletochronology to determine the ages of individuals and qPCR to determine telomere length in a cross-sectional study. For both sexes, telomere length was positively related to body condition. Telomere length decreased with age in male garter snakes, but remained stable in female snakes. There was no correlation between telomere length and growth in either sex, suggesting that our results are a consequence of divergent selection on life histories of males and females. Different selection on the sexes may be the physiological consequence of the sexual dimorphism and mating system dynamics displayed by this species. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... 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 andWeatherhead 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.
... 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 the population biology and vital rates in N. e. neglecta to help elucidate potential mechanisms of their decline and thus 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.
... (Naulleau and Bonnet 1996;Taylor et al. 2005), as well as survival ( Shine et al. 2001). All physiological processes are temperature-dependent. ...
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.
... Variation in exploration as a function of body size suggests that different intensities of exploration could be favoured at different sizes, and these differences could be explained by varying levels of hormones (e.g., Bell and Stamps 2004;Dammhahn and Almeling 2012) associated with maturation and reproduction. The variation in exploration between small males and large males may be related to the fact that smaller snakes are targeted more often by avian predators (Shine et al. 2001). Therefore, smaller males could be more reluctant to expose themselves for exploration and foraging. ...
Phenotypic traits are important to consider when examining behaviour because they can help explain behavioural trait variation. Behaviours such as exploration, boldness, and defense may vary between individuals because different intensities of a behaviour may be advantageous for males versus females, or at different body sizes. We tested the hypothesis that exploration, boldness, and defensive behaviours are related to body size, sex, and reproductive status in eastern garter snakes, Thamnophis sirtalis. We also tested whether the measured behavioural traits were consistent through time (i.e., whether eastern garter snakes could have personalities) and whether the measured behavioural traits were related to one another (i.e., whether behavioural syndromes could be present in eastern garter snakes). Males and non-gravid females were more likely to flee than gravid females when faced with an attack. Males and non-gravid females were also more active after the attack than before the attack, whereas gravid females were more active before the attack. Furthermore, longer females explored less than smaller females, with a more precipitous decline of exploration as a function of size in gravid females than in non-gravid females. In contrast, longer males explored more than smaller males. Although we did not detect behavioural syndromes, within individuals the measured behavioural traits were repeatable through time, suggesting that eastern garter snakes could have personalities.
... 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.
... c o m / l o c a t e / b i o c o n 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. ...
The assessment of the health and protection of anuran amphibian populations in biotopes damaged by anthropogenic activity is today a priority and a global problem. The aim of this study is to determine the individual physical fitness of Pelophylax ridibundus individuals inhabiting a polluted area in Southern Bulgaria by calculating the scaled mass index (SMI) of frogs. We used frogs inhabiting a less disrupted habitat (less disturbed site) in order to make a comparison. Our working hypothesis was based upon the assumption that the two populations were expected to show differences in the values of the calculated scaled mass indices. That would allow us to assess how anthropogenic stress affects the individual body condition of frogs inhabiting a polluted area. A two-way ANOVA analysis revealed that there was a statistically significant interaction between the effects of site and sex on SMI. The simple main effects analysis showed that the site of origin alone has had a significant effect on SMI. In general, lower SMI values were indicative of deteriorated body fitness and suggested unfavorable environmental conditions. We found during this study that SMI can be discussed as a more accurate sex-independent discriminative marker for the habitat than the original unscaled SVL and BW parameters.
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 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.
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.
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.
Sit-and-wait ambushing and active hunting are two strategies used by predators to capture prey. In snakes, hunting strategy is conserved phylogenetically; most species employ only one strategy. Active hunters encounter and capture more prey but invest more energy in hunting and have higher risks of being predated. This trade-off is important to small predators. The small Cerastes vipera employs both modes of hunting, which is unlike most viperids which use only sit-and wait ambushing. This species hibernates in October and emerges in April. Energy intake should be high prior to hibernation to overcome the non-feeding hibernation period and for reproduction on their emergence. We predicted that more individuals would hunt actively towards hibernation and an abiotic factor would trigger this response. Furthermore, since more energy is required for active hunting, we predicted that snakes in good body condition would use active hunting to a greater extent than snakes in poor body condition. To test our predictions, we tracked free-living snakes year round and determined their hunting strategy, estimated their body condition index (BCI), and calculated circannual parameters of day length as environmental cues known to affect animal behaviour. Two novel findings emerged in this study, namely, hunting strategy was affected significantly by 1) the circannual change in day length and 2) by BCI. The proportion of active hunters increased from 5% in April to over 30% in October and BCI of active foragers was higher than that of sit-and-wait foragers and, therefore, our predictions were supported. The entrainment between the proportion of active hunting and the abiotic factor is indicative of an adaptive function for choosing a hunting strategy. A trend was evident among life stages. When all life stages were present (September-October), the proportion of active foragers increased with age: 0.0% among neonates, 18.2% among juveniles and 31.4% among adults. We concluded that vulnerable small neonates used sit-and-wait ambush not only as a hunting strategy but also as a hiding technique.
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.
Numerous behaviors of natricine snakes are plausibly interpreted as antipredator mechanisms that are useful at different stages of an encounter with a predator. Several of these behaviors have been described in detail, often in the laboratory, but we know little about the factors that influence their expression and effectiveness in the field, especially against real predators. Thus, one question that we might ask is: How effective are humans and artificial stimuli as proxies for real predators? Other areas that would profit from further research include the role of color and pattern in avoidance of predation, the effect of injury on subsequent survival, growth, or other measures of demographic performance, the role of previous experience in shaping future antipredator behavior, and the links among fear, stress physiology, and antipredator behavior.
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.
Models of population dynamics generally neglect the presence of males. While this assumption holds under many circumstances, behavioural ecology increasingly tells us that the presence (or absence) of males may have an impact on female fitness, and hence population sizes. Here we ask the question of whether males matter to population dynamics, operationally defined as a dependency of population growth on the relative density of males. We provide simple models, and evaluate the current empirical evidence for them, that illustrate various mechanisms of such male influence: mate searching behavior, male resource use (including effects of sexual dimorphism), sexual harassment and sexual segregation. In each case, theory predicts that males can have an effect on population densities, and in some extreme cases a positive feedback between an increasingly male-biased sex ratio and the effects on female harassment may theoretically even bring about population extinction. The results of this study, and the literature reviewed, show that the males can have a substantial effect on population dynamics, particularly so when human influences result in biased sex ratios.
Increasing appreciation that male and female reproductive strategies may be not only divergent but also incompatible has highlighted the potential importance of sexually antagonistic coevolution as a third force of sexual selection. Here, I review evidence for this mechanism in nonhuman primates. Sexual conflict has been studied primarily in its behavioral form, sexual coercion, for which relevant data still remain surprisingly limited. Nevertheless, current evidence reveals three forms of coercion: forced copulation, sexual harassment, and sexual intimidation. Many new data have confirmed the importance of forced copulation in orangutans, and clarified its variation and contexts, but have left unclear its adaptive significance. Evidence for sexual harassment and sexual intimidation has come from diverse taxa, but there are indications that the former may be expressed relatively more often in the nongregarious strepsirrhines and the latter among group-living haplorrhines. Two temporal domains for the action of sexual intimidation are suggested by evidence that it can improve male mating success both immediately and prospectively. Some researchers also suggest that female mate choice may underlie "coercion" in some taxa and that nonmating functions, such as social control, may be relevant. A key element of sexual conflict theory is female counterstrategies mitigating the costs of male adaptations. Current evidence now implicates strongly a great range of possible counterstrategies, involving female reproductive physiology, sexual behavior, and social strategies, although more data are needed to determine the effectiveness of these counterstrategies. Limited but suggestive data also indicate postcopulatory sexual conflict involving genitalia, seminal fluids, and their genetic bases.
Studying the behavior of snakes is a difficult logistical challenge in most cases, but a few populations make it easy. Most notably, many thousands of red-sided gartersnakes (Thamnophis sirtalis parietalis) emerge from communal dens in Manitoba in early spring and court and mate before dispersing to their summer ranges. We have exploited that opportunity to conduct detailed investigations of gartersnake behavior. Our observations and field experiments reveal intense sexual conflict, sophisticated chemical communication systems, and a flexible adjustment of reproductive tactics to local biotic and abiotic conditions. For example, newly emerged male snakes produce female-like pheromones and thereby attract courtship from other males, thereby warming the she-male and accelerating his recovery from overwintering. With a few flicks of his tongue, a mate-searching male can identify another snake's species, sex, body length, body condition, and mating history. The distinctive courting behaviors of male snakes impede female respiration, inducing an antipredator response (cloacal gaping) that allows forcible insemination. Females use facultative tactics to avoid harassing males. Our research on a snake population that (almost uniquely) allows direct observations and experiments has revealed a suite of complex and flexible behaviors that snakes use to enhance their individual reproductive success.
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.
An animal's relative body mass (i.e., mass adjusted for length or some other size dimension) is a potential indicator of its body condition, which in turn can influence demographic traits. In this study, I revisited data collected in 1969–1970 on garter snakes, Thamnophis sirtalis parietalis, at a communal hibernaculum in Manitoba, to test hypotheses generated by more recent literature. First, I compared fall-through-spring variation in relative mass to a similar study of another species of Thamnophis in a milder, Mediterranean climate and found a similar temporal pattern, suggesting common features across a wide latitudinal range. Female snakes had a higher relative mass than males and experienced lower decline in relative mass overwinter and through the spring. This suggests different hibernation strategies of the 2 sexes, possibly involving different temperatures or differences in metabolism, and also reflects the preoccupation of males upon spring emergence with searching for mates, at energetic cost while not feeding. Comparison of my data with a second study of the same species at another den in Manitoba indicated nearly identical patterns of loss of mass, based on recaptures of males throughout the spring, and also corroborated that study's finding that initially relatively heavy males remained at the den longer. Thus, males that have accumulated more capital the previous year presumably have more opportunities to mate. Although recapture intervals of most males were only a few days long, similar to the previous study, some males remained in the vicinity of the den for up to 5 weeks. These findings underscore the fundamental differences between males and females in the temporal distribution of their costs of reproduction.
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.
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.
In most snake species, males have longer tails than females of the same body length. The adaptive significance of this widespread dimorphism has attracted much speculation, but few tests. We took advantage of huge mating aggregations of red-sided gartersnakes (Thamnophis sirtalis parietalis) in southern Manitoba to test two (non-exclusive) hypotheses about the selective forces responsible for this dimorphism. Our data support both hypotheses. First, relative tail length affects the size of the male copulatory organs (hemipenes). Males with longer tails relative to body length have longer hemipenes, presumably because of the additional space available (the hemipenes are housed inside the tail base). Second, relative tail length affects male mating success. Males with partial tail loss (due to predation or misadventure) experienced a threefold reduction in mating success. Among males with intact tails, we detected strong stabilizing selection on relative tail length in one of the two years of our study. Thus, our data support the notion that sex divergence in tail length relative to body length in snakes reflects the action of sexual selection for male mating success.
Because snakes have a highly simplified morphology, and many species have a wide (and broadly overlapping) range of adult body sizes within each sex, they offer an excellent opportunity to compare body composition of males and females. Evolutionary theory predicts that particular body components should be differentially enlarged in the two sexes. For example, we might expect the reproductive success of females to be enhanced by enlargement of organ systems involved in the processing and storage of energy (e.g. alimentary tract, liver, fat stores) whereas males would benefit from the enlargement of systems important for mate-searching, male–male combat and sperm competition (e.g. larger mass of skeletal muscles, tail, and kidneys). Dissection of 243 specimens of three snake species (117 Vipera aspis, 43 Elaphe longissima, 83 Coluber viridflavus) broadly supported these predictions. Strong sex differences were apparent in relative sizes (masses) of all the non-gonadal body components that we weighed. For example, males consistently had more musculature (relative to body length) than did conspecific females. Dimorphism in relative muscle mass is likely to be one of the most fundamental and widespread morphological differences between males and females in the Animal Kingdom.
Mating in red-sided garter snakes is characterized by the formation of mating balls. Up to 100 males simultaneously court single females. The social dynamics of the formation of these mating balls was examined to determine whether the mating balls are formed simply because of a common attraction to the female or whether males are stimulated by the mating balls themselves. A sexually attractive female garter snake appears to be even more attractive to a male when she is being courted by other males than when she is alone. Male garter snakes courted females more actively when other males were also courting the female than when they were alone with her. There is a positive correlation between the number of additional males present and the amount of courtship activity shown by the test male toward the stimulus female. The extent to which the courtship activity of the test males was stimulated by the presence of additional courting males was not influenced by how actively the additional males courted.
The red-sided garter snake, Thamnophis sirtalis parietalis is an ideal model for the study of chemical or pheromonal communication in vertebrates. Results of long-term field and laboratory investigations of the chemical ecology of these unusual animals is summarized. These studies include a description of the characterization of the female attractiveness pheromone that serves to induce male courtship behavior. The male sex recognition pheromone system that identifies males as inappropriate individuals to court is also described. She-males, individual males that are courted as if they were females, seem to possess semiochemical components intermediate to both males and females. Finally, investigations of the species-specific nature of these pheromones indicate that chemical differences exist in the methyl ketones of all species examined to date.
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.
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.
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.
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.
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.
Life-history parameters of the red-sided garter snake (Thamnophis sirtalis parietalis) in an extreme environment, the Interlake region of Manitoba
. 1977. Life-history parameters of the red-sided garter snake
(Thamnophis sirtalis parietalis) in an extreme environment, the
Interlake region of Manitoba. Nat. Mus. Canada, Publ. Zool. 13:
1-44.
Movements and behavior of migratory garter snakes, Thamnophis sirtalis
- K Larson
Larson, K. 1987. Movements and behavior of migratory garter
snakes, Thamnophis sirtalis. Can. J. Zool. 65:2241-2247.
The dynamics of populations of squamates, crocodilians and rhyncocephalians
- F B Turner
Turner, F. B. 1977. The dynamics of populations of squamates,
crocodilians and rhyncocephalians. Pp. 157-264 in C. Gans and
D. W. Tinkle, eds. Biology of the Reptilia. Academic Press,
New York.