Prenatal and postnatal effects of corticosterone on behavior in juveniles of the common lizard, Lacerta vivipara

Validation of two enzyme immunoassays for non-invasive glucocorticoid measurement in a lacertid lizard (Podarcis muralis): Effects of pharmacological and biological stimuli on faecal corticosterone metabolites and behaviour

The assessment of stress-related hormone levels using non-invasive methods has gained popularity in mammal and bird welfare, yet its application in reptiles remains limited. Particularly, the exploration of physiological measures such as faecal corticosterone metabolites (FCMs) for reptilian welfare has scarcely been explored. This study aims to validate two enzyme immunoassays (5α-pregnane-3ß,11ß,21-triol-20-one and 11-oxoaetiocholanolone EIA) for monitoring FCM levels in the European common wall lizard (Podarcis muralis). We collected daily faecal samples before (baseline) and after (post-treatment phase) inducing elevated corticosterone levels using transdermal administration of corticosterone (pharmacological treatment) and handling/confinement (biological treatment). We also conducted daily behavioural observations to explore the relationship between stress-related corticosterone changes and behaviour. Although treatments induced significant increases in FCM levels, the effect was much larger in the pharmacological one. Transdermal corticosterone induced a cumulative increase in FCMs over the treatment period, with a higher response observed in females. In contrast, the biological treatment yielded smaller FCM peaks, with no significant sex differences. Overall, 5α-pregnane-3ß,11ß,21-triol-20-one EIA appeared to be more sensitive in detecting these effects. Regarding lizard behaviour, both treatments led to increased hiding and decreased basking compared to baseline. The effects were more pronounced in animals subjected to handling/confinement, despite smaller FCM increases. Our results confirm the suitability of an EIA for monitoring FCMs in both male and female common wall lizards and provide insights into the complexities of using integrated approaches to assess stress, highlighting the need for further research on direct measures to evaluate reptile welfare.

Frank Beach Award Winner: The centrality of the hypothalamic-pituitary-adrenal axis in dealing with environmental change across temporal scales

Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenotypic plasticity and/or bet hedging. Adaptive plasticity could enable individuals to match their phenotypes to the expected environment if there is an accurate cue predicting the selective environment. Diversifying bet hedging involves the production of seemingly random phenotypes in an unpredictable environment, some of which may be adaptive. Here, I review the central role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) in enabling vertebrates to cope with environmental change through adaptive plasticity and bet hedging. I first describe how the HPA axis mediates three types of adaptive plasticity to cope with environmental change (evasion, tolerance, recovery) over short timescales (e.g., 1-3 generations) before discussing how the implications of GCs on phenotype integration may depend upon the timescale under consideration. GCs can promote adaptive phenotypic integration, but their effects on phenotypic co-variation could also limit the dimensions of phenotypic space explored by animals over longer timescales. Finally, I discuss how organismal responses to environmental stressors can act as a bet hedging mechanism and therefore enhance evolvability by increasing genetic or phenotypic variability or reducing patterns of genetic and phenotypic co-variance. Together, this emphasizes the crucial role of the HPA axis in understanding fundamental questions in evolutionary ecology.

Maternal and personal information mediates the use of social cues about predation risk

Organisms can gain information about predation risks from their parents, their own personal experience, and their conspecifics and adjust their behavior to alleviate these risks. These different sources of information can, however, provide conflicting information due to spatial and temporal variation of the environment. This raises the question of how these cues are integrated to produce adaptive antipredator behavior. We investigated how common lizards (Zootoca vivipara) adjust the use of conspecific cues about predation risk depending on whether the information is maternally or personally acquired. We experimentally manipulated the presence of predator scent in gestating mothers and their offspring in a full-crossed design. We then tested the consequences for social information use by monitoring offspring social response to conspecifics previously exposed to predator cues or not. Lizards were more attracted to the scent of conspecifics having experienced predation cues when they had themselves no personal information about predation risk. In contrast, they were more repulsed by conspecific scent when they had personally obtained information about predation risk. However, the addition of maternal information about predation risk canceled out this interactive effect between personal and social information: lizards were slightly more attracted to conspecific scent when these two sources of information about predation risk were in agreement. A chemical analysis of lizard scent revealed that exposure to predator cues modified the chemical composition of lizard scents, a change that might underlie lizards’ use of social information. Our results highlight the importance of considering multiple sources of information while studying antipredator defenses.

Maternal Temperature, Corticosterone, and Body Condition as Mediators of Maternal Effects in Jacky Dragons (Amphibolurus muricatus)

AbstractTemperature is a crucial environmental component that imposes physiological constraints and ultimately produces variation in life-history traits. Temperatures experienced by mothers can influence offspring phenotypes, including growth and sex ratios, especially in ectothermic species. However, mechanisms by which thermal information can be passed onto offspring have been underexplored. Here, we investigated corticosterone as a potential mediator of thermal maternal effects. We held female jacky dragons (Amphibolurus muricatus) in two different thermal regimes (short [7 h] or long [11 h] basking treatments), then quantified plasma corticosterone levels and tested for correlations between the resulting corticosterone levels and reproductive outputs. Lizards in the long-bask treatment had significantly higher corticosterone levels than those in the short-bask treatment. Maternal corticosterone, in turn, had sex-dependent effects on offspring hatching size but was not associated with maternal reproductive effort or offspring sex or growth. In contrast, maternal body condition was strongly positively related to both reproductive output (including clutch size and total number of eggs) and offspring size at hatching but had no effect on offspring growth. Basking treatment also interacted with condition and corticosterone to affect egg mass and hatchling snout-vent length, respectively. When we tested for relationships between corticosterone levels and body condition, we found corticosterone to be negatively related to condition in long-bask lizards but only in the postbreeding season. These findings indicate that thermal opportunity alters physiology, with potential consequences for fitness. Moreover, the results suggest interactive influences of temperature, corticosterone, and condition as mediators of maternal effects.

Effects of Maternal Stress on Measures of Anxiety and Fearfulness in Different Strains of Laying Hens

Maternal stress can affect the offspring of birds, possibly due to hormone deposition in the egg. Additionally, phenotypic diversity resulting from domestication and selection for productivity has created a variety of poultry lines that may cope with stress differently. In this study, we investigated the effects of maternal stress on the behavior of different strains of laying hens and the role of corticosterone as its mediator. For this, fertilized eggs of five genetic lines-two brown (Brown 1 and 2), two white (White 1 and 2), and one pure line White Leghorn-were reared identically as four flocks of 27 birds (24F: 3M) per strain. Each strain was equally separated into two groups: Maternal Stress ("MS"), where hens were subjected to a series of daily acute psychological stressors for 8 days before egg collection, and "Control," which received routine husbandry. Fertile eggs from both treatments were collected at three different ages forming different offspring groups that were treated as replicates; additional eggs from Control were injected either with corticosterone diluted in a vehicle solution ("CORT") or just "Vehicle." Eggs from each replicate were incubated and hatched, and offspring (N = 1,919) were brooded under identical conditions. To measure the effects of maternal stress on anxiety and fear-like behavior, offspring were subjected to a social isolation test (SI) between 5 and 10 days of age and a tonic immobility test (TI) at 9 weeks of age. Compared to Control, MS decreased the number of distress vocalizations emitted by White 2 in SI. No effects of MS were observed in TI, and no effects of CORT were observed in any tests. Overall, brown lines vocalized more in SI and remained in TI for a longer duration than white strains, suggesting genetic differences in fear behavior. Females vocalized more than males in TI and showed a trend toward significance for the same trait in SI. Overall, results suggest that the effects of maternal stress on fearfulness are not directly mediated by corticosterone. Moreover, it highlights behavioral differences across various strains of laying hens, suggesting that fear responses are highly dependent on genotype.

History of predator exposure affects cell-mediated immunity in female eastern fence lizards, Sceloporus undulatus (Squamata: Phrynosomatidae)

On exposure to stressors, energy is diverted from non-urgent functions towards those important for immediate survival. The degree and nature of reallocation may be affected by the evolutionary history of the animal. The eastern fence lizard (Sceloporus undulatus) coexists in parts of its range with invasive fire ants (Solenopsis invicta), which attack and wound lizards and elevate stress-relevant hormones (corticosterone), whereas other populations have never been exposed to fire ants. We examined how a history of fire ant invasion affected the immune response in female lizards after exposure to exogenous corticosterone (mimicking exposure to a stressor) during gestation (dosing regimens differed among corticosterone-exposed lizards owing to the constraints of the original studies, but we found no evidence that this affected the outcome of the present study). A history of exposure to predatory stressors (fire ants) and corticosterone treatment affected cell-mediated immunity. Lizards from fire ant-invaded sites had a reduced immune response compared with those from uninvaded sites. Corticosterone treatment had no effect on the immune response of lizards from invaded sites but reduced the immune response of lizards from uninvaded sites. This suggests that an evolutionary history of exposure to wounding alters the immune response to corticosterone. Future work on how the immune system responds to environmental threats will be informative for the prediction and management of these threats.

Corticosterone in Lizard Egg Yolk Is Reduced by Maternal Diet Restriction but Unaltered by Maternal Exercise

When females face adverse environmental conditions, physiological changes, such as elevated corticosterone levels, to cope with the stressors may also impact their offspring. Such maternal effects are often considered adaptive and may "prime" the offspring for the same adverse environment, but maternal corticosterone levels do not always match that of the eggs produced. We examined how diet restriction and increased locomotor activity, via exercise training, affected steroid hormone levels of female green anole lizards, as well as the hormone levels in the yolk of their eggs. Diet restriction did not affect female hormone levels, but training increased corticosterone levels. Despite this, training did not affect yolk steroid levels, but eggs from females with diet restriction had lower corticosterone levels in yolk. This suggests that two common stressors, food shortage and increased locomotor activity, impact female physiology in a way that is not translated to her offspring.

Corticosterone mediated mate choice affects female mating reluctance and reproductive success

The study of stress-related hormones as mediators of sexual selection has traditionally focused on the effect of glucocorticoids on male quality and competing ability. However, environmental stressors are expected to affect both males and females, and the strength of sexual selection might be affected by changes in female mating decisions, a hypothesis that has rarely been tested. Here, we investigated whether female common lizard (Zootoca vivipara) mating behaviour and mating preferences are affected by different levels of administered corticosterone and conditioned by the familiarity of their partners, which is known to influence Z. vivipara social behaviour. To this end, two females, one corticosterone-treated and one control female, were simultaneously presented with an unfamiliar male and the following day with either a familiar or an unfamiliar male. Females treated with corticosterone (Cort) were more aggressive towards males and mated less. Furthermore, copulation probability in Cort females, but not in control females, increased with body size. On the second day, Cort females only mated with familiar partners. In contrast, male behaviour towards females was not affected by treatment and only bigger males successfully copulated with Cort females. This shows that corticosterone directly affected female mating behaviour and mating preferences, while male mating behaviour was unaffected by the female's level of corticosterone. Environmental and social stressors may affect reproductive strategies of females, the strength of sexual selection, and sexual conflict through their effects on female glucocorticoid levels, potentially in a wide range of species.

Glucocorticoids do not influence a secondary sexual trait or its behavioral expression in eastern fence lizards

Secondary sexual traits and associated behaviors can be influenced by environmental factors such as exposure to stressors. Such effects may be mediated by the physiological stress response, which is typified by the release of glucocorticoid hormones. The effects of glucocorticoids on sexual traits such as plumage and display coloration have most commonly been studied in isolation rather than in conjunction with other pertinent aspects of signalling, such as behavior and habitat use, though these have substantial potential to alter signal perception. Here we test the effects of corticosterone (CORT), a common glucocorticoid, on a secondary sexual trait (badge coloration) in male eastern fence lizards (Sceloporus undulatus), and behaviors associated with its expression. We show that neither baseline nor experimentally manipulated CORT levels were associated with badge coloration. Further, elevation of CORT levels in the field did not alter signalling or associated territorial behaviors. There was a trend for CORT-treatment to influence perch height selection, which may influence signal perception. We suggest that future studies investigating the effects of environmental stressors and associated physiological changes on secondary sexual traits should consider behaviors and ecology relevant to signal perception in order to best understand the influence of stressors in nature.

Interactions between corticosterone phenotype, environmental stressor pervasiveness and irruptive movement-related survival in the cane toad

Animals use irruptive movement to avoid exposure to stochastic and pervasive environmental stressors that impact fitness. Beneficial irruptive movements transfer individuals from high-stress areas (conferring low fitness) to alternative localities that may improve survival or reproduction. However, being stochastic, environmental stressors can limit an animal's preparatory capacity to enhance irruptive movement performance. Thus individuals must rely on pre-existing, or rapidly induced, physiological and behavioural responses. Rapid elevation of glucocorticoid hormones in response to environmental stressors are widely implicated in adjusting physiological and behaviour processes that could influence irruptive movement capacity. However, there remains little direct evidence demonstrating that corticosterone-regulated movement performance or interaction with pervasiveness of environmental stress, confers adaptive movement outcomes. Here, we compared how movement-related survival of cane toads (Rhinella marina) varied with three different experimental corticosterone phenotypes across four increments of increasing environmental stressor pervasiveness (i.e. distance from water in a semi-arid landscape). Our results indicated that toads with phenotypically increased corticosterone levels attained higher movement-related survival compared with individuals with control or lowered corticosterone phenotypes. However, the effects of corticosterone phenotypes on movement-related survival to some extent co-varied with stressor pervasiveness. Thus, our study demonstrates how the interplay between an individual's corticosterone phenotype and movement capacity alongside the arising costs of movement and the pervasiveness of the environmental stressor can affect survival outcomes.

Does repeated human handling of study animals during the mating season affect their offspring?

Minimizing disturbance of study animals is a major consideration in ethological and ecological research design. One nearly universal type of disturbance is the handling of study animals as a component of trial setup. Even low to moderate levels of handling can be a substantial stressor to study animals, which may negatively affect their offspring via maternal effects. Understanding how routine human handling and manipulation may affect the outcome of research studies is therefore critical for interpreting study outcomes. We tested whether repeatedly handling and manipulating (i.e., manually disengaging) amplexed pairs of wood frogs (Rana sylvatica [Lithobates sylvaticus]), which have an explosive breeding season, would affect their reproductive output and offspring fitness. Handling and manipulation did not alter any parameter that we measured: reproductive timing, hatching success, and offspring larval duration, survival, and size at metamorphosis. These results suggest that handling and manipulation by researchers may have a negligible effect on wood frog reproduction and offspring fitness. It is possible that many species that are commonly used in reproductive studies because they suppress behavioral and physiological responses during the mating season are likewise unaffected by human handling. Nevertheless, researchers should examine possible consequences of methodological interventions on their study species in order to determine any potential influence on their results. Having a broad understanding of these effects on species that have robust or dampened stress responsiveness during the breeding season would be useful for making generalizations about potential effects.

Pre- and Postnatal Effects of Corticosterone on Fitness-Related Traits and the Timing of Endogenous Corticosterone Production in a Songbird

Maternally derived corticosterone in the egg and corticosterone produced endogenously by altricial nestling birds play essential roles during development. Although persistently high corticosterone levels can be harmful, moderately elevated levels above baseline can lead to reallocation of resources between growth and maintenance to ensure immediate survival or to enhance the development of fitness-related traits. We tested two hypotheses concerning the fitness consequences of elevated corticosterone during prenatal and postnatal development in altricial house wrens: (1) elevated corticosterone shifts resources away from growth and immune function and (2) elevated corticosterone serves as a signal to allocate resources to fitness-related traits. We also explored the development of the stress response, hypothesizing that early-stage nestlings have little endogenously produced corticosterone, but that their baseline and stress-induced corticosterone levels increase with age. Nestlings hatching from corticosterone-injected eggs were lighter at hatching, but through compensatory growth, ended up heavier than controls near the time of fledging, an important, fitness-related trait. Nestlings that hatched from corticosterone-injected eggs and those given oral doses of corticosterone did not differ from controls in three other fitness-related traits: immunoresponsiveness, size, or haematocrit. Early- and late-stage nestlings had similar baseline corticosterone levels, and all nestlings increased their plasma corticosterone levels in response to a capture-and-restraint protocol, with older nestlings mounting a stronger stress-induced response than younger nestlings. These results suggest that prenatal exposure to corticosterone is important in shaping offspring phenotype and are consistent with the hypothesis that maternally derived corticosterone in the egg can have long-term, fitness-related effects on offspring phenotype.

Water deprivation increases maternal corticosterone levels and enhances offspring growth in the snake Vipera aspis

Circulating glucocorticoids (GCs) levels may increase as a result of reproductive effort or in response to unpredictable events. However, the GCs secretion can vary with the availability of vital trophic resources such as energy. While water represents another critical resource, the impact of water deprivation on GCs secretion during reproduction has not yet been thoroughly investigated. Here, we examined the effects of water deprivation on plasma corticosterone (CORT) concentrations of female aspic vipers (Vipera aspis), and we determined the impacts of water deprivation on offspring traits. We exposed both pregnant and non-reproductive females to a 20-day water deprivation and compared their pre- and post-deprivation CORT levels to those of control females. At the end of the treatment, only water-deprived pregnant females showed a significant increase in CORT levels. In pregnant females, changes in baseline CORT level were correlated to changes in female hydration state. Changes in baseline CORT levels were also negatively influenced by maternal reproductive effort in pregnant control females, while such relationship was not apparent in pregnant water-deprived females. Finally, we found that offspring from water-deprived females had higher growth rates than offspring from control females. Offspring growth was also positively correlated to changes in both maternal osmolality and baseline CORT levels. Together, our results suggest that dehydration increases maternal CORT levels which may subsequently influence offspring development. Further long-term field studies are therefore required to assess whether there is an adaptive significance of this response.

Turtle hatchlings show behavioral types that are robust to developmental manipulations

There can be substantial variation among individuals within a species in how they behave, even under similar conditions; this pattern is found in many species and across taxa. However, the mechanisms that give rise to this behavioral variation are often unclear. This study investigated the influence of environmental manipulations during development on behavioral variation in hatchlings of the red-eared slider turtle (Trachemys scripta). First, we examined the effects of three manipulations during incubation (estrone sulfate exposure, corticosterone exposure, and thermal fluctuations) on hatchling righting response and exploration. Second, we determined whether hatchlings showed consistent differences (i.e. behavioral types) in their righting response and exploration across days and months, and whether these behaviors were correlated with one another. Finally, we examined whether righting response was predictive of ecologically relevant behaviors such as habitat choice and dispersal. Hatchling behavior was robust to our early manipulations; none of the pre-hatch treatments affected later behavior. There were significant clutch effects, which due to the split-clutch design suggests genetic underpinnings and/or maternal effects. We found evidence for behavioral types in turtles; both righting response and exploration were strongly repeatable and these behaviors were positively correlated. Righting response was not predictive of dispersal ability in the field, necessitating a revision in the general interpretations of righting response as a proxy for dispersal ability in turtles. Thus, turtle hatchlings show consistent behavioral differences that are robust to early developmental manipulations, and while not necessarily predictive of dispersal, these behavioral types can have important consequences throughout ontogeny.

Maternal exposure to predator scents: offspring phenotypic adjustment and dispersal

Predation is a strong selective pressure generating morphological, physiological and behavioural responses in organisms. As predation risk is often higher during juvenile stages, antipredator defences expressed early in life are paramount to survival. Maternal effects are an efficient pathway to produce such defences. We investigated whether maternal exposure to predator cues during gestation affected juvenile morphology, behaviour and dispersal in common lizards (Zootoca vivipara). We exposed 21 gravid females to saurophagous snake cues for one month while 21 females remained unexposed (i.e. control). We measured body size, preferred temperature and activity level for each neonate, and released them into semi-natural enclosures connected to corridors in order to measure dispersal. Offspring from exposed mothers grew longer tails, selected lower temperatures and dispersed thrice more than offspring from unexposed mothers. Because both tail autotomy and altered thermoregulatory behaviour are common antipredator tactics in lizards, these results suggest that mothers adjusted offspring phenotype to risky natal environments (tail length) or increased risk avoidance (dispersal). Although maternal effects can be passive consequences of maternal stress, our results strongly militate for them to be an adaptive antipredator response that may increase offspring survival prospects.

Contextual modulation of social and endocrine correlates of fitness: insights from the life history of a sex changing fish

Steroid hormones are critical regulators of reproductive life history, and the steroid sensitive traits (morphology, behavior, physiology) associated with particular life history stages can have substantial fitness consequences for an organism. Hormones, behavior and fitness are reciprocally associated and can be used in an integrative fashion to understand how the environment impacts organismal function. To address the fitness component, we highlight the importance of using reliable proxies of reproductive success when studying proximate regulation of reproductive phenotypes. To understand the mechanisms by which the endocrine system regulates phenotype, we discuss the use of particular endocrine proxies and the need for appropriate functional interpretation of each. Lastly, in any experimental paradigm, the responses of animals vary based on the subtle differences in environmental and social context and this must also be considered. We explore these different levels of analyses by focusing on the fascinating life history transitions exhibited by the bi-directionally hermaphroditic fish, Lythrypnus dalli. Sex changing fish are excellent models for providing a deeper understanding of the fitness consequences associated with behavioral and endocrine variation. We close by proposing that local regulation of steroids is one potential mechanism that allows for the expression of novel phenotypes that can be characteristic of specific life history stages. A comparative species approach will facilitate progress in understanding the diversity of mechanisms underlying the contextual regulation of phenotypes and their associated fitness correlates.

Consequences of experimental cortisol manipulations on the thermal biology of the checkered puffer (Sphoeroides testudineus) in laboratory and field environments

Anthropogenic climate change is altering temperature regimes for coastal marine fishes. However, given that temperature changes will not occur in isolation of other stressors, it is necessary to explore the potential consequences of stress on the thermal tolerances and preferences of tropical marine fish in order to understand the thresholds for survival, and predict the associated coastal ecological consequences. In this study, we used exogenous cortisol injections to investigate the effects of a thermal challenge on checkered puffers (Sphoeroides testudineus) as a secondary stressor. There were no significant differences between control and cortisol-treated fish 48h following cortisol treatment for swimming ability (using a chase to exhaustion protocol), blood glucose concentrations or standard metabolic rate. In the lab, control and cortisol-treated puffers were exposed to ambient (29.1±1.5°C), ambient +5°C (heat shock) and ambient -5°C (cold shock) for 4h and to evaluate the consequences of abrupt temperature change on puff performance and blood physiology. Following cold shock, control fish exhibited increases in cortisol levels and weak 'puff' performance. Conversely, fish dosed with cortisol exhibited consistently high cortisol levels independent of thermal treatment, although there was a trend for an attenuated cortisol response in the cortisol-treated fish to the cold shock treatment. A 20-day complementary field study conducted in the puffer's natural habitat, a tidal creek in Eleuthera, The Bahamas, revealed that cortisol-injected fish selected significantly cooler temperatures, measured using accumulated thermal units, when compared to controls. These results, and particularly the discrepancies between consequences documented in the laboratory and the ecological trends observed in the field, highlight the need to establish the link between laboratory and field data to successfully develop management policies and conservation initiatives with regards to anthropogenic climate change.

Temperature has species-specific effects on corticosterone in alligator lizards

In response to conditions that threaten homeostasis and/or life, vertebrates generally increase production of glucocorticoid hormones, such as corticosterone (CORT), which induces an emergency physiological state referred to as the stress response. Given that extreme temperatures pose a threat to performance and survival, glucocorticoid upregulation might be an important component of a vertebrate ectotherm's response to extreme thermal conditions. To address this hypothesis, we experimentally examined the effects of body temperature (10, 20, 28, and 35°C; 5-h exposure) on CORT in two congeneric species of lizard naturally exposed to different thermal environments, northern and southern alligator lizards (Elgaria coerulea and Elgaria multicarinata, respectively). In both species, CORT was similarly elevated at medium and high temperatures (28 and 35°C, respectively), but CORT was only elevated at low temperatures (10°C) in southern alligator lizards. We also examined CORT before and after adrenocorticotrophic hormone (ACTH) challenge. In both species, ACTH induced higher CORT levels than any temperature, suggesting that these animals could respond to further stressors at all experimental temperatures. Finally, we compared our laboratory results to measurements of CORT in field-active southern alligator lizards. Plasma CORT concentrations from our laboratory experiment had the same mean and less variance than the field lizards, suggesting that our laboratory lizards displayed CORT within natural levels. Our results demonstrate that body temperature directly affects CORT in alligator lizards. Moreover, the CORT response of these lizards appears to be adapted to their respective thermal environments. Species-specific differences in the thermal CORT response might be common in vertebrate ectotherms and have implications for species' biogeography and responses to climate change.

Evaluating the thermal effects of translocation in a large-bodied pitviper

Acute stressors can be costly, often requiring alteration of normal physiological processes to mitigate their effects. Animal translocation may be a very stressful event and result in a reduced ability to maintain homeostasis. The impacts of translocation on the thermal ecology of ectothermic vertebrates, which may rely on preferred habitats for thermoregulation, are currently unknown. In this study, 22 adult male Northern Pacific rattlesnakes (Crotalus oreganus oreganus) were implanted with automated temperature loggers and radio-tracked. Snakes were assigned to one of three treatments: translocation, handling control, and undisturbed control. Short-distance translocation (SDT) and handling treatments were applied weekly for 6 weeks. Hourly body temperature (Tb ) was recorded during the course of the study. Mean Tb was impacted in a time-dependent fashion, where translocated snakes had lower mean Tb than handled controls during the first week of the study only, especially the first 24 hr after translocation. Separating the dataset into day and night revealed that this effect was localized to Tb variation during the day only. Variance in temperature was not impacted by translocation or handling. Snake body mass and time of year were the major factors influencing the thermal profiles of these rattlesnakes. Thermal ecology in male rattlesnakes is resilient to SDT, suggesting that they quickly resume normal behaviors following repeated bouts of acute capture stress and disturbance of their spatial ecology. This study provides support for SDT as a safe measure for mitigating human-snake interactions and facilitating conservation practices regarding male snakes, which are the most frequently encountered sex.

Modulation of corticosterone secretion in tuatara (Sphenodon punctatus): Evidence of a dampened stress response in gravid females

Baseline and stress response glucocorticoid (GC) secretion can be modulated by individuals to support activities and physiological functions connected with reproduction (migration, mating, oviposition and/or parturition, care of young). Corticosterone (CORT) is the primary GC in reptiles and, in accordance with other vertebrates, an adrenocortical stress response is observed. Modulation of CORT secretion occurs in several reptile species, such that elevated baseline CORT concentration and/or a dampened CORT response are common during reproductive life-history events. We investigated CORT secretion after 24 h capture-restraint in the oviparous tuatara (Sphenodon punctatus), the last living rhynchocephalian, and tested whether gravid females have a dampened CORT response compared with non-gravid females. We also included males as a comparison. We confirmed that gravid females have significantly higher baseline plasma CORT concentrations than non-gravid females, suggesting increased CORT secretion during nesting. Furthermore, we found that gravid females exhibit a dampened CORT response compared to non-gravid females and males. Our results demonstrate that female reproductive condition influences CORT secretion in tuatara, and suggest that gravid females modulate CORT secretion during nesting to maintain homeostasis, effectively increasing chances of reproductive success and promoting overall fitness.

Influence of temperature on the corticosterone stress-response: an experiment in the Children's python (Antaresia childreni)

To cope with environmental challenges, organisms have to adjust their behaviours and their physiology to the environmental conditions they face (i.e. allostasis). In vertebrates, such adjustments are often mediated through the secretion of glucocorticoids (GCs) that are well-known to activate and/or inhibit specific physiological and behavioural traits. In ectothermic species, most processes are temperature-dependent and according to previous studies, low external temperatures should be associated with low GC concentrations (both baseline and stress-induced concentrations). In this study, we experimentally tested this hypothesis by investigating the short term influence of temperature on the GC stress response in a squamate reptile, the Children's python (Antaresia childreni). Snakes were maintained in contrasting conditions (warm and cold groups), and their corticosterone (CORT) stress response was measured (baseline and stress-induced CORT concentrations), within 48h of treatment. Contrary to our prediction, baseline and stress-induced CORT concentrations were higher in the cold versus the warm treatment. In addition, we found a strong negative relationship between CORT concentrations (baseline and stress-induced) and temperature within the cold treatment. Although it remains unclear how cold temperatures can mechanistically result in increased CORT concentrations, we suggest that, at suboptimal temperature, high CORT concentrations may help the organism to maintain an alert state.

The impacts of invaders: basal and acute stress glucocorticoid profiles and immune function in native lizards threatened by invasive ants

As anthropogenic stressors increase exponentially in the coming decades, native vertebrates will likely face increasing threats from these novel challenges. The success or failure of the primary physiological mediator of these stressors--the HPA axis--will likely involve numerous and chaotic outcomes. Among the most challenging of these new threats are invasive species. These have the capacity to simultaneously challenge the HPA axis and the immune system as they are often associated with, or the cause of, emerging infectious diseases, and energetic tradeoffs with the HPA response can have immunosuppressive effects. To determine the effects of invasive species on the vertebrate GC response to a novel stressor, and on immunity, we examined the effects of invasive fire ants on native lizards, comparing lizards from sites with long histories with fire ants to those outside the invasion zone. We demonstrated higher baseline and acute stress (captive restraint) CORT levels in lizards from within fire ant invaded areas; females are more strongly affected than males, suggesting context-specific effects of invasion. We found no effect of fire ant invasion on the immune parameters we measured (complement bacterial lysis and antibody hemagglutination) with the exception of ectoparasite infestation. Mites were far less prevalent on lizards within fire ant invaded sites, suggesting fire ants may actually benefit lizards in this regard. This study suggests that invasive species may impose physiological stress on native vertebrates, but that the consequences of this stress may be complicated and unpredictable.

Experimental litter size reduction reveals costs of gestation and delayed effects on offspring in a viviparous lizard

Experimental studies have often been employed to study costs of reproduction, but rarely to study costs of gestation. Disentangling the relative importance of each stage of the reproductive cycle should help to assess the costs and benefits of different reproductive strategies. To that end, we experimentally reduced litter size during gestation in a viviparous lizard. We measured physiological and behavioural parameters during gestation and shortly after parturition, as well as survival and growth of females and their offspring. This study showed four major results. First, the experimental litter size reduction did not significantly affect the cellular immune response, the metabolism and the survival of adult females. Second, females with reduced litter size decreased their basking time. Third, these females also had an increased postpartum body condition. As postpartum body condition is positively related to future reproduction, this result indicates a gestation cost. Fourth, even though offspring from experimentally reduced litters had similar weight and size at birth as other offspring, their growth rate after birth was significantly increased. This shows the existence of a maternal effect during gestation with delayed consequences. This experimental study demonstrates that there are some costs to gestation, but it also suggests that some classical trade-offs associated with reproduction may not be explained by gestation costs.

Effects of early stress on behavioral syndromes: an integrated adaptive perspective

This paper presents a behavioral ecologist's view on adaptive responses to early stress. I first summarize two approaches to this topic drawn from other papers in this Special Issue: the 'inoculation model' and the 'adaptive calibration model'. I then describe three relevant modeling approaches from behavioral and evolutionary ecology: models of adaptive plasticity, models of adaptive prey behavior under uncertainty about risk, and models of state-dependent adaptive behavioral syndromes. These models generate some novel predictions on factors that explain variation in how organisms might respond adaptively to early stress. In particular, the state-dependent models of adaptive behavioral syndromes emphasize the importance of feedback loops between behavior and state variables in explaining the long-term persistence of effects of early experiences. State variables can include aspects of physiology, morphology or life history, differences among individuals in information state or skill, or even in social state (e.g., social rank). The feedbacks between behavior and individual state suggest a framework for an integrative approach to understanding responses to stress. The behavioral syndrome approach also emphasizes the importance of understanding stress carryovers - e.g., situations where effects of one kind of stressor (e.g., early social stress) carry over to influence other stress responses (e.g., response to danger) later in life. Finally, I discuss how responses to early stress might relate to variation in the ability of animals to cope well with novel conditions associated with human-induced rapid environmental change, a ubiquitous problem that animals face in the modern world.

Seasonal variation in plasma corticosterone concentrations in wild and captive adult Duvaucel's geckos (Hoplodactylus duvaucelii) in New Zealand

Most of New Zealand’s herpetofauna species are threatened and in decline. Yet, little is known about their basic physiology and endocrinology. This study examined plasma corticosterone (CORT) concentrations in a threatened endemic New Zealand reptile, the Duvaucel’s gecko, in relation to season, sex, body temperature, body condition and female reproductive condition (pregnant versus non-pregnant). In addition, seasonal plasma CORT concentrations were compared between captive geckos from a breeding facility and a wild population to determine whether concentrations of CORT were chronically elevated in captive lizards. Plasma CORT concentrations showed significant seasonal variation, but were not related to sex, body temperature, body condition or female reproductive condition. Geckos, which successfully bred in captivity each year, did not exhibit chronically elevated plasma CORT levels but showed an elevation of plasma CORT concentrations in summer compared with wild geckos. Information on basal CORT concentrations in species of conservation concern can be beneficial for improving their management and can aid in identifying and evaluating stress-related changes in hormone patterns of individuals and chronic stress, which is particularly relevant for threatened species breeding programs.

The effects of maternal corticosterone levels on offspring behavior in fast- and slow-growth garter snakes (Thamnophis elegans)

During embryonic development, viviparous offspring are exposed to maternally circulating hormones. Maternal stress increases offspring exposure to corticosterone and this hormonal exposure has the potential to influence developmental, morphological and behavioral traits of the resulting offspring. We treated pregnant female garter snakes (Thamnophis elegans) with low levels of corticosterone after determining both natural corticosterone levels in the field and pre-treatment levels upon arrival in the lab. Additional measurements of plasma corticosterone were taken at days 1, 5, and 10 during the 10-day exposure, which occurred during the last third of gestation (of 4-month gestation). These pregnant snakes were from replicate populations of fast- and slow-growth ecotypes occurring in Northern California, with concomitant short and long lifespans. Field corticosterone levels of pregnant females of the slow-growth ecotype were an order of magnitude higher than fast-growth dams. In the laboratory, corticosterone levels increased over the 10 days of corticosterone manipulation for animals of both ecotypes, and reached similar plateaus for both control and treated dams. Despite similar plasma corticosterone levels in treated and control mothers, corticosterone-treated dams produced more stillborn offspring and exhibited higher total reproductive failure than control dams. At one month of age, offspring from fast-growth females had higher plasma corticosterone levels than offspring from slow-growth females, which is opposite the maternal pattern. Offspring from corticosterone-treated mothers, although unaffected in their slither speed, exhibited changes in escape behaviors and morphology that were dependent upon maternal ecotype. Offspring from corticosterone-treated fast-growth females exhibited less anti-predator reversal behavior; offspring from corticosterone-treated slow-growth females exhibited less anti-predator tail lashing behavior.

In search of relationships between the acute adrenocortical response and fitness

The assumption that the acute response to stress is adaptive is pervasive in the literature, but there is little direct evidence regarding potential positive fitness consequences of an acute stress response. If acute glucocorticoid (GC) elevation increases lifetime reproductive success (fitness), in what contexts does this occur, and through what combination of effects on annual reproductive output and interannual survival? Here we examine the framework under which most comparative acute GC studies fall, evaluate the commonalities of those studies in the light of expected fitness effects, and suggest methods to better examine the potentially beneficial effects of the acute GC response for free living animals. An overwhelming majority of papers from this area examine environmental-physiological-social effects on GC reactivity. Fewer evaluate intermediate performance measures (fitness proxies). We could only find 11 that directly examine GC effects on reproductive output and survival. The environment-GC-performance papers suggest that greater GC reactivity favors self-maintenance behavior (survival) at the expense of current reproduction. However, the two studies that directly address GC reactivity and fitness (2 of the 11) find the opposite effect (greater GC reactivity predicts lower annual survival). We suggest that it is time to move past simple evaluation of factors regulating GC secretion. These studies will be much richer and informative if researchers include performance and fitness measures. We especially support incorporating and testing ideas of context dependency, coping strategies, and possible fluctuating selection pressures when considering the fitness benefits of the acute GC response.

Colour variation and alternative reproductive strategies in females of the common lizard Lacerta vivipara

Within-sex colour variation is a widespread phenomenon in animals that often plays a role in social selection. In males, colour variation is typically associated with the existence of alternative reproductive strategies. Despite ecological conditions theoretically favourable to the emergence of such alternative strategies in females, the social significance of colour variation in females has less commonly been addressed, relative to the attention given to male strategies. In a population of the common lizard, females display three classes of ventral colouration: pale yellow, orange and mixed. These ventral colours are stable through individual's life and maternally heritable. Females of different ventral colourations displayed different responses of clutch size, clutch hatching success and clutch sex-ratio to several individual and environmental parameters. Such reaction patterns might reflect alternative reproductive strategies in females. Spatial heterogeneity and presence of density- and frequency-dependent feedbacks in the environment could allow for the emergence of such alternative strategies in this population and the maintenance of colour variation in females.

Corticosterone, locomotor performance, and metabolism in side-blotched lizards (Uta stansburiana)

Elevated levels of circulating corticosterone commonly occur in response to stressors in wild vertebrates. A rise in corticosterone, usually in animals of subordinate rank, results in a variety of effects on behavior and physiology. Behavioral and physiological responses to short-term increases in corticosterone are well studied. In contrast, the effects of chronic elevated levels of corticosterone are poorly understood, particularly in lizards. Here, we examined the long-term effects of exogenous corticosterone on locomotor performance, resting and active metabolic rate, and hematocrit in male side-blotched lizards Uta stansburiana. Corticosterone implantation resulted in higher levels of stamina relative to sham-surgery controls. In addition, lizards with elevated corticosterone exhibited lower resting metabolic rates relative to controls. Corticosterone had no effect on peak activity metabolism but did result in faster recovery times following exhaustive exercise. We suggest that elevated levels of corticosterone in response to dominance interactions promote enhanced locomotor abilities, perhaps as a flight response to avoid agonistic interactions. Furthermore, stressed lizards are characterized by lower resting metabolic rates, which may serve as strategy to conserve energy stores and enhance survival.

Mother's timing and duration of corticosterone exposure modulate offspring size and natal dispersal in the common lizard (Lacerta vivipara)

Although multiple condition dependence in dispersal is common, the proximate mechanisms that integrate information from multiple sources remain largely unknown. In the common lizard (Lacerta vivipara), earlier studies have shown that maternal plasma corticosterone level interacts with maternal phenotype to affect offspring phenotype and dispersal strategy, and may reflect the mother's external and/or internal environment. However, the mechanism by which these two types of environmental information are integrated has not been identified. We explored the possibility that the timing and duration of the corticosterone signal are the key factors by which the message is modulated. We found that the timing of corticosterone exposure affects the juvenile phenotype: an exposure to corticosterone early in development has negative effects on juvenile size, weight, and body condition, that can nevertheless be restored in the case of a prolonged exposure. The duration of corticosterone exposure affects the dispersal strategy, although the precise effect depends on the sex ratio of the clutch. That is, in female-biased clutches, a prolonged exposure during gestation promotes philopatry of juveniles, while a short exposure enhances their dispersal, a result that is consistent with kin competition theory. Therefore, our results demonstrate that while corticosterone titer may signal a mother's external and/or internal environment to her developing young, differences in the timing and duration of this endocrine signal produce offspring with specialized phenotypes that exhibit different dispersal strategies.

Does adrenal responsiveness vary with sex and reproductive status in Egernia whitii, a viviparous skink?

In mammals, oestrogens generally stimulate adrenal function whilst androgens are inhibitory, and gestating females down-regulate their acute response to stressors in order to protect current reproductive investment. This study aimed to determine if adrenocortical function is similarly modulated by sex and reproductive status in the viviparous lizard, Egernia whitii. We compared the adrenocortical response to acute capture stress in female E. whitii during active (post-ovulatory and gestating) and quiescent (post-partum) phases of their reproductive cycle. We also compared the responses of reproductively quiescent males and females to acute stress and ACTH challenge to determine if there are sex-related differences in HPA axis activity when the influence of reproductive hormones is minimal. The females' responses to acute capture stress varied significantly with reproductive stage, and quiescent females displayed the strongest immediate response, with a rapid and sustained increase in plasma corticosterone (CORT) concentrations. Post-ovulatory females showed the most conservative adrenocortical response and while gestating females showed a large immediate response, this was not as prolonged as in quiescent females. Reproductively quiescent males and females exhibited similar responses to acute stress, and also responded similarly to ACTH injection, with plasma CORT reaching maximal concentrations of 52.1 and 59.4 ng/mL, respectively. Reproductively quiescent females treated with oestrogen exhibited greater responsiveness to ACTH than control females, although basal plasma CORT concentrations were unaltered: these results suggest that the attenuation of the acute stress response observed in reproductively active females of E. whitii may be regulated upstream of ACTH secretion. Our results demonstrate that the activity of the HPA axis is modulated by reproductive status in this viviparous reptile, and that gestating females are able to buffer their embryos from the potentially adverse effects of elevated plasma corticosteroids.

How much stress do researchers inflict on their study animals? A case study using a scincid lizard, Eulamprus heatwolei

Research on live vertebrates is regulated by ethics committees, who prohibit ;excessively stressful' procedures. That judgment is based on intuition - a notoriously unreliable criterion when dealing with animals phylogenetically distant from humans. To objectively evaluate the stress imposed by research practices, we measured plasma corticosterone levels in lizards (Eulamprus heatwolei Wells & Wellington, Scincidae). Some procedures (handling and measuring, toe-clipping for identification, exposure to predator scent) did not induce significant increases in corticosterone levels, suggesting that these stimuli generated relatively little stress. However, other stimuli (testing locomotor speed, microchip implantation, blood sampling, an unfamiliar enclosure, tail autotomy, exposure to a heterospecific lizard) were more stressful, with corticosterone levels increasing only transiently in some treatments (<2 h for tail autotomy), but persisting much longer in others (14 days for microchip implantation). Overall, our data suggest that the levels of stress induced by routine laboratory procedures are no greater than those often experienced by lizards in nature; but that intuition provides a poor basis for evaluating the levels of stress induced by research. For example, toe-clipping is often criticized and sometimes banned; but our data suggest that this method is actually less stressful than the technique frequently recommended to replace it on ethical grounds (microchip implantation). Toe-clipping also was less stressful than superficially trivial manipulations such as housing the animal in an unfamiliar enclosure. More generally, we urge researchers to seek objective information on the effects of their activities on research subjects, rather than relying upon subjectivity and anthropomorphism in making these evaluations.

Experimental enhancement of corticosterone levels positively affects subsequent male survival

Corticosterone is an important hormone of the stress response that regulates physiological processes and modifies animal behavior. While it positively acts on locomotor activity, it may negatively affect reproduction and social activity. This suggests that corticosterone may promote behaviors that increase survival at the cost of reproduction. In this study, we experimentally investigate the link between corticosterone levels and survival in adult common lizards (Lacerta vivipara) by comparing corticosterone-treated with placebo-treated lizards. We experimentally show that corticosterone enhances energy expenditure, daily activity, food intake, and it modifies the behavioral time budget. Enhanced appetite of corticosterone-treated individuals compensated for increased energy expenditure and corticosterone-treated males showed increased survival. This suggests that corticosterone may promote behaviors that reduce stress and it shows that corticosterone per se does not reduce but directly or indirectly increases longer-term survival. This suggests that the production of corticosterone as a response to a stressor may be an adaptive mechanism that even controls survival.

Current research on the behavioral neuroendocrinology of reptiles

Selected reptilian species have been the targets of investigations in behavioral neuroendocrinology for many years. Reptiles offer a particularly powerful set of traits that facilitate comparisons at multiple levels, including those within and between individuals of a particular species, between different environmental and social contexts, as well as across species. These types of studies, particularly as they are considered within the framework of results from other vertebrates, will enhance our understanding of the genetic and hormonal influences regulating changes in the structure and function of the nervous system. Work on the hormonal and environmental factors influencing courtship and copulatory behaviors in green anoles, including the development and maintenance of the neuromuscular structures critical for their display, is highlighted. Some very recent work on other model systems is also discussed to provide a context for suggested future research directions.

Is corticosterone-mediated phenotype development adaptive? Maternal corticosterone treatment enhances survival in male lizards

Hormones are an important interface between genome and environment, because of their ability to modify the phenotype. More particularly, glucocorticoids are known to affect both morphological, physiological and behavioral traits. Many studies suggest that prenatal stress (associated with an elevation of corticosterone) has deleterious effects on offspring, an altered physiology resulting in retardation of fetal growth and higher percentage of dead neonates. In this study, we investigate the consequences of an artificial increase of corticosterone in pregnant female Lacerta vivipara on two important fitness components: growth and survival. Do stressed females decrease or enhance offspring survival? In 2000 and 2001, we collected pregnant females from four populations of the Cevennes and kept them in the laboratory until parturition. We applied a corticosterone solution daily onto the backs of some females. A similar solution, but without corticosterone, was applied to the remaining females as a control. Immediately after birth, we measured juveniles' morphological characteristics and released them on the field. In September of the year of release and in May of the following year, we recaptured offspring to estimate growth and survival. The elevation of the corticosterone level in pregnant females L. vivipara had a profound impact on juvenile traits. The size, the body condition and the growth of juveniles were decreased by the corticosterone treatment. In contrast, in male juveniles, survival was higher for juveniles from corticosterone-treated females than from placebo females. Thus, corticosterone does not seem to have detrimental effects on offspring survival, suggesting that it may have an adaptive function.

Is sexual dimorphism affected by the combined action of prenatal stress and sex ratio?

During embryonic development, offspring are exposed to hormones of both maternal and sibling origin. Maternal stress increases offspring exposure to corticosterone, and, in polytocous animals, the sex ratio or intrauterine position can influence the levels of androgens and estrogens experienced by the offspring. Such hormone exposure has the potential to influence many important morphological and behavioural aspects of offspring, in particular sexually dimorphic traits. Although well known in rodents, the impact of prenatal hormone exposure in other vertebrates is poorly documented. We experimentally investigated the relationship between maternal stress, population density, sex ratio (a surrogate for the degree of exposure to steroids produced by siblings), and sexual dimorphism in a viviparous lizard, Lacerta vivipara. Our results show that prenatal sex ratios have consequences for sexually dimorphic morphology (ventral scale count) in both sexes, but with no effect of maternal stress or any interaction between the two. Embryonic steroid exposure can potentially be an important factor in generating individual variation in natural populations of viviparous animals.

ACTH-induced stress response during pregnancy in a viviparous gecko: no observed effect on offspring quality

The typical stress response in reptiles involves the release of corticosterone from the adrenal glands. Elevated maternal concentrations of corticosterone in mammals during pregnancy may have deleterious effects on offspring fitness, and recent work has shown a suppression of the hormonal response to stress during pregnancy in rats. Little is known about the influence of reproductive state on the secretion of corticosterone in viviparous reptiles or on the effects of high levels of corticosterone during reproduction on the developing embryos. We examined whether New Zealand common geckos (Hoplodactylus maculatus), pregnant with embryos at stages 34-35 of development, secrete corticosterone in response to adrenocorticotrophic hormone (ACTH) and whether an ACTH-induced increase in maternal corticosterone affects the outcome of pregnancy. Corticosterone concentrations in pregnant lizards increased more than seven-fold over basal levels following injection of ACTH. However, there were no significant effects of elevated corticosterone on the duration or success of pregnancy, or on various morphological measures, growth, or sprint speed of the offspring. This may reflect a lack of sensitivity of relevant embryonic tissues to corticosterone under the conditions of the present experiment or an ability of the embryos to bind, degrade, or restrict placental transport of corticosterone. Future studies should investigate the possibility of corticosteroid effects on other offspring tissues, including effects in adult life.