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Natural regulation of reproductive cycles
... Both in birds and mammals, photoperiod is the primary cue used to initiate and regulate the physiological and behavioural cascades for most seasonal events. The annual variation in day length for example triggers the activation of the reproductive system that translates into hormonal changes, development of the gonads (usually, in birds, regressed outside the breeding period), courtship behaviours, pairing and ultimately, egg fertilizations (Lofts and Murton 1968, Murton and Westwood 1977, Wingfield and Kenagy 1991, Silverin 1994, Reparaz et al. 2014. ...
... The relationship between photoperiod and laying date is likely modulated by supplementary cues such as food availability and temperature (Wingfield and Kenagy 1991). Photoperiod could serve as initial cue that generates a time window in which reproduction can potentially occur, and other cues would fine-tune when reproduction actually occurs. ...
... Moreover, birds had access to ad libitum food conditions. In the blue tit studies, photoperiod might thus have overridden some of the supplementary cues like temperature, social information, vegetation development or food availability, which might play an important role in our, as well as other, studies (Wingfield and Kenagy 1991, Perfito et al. 2004, Voigt et al. 2007, Davies and Deviche 2014. The necessity of intermediate-duration day lengths for supplementary cues to be taken into account was shown in Siberian hamsters Phodopus sungorus, where supplemental cues like food abundance and social information only acted when hamsters were exposed to 13.5 h light/day, and not when exposed to 16 h light day -1 (Paul et al. 2009). ...
In seasonal environments, organisms use biotic and abiotic cues to time various biological processes that are crucial for growth, survival and reproductive success. Photoperiod is the best‐known cue used to regulate gonadal development, migration and moult of many animal species. In birds, the relationship between photoperiod and gonadal development is clearly established, but we have little understanding on whether photoperiod also regulates actual timing of egg laying under natural conditions. Elucidating the link between photoperiod and timing of breeding is however key to understand whether an evolutionary change in sensitivity to photoperiod is a possible mechanism through which organisms could adjust their seasonal timing in response to climate warming. Here, we investigated the causal relationship between photoperiod, gonadal growth and laying date in wild female great tits. We experimentally increased the photoperiod perceived by the birds in spring by clipping head feathers, and we subsequently monitored gonadal development in the lab and egg laying dates in the wild. We show that our manipulation increased the photoperiod perceived by the birds to a level that approximately corresponds to an advancement of ten calendar days. This increase in perceived photoperiod led to an acceleration of gonadal development, but not to an advancement of egg laying dates. Our results indicate that photoperiod sensitivity is not constraining the advancement of laying date under current environmental conditions and suggest that evolution of sensitivity to other supplementary cues is necessary to advance reproduction under global warming. This article is protected by copyright. All rights reserved.
... To maximize reproductive success, organisms often temporally synchronize their breeding period with optimal environmental conditions (Baker 1938;Wingfield & Kenagy 1986;Lindstr€ om 1999;Lourdais et al. 2002). This synchronization has been demonstrated in a variety of taxa (Munro, Scott & Lam 1990;Boyd 1991;Nager & van Noordwijk 1995;Olsson & Shine 1998;Olive, Lewis & Beardall 2000). ...
... Food availability, in particular, is thought to modulate reproductive activity partly through an individual's energetic status. Accordingly, within the window of opportunity for breeding determined by day length, a bird's energetic status is predicted to constrain the timing of reproductive development (Drent & Daan 1980;Wingfield & Kenagy 1986;Meijer & Drent 1999;Hahn et al. 2005). Thus, birds in good energetic status can begin this development shortly after stimulation by sufficiently long days, whereas birds in poor energetic status delay development until they have acquired sufficient energy stores. ...
... Food availability is thought to modulate reproductive development partly via energetic status. Limited food availability may constrain this development because birds lack the necessary energy stores for tissue growth and hormone production (Drent & Daan 1980;Wingfield & Kenagy 1986;Meijer & Drent 1999;Hahn et al. 2005). Studies in controlled laboratory conditions aimed at testing whether food availability modulates reproductive development through its effects on energetic status must, therefore, ensure that food availability treatments produce a disparity in the energetic condition. ...
In many organisms, food availability is a proximate cue that synchronizes seasonal development of the reproductive system with optimal environmental conditions. Growth of the gonads and secondary sexual characteristics is orchestrated by the hypothalamic–pituitary–gonadal (HPG) axis. However, our understanding of the physiological mechanisms by which food availability modulates activity of the HPG axis is limited.
It is thought that many factors, including energetic status, modulate seasonal reproductive activation. We tested the hypothesis that food availability modulates the activity of the HPG axis in a songbird. Specifically, we food‐restricted captive adult male Abert's Towhees Melozone aberti for 2 or 4 weeks during photoinduced reproductive development. A third group (control) received ad libitum food throughout. We measured multiple aspects of the reproductive system including endocrine activity of all three levels of the HPG axis [i.e. hypothalamic gonadotropin‐releasing hormone‐I (GnRH‐I), plasma luteinizing hormone (LH) and testosterone (T)], and gonad morphology. Furthermore, because gonadotropin‐inhibitory hormone (GnIH) and neuropeptide Y (NPY; a potent orexigenic peptide) potentially integrate information on food availability into seasonal reproductive development, we also measured the brain levels of these peptides.
At the hypothalamic level, we detected no effect of food restriction on immunoreactive (ir) GnRH‐I, but the duration of food restriction was inversely related to the size of ir‐GnIH perikarya. Furthermore, the number of ir‐NPY cells was higher in food‐restricted than control birds. Food restriction did not influence photoinduced testicular growth, but decreased plasma LH and T, and width of the cloacal protuberance, an androgen‐sensitive secondary sexual characteristic. Returning birds to ad libitum food availability had no effect on plasma LH or T, but caused the cloacal protuberance to rapidly increase in size to that of ad libitum‐fed birds.
Our results support the tenet that food availability modulates photoinduced reproductive activation. However, they also suggest that this modulation is complex and depends upon the level of the HPG axis considered. At the hypothalamic level, our results are consistent with a role for the GnIH and NPY systems in integrating information on energetic status. There also appears to be a role for endocrine function at the anterior pituitary gland and testicular levels in modulating reproductive development in the light of energetic status and independently of testicular growth.
... The short time-window dedicated to reproduction generally occurs in spring, when temperatures are mild and large amounts of nutrient-and protein-rich food necessary for raising offspring become available. To time and organize the complex temporal pattern of reproductive behaviours, animals use environmental cues that predict, well in advance, the onset of suitable conditions for breeding [1,2]. Among these cues, the most reliable predictive signal is the annual change in photoperiod: every year, favourable spring conditions for breeding coincide with a progressive increase in day length. ...
... Exposure to increasingly longer photoperiods triggers a cascade of neuroendocrine reactions that prepare animals for breeding: e.g., genes are activated in the brain, reproductive hormones increase in concentration in the blood, and gonads mature and start producing gametes [3][4][5][6]. These physiological changes in turn stimulate the expression of a complex and well-organized suite of reproductive behaviours such as territory defence, courting, nest preparation and communication displays, like songs in songbirds [1]. ...
... For most animals living in temperate and arctic zones, the increasing photoperiod in late winter and spring correlates reliably with forthcoming improvement of environmental conditions to a level that supports the energetic and nutritional requirements for successful reproduction [1,3]. Photoperiod thus acts as a cue signalling the approach of suitable conditions for breeding, and many species use that cue to orchestrate their reproductive behaviours. ...
Organisms use environmental cues to time their life-cycles and among these cues, photoperiod is the main trigger of reproductive behaviours such as territory defence or song activity. Whether photoperiod is also important for another behaviour closely associated with reproduction, mate choice, is unknown. In many bird species, mate choice occurs at two different times during the annual cycle that strongly differ in daylength: in late winter when photoperiod is short and social mates are chosen, and again around egg-laying when photoperiod is longer and extra-pair mates are chosen. This duality makes the role that photoperiod plays on mate choice behaviours intriguing. We investigated the effect of photoperiod on mate choice using three experimental photoperiodic treatments (9 L:15 D, 14 L:10 D, 18 L:6 D), using blue tits (Cyanistes caeruleus) as a biological model. We show that female choice was stronger under long photoperiods. In addition, female blue tits spent significantly more time near males with long tarsi and long wings. This latter preference was only expressed under long photoperiods, suggesting that some indices of male quality only become significant to females when they are strongly photostimulated, and therefore that females could select their social and extra-pair mates based on different phenotypic traits. These results shed light on the roles that photoperiod may play in stimulating pair-bonding and in refining female selectivity for male traits.
... In birds, timing of reproduction is further complicated by the fact that non-tropical species regress their gonads outside of the reproductive season 3 . They thus need to induce gonadal growth ahead of optimal conditions to reproduce and lay eggs 4,5 . ...
... While photoperiod often serves as a predominant, proximate cue to induce gonadal growth and the onset of breeding [3][4][5][6] , the precise timing of egg-laying and hatching will depend on local environmental conditions 7 . Birds therefore use further environmental cues to better predict the nesting season in advance [8][9][10] . ...
To track peaks in resource abundance, temperate-zone animals use predictive environmental cues to rear their offspring when conditions are most favourable. However, climate change threatens the reliability of such cues when an animal and its resource respond differently to a changing environment. This is especially problematic in alpine environments, where climate warming exceeds the Holarctic trend and may thus lead to rapid asynchrony between peaks in resource abundance and periods of increased resource requirements such as reproductive period of high-alpine specialists. We therefore investigated interannual variation and long-term trends in the breeding phenology of a high-alpine specialist, the white-winged snowfinch, Montifringilla nivalis, using a 20-year dataset from Switzerland. We found that two thirds of broods hatched during snowmelt. Hatching dates positively correlated with April and May precipitation, but changes in mean hatching dates did not coincide with earlier snowmelt in recent years. Our results offer a potential explanation for recently observed population declines already recognisable at lower elevations. We discuss non-adaptive phenotypic plasticity as a potential cause for the asynchrony between changes in snowmelt and hatching dates of snowfinches, but the underlying causes are subject to further research.
... Seasonal changes in photoperiod and sex-steroid hormone concentrations prepare seasonally breeding animals to engage in behavior appropriate for the time of year. For example, increasing photoperiods and concentrations of testosterone (T) or estradiol underlie the activation of sexual behaviors in many species at a time of year when conditions favor breeding (Ball and Balthazart, 2004;Ball and Ketterson, 2008;Bronson, 2009;Dawson et al., 2001;Wingfield and Kenagy, 1991). In contrast, outside the breeding season, when sexsteroid hormone concentrations are low and resources are scarce, animals refrain from producing sexual behaviors (Dawson et al., 2001;Kriegsfeld et al., 2015;Wingfield and Kenagy, 1991). ...
... For example, increasing photoperiods and concentrations of testosterone (T) or estradiol underlie the activation of sexual behaviors in many species at a time of year when conditions favor breeding (Ball and Balthazart, 2004;Ball and Ketterson, 2008;Bronson, 2009;Dawson et al., 2001;Wingfield and Kenagy, 1991). In contrast, outside the breeding season, when sexsteroid hormone concentrations are low and resources are scarce, animals refrain from producing sexual behaviors (Dawson et al., 2001;Kriegsfeld et al., 2015;Wingfield and Kenagy, 1991). Sex-steroid hormones and photoperiod are proposed to alter behavior in part by modifying the activity of other neuromodulators (Ball and Balthazart, 2010); however, mechanisms by which they do so are still unclear (e.g., Cornil and de Bournonville, 2018;Hellier et al., 2018). ...
In seasonally breeding animals, changes in photoperiod and sex-steroid hormones may modify sexual behavior in part by altering the activity of neuromodulators, including opioids and dopamine. In rats and birds, activation of mu-opioid receptors (MOR) and dopamine D1 receptors in the medial preoptic area (mPOA) often have opposing effects on sexual behavior, yet mechanisms by which the mPOA integrates these opposing effects to modulate behavior remain unknown. Here, we used male European starlings (Sturnus vulgaris) to provide insight into the hypothesis that MOR and D1 receptors modify sexual behavior seasonally by altering activity in the same neurons in the mPOA. To do this, using fluorescent immunohistochemistry, we examined the extent to which MOR and D1 receptors co-localize in mPOA neurons and the degree to which photoperiod and the sex-steroid hormone testosterone alter co-localization. We found that MOR and D1 receptors co-localize throughout the mPOA and the bed nucleus of the stria terminalis, a region also implicated in the control of sexual behavior. Numbers of single and co-labeled MOR and D1 receptor labeled cells were higher in the rostral mPOA in photosensitive males (a condition observed just prior to the breeding season) compared to photosensitive males treated with testosterone (breeding season condition). In the caudal mPOA co-localization of MOR and D1 receptors was highest in photosensitive males compared to photorefractory males (a post-breeding season condition). Seasonal shifts in the degree to which neurons in the mPOA integrate signaling from opioids and dopamine may underlie seasonal changes in the production of sexual behavior.
... Here we report for the first time how the usage of mating signals (song) varies with these anthropogenic factors in the tropics, where the photoperiod varies very little across the year. In the temperate zones with the marked seasonal changes in day length, photoperiod is a cue for the timing of reproductive stages of birds in general and for the onset of the dawn chorus in particular (Dawson et al., 2001;Gwinner, 2003;Wingfield and Farner, 1993;Wingfield and Kenagy, 1991). On a seasonal level, light at night can advance the timing of breeding (e.g. ...
... In the temperate zones, seasonal changes in day length are very evident. Thus, birds use photoperiod as a cue to start breeding season in a broad context and in particular it is use for the onset of the dawn chorus as well (Dawson et al., 2001;Gwinner, 2003;Wingfield and Farner, 1993;Wingfield and Kenagy, 1991). Light at night has been related to advancement of the breeding time (Dominoni et al., 2013b), and to a change in the onset time of the dawn chorus (Da Silva et al., 2015;Dominoni et al., 2013a;Kempenaers et al., 2010;Miller, 2006). ...
... Using the date of egg-laying from 254 species, Baker found that the higher the latitude, the more seasonal is the breeding (Figure 1.33, Baker 1939). This hypothesis was supported by the fact that at high latitudes seasonal breeding is primarily controlled by photoperiod (Wingfield & Kenagy 1991), with brief and synchronized breeding seasons during the short spring-summer period when prey is sufficiently abundant to support high predation rates and to limit competition (Martin 1987). In contrast, in mid and low latitude ecosystems, with only slight seasonal fluctuations, most of the species may display opportunistic breeding. ...
... For seabirds of temperate and polar marine ecosystems, seasonal breeding is primarily controlled by photoperiod (Wingfield & Kenagy 1991), and the precise date of egg-laying appears to be driven by egg laying constraints Shultz et al. 2009). In contrast, in tropical ecosystems, seasonal changes in photoperiod are small and few studies have examined the correspondence between seasonal ecosystem productivity and seabird seasonal breeding from a bottom-up perspective (Le Corre 2001, Jaquemet et al. 2007). ...
In the highly productive Northern Humboldt Current System, 3 seabird species, the Guanay cormorant Phalacrocorax bougainvillii, the Peruvian booby Sula variegata and the Peruvian pelican Pelecanus thagus, commence breeding in austral spring, coinciding with the lowest availability of their prey, the Peruvian anchovy Engraulis ringens. This strategy ensures the matching of increased prey availability when young achieve independence in summer. This pattern
was observed during the last decade when anchovy was abundant. However, over the last century, the abundance of anchovy has varied widely due to contrasting interdecadal regimes in oceanographic conditions and fishing activity. We hypothesized that these regime shifts affected the abundance and availability of prey and may have conditioned the breeding seasonality of seabirds. We examined the timing and magnitude of the onset of breeding using dynamic occupancy models and related these parameters to the seasonality of oceanographic conditions, abundance of anchovy and fishing pressure. During a regime of lower anchovy abundance (1977−1990), cormorants showed the highest flexibility, adjusting the timing of breeding from spring to winter and skipping reproduction in the worst conditions. Boobies showed the lowest flexibility, maintaining
the same magnitude and timing of onset of breeding in spring. Pelicans showed intermediate flexibility, foregoing breeding during the worst conditions, but maintaining the onset of breeding in
spring. The 3 species used sea surface temperature as a cue for the initiation of breeding. Furthermore, given their better diving abilities, cormorants could monitor prey availability changes associated
with the reversion in the seasonality of the oxycline depth.
... Using the date of egg-laying from 254 species, Baker found that the higher the latitude, the more seasonal is the breeding (Figure 1.33, Baker 1939). This hypothesis was supported by the fact that at high latitudes seasonal breeding is primarily controlled by photoperiod (Wingfield & Kenagy 1991), with brief and synchronized breeding seasons during the short spring-summer period when prey is sufficiently abundant to support high predation rates and to limit competition (Martin 1987). In contrast, in mid and low latitude ecosystems, with only slight seasonal fluctuations, most of the species may display opportunistic breeding. ...
... For seabirds of temperate and polar marine ecosystems, seasonal breeding is primarily controlled by photoperiod (Wingfield & Kenagy 1991), and the precise date of egg-laying appears to be driven by egg laying constraints Shultz et al. 2009). In contrast, in tropical ecosystems, seasonal changes in photoperiod are small and few studies have examined the correspondence between seasonal ecosystem productivity and seabird seasonal breeding from a bottom-up perspective (Le Corre 2001, Jaquemet et al. 2007). ...
The Northern Humboldt Current System (NHCS) is a place of a high biological activity due to an intense coastal upwelling. It supports one of the biggest forage fish populations, the Peruvian anchovy, and the world-leading monospecific fishery in terms of landings. The NHCS also hosts large, although variable, seabird populations, composed among others by three guano-producing sympatric species: the Guanay cormorant (Phalacrocorax bougainvillii), the Peruvian booby (Sula variegata) and the Peruvian pelican (Pelecanus thagus), which all feed primarily on anchovy.In this work we reviewed the fluctuations of these three seabird populations, focusing on the seasonal cycle of their breeding, to address the following questions: How different are the seasonality of reproduction among species? To what extent may they be plastic in space and time? What from the natural environment and the anthropogenic activities impact more the breeding of seabirds?We addressed these questions using the monthly occupancy of breeders (1) in >30 Peruvian sites between 06°S and 18°S and from 2003 to 2014; and (2) in one site during three decadal periods (1952-1968, 1972-1989, 2003-2014). We also used environmental covariates from satellite and at-sea monitoring such as oceanographic conditions, prey abundance, availability and body conditions, and fisheries pressure covariates. We used multiseason occupancy models to characterize the seasonality of breeding and relate it with environmental covariates. We also used functional principal component analysis for classifying the differences in seasonality among sites, and random forest regression for analyzing the relative contribution of covariates in the variability of the seasonal breeding.We found that in average seasonal breeding mainly started during the austral winter/ early spring and ended in summer/ early fall, this pattern being stronger in boobies and pelicans than in cormorants. The breeding onset of seabirds is timed so that fledging independence occurs when primary production, prey conditions and availability are maximized. This pattern is unique compared with other upwelling ecosystems and could be explained by the year-round high abundances of anchovy in the NHCS.The average seasonal breeding may differ among nesting sites. Seabirds breed earlier and are more persistent when colonies are larger, located on islands, within the first 20km of the coast, at lower latitudes and with greater primary production conditions. These results suggest that in the NHCS, the seasonality of breeding is more influenced by local environmental conditions than by large-scale environmental gradients. These results provides critical information to a better coordination of guano extraction and conservancy policies.Seabirds may also adapt the seasonality of their breeding to drastic ecosystem changes caused by regime shifts. We found that the three study species exhibited a gradient of plasticity regarding the seasonality of their breeding. Cormorants showed a greater plasticity, modulating the timing and magnitude on their breeding seasonality. This is probably authorized by the greater foraging flexibility offered its great diving capacities. Fixed onset and magnitudes of breeding in boobies may be related to their specific foraging strategy and/or to changes of prey items when anchovy stock was low. We also suggested that boobies may adapt other fecundity traits as growth rate of chicks to lower abundance of anchovy.The specific differences in the adaptation of seasonal breeding allow seabirds to take profit differently from local prey conditions or to face differently regime shifts. Further researches, implementing a large-scale capture-recapture methodology in parallel with monthly census, are proposed in order to fulfill gaps in the basic knowledge on vital traits (adult survival, first age at reproduction, and juvenile recruitment) which are critical parameters to evaluate the dynamic of a population.
... Reproductive success requires animals to adjust social and sexual behaviors in response to changes in environmental resources. The hypothalamicpituitary-gonadal (HPG) axis is critical for animals to time sexual behaviors to match the availability of essential resources (e.g., breeding territory, rainfall, food, and mate availability (Wingfield and Kenagy 1991;Calisi et al. 2011;Watts and Hahn 2012;Williams 2012;Davies et al. 2015)). Acquiring limited environmental resources stimulates the HPG axis, after which animals begin responding to potential mating stimuli with courtship, approach behavior or copulation solicitation (e.g., Wingfield and Farner 1980;Wingfield and Kenagy 1991;Zann et al. 1995;Riters et al. 2000;Maruska and Fernald 2010;Spool et al. 2016). ...
... The hypothalamicpituitary-gonadal (HPG) axis is critical for animals to time sexual behaviors to match the availability of essential resources (e.g., breeding territory, rainfall, food, and mate availability (Wingfield and Kenagy 1991;Calisi et al. 2011;Watts and Hahn 2012;Williams 2012;Davies et al. 2015)). Acquiring limited environmental resources stimulates the HPG axis, after which animals begin responding to potential mating stimuli with courtship, approach behavior or copulation solicitation (e.g., Wingfield and Farner 1980;Wingfield and Kenagy 1991;Zann et al. 1995;Riters et al. 2000;Maruska and Fernald 2010;Spool et al. 2016). A stimulus that activates approach behaviors is considered an incentive (Berridge and Robinson 1998;Ikemoto and Panksepp 1999;Berridge 2004). ...
Reproductive success requires animals to adjust social and sexual behaviors in response to changes in environmental resources. In many species, males produce courtship signals to attract females; however, not all females are attracted by these signals. One possible explanation for this is that environmental resources alter neural mechanisms underlying motivation and reward in females so that male courtship is attractive when conditions are most favorable for an individual to breed. Here, we first introduce resource-dependent breeding behaviors of female songbirds. We then review studies that show associations between neural systems underlying motivation and reward, female responses to male courtship stimuli, and environmental resources necessary for breeding success (e.g., in female starlings, a nest cavity). Overall, we review evidence supporting the working hypotheses that (1) dopamine underlies sexually-motivated female responses to male courtship stimuli (i.e., song), (2) opioids underlie reward induced in females by hearing male courtship song, and (3) these systems are possibly modified by resources such that male courtship song is only attractive and rewarding to females with access to limited environmental resources essential for breeding success.
... Phenotypic plasticity, the ability of an organism to alter its phenotype in response to environmental change, is a crucial adaptation to seasonal environments (Lourdais et al., 2002;Miner et al., 2005;Wingfield and Kenagy, 1986). A major seasonal phenotypic change for many animals is the cycle of gonad growth (Bubenik et al., 1997;Dawson, 1983;Itoh et al., 1990), which is regulated by a rise in reproductive hormone secretion (Deviche et al., 2010;Wingfield and Kenagy, 1986). ...
... Phenotypic plasticity, the ability of an organism to alter its phenotype in response to environmental change, is a crucial adaptation to seasonal environments (Lourdais et al., 2002;Miner et al., 2005;Wingfield and Kenagy, 1986). A major seasonal phenotypic change for many animals is the cycle of gonad growth (Bubenik et al., 1997;Dawson, 1983;Itoh et al., 1990), which is regulated by a rise in reproductive hormone secretion (Deviche et al., 2010;Wingfield and Kenagy, 1986). It is often assumed that inter-individual and inter-annual variation in the phenology of hormone secretion determines corresponding variation in the timing of gonad growth. ...
Birds often adjust to urban areas by advancing the timing (phenology) of vernal gonad growth. However, the ecological and physiological bases of this adjustment are unclear. We tested whether the habitat-related disparity in gonad growth phenology of male Abert’s towhees, Melozone aberti, is due to greater food availability in urban areas of Phoenix, Arizona USA or, alternatively, a habitat-related difference in the phenology of key food types. To better understand the physiological mechanism underlying variation in gonad growth phenology, we compared the activity of the reproductive system at all levels of hypothalamo-pituitary-gonadal (HPG) axis. We found no habitat-associated difference in food availability (ground arthropod biomass), but, in contrast to the seasonal growth of leaves on desert trees, the leaf foliage of urban trees was already developed at the beginning of our study. Multiple estimates of energetic status did not significantly differ between the non-urban and urban populations during three years that differed in the habitat-related disparity in gonad growth and winter precipitation levels. Thus, our results provide no support for the hypothesis that greater food abundance in urban areas of Phoenix drives the habitat-related disparity in gonad growth phenology in Abert’s towhees. By contrast, they suggest that differences in the predictability and magnitude of change in food availability between urban and desert areas of Phoenix contribute to the observed habitat-related disparity in gonad growth. Endocrine responsiveness of the gonads may contribute to this phenomenon as desert – but not urban – towhees had a marked plasma T response to GnRH challenge.
... Animals typically use the seasonality of their environmental to time annual cycles in behavior (Murton andWestwood 1977, Wingfield andKenagy 1991). However, the ability of animals to make use of fluctuations in the environment to time life-history stages depends on the predictability and amplitude of the seasonal fluctuations they experience (Colwell 1974, Wingfield et al. 1992, Dawson 2008). ...
... Seasonal reproduction is the norm in birds breeding in the temperate zones (latitudes higher than the tropics of Cancer and Capricorn, 23° 26′ N and S, respectively) and in the Arctic and Antarctic, where there are strong seasonal changes in temperature, precipitation, and biotic resources. Birds breeding in the temperate zones rely primarily on the change in photoperiod (day length) to predict and schedule behavioral and physiological changes with changes in environmental conditions through their annual cycles (Baker 1938, Murton and Westwood 1977, Wingfield and Kenagy 1991. Most species resident in the tropics also reproduce seasonally, even though the correlation between photoperiod and environmental seasonality is weak (Murton andWestwood 1977, Stutchbury andMorton 2001). ...
Tropical vertebrates are considered to have greater flexibility in the timing of life-history stages than are temperate-zone vertebrates. Yet the annual cycles of most resident tropical species are poorly understood, making latitudinal comparisons of phenology difficult. We investigated the reproductive seasonality and synchrony of a mid-elevation (∼2100 m), equatorial population of the Rufous-collared Sparrow (Zonotrichia capensis) and compared our data with data from three other populations of Zonotrichia across a range of latitudes and elevations (one equatorial high-elevation population of Z. capensis and two temperate-zone populations of Z. leucophrys, one at high elevation and one at sea level). We predicted that (1) the reproductive synchrony and seasonality of temperate-zone populations should be greater than those of the equatorial populations and (2) the reproductive synchrony and seasonality of populations breeding at high elevations should be greater than those of populations breeding at lower elevations. We found no seasonal pattern in the proportion of adults' life-history stages in the mid-elevation equatorial population of Z. capensis. Broader comparisons revealed that the reproductive synchrony and seasonality of temperate-zone populations were not always higher than those of the equatorial populations. Elevation of the breeding population had a strong effect on reproductive seasonality in both temperate-zone and equatorial populations. However, reproductive synchronies of temperate-zone populations were very different, while those of equatorial populations were similar. Thus elevation and climatic factors associated with latitude of breeding are important to reproductive seasonality and synchrony.
... Changes in environmental factors such as photoperiod, temperature, and food availability act on the upper brain center (hypothalamus) to regulate the synthesis and secretion of neuropeptides involved in reproduction [2,[5][6][7][8]. Photoperiod is considered the primary reliable cue to entrain seasonal reproduction, and supplementary environmental cues, such as temperature, fine-tune the timing of breeding [9][10][11]. The presence of non-visual, non-pineal photoreceptors (deep brain photoreceptors) was suggested over a century ago when von Frisch showed that blinded and pinealectomized European minnows (Phoxinus phoxinus) retained an ability to change color in response to light [12]. ...
Seasonal breeders predominantly use photoperiod as the predictable environmental cue to time their reproduction. Terai tree frogs are long-day seasonal breeders, but the molecular mechanism is unknown. We tested the role of different photoperiodic conditions on expression levels of candidate genes involved in seasonal reproduction and epigenetic regulation. Four experiments were performed. In experiment 1, frogs were exposed to long (LD: 16L:8D) or short photoperiod (SD: 8L:16D). In experiment 2, animals were procured at four different phases of breeding, i.e., during April (emergence just after hibernation), June (breeding phase), August (post-breeding), and October (just before hibernation). In experiments 3 and 4, frogs were exposed to equinox photoperiod but different (10, 100, or 500 lx) light intensities (exp. 3) or wavelength (red: 640 nm, green: 540 nm, blue: 450 nm or white; exp. 4). After 2 weeks, animals were euthanized, and their brain was harvested. mRNA levels of transcripts involved in photoperiodic transduction (Eya3 and Opn5), reproduction (Tshß, GnRH, Dio2, and Dio3), and epigenetics regulation (Dnmt1, Dnmt3a, Hdac1, Hdac3, and Tet2) were measured. Results show that LD promotes the upregulation of Eya3, Opn5, Tshß, GnRH, and Dio2. Differential expression of Opn5 during LD and SD suggests its involvement in light perception. Dio3 levels were upregulated in SD (exp.1) and during the post-breeding phase (exp. 2). These results employ the limited role of light intensity and spectrum in reproduction. This is the first study showing molecular machinery involved in the amphibian system's seasonal reproduction and epigenetic regulation.
... The onset, timing and intensity of reproductive activity is therefore likely to have significant fitness consequences for both males and females. For many seasonally reproducing species, breeding can also occur over prolonged periods (weeks to months), with multiple cycles of reproductive activity punctuated by distinct periods of inactivity within the same breeding season (Wingfield & Kenagy, 1991). Such reproductive cycling provides a good opportunity to study fine-scale sex specific differences in climatic triggers for reproduction. ...
... The greater amount of evidence of reproductive activity in fewer peaks at HE than LE could be regulated by environmental factors. In fact, local environmental factors, such as rainfall, temperature, and food availability, are supplementary cues that can influence the timing and length of the reproductive season and the development of cloacal protuberance in males (Lack 1966, Wingfield & Kenagy 1991.We found three peaks of reproductive activity at each elevation; two of them occurred at the beginning of the major rainfall season, i.e., March and October, and the other peak occurred during the minor rainfall season, specifically, in July. It is possible that harsher environmental conditions limited the length of the reproductive activity at the high elevation locality as opposed to the low elevation. ...
Breeding biology in a population of Rufous-collared Sparrow (Zonotrichia capensis, Statius Müller, 1776) at different elevations in the Tropical Andes. Elevation strongly influences the evolution of life history traits associated with bird physiology and reproduction. Since life history traits in birds are modulated by environmental factors that vary with elevation, we expected to find changes in breeding biology traits of Z. capensis at different elevations. In this study, we compared the breeding biology (clutch size, egg volume, and reproductive activity) of a non-migratory population of Z. capensis in two localities at different elevations (low and high elevations, 1 800 m a.s.l., and 3 800 m a.s.l., respectively) and same latitude in the Colombian Tropical Andes for a one-year period. We found no differences in clutch size between the localities; however, egg volume was higher at high elevation. Furthermore, the reproductive activity differed significantly between localities. We propose that clutch size is likely conserved throughout the altitudinal distribution of Z. capensis since the species evolved in Tropical lowlands. On the other hand, the larger egg volume at high elevation could obey local environmental factors that may favor the reproductive success of the population.
... Seasonality has been well recognized as one of the driven forces for the irregular periodicities [1,11,30]. The seasonal mechanisms include the external influences on the host contact rate. ...
Multiple recurrent outbreak cycles have been commonly observed in infectious diseases such as measles and chicken pox. This complex outbreak dynamics in epidemiologicals is rarely captured by deterministic models. In this paper, we investigate a simple 2-dimensional SI epidemiological model and propose that the coexistence of multiple attractors attributes to the complex outbreak patterns. We first determine the conditions on parameters for the existence of an isolated center, then properly perturb the model to generate Hopf bifurcation and obtain limit cycles around the center. We further analytically prove that the maximum number of the coexisting limit cycles is three, and provide a corresponding set of parameters for the existence of the three limit cycles. Simulation results demonstrate the case with the maximum coexisting attractors, which contains one stable disease free equilibrium and two stable endemic periodic solutions separated by one unstable periodic solution. Therefore, different disease outcomes can be predicted by a single nonlinear deterministic model based on different initial data.
... The attenuated size of testes and plasma T levels are consistent with idea that food-restriction causes an inadequate supply of energy spared for the tissue growth, hormone production and reproductive development (Wingfield and Kenagy, 1991;Hahn et al., 2005). This may be adaptive since smaller testes and depressed T levels will avoid birds to engage in the energy-consuming T-dependent reproductive behavioral displays during the period of the shortened food supply (Davies et al., 2015). ...
Food availability affects metabolism and reproduction in higher vertebrates including birds. This study tested the idea of adaptive homeostasis to time-restricted feeding (TRF) in diurnal zebra finches by using multiple (behavioral, physiological and molecular) assays. Adult birds were subjected for 1 week or 3 weeks to food restriction for 4 h in the evening (hour 8–12) of the 12 h light-on period, with controls on ad lib feeding. Birds on TRF showed enhanced exploratory behavior and plasma triglycerides levels, but did not show differences from ad lib birds in the overall food intake, body mass, and plasma corticosterone and thyroxine levels. As compared to ad lib feeding, testis size and circulation testosterone were reduced after first but not after third week of TRF. The concomitant change in the mRNA expression of metabolic and reproductive genes was also found after week 1 of TRF. Particularly, TRF birds showed increased expression of genes coding for gonadotropin releasing hormone (GnRH) in hypothalamus, and for receptors of androgen (AR) and estrogen (ER-alpha) in both hypothalamus and testes. However, genes coding for the deiodinases (Dio2, Dio3) and gonadotropin inhibiting hormone (GnIH) showed no difference between feeding conditions in both hypothalamus and testes. Further, increased Sirt1, Fgf10 and Ppar-alpha, and decreased Egr1 expression in the liver suggested TRF-effects on the overall metabolism. Importantly, TRF-effects on gene expressions by week 1 seemed alleviated to a considerable extent by week 3. These results on TRF-induced reproductive and metabolic effects suggest homeostatic adaptation to food-restriction in diurnal vertebrates.
... Among all available cues that can indicate approaching spring, such as ambient temperature, plant growth, and food availability, celestial cues are the most reliable. Most seasonally breeding birds use daylength as a cue to initiate gonadal recrudescence and the onset of reproduction (Wingfield and Kenagy, 1991). As daylength increases in the spring, it eventually reaches a threshold that triggers release of gonadotropin releasing hormone I (hereafter referred to as GnRH) from the median eminence, thus stimulating secretion of luteinizing hormone (LH) and follicle stimulating hormone and, in turn, gonadal development and secretion of sex steroids. ...
Many seasonally-breeding species use daylength to time reproduction. Light-induced release of progonadal hormones involves a complex cascade of responses both inside and outside the brain. In this study, we used induction of early growth response 1 (Egr-1), the protein product of an immediate early gene, to evaluate the time course of such responses in male white-throated sparrows (Zonotrichia albicollis) exposed to a single long day. Induction of Egr-1 in the pars tuberalis began ∼11 h after dawn. This response was followed ∼6 h hours later by dramatic induction in the tuberal hypothalamus, including in the ependymal cells lining the third ventricle. At approximately the same time, Egr-1 was induced in dopaminergic and vasoactive intestinal peptide neurons in the tuberal hypothalamus and in dopaminergic neurons of the premammillary nucleus. We noted no induction in gonadotropin-releasing hormone (GnRH) neurons until 2 h after dawn the following morning. Overall, our results indicate that Egr-1 responses in GnRH neurons occur rather late during photostimulation, compared with responses in other cell populations, and that such induction may reflect new synthesis related to GnRH depletion rather than stimulation by light cues.
... However, its invariability from year to year does not allow females to track yearto-year variation in local conditions (Bradshaw and Holzapfel, 2007;Visser et al., 2004) and, as such, photoperiod alone cannot explain individual year-to-year differences in the timing of breeding. Temperature is highly variable between years and provides information about local conditions, such as insect emergence, which allows females to fine-tune the timing of breeding (Dawson, 2008;Wingfield and Kenagy, 1991;Wingfield et al., 1992) and subsequently match offspring needs to food abundance. Temperature is the major driving force of biological seasonality in temperate zones (Parmesan, 2007) and the most influential environmental cue in fine-tuning the timing of avian seasonal breeding (Caro et al., 2013;Lambrechts and Visser, 1999;Visser et al., 2009). ...
Phenotypic plasticity is an important mechanism by which an individual can adapt its seasonal timing to predictable, short-term environmental changes by using predictive cues. Identification of these cues is crucial to forecast species' response to long-term environmental change and to study their potential to adapt. Individual great tits (Parus major) start reproduction early under warmer conditions in the wild, but whether this effect is causal is not well known. We housed 36 pairs in climate-controlled aviaries and 40 pairs in outdoor aviaries, where they bred under artificial contrasting temperature treatments or in semi-natural conditions, respectively, for two consecutive years, using great tits from lines selected for early and late egg laying. We thus obtained laying dates in two different thermal environments for each female. Females bred earlier under warmer conditions in climate-controlled aviaries, but not in outdoor aviaries. The latter was inconsistent with laying dates from our wild population. Further, early selection line females initiated egg laying consistently ∼9 days earlier compared to late selection line females in outdoor aviaries, but we found no difference in the degree of plasticity (i.e. the sensitivity to temperature) in laying date between selection lines. Because we find that temperature causally affects laying date, climate change will lead to earlier laying. This advancement is however unlikely to be sufficient, thereby leading to selection for earlier laying. Our results suggest that natural selection may lead to a change in mean phenotype, but not to a change in the sensitivity of laying dates to temperature.
... Birds, similar to other vertebrates, temporally synchronise their annual breeding period with food abundance times, aiming to maximise their reproductive success. 1,2 Hence, most species inhabiting the predictable environments of mid and high latitudes reproduce seasonally and, using annual photoperiodic cycles, time their gonadal maturation cycle such that offspring births coincide with the period of optimal food availability in the year. 3 By contrast, in environments where food availability can be transient and/or vary unpredictably in time and space, birds need to maintain the ability to reproduce year round. ...
Previous studies have demonstrated ‘quality‐quantity’ trade‐offs with daily food availability times in zebra finches. As compared to food access ad libitum, zebra finch pairs with restricted food access for 4 h in the morning produced poor quality offspring, whereas those with the same food access in the evening produced fewer but better quality offspring. The present study investigated whether food‐time‐dependent differential effects on reproductive performance involved brain peptides associated with reproduction and energy homeostasis in zebra finches. We measured peptide/protein expression of GnRH‐I, GnRH‐II, GnIH, TH, NPY, CART and ZENK by immunohistochemistry and mRNA expression of genes coding for the type 2 (DIO2) and type 3 (DIO3) deiodinase by qPCR in male and female zebra finches that were paired and kept on 12L: 12D at 24 ± 2 °C temperature for >12 mo with access to food ad libitum, or for only 4 h in the morning or evening. In both sexes, GnRH‐I, DIO2 and DIO3 expression did not differ significantly between the three feeding conditions, although levels showed an overall food effect. However, in males, GnIH expression was significantly higher in evening‐fed birds than in ad libitum fed birds. Interestingly, GnRH‐II and TH levels were significantly lower in restricted feeding than in the ad libitum group, and importantly, GnRH‐II and TH‐ir levels were negatively and positively correlated with egg laying latency and reproductive success (offspring/brood/pair), respectively. At the same time, we found no effect on the hypothalamic expression of orexigenic (NPY) and anorexigenic (CART) peptides, or ZENK protein (the neuronal activity marker). These results suggest the involvement of reproductive neuropeptides with putative roles for GnRH‐II and TH in the food‐time‐dependent effect on reproductive performance, albeit with subtle sex differences, in diurnal zebra finches, which possess the ability to reproduce year‐round, in a similar manner to other continuously breeding vertebrates.
... According to Wingfield and Kenagy (1991) and Blank (1992), seasonal changes are cyclic, largely predictable and represent the strongest and most abundant source of external variation influencing human and natural systems. Although generalisations can be made about the climate in the various provinces, there are considerable variations within each province. ...
South Africa is a large country of approximately 1.22 million km2, made up of nine provinces with three climatic zones. Farming in the country is mostly defined by regional differences. Of the different organisms isolated from milk samples of dairy cows, Staphylococcus aureus poses a challenge to maintain udder health and wholesome dairy products for human consumption. Antibiotic resistant bacteria are therefore a potential health hazard. The objective of this study was to investigate the seasonal and regional relationships of antibiotic resistance of S. aureus, of which little is known. This study was undertaken to evaluate a data set of 3410 S. aureus isolates, taken from milk samples with a somatic cell count of > 400 000 cells/mL from commercial dairy herds. These isolates were tested for antimicrobial susceptibility using the Kirby Bauer method for ampicillin, cloxacillin, penicillin G, clindamycin, oxy-tetracycline, cephalexin, cefuroxime and tylosin. The samples were from 830 dairy herds, out of the estimated 2000 commercial dairy herds in South Africa. All the antibiotics tested, except for cephalosporins, showed a predicted prevalence of resistance of above 50% in most provinces, which is a concern. The lowest prevalence of resistance to the majority of the categories of antibiotics tested was present in KwaZulu-Natal during spring. The cephalosporins had the lowest levels of prevalence of bacterial resistance in Gauteng during winter. Resistance patterns of S. aureus to the eight antibiotics varied in the different seasons and provinces, possibly because of different weather conditions, and the action and spectrum of antibiotics.
... There is clear evidence in many photoperiodic avian species that the female requires supplementary factors including temperature and long photoperiod for the follicle to develop fully, while the male can attain full testicular size based on photoperiodic stimulation alone (Ball and Ketterson 2008). It may be possible that the first stage of follicular growth is primarily driven by photoperiod and that the fine-tuning effect of temperature is only at the end, or even after full development, but before initiation of vitellogenesis and rapid follicle development in females (Wingfield and Kenagy 1991). A study by Visser et al. (2009) on great tits using climatized aviaries in a 6 years experiment revealed that the egg-laying dates were significantly affected by temperature directly. ...
We studied the effects of temperature on the photoperiodic regulation of seasonal reproduction and related events in the subtropical tree sparrow at Shillong, India. In the first experiment, one group of birds was maintained in an outdoor open aviary receiving natural photoperiod and temperature conditions, while the other group was exposed to natural photoperiod and constant temperature of 17 ± 2 °C in an outdoor closed aviary for 12 months. Although both sexes achieved peak gonadal growth at the same time (May) under the two conditions, gonadal regression and feathers molt were delayed under the temperature controlled condition. In the second experiment, the groups of birds were exposed to three different temperatures (17, 25 and 30 °C) under both long (LD-14L:10D) and short (SD-9L:15D) day lengths for 7 months. Birds showed relatively small but significant gonadal growth, darkening of bill color and feathers molt only at 30 °C under SD. However, they behaved as though they were under natural conditions and exhibited the above responses significantly at all temperatures under LD. There was delayed gonadal regression at the lower temperature (17 °C), while feathers molt delayed with increasing temperature (25, 30 °C) under LD. These results clearly indicate that temperature modulates photoperiodic seasonal responses in the tree sparrow.
... To optimize breeding success, animals must coordinate breeding behavior with the availability of environmental resources such as breeding territories, rainfall, food, and mate availability. Advances have been made in understanding the roles of photoperiod, the hypothalamic-pituitary-gonadal (HPG) axis and steroid hormones in timing sexual behaviors to match the availability of these critical resources (Calisi et al., 2011;Davies and Deviche, 2014;Small et al., 2008;Watts and Hahn, 2012;Williams, 2012;Wingfield and Kenagy, 1991). Studies also suggest that such resources may alter activity in brain regions underlying sexual motivation (Kelm et al., 2011;Riters et al., 2000); however, mechanisms by which this occurs have not been well-studied. ...
Environmental resources are proposed to fine-tune the timing of breeding, yet how they may do so remains unclear. In female European starlings (Sturnus vulgaris), nest cavities are limited resources that are necessary for breeding. Females that explore nest cavities, compared to those that do not, readily perform sexually-motivated behaviors. We assigned female starlings to aviaries with 1) no nest boxes, 2) nest boxes, or 3) nest boxes, plants, flowing water, insects and berries to test the hypothesis that environmental resources alter neural systems to stimulate mating behavior. Compared to other females, females that were housed with and explored nest boxes had higher estradiol, higher preproenkephalin (PENK) mRNA, and lower levels of D1 and D2 dopamine receptor mRNA in the medial preoptic area (mPOA), a region in which opioids and dopamine modify female sexual behaviors and sexual motivation. Additionally, in the mPOA, PENK and tyrosine hydroxylase mRNA positively predicted, whereas estrogen receptor beta mRNA negatively predicted nest box exploration. In the ventromedial hypothalamus, a region in which estradiol acts to stimulate sexual behavior, estrogen receptor alpha mRNA was highest in females that had access to but did not explore nest cavities. It is likely that seasonal increases in estradiol modify mRNA in the mPOA to facilitate nest cavity exploration. It is also possible that nest cavity exploration further alters gene expression in the mPOA, functioning to coordinate mating with resource availability. Thus nest cavity exploration may be a form of self-stimulation that alters neural systems to fine-tune sexual behavior.
... Animals living in variable or unpredictable environments can maximize fitness by timing energetically expensive life history states (e.g. reproduction) to overlap with periods of high resource availability (Bronson, 1985;Wingfield and Kenagy, 1991). In unpredictable environments, resources can vary erratically within or between seasons driving high levels of variability in reproductive opportunities (Robin et al., 2009). ...
Opportunistic breeding is a strategy used to maximize reproductive success in unpredictable environments. Birds that breed opportunistically are thought to maintain partial activation of the reproductive axis in order to rapidly initiate breeding when environmental conditions become suitable. The physiological mechanisms that modulate reproduction in seasonally breeding birds have been well explored. In contrast, the physiological mechanisms that allow opportunistic breeding birds to maintain a continued state of reproductive readiness has not been well established. Here, we tested the hypothesis that reproductive readiness is modulated through condition-mediated effects on the hypothalamic-pituitary-adrenal (HPA) axis and its downstream effects on corticosterone (CORT) secretion in wild zebra finches (Taeniopygia guttata). We examined the variation in body condition, HPA-axis activity (endogenous and adrenocorticotropic hormone (ACTH)-induced responses), and HPG-axis activity (baseline and gonadotropin-releasing hormone (GnRH) induced testosterone and estradiol levels) in zebra finches across five sites in the Northern Territory in Australia. We found that birds at the sites in the lowest condition had the highest level of baseline and peak CORT. Additionally, males at the sites in the lowest condition had the highest fold increase in testosterone following a GnRH challenge. Across sites, birds with low body condition had the highest baseline and restraint stress and ACTH-induced levels of CORT. Our data suggest that reproductive readiness in opportunistically breeding birds is modulated by condition-mediated trade-offs between the HPA- and the HPG- axes. Further work is needed to understand the environmental conditions that influence reproductive activation in opportunistically breeding birds.
... For social species these factors are also central in shaping a populations's social organization (Eisenberg et al. 1972;Würsig & Würsig, 1979;Sterck & Steenbeek, 1997), which can be a driving factor in population dynamics. Cycles in the life-histories of many populations are often influenced by the seasonality of the environments they inhabit (Murton & Westwood, 1977;Wingfield & Kenagy, 1991), especially when resources are variable in space and time. Resource and risk distribution plays an important role in determining the social strategies and patterns in populations of many social species (Cezilly & Benhamouv, 1996;Geffen et al. 1996;Johnson et al. 2002). ...
Photography is one of the most widely used tools in conservation biology. In the analysis of social species, analyses of photographic identification data are used to infer the degree of association among uniquely marked individuals. The present study aimed to develop and assess the practicality of a new time-based method for defining associations among individuals, comparing results to the commonly used group membership method. The method was applied to archived photographs from long-term monitoring of the population of bottlenose dolphins of Doubtful Sound, New Zealand, to assess differences in seasonal association rates among individuals.
The time-based method produced analyses of association at finer scales than the group membership method, and produced greater precision in association indices. Importantly the method can be applied retrospectively to any dataset in which individuals, marine or terrestrial, are uniquely identified via time-stamped photographs. Applied to the long-term dataset, results indicate differences in association rates between summer and winter seasons. During summer months the degree of sociality was generally higher; larger mixed-sex groups and greater rates of association among individuals were observed. Sociality in this population is female orientated; the majority of top-scoring individuals in centrality analyses were female.
Explorations of whether a mother’s position in the social network influences the survival of her calves were inconclusive. Who the mother is significantly affects calf survival, but why this is so remains unclear. The most important influence on calf survival is birth timing; those born during the months of February, March and April have much higher chances of survival than calves born outside of this period. This is in agreement with previous studies on this population, though further research is required in order to tease apart the relative importance of driving factors of calf survival in this endangered and isolated population.
... For instance, previous studies have found that endogenous testosterone levels are typically lower in laboratory-reared species, including reptiles, and this may be due to environmental factors in the laboratory that differ from those in the field (e.g., Callard et al., 1976;Licht et al., 1985;Krohmer et al., 1987;Moore et al., 1991;Soto-Gamboa et al., 2005;Calisi and Bentley, 2009). Changes in day length have often been shown to be important in inducing changes in testosterone levels, reproductive physiology, and behavior, particularly in the laboratory (e.g., Wingfield and Kenagy, 1991). However, our changes in day length mimicked ambient and thus was likely not the modulator of these differences. ...
Variation in an animal's spatial environment can induce variation in the hippocampus, an area of the brain involved in spatial cognitive processing. Specifically, increased spatial area use is correlated with increased hippocampal attributes, such as volume and neurogenesis. In the side-blotched lizard (Uta stansburiana), males demonstrate alternative reproductive tactics and are either territorial—defending large, clearly defined spatial boundaries—or non-territorial—traversing home ranges that are smaller than the territorial males' territories. Our previous work demonstrated cortical volume (reptilian hippocampal homolog) correlates with these spatial niches. We found that territorial holders have larger medial cortices than non-territory holders, yet these differences in the neural architecture demonstrated some degree of plasticity as well. Although we have demonstrated a link among territoriality, spatial use, and brain plasticity, the mechanisms that underlie this relationship are unclear. Previous studies found that higher testosterone levels can induce increased use of the spatial area and can cause an upregulation in hippocampal attributes. Thus, testosterone may be the mechanistic link between spatial area use and the brain. What remains unclear, however, is if testosterone can affect the cortices independent of spatial experiences and whether testosterone differentially interacts with territorial status to produce the resultant cortical phenotype. In this study, we compared neurogenesis as measured by the total number of doublecortin-positive cells and cortical volume between territorial and non-territorial males supplemented with testosterone. We found no significant differences in the number of doublecortin-positive cells or cortical volume among control territorial, control non-territorial, and testosterone-supplemented non-territorial males, while testosterone-supplemented territorial males had smaller medial cortices containing fewer doublecortin-positive cells. These results demonstrate that testosterone can modulate medial cortical attributes outside of differential spatial processing experiences but that territorial males appear to be more sensitive to alterations in testosterone levels compared with non-territorial males.
... Many songbirds breed seasonally in response to changes in environmental cues like photoperiod and food availability. In these species, the brain integrates environmental and internal cues, activating the pituitary and gonads under appropriate conditions and allowing the reproductive system to regress when environmental conditions are unsuitable for breeding (Farner, 1986;Wingfield and Kenagy, 1991). In general, when the testes are stimulated by gonadotropins, the Leydig cells are large and numerous and exhibit morphological properties consistent with steroidogenesis (Chan, 1974;Lam and Farner, 1976;Rohss and Silverin, 1983;Silverin and Sharp, 1996). ...
Birdsong is a complex learned behavior performed by the oscine passerine birds. Birds sing in reproductive and aggressive contexts, but there is a great diversity in song behavior across species, seasons, and sexes. Song learning and production are controlled by a specialized neural circuit, the song control system, that is unique to this group of birds. The growth, maturation, and adult function of this circuit depend on hormonal signals, especially the reproductive steroid hormones. This chapter reviews studies examining the neural control of song and functions of endocrine systems that influence the song control system. They reveal how sex steroids can act to build motor and learning pathways and then stimulate plasticity of these circuits to modify song throughout adult life. Much of the observed behavioral diversity can be accounted for by individual differences in the neural distribution of steroid receptors or in age, sex, or seasonal differences in the gonadal secretion of sex steroids. Songbirds may also synthesize steroids in nongonadal sites and use nontraditional steroids or cellular mechanisms to control song. The evolution in songbirds of multiple mechanisms to synthesize and respond to sex steroids contributes to a growing body of work expanding traditional concepts about the relationship between hormones, brain, and behavior.
... Here we report for the first time how the usage of mating signals (song) varies with these anthropogenic factors in the tropics, where the photoperiod varies very little across the year. In the temperate zones with the marked seasonal changes in day length, photoperiod is a cue for the timing of reproductive stages of birds in general and for the onset of the dawn chorus in particular [43][44][45][46]. On a seasonal level, light at night can advance the timing of breeding (e.g. ...
Birds in cities start singing earlier in the morning than in rural areas; commonly this shift is attributed to light pollution. Some studies have suggested that traffic noise has a stronger influence on singing activity than artificial light does. Changes in the timing of singing behaviour in relation to noise and light pollution have only been investigated in the temperate zones. Tropical birds, however, experience little seasonal variation in day length and may be less dependent on light intensity as a modifier for reproductive behaviours such as song. To test whether noise or light pollution has a stronger impact on the dawn chorus of a tropical bird, we investigated the singing behaviour of rufous-collared sparrows (Zonotrichia capensis) in Bogota, Colombia at two times during the year. We found that birds in places with high noise levels started to sing earlier. Light pollution did not have a significant effect. Birds may begin to sing earlier in noisy areas to avoid acoustic masking by traffic later in the morning. Our results also suggest that some tropical birds may be less sensitive to variations in day length and thus less sensitive to light pollution.
... In other cases, such as Microtus californicus and Peromyscus californicus, day length has also been shown to be a cue for the onset of reproduction (Nelson et al., 1983;Nelson et al., 1995). Alternatively, high precipitation may also be a condition for successful reproduction in these extreme environments, mainly through its influence on plant productivity and, hence, on food availability (Wingfield and Kenagy, 1991;Mateos-Quesada and Carranza, 2000). ...
Desert areas represent heterogeneous environments where animals must reproduce under extreme conditions, and where a combination of environmental factors may contribute to trigger or inhibit reproduction. Microcavia australis is a caviomorph rodent that occurs in arid and semiarid habitats of Argentina. We examined how reproductive activity in male M. australis from a Monte Desert population is responsive to environmental conditions, including precipitation. Our results showed that reproductive activity of these animals is predicted exclusively by precipitation. This research adds new evidence to the ecology of this species, which could explain its wide distribution. RESUMEN. Las precipitaciones conducen la actividad reproductiva en machos de Microcavia australis en el desierto del Monte. Las áreas desérticas representan ambientes heterogéneos donde los animales deben re-producirse bajo condiciones extremas y donde una combinación de factores ambientales puede contribuir para iniciar o inhibir la reproducción. Microcavia australis es un roedor caviomorfo que vive en hábitats áridos y semiáridos de Argentina. Examinamos cómo la actividad reproductiva en machos de M. australis en una población del Desierto del Monte responde a condiciones ambientales, incluyendo la precipitación. Nuestros resultados mostraron que la actividad reproductiva de estos animales es predicha exclusivamente por la precipitación. Este estudio incorpora nuevas evidencias a la ecología de esta especie que podrían explicar su amplia distribución.
... Because photoperiod (day length) often forecasts environmental conditions at a given location, many seasonal breeders use the vernal increase in photoperiod as the primary cue to stimulate GnRH secretion and initiate gonadal development (Farner and Wingfield, 1980;Dawson et al., 2001;Wingfield, 2008). As changes in day length at a given latitude are constant from year to year, the activity of the HPG axis can still be modulated by non-photoperiodic cues, such as ambient temperature (Dawson, 2005;Schaper et al., 2012b) and food availability (Wingfield and Kenagy, 1986;Hahn et al., 2005;Davies and Deviche, 2014). The use of these cues is thought to improve the synchronization of reproductive development and behaviors with optimal environmental conditions in a given year (Baker, 1938;Lack, 1968;Bronson and Heideman, 1994). ...
Energy deficiency can suppress reproductive function in vertebrates. As the orchestrator of reproductive function, endocrine activity of the hypothalamo-pituitary-gonadal (HPG) axis is potentially an important mechanism mediating such effects. Previous experiments in wildcaught birds found inconsistent relationships between energy deficiency and seasonal reproductive function, but these experiments focused on baseline HPG axis activity and none have investigated the responsiveness of this axis to endocrine stimulation. Here, we present data from an experiment in Abert's towhees, Melozone aberti, using gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) challenges to investigate whether energy deficiency modulates the plasma testosterone responsiveness of the HPG axis.Wild-caught birdswere either ad libitum fed or energetically constrained via chronic food restriction during photoinduced reproductive development. Energy deficiency did not significantly affect the development of reproductive morphology, the baseline endocrine activity of the HPG axis, or the plasma testosterone response to GnRH challenge. Energy deficiency did, however, decrease the plasma testosterone responsiveness to LH challenge. Collectively, these observations suggest that energy deficiency has direct gonadal effects consisting of a decreased responsiveness to LH stimulation. Our study, therefore, reveals a mechanism by which energy deficiency modulates reproductive function in wild birds in the absence of detectable effects on baseline HPG axis activity.
... For seabirds of temperate and polar marine ecosystems, seasonal breeding is primarily 69 controlled by photoperiod (Wingfield and Kenagy 1991), and the precise date of egg-laying 70 appears to be driven by egg laying constraints , Shultz et al. 2009). In 74 Passuni , Giannina. ...
In fluctuating environments, matching breeding timing to periods of high resource availability is crucial for the fitness of many vertebrate species, and may have major consequences on population health. Yet, our understanding of the proximate environmental cues driving seasonal breeding is limited. This is particularly the case in marine ecosystems where key environmental factors and prey abundance and availability are seldom quantified. The Northern Humboldt Current System (NHCS) is a highly productive, low latitude, ecosystem of moderate seasonality. In this ecosystem, three tropical seabird species (the Guanay cormorant Phalacrocorax bougainvillii, the Peruvian booby Sula variegata and the Peruvian pelican Pelecanus thagus) live in sympatry and prey almost exclusively on anchovy Engraulis ringens. From January 2003 to December 2012, we monitored 31 breeding sites along the Peruvian coast, to investigate the breeding cycle of these species. We tested for relationships between breeding timing, oceanographic conditions and prey availability using occupancy models. We found that all 3 seabird species exhibited seasonal breeding patterns, with marked interspecific differences. Whereas breeding mainly started during the austral winter/ early spring and ended in summer/ early fall, this pattern was stronger in boobies and pelicans than in cormorants. Breeding onset mainly occurred when upwelling was intense but ecosystem productivity was below its annual maxima, and when anchovy were less available and in poor physiological condition. Conversely, the abundance and availability of anchovy improved during chick rearing and peaked around the time of fledging. These results suggest that breeding timing is adjusted so that fledging may occur under optimal environmental conditions, rather than being constrained by nutritional requirements during egg-laying. Adjusting breeding time so that fledglings meet optimal conditions at independence is unique compared with other upwelling ecosystems and could be explained by the relatively high abundances of anchovy occurring throughout the year in the NHCS.
... Environmental signals will ultimately impact on the hypothalamic-pituitary axis, although different signals may impact on different components of the axis. For instance, photoperiod appears to act via the GnRH neurons of the hypothalamus to ultimately affect gonadal growth and steroid production through the activity of pituitary GTH (Wingfield and Kenagy, 1991). Tempe> ature, however, may act via alternate hypothalamicpituitary axes to affect the production of gonadal steroids (Wingfield et al., 1996). ...
This chapter reveals that in all vertebrates, the integrative components controlling reproduction are represented in a finely tuned physiological system called the brain-pituitarygonad (BPG) axis. Receptor organs of environmental signals along with internal physiological signals transmit information, which acts as timers or triggers on specific neuroendocrine centers in the brain which produces gonadotropin-releasing hormone (GnRH). This neuropeptide is commonly released into the bloodstream at the median eminence of the hypothalamus, whereupon, it then travels to the adenohypophysis of the pituitary gland and stimulates specific endocrine cells to secrete the gonadotropic hormone (GTH). GTH then acts on the gonads to affect gametogenesis and the production of sex steroids. The sex steroids act back on the pituitary gland and the GnRH centers in the brain, establishing, via negative feedback loops, the homeostasis of hormone levels.
... In temperate zone songbird species such as canaries (Serinus canaria), photoperiodic changes, along with a variety of supplementary cues, regulate the timing of the breeding season and modulate the associated anatomical, physiological, and behavioral changes (e.g., Nottebohm 1981;Wingfield and Kenagy 1991;Wingfield et al., 1993;Leitner et al., 2001;Hurley et al., 2008). In spring, gonadal volume and blood concentrations of testosterone increase in parallel with increases in day length. ...
In songbirds, such as canaries (Serinus canaria), the song control circuit has been shown to undergo a remarkable change in morphology in response to exogenous testosterone (T). It is also well established that HVC, a telencephalic nucleus involved in song production, is significantly larger in males than in females. T regulates seasonal changes in HVC volume in males and exposure to exogenous T in adult females increases HVC volume and singing activity such that their song becomes more male-like in frequency and structure. However, whether there are sex differences in the ability of T to modulate changes in the song system and song behavior has not been investigated in canaries. In this study, we compared the effects of increasing doses of T on singing and song control nuclei volumes in adult male and female American Singer canaries exposed to identical environmental conditions. Males were castrated and all birds were placed on short days (8L:16D) for 8weeks. Males and females were implanted either with a 2, 6 or 12mm long Silastic™ implant filled with crystalline T or an empty 12mm implant as control. Birds were then housed individually in sound attenuated chambers. Brains were collected from six birds from each group after 1week or 3weeks of treatment. Testosterone was not equally effective in increasing singing activity in both males and females. Changes in song quality and occurrence rate took place after a shorter latency in males than in females however, females did undergo marked changes in a number of measures of song behavior if given sufficient time. Males responded with an increase in HVC volume at all three doses. In females, T-induced changes in HVC volume only had limited amplitude and these volumes never reached male-typical levels a suggesting that there are sex differences in the neural substrate that responds to T.
... Males that were paired with 2 females appeared to be most influenced by the dominant female. This social rather than seasonal pattern agrees with previous male sun bear findings (Hesterman et al. 2005) and fits with more general observations that in nonseasonal breeders, social cues can be as important as environmental cues (Wingfield and Kenagy 1991). ...
Most species of bears exhibit a reproductive strategy that includes a highly defined breeding season, delayed implantation, pseudopregnancy, and no postpartum estrus. Sun bears (Helarctos malayanus), a tropical lowland species, represent a potential departure from the typical ursid reproductive pattern. We studied reproductive timing in captive sun bears by examining fecal hormones and behavior of 13 female and 5 male sun bears, the entire North American population of H. m. euryspilus at the time of the study. Fecal estrogens and progestins in females did not vary by season or month, nor did fecal androgens in males. Estrus occurred in 11 of 12 months; breeding and births occurred year-round. However, birth rates were lower in the spring and higher in the fall and winter. Our study documented 1 complete pregnancy, in which delayed implantation did not occur; the delay between estrus and the progesterone rise (i.e., implantation) in the pregnant bear was similar to that seen in nonpregnant bears. All bears, whether nonpregnant or pregnant, exhibited a prolonged period of high progesterone after estrus, indicating obligate pseudopregnancy. Studbook records show that estrus can occur within 6 months after parturition; these cases were typically associated with loss of the previous cub. Our findings suggest that sun bears are unique among ursids, being polyestrous, nonseasonal breeders that do not appear to exhibit delayed implantation and that are capable of initiating estrus in the event of early loss of a cub.
This paper reviews the information available over the last 20 years on studies of the temporal variability of parasitic infections caused by parasitic crustaceans of fish in the Mexican territory. The possible responses of these parasitic infections to changes in the aquatic ecosystems caused by anthropogenic climate change are described. By studying the intensity of infection of Argulus yucatanus (a case study of parasite crustaceans of fish), the response of infections to changes in water temperature can be detected. Into this context and based on previous investigations reviewed, it is highlighted the importance of monitoring for long-time the behavior of these parasites. Also, it is indicated that parasitic crustaceans represent a good study model as bioindicators of environmental changes because they are in direct contact or exposed to hazardous substances of the environment. Extensive and precise data on parasitic biodiversity along with their ecological and experimental information are necessary to understand the possible responses of the parasitic infections caused by crustaceans in the face of climate change. Based on this kind of information it would be possible to deal with issues on control strategies and prevention of parasitic infections caused by crustaceans in aquaculture as well as for the sustainable development of aquatic ecosystems. Keywords: Long-term monitoring, sentinel species, parasitic infections, parasitic crustaceans, climate change.
Birdsong is controlled in part by a discrete network of interconnected brain nuclei regulated in turn by steroid hormones and environmental stimuli. This complex interaction results in neural changes that occur seasonally as the environment varies (e.g., photoperiod, food/water availability, etc.). Variation in environment, vocal behavior, and neuroendocrine control has been primarily studied in male songbirds in both laboratory studies of captive birds and field studies of wild caught birds. The bias toward studying seasonality in the neuroendocrine regulation of song in male birds comes from a historic focus on sexually selected male behaviors. In fact, given that male song is often loud and accompanied by somewhat extravagant courtship behaviors, female song has long been overlooked. To compound this bias, the primary model songbird species for studies in the lab, zebra finches (Taeniopygia guttata) and canaries (Serinus canaria), exhibit little or no female song. Therefore, understanding the degree of variation and neuroendocrine control of seasonality in female songbirds is a major gap in our knowledge. In this review, we discuss the importance of studying sex differences in seasonal plasticity and the song control system. Specifically, we discuss sex differences in 1) the neuroanatomy of the song control system, 2) the distribution of receptors for androgens and estrogens and 3) the seasonal neuroplasticity of the hypothalamo-pituitary-gonadal axis as well as in the neural and cellular mechanisms mediating song system changes. We also discuss how these neuroendocrine mechanisms drive sex differences in seasonal behavior. Finally, we highlight specific gaps in our knowledge and suggest experiments critical for filling these gaps.
Many temperate zone animals engage in seasonal reproductive physiology and behavior as a strategy to maximise the propagation of the species. The hypothalamus integrates environmental cues and hormonal signalling to optimize the timing of reproduction. Recent work has revealed that epigenetic modifications, such as DNA methylation, vary across seasonal reproductive states. Multiple hormones act in the hypothalamus to permit or inhibit reproductive physiology, and the increase in thyroid hormone triiodothyronine (T3) has been implicated in the initiation of breeding in many species. The objective of this study was to examine the effect of T3 on the photoperiod-dependent regulation of reproductive physiology and hypothalamic DNA methyltransferase enzyme expression in female Siberian hamsters (Phodopus sungorus). We tested the hypothesis that T3 in short days (SD) would stimulate hypothalamic Rfrp3 and de novo DNA methyltransferase (Dnmt) expression in female Siberian hamsters. 10 weeks of SD lengths induced a decrease in body and uterine mass. Hamsters maintained in SD were found to express lower levels of GnRH, Rfrp3, Dnmt3a and Dnmt3b. Two weeks of daily T3 injections did not affect body mass, uterine mass, Gnrh, Rfrp3, Dnmt3a or Dnmt3b expression in neuroendocrine tissues. SD significantly lowered Tshβ mRNA expression and T3 reduced Tshβ in LD hamsters. Our data indicate sex-dependent effects of T3 for the neuroendocrine regulation of seasonal reproduction in hamsters.
Seasonal reproduction is a widespread adaptation in vertebrates, such that individuals time their reproductive efforts to match peak resource abundance. Individuals rely on environmental cues to regulate hormonal mechanisms governing timing of breeding. Historically, studies on physiological mechanisms of seasonal reproduction, specifically in birds, have disproportionately focused on males compared to females. For this review, I conducted a literature search of the last decade of avian research and found a persistent sex bias in the field of physiological mechanisms of seasonal reproduction. Using work conducted with the dark-eyed junco (Junco hyemalis) as a case study, I present a possible solution to combat the sex bias: natural comparisons of populations that differ in reproductive timing to investigate mechanisms of reproduction in both sexes. Populations of dark-eyed juncos that differ in migratory behavior (i.e., migrant and resident) exhibit overlapping ranges during winter and early spring; residents begin breeding in early spring prior to the departure of migrants. This system, and others like it, provides an opportunity to compare mechanisms of reproduction in populations that differ in reproductive timing despite experiencing the same environmental conditions in early spring. In juncos, migrant and resident females and males exhibit similar patterns of hypothalamic regulation of reproduction in early spring, but sex differences in gonadal sensitivity between the populations could be an important distinction that partially explains sex differences in reproductive development. Comparing mechanisms of reproduction in free-living populations and in captivity can reveal important mechanisms that determine the onset of reproductive development, as well as potential sex differences in these mechanisms. Understanding the mechanisms of reproductive phenology has important implications for understanding how species will survive and reproduce in a changing climate.
Most organisms live in seasonal environments that fluctuate on a predictable schedule and sometimes unpredictably. Individuals must, therefore, adjust so as to maximize their survival and reproductive success over a wide range of environmental conditions. In birds, as in other vertebrates, endocrine secretions regulate morphological, physiological, and behavioral changes in anticipation of future events. The individual thus prepares for predictable fluctuations in its environment by changing life-cycle stages. We have applied finite-state machine theory to define and compare different life-history cycles. The ability of birds to respond to predictable and unpredictable regimes of environmental variation may be constrained by the adaptability of their endocrine control systems. We have applied several theoretical approaches to natural history data of birds to compare the complexity of life cycles, the degree of plasticity of timing of stages within the cycle, and to determine whether endocrine control mechanisms influence the way birds respond to their environments. The interactions of environmental cues on the timing of life-history stages are not uniform in all populations. Taking the reproductive life-history stage as an example, arctic birds that have short breeding seasons in severe environments appear to use one reliable environmental cue to time reproduction and they ignore other factors. Birds having longer breeding seasons exhibit greater plasticity of onset and termination and appear to integrate several environmental cues. Theoretical approaches may allow us to predict how individuals respond to their environment at the proximate level and, conversely, predict how constraints imposed by endocrine control systems may limit the complexity of life cycles.
Timing of breeding in Florida Scrub-Jays (Aphelocoma coerulescens) varies both within and between years. Social status and breeding experience may explain much of the within-year variation, but the availability of certain foods may partially explain between-year patterns. Scrub-jays in suburban habitats with access to unlimited human-provided foods breed earlier and with less between-year variation in timing of breeding than jays in wildland habitats. We hypothesized that those differences in timing of breeding result from access to human-provided foods in the suburban site. Human-provided food may influence timing of breeding by improving the overall body condition of females, or it may influence breeding by providing nutrients essential for breeding. If condition mediated, breeding females in the two habitats should differ in certain physiological parameters relative to time before egg laying and calendar date. If the effect is not related to body condition, we expect differences in prebreeding females relative to calendar date, but not in relation to time before egg laying. To test those predictions, we measured plasma levels of total protein, calcium, luteinizing hormone, and estradiol. We also measured variables associated with body condition—body mass, a size-corrected condition index, and total body lipids. Most variables tended to increase with both days before laying and calendar date, except total body lipids, which decreased. Suburban females had higher levels of plasma protein relative to both days before egg laying and calendar date than female breeders in the wildland habitat. Luteinizing hormone differed between sites relative to calendar date but not days before laying. Our data suggest that suburban scrub-jays with access to predictable sources of high-quality human-provided foods accumulate endogenous protein that can be used to breed earlier.
Timing of breeding activities by birds hasimportant fitness consequences, as deciding when tonest can affect nest success. For three breedingseasons, we provided supplemental food to Wrentits(Chamaeafasciata) inhabitingsemiarid shrublands. We tested the effects of foodsupplementation on timing of initial egg laying,number of nests attempted, timing of fledging, andlength of the breeding season. We also evaluatedwhether Wrentits timed nest initiation to avoidperiods of greatest predation risk. Our study wasconducted during a period of high interannualvariation in precipitation. Supplemental food didnot advance laying date in Wrentits. During adrought, even Wrentits given supplemental fooddelayed nesting, initiated fewer nesting attempts,fledged young earlier, and reduced the length ofthe breeding season. In a year of average rainfall,supplemental food allowed pairs to continuerenesting late into the summer, after repeated nestlosses from predation. Wrentits did not timenesting to avoid periods of greatest predationrisk. In timing initial breeding, Wrentits appearedto be responding to climatic conditions and toindirect cues that predicted environmentalconditions later in the breeding season rather thanto food availability at the time of egg laying.
Courtship and copulation constitute crucial elements of avian reproduction and fitness. Despite the potential impact of environmental perturbations and long-term climate change on avian reproduction, few studies provide quantitative information on courtship and copulation behaviors and their responses to proximate environmental factors. We provide the first quantitative description of courtship and copulation behavior in Glaucous-winged Gulls (Larus glaucescens), an important indicator species of marine environmental quality in North America's Pacific Northwest. Male and female Glaucous-winged Gulls exhibited similar frequencies of most pre- and post-mount behaviors, which closely resemble those used by other larids. Mounts were more frequent than expected during the pre-egg-laying and egg-laying stages of the breeding season and less frequent than expected during the incubation stage. In 2008, numbers of successful copulations vs. unsuccessful copulations, numbers of cloacal contacts per successful copulation, and copulation duration did not differ by reproductive stage. In 2012, copulation duration increased with day of the year and decreased with wind speed, and the number of cloacal contacts per copulation decreased with wind speed. The odds of paired head toss increased with tide height and decreased with solar elevation. The odds of female courtship beg increased with the number of days from its peak occurrence, and also with solar elevation, tide height, and Bald Eagle (Haliaeetus leucocephalus) disturbances. Mount interval, the time from the start of one mount in the study area to that of another, was positively related to time of day, barometric pressure, and solar elevation but was negatively related to solar radiation and colony occupancy. Both the temporal and spatial occurrence of copulation were socially facilitated by the behavior of neighboring birds in the colony. Our results suggest that changes in environmental variables due to climate change could affect reproductive behaviors and reproductive success in this species.
Conservation biology as a scientific discipline is dominated by natural history and population biology. However, there are several challenges and questions in conservation biology that can be elegantly addressed with new techniques from endocrinology. The major change in endocrinology that makes this possible is the development of field techniques that allow us to probe an animal’s hormonal status while the animal ranges free in the wild (Wingfield and Farner 1976). Clearly hormones are as crucial an attribute to an animal as are its body size, general health, and reproductive rates. In fact, from one perspective, hormones might be the most fundamental measure of an animal’s likely success. After all, it is hormones that largely control reproduction and coordinate the physiological responses necessary for survival in a stressful environment. Thus, endocrinology offers us a window to better understand the factors impairing a species’ demographic vitality, and it may even offer us early-warning signals of a risk before survivorship or reproductive rates plummet. In this chapter we sketch the recent advances in endocrinology that have the greatest potential as tools in the service of conservation biology. Before turning to case studies that document the role that endocrinology can play in conservation, we briefly review some pertinent aspects of vertebrate endocrine systems.
John C. Wingfield, PhD, currently a professor at the University of California – Davis, received his doctorate degree from the University College of North Wales, Bangor. He is also the Endowed Chair in physiology at the University of California – Davis. His research focuses on how animals (mostly birds) deal with a changing environment and organize their life cycles accordingly. A changing environment involves the predictable (e.g., night and day, seasons, tides) and the unpredictable (e.g., severe storms, drought, human disturbance). He is particularly interested in how animals perceive the environment (and what cues they use to time the stages of the life cycle), the neural pathways by which those signals are transduced into neuroendocrine and endocrine secretions, and the mechanisms by which these hormones regulate morphology, physiology, and behavior.
This chapter concerns the inter-relationships between hormones, brain, and behavior that mediate the occurrence of reproductive cycles and reproductive behavior among adults in avian species. The chapter ranges from a consideration of the neuroendocrine basis of seasonal reproduction to a description of the neural, and endocrine mechanisms that regulate male and female sexual behavior and parental behavior. Many of the individual sections of this chapter correspond to entire chapters in this multivolume work on hormones, brain, and behavior. A consideration of the neuroendocrine basis of reproductive cycles and reproductive behavior in bird species is potentially particularly beneficial. Many of the pioneering studies concerning different aspects of the inter-relations among hormones, brain, and behavior are conducted on birds. Therefore, the neuroendocrinology of reproductive behavior in birds can be considered more easily in a natural context than in many other taxa.
With final maturation of ovarian follicles, birds are committed to a major energetic investment: egg-laying. Follicles develop in a two-step process 1) initial development of regressed follicles stimulated by long days and 2) yolk incorporation into hierarchical follicles, ovulation and oviposition. We know little about how females transduce environmental cues into neuroendocrine signals regulating the second step. The present study measures gene expression in tissues within the hypothalamo-pituitary gonadal (HPG) axis. Females were housed in semi-natural enclosures experiencing natural changes in photoperiod and environmental cues (e.g. temperature, rainfall, etc.), without males or with constant access to males (January to April). By April, females with males had begun to lay eggs, whereas those without males had not. In a second study, females without males for 3.5 months were then given access to males for seven days. Restricting male access completely inhibited final follicle maturation, whereas seven-day male access stimulated full vitellogenesis and follicle maturation. Few gene expression changes were attributable to constant male access (January to March), but naïve females given seven-day male access had increased DIO2 and decreased DIO3 synthesis in the hypothalamus, potentially influencing local thyroid hormone metabolism, increased expression of LH receptor and aromatase in follicles and vitellogenin in liver. Our data suggest initial follicle development may be more heavily influenced by photoperiod, but the second step (final maturation) is sensitive to other cues such as social interactions. This is the first demonstration of a social effect on the Dio2/Dio3 system - previously thought only responsive to photoperiod cues.
In his seminal paper about potential circannual rhythms, Aschoff (1955) predicted their presence in species that live in relatively constant, tropical environments. Detailed follow-up investigations largely supported this idea, but life-history stages (such as breeding, moult, migration) of wild tropical species can both be rhythmic or arrhythmic. We present some classical findings on circannual biology of tropical species and provide ecological and evolutionary context by reviewing the diverse patterns of seasonality in tropical environments. We relate this to the seasonality of life-histories in tropical birds and discuss the potential Zeitgeber of circannual rhythms, which are still elusive. We emphasize the diversity of tropical environments – roughly covered by the biome concept - which range from extremely erratic and unpredictable to very predictable environments. Predictable environments, which arguably favour evolution of circannual rhythms, are characterized either by a rather constant climate throughout the year or by a pronounced and regular climatic seasonality. Colwells’ (1974) concept of predictability, constancy and contingency allows a quantification of such diversity of tropical biomes and forms the basis of our discussion of the seasonality of life histories in tropical birds.
The Brown brocket deer (Mazama gouazoubira) is the most common free-living and captive deer in South America, especially in Brazil, and has great ecological and scientific significance. However, data on hematological and biochemical parameters in brown brocket deer are scarce. The goal of this study was to establish reference ranges for hematological and biochemical parameters of Mazama gouazoubira, comparing differences during the seasons of the year and between sex. Blood samples from ten adult healthy brown brocket deer (6 female and 4 male) were collected during daytime, monthly, during 12 months. The animals were maintained in individual stable, protected from noise and fed ad libitum with commercial ration and green fodder. For blood collection, animals were submitted to physical restrain for no longer than 2 minutes. The following parameters were determined: red blood cell count (RBC), haemoglobin concentration, packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), white blood cell count (WBC), platelet count, enzyme activity of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT) and serum levels of alkaline phosphatase (ALP), creatine kinase (CK), total protein (TP), albumin, cholesterol, total calcium, ionic calcium, sodium, potassium, magnesium, triglycerides, creatinine and urea. Values were compared according to season and sex. RBC count, WBC count and MCV suggested seasonal influence. Haemoglobin concentration, PCV and MCV were influenced by sex. Serum concentration of total calcium, ionic calcium, sodium, potassium and magnesium were influenced by season. Serum magnesium was also influenced by sex. The blood parameters herein reported may be useful as reference values for diagnostic and prognostic purposes in captive brown-brocket deer.
Timing plays a central role in the success of breeding activities, particularly in variable and unpredictable climates. In this paper we investigate the proximate factors influencing the timing of breeding behaviour in the azure-winged magpie (Cyanopica cyanus) in a Mediterranean environment. The azure-winged magpie is a social corvid, colonial breeder, mostly single-brooded, which shows cooperative breeding in some populations. The study population was intensively monitored for a period of three years. The breeding season started in late March or early April and lasted around three months. The laying date varied significantly among the three years of intensive study (1995-1997). Data on the first laid egg in the whole population were related to the temperature and precipitation in the month preceding egg laying (March, data for 11 years). The timing of the first egg was significantly delayed after heavy rainfall in March. When corrected for the effect of precipitation, the timing of the first egg was no longer significantly related to the temperature in March. Comparing data from 10 populations of this species (8 from Spain, 2 from Japan) revealed that breeding dates were not related to latitude but to altitude, so that every 100 meter increase above sea level produced a delay of 4 days in the average timing of the first egg in the population.
In males, the acquisition and development of behavioral and morphological secondary sexual traits typically depends on testosterone and correlates with mating success. Testosterone level could affect competition for mates and thus be a target of sexual selection. We sought to relate testosterone levels to male mating competitiveness, by teasing apart the relationships between testosterone, behavior, and growth before the mating period. We monitored 24 adult bighorn rams (Ovis canadensis) at Ram Mountain, Alberta, from 2008 to 2011. Using linear mixed models, we tested the relationships between testosterone metabolites in feces, social rank, and both growth and size of two sexually selected traits: horns and body mass. The correlation between testosterone and social rank varied with age. Testosterone and rank were weakly and negatively correlated for young rams, positively correlated for prime-aged rams, and negatively correlated for older rams. Although testosterone had an increasingly positive effect on total horn length until 8 years of age, we could not detect any effects on annual growth rate of horns or body mass. Testosterone may be related to male’s ability to compete for mates through its relationship with behaviors determining social rank, rather than by influencing the development of morphological traits. Differences in testosterone levels among competitors may be a proximate cause of variance in fitness.
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