Turtle hatchlings show behavioral types that are robust to developmental manipulations

Ecological and Fitness Correlates of Personality in a Long-lived Terrestrial Turtle

An individual's behavioral tendencies (i.e., personality or temperament) can influence its interactions with the environment and thus have important ecological and evolutionary consequences for animal populations. Boldness, defined as an individual's tendency to engage in risk-taking activities, is a phenotypically variable trait linked with numerous behavioral and fitness outcomes in free-ranging animals. We examined variation and repeatability of boldness and other behavioral characteristics in two wild Eastern Box Turtle (Terrapene carolina carolina) populations using radiotelemetry, and assessed fitness correlates of boldness over multiple years. We observed large amounts of among-individual variation and within-individual consistency (i.e., repeatability) of boldness as measured by their head emergence latency following a standardized confinement assay. Individuals were also consistent in several in-field behaviors including movement rate, home range size, and date of emergence from overwintering refuges. Individuals with shorter head emergence latencies (i.e., bolder turtles) had larger home ranges, emerged earlier from overwintering dormancy, and experienced moderately lower survival compared with shy individuals. Boldness did not affect time spent within the thermal preference range, somatic growth rates, or the frequency of mating or same-sex aggressive encounters. Boldness and its effects on in-field behaviors differed between sexes and populations, and the relationship between boldness and survival was temporally variable. Our results suggest possible intrinsic behavioral types in T. c. carolina and highlight the importance of long-term and multipopulation studies when examining ecological and evolutionary processes that shape personality phenotypes in turtles.

Prenatal yolk corticosterone exposure promotes skeletal growth and induces oxidative imbalance in yellow-legged gull embryos

Maternally derived hormones induce variation in offspring phenotype, with consequences that can carry over into post-natal life and even into adulthood. In birds, maternal egg corticosterone (CORT) is known to exert contrasting effects on offspring morphology, physiology and behaviour after hatching. However, information on the effects of CORT exposure on pre-hatching embryonic development is limited. We experimentally increased yolk CORT levels in yellow-legged gull (Larus michahellis) eggs, and assessed the effects on embryo pre-hatching development and oxidative status of brain and liver. CORT-supplemented embryos reached a larger skeletal size and liver mass compared with controls. Embryos from CORT-injected last-laid eggs showed decreased activity of the hepatic antioxidant enzymes superoxide dismutase and catalase, while intermediate-laid eggs showed increased levels of lipid peroxidation. However, elevated yolk CORT did not affect oxidative stress endpoints in the brain. Our results indicate that elevated yolk CORT levels affect prenatal embryo development by promoting skeletal growth, and induce laying sequence- and organ-specific oxidative imbalance, with potential adverse consequences during postnatal life, especially for late-hatched offspring.

Temperament and sexual behaviour in the Furrowed Wood Turtle Rhinoclemmys areolata

The variation in temperament among animals has consequences for evolution and ecology. One of the primary effects of consistent behavioral differences is on reproduction. In chelonians some authors have focused on the study of temperament using different methods. In our research our first aim was i) establish a methodology to determine the degree of boldness among individuals Rhinoclemmys areolata. Our second aim was to ii) determine the role boldness plays during reproduction, with emphasis on courtship and copulation, considering a) the interactions between males and females, and b) competition between males. We used 16 sexually mature individuals of each sex. Males were observed in four different situations and 17 behavioral traits were recorded. We selected 12 traits that allowed us distinguish between the bolder and the shier individuals and found that five behavioral traits were specific for bolder individuals and five others for shier individuals. In a second step, we observed a male in presence of a female and recorded courtship behaviors and breeding attempts. Bolder individuals did not display courtship behaviors and just attempted to copulate. Shier individuals displayed courtship behaviors and copulation attempts were rarely observed. Finally, in the simulations that compared two males in the presence of a female we noticed that bolder individuals displayed courtship behaviors while the shier ones simply ignored the female. Our results first allowed us to determine which methodology is the best to determine temperament in turtles. Secondly, temperament seems to be an important factor in modulating interaction between males and females. Bolder individuals have an advantage during competition and display courtship behaviours only if other males are present. Shier males displayed courtship behaviors and only try to copulate when no competitors were present. These two different temperament-dependant strategies are discussed in terms of ecology, evolution and management.

Incubation temperature and satiety influence general locomotor and exploratory behaviors in the common snapping turtle (Chelydra serpentina)

Temperature during embryogenesis determines sex and has been shown to influence other physiological traits in reptiles. The common snapping turtle (Chelydra serpentina) is an ideal model for testing how temperature impacts behavior in species that display temperature-dependent sex determination. Behavioral assays are crucial to understanding how a changing climate may affect whole organism function in the snapping turtle. Currently, there are few behavioral assays for semi-aquatic vertebrates like turtles. In this study, we used digital cameras to record behavior of fed and fasted hatchling turtles from different incubation temperatures in an open field setting for 20 min in 2018 and repeated the experiment in 2019. Open fields were circular tanks filled with water to a depth of 3.5 cm. Each field was split into four quadrants and two zones (inner and outer). The amount of time turtles spent actively moving, total distance travelled, and several other measures were collected and summarized automatically from videos with open source image analysis software (ImageJ). Satiety and incubation temperature had significant effects on total distance moved, time spent moving, and time moving in the outer zone. These findings indicate that temperature during embryogenesis has a long-lasting effect on neural mechanisms underlying exploratory or general locomotor behavior in turtles.

The Devil is in the Details: Identifying Aspects of Temperature Variation that Underlie Sex Determination in Species with TSD

Most organisms experience thermal variability in their environment; however, our understanding of how organisms cope with this variation is under-developed. For example, in organisms with temperature-dependent sex determination (TSD), an inability to predict sex ratios under fluctuating incubation temperatures in the field hinders predictions of how species with TSD will fare in a changing climate. To better understand how sex determination is affected by thermal variation, we incubated Trachemys scripta eggs using a "heat wave" design, where embryos experienced a male-producing temperature of 25 ± 3°C for the majority of development and varying durations at a female-producing temperature of 29.5 ± 3°C during the window of development when sex is determined. We compared the sex ratios from these incubation conditions with a previous data set that utilized a similar heat wave design, but instead incubated eggs at a male-producing temperature of 27 ± 3°C but utilized the same female-producing temperature of 29.5 ± 3°C. We compared the sex ratio reaction norms produced from these two incubation conditions and found that, despite differences in average temperatures, both conditions produced 50:50 sex ratios after ∼8 days of exposure to female-producing conditions. This emphasizes that sex can be determined in just a few days at female-producing conditions and that sex determination is relatively unaffected by temperatures outside of this short window. Further, these data demonstrate the reduced accuracy of the constant temperature equivalent model (the leading method of predicting sex ratios) under thermally variable temperatures. Conceptualizing sex determination as the number of days spent incubating at female-producing conditions rather than an aggregate statistic is supported by the mechanistic underpinnings of TSD, helps to improve sex ratio estimation methods, and has important consequences for predicting how species with TSD will fare in a changing climate.

Glucocorticoid and triiodothyronine concentrations do not correlate with behavior in vicuñas (Vicugna vicugna)

State-dependent foraging theory posits that animals should make foraging decisions based on energetic condition, where animals with fewer energetic reserves prioritize foraging over other behaviors, including antipredator behaviors. However, few studies have investigated these trade-offs at an individual level in wild, free-ranging animals. We investigated the relationships between internal condition and behavior in a wild mammal, the vicuña (Vicugna vicugna), which makes state-dependent decisions about the use of two habitats with different characteristics that contribute to their internal condition. Using non-invasively collected fecal samples, we measured glucocorticoid metabolites (GCMs) and thyroid hormones (THs) as indicators of combined stress (predation and nutritional), and just nutritional stress, respectively. We video recorded 20-minute behavioral observations and focused on behaviors which often demand a trade-off between energy acquisition and antipredator behaviors-vigilance and foraging. We found differences in expression of these behaviors between the two sites but found no relationships between physiological parameters (GCMs and THs) and behavior (vigilance and foraging) at either site. We suggest that state-dependent foraging may be difficult to observe in large mammals under baseline conditions and that GCMs and THs may be insensitive to small changes in stress stimuli at this scale, and where these wild animals have the entire suite of behavioral responses available to them.

Personality in Zoo-Hatched Blanding's Turtles Affects Behavior and Survival After Reintroduction Into the Wild

Reintroduction programs in which captive-bred or reared animals are released into natural habitats are considered a key approach for conservation; however, success rates have generally been low. Accounting for factors that enable individual animals to have a greater chance of survival can not only improve overall conservation outcomes but can also impact the welfare of the individual animals involved. One such factor may be individual personality, and personality research is a growing field. We designed a project to ascertain the presence of personality traits in Blanding's turtles (Emydoidea blandingii), a species of special concern in the state of Michigan, and to assess potential links between traits and post-release success. As hypothesized, the Blanding's turtles in this study displayed behavioral responses to modified open field tests indicative of distinct personality traits: exploration, boldness, and aggression. Additionally, the personality traits were correlated differently with survival and behavior patterns when the turtles were released into the Shiawassee National Wildlife Refuge. More exploratory turtles had higher survival rates, while neither boldness nor aggression was related to survival. Exploratory turtles were also more likely to travel longer distances after release. The use of muskrat dens was related to increased survival, and both bolder and more exploratory turtles made higher use of this feature. Exploratory and aggressive turtles were found basking outside of water more often, while bold turtles were more likely to be found at the water surface. Both these basking behaviors may increase the risk of predation and may be reflective of a trade-off between the risk and behaviors related to physiological health. Understanding how personality affects behavior and survival post-release can be a critical tool for improving reintroduction success. Zoo animal welfare scientists and practitioners can implement approaches that improve the welfare of individuals within the context of conservation initiatives.

Learning and behavior in hatchling Trachemys scripta exposed to bisphenol-a during embryonic development

Steroids play an integral role in orchestrating embryonic development, and they can affect a suite of phenotypic traits, including learning and behavior. Endocrine disrupting compounds (EDCs) can alter steroid-dependent phenotypic traits during embryonic development. Bisphenol-A (BPA) is an EDC that disrupts the action of estrogen, and recent work indicates that BPA can affect learning and behavior similarly to estrogen. We exposed red-eared slider turtle (Trachemys scripta) eggs to BPA during embryonic development and tested hatchlings for effects on learning and behavior in modified T-mazes over the course of two weeks. We found that behavioral patterns changed within a day and over the course of the experiment, but we found no effect of BPA treatment. Further, we found that hatchling turtles were highly consistent in their behaviors. These behaviors varied among individuals, suggesting that there are discrete behavioral types in T. scripta hatchlings. The highly repetitive nature of behaviors in the hatchlings might explain the innate biases that we observed and warrants further study.

Variation and repeatability of home range in a forest-dwelling terrestrial turtle: implications for prescribed fire in forest management

Animal movements and use of space are in part determined by interactions between individual attributes such as sex and body size and extrinsic environmental factors such as the seasonal availability, quality and spatial configuration of resource patches in the landscape. Fire is a common and widespread disturbance process that has the potential to affect animal movements through modifications to the environment. Using radiotelemetry, we examined the contribution of these factors to variation in movements and home range over a 5-year period in a forest-dwelling terrestrial turtle, Terrapene carolina, at fire-maintained and unburned habitats in the southeastern United States. Female turtles had annual home-range sizes twice as large as males and moved longer distances per day during the nesting season (June and July), but males exhibited greater spatial fidelity from year to year. Turtles at the unburned site had home-range sizes twice as large as those at the fire-maintained site, and home-range size also decreased with increasing frequency and extent of fire, but this latter effect was strongest in females. Home-range behavior was highly repeatable within individuals of both sexes over time. This is the first evidence that fire influences the spatial ecology and movements of turtles, most likely through fire's impact on the spatial configuration, availability and quality of critical resources. That individuals behaved consistently through time, but differently from one another according to both intrinsic individual attributes and extrinsic environmental factors provides strong evidence of consistent inter- and intra-population variation in space use and movement behaviors in T. carolina. Such intra-specific behavioral variation suggests applying caution when extrapolating results to other sites across the geographic range of a species for use in conservation and management.

Red-eared slider hatchlings (Trachemys scripta) show a seasonal shift in behavioral types

Correlated and repeatable patterns of behavior, termed behavioral types, can affect individual fitness. The most advantageous behavioral type may differ across predictable environments (e.g., seasonally), and maternally mediated effects may match hatchling behavior to the environment. We measured righting response, an indicator of behavioral type, of juvenile red-eared slider turtles (Trachemys scripta) emerging from early and late season clutches to understand if the production of behavioral types differs across the nesting season. There was a significant effect of season, with early season hatchlings righting more quickly than late season hatchlings, and we explored two potential underlying mechanisms, maternal estrogens and maternal investment (e.g., yolk allocation). We dosed early season eggs with an estrogen mixture to mimic late season eggs and assayed hatchling righting response, but found no significant effect of this maternal effect. We assessed maternal investment by measuring egg, hatchling, and residual yolk masses. We found a seasonal pattern in yolk allocation, where early season eggs have more yolk than late season eggs. Early season hatchlings used more yolk for growth rather than maintenance of existing tissues, resulting in larger hatchlings. Interestingly, across both seasons, hatchlings that received less maternal yolk appeared to be more efficient at converting yolk to tissue, but we found no direct correlation with righting behavior. We demonstrate that the prevalence of behavioral types varies across the nesting season, creating correlated suites of seasonal phenotypes in turtle hatchlings, but it appears that neither maternal estrogens or investment in yolk directly underlie this shift in behavior.

Parental habituation to human disturbance over time reduces fear of humans in coyote offspring

A fundamental tenet of maternal effects assumes that maternal variance over time should have discordant consequences for offspring traits across litters. Yet, seldom are parents observed across multiple reproductive bouts, with few studies considering anthropogenic disturbances as an ecological driver of maternal effects. We observed captive coyote (Canis latrans) pairs over two successive litters to determine whether among‐litter differences in behavior (i.e., risk‐taking) and hormones (i.e., cortisol and testosterone) corresponded with parental plasticity in habituation. Thus, we explicitly test the hypothesis that accumulating experiences of anthropogenic disturbance reduces parental fear across reproductive bouts, which should have disparate phenotypic consequences for first‐ and second‐litter offspring. To quantify risk‐taking behavior, we used foraging assays from 5–15 weeks of age with a human observer present as a proxy for human disturbance. At 5, 10, and 15 weeks of age, we collected shaved hair to quantify pup hormone levels. We then used a quantitative genetic approach to estimate heritability, repeatability, and between‐trait correlations. We found that parents were riskier (i.e., foraged more frequently) with their second versus first litters, supporting our prediction that parents become increasingly habituated over time. Second‐litter pups were also less risk‐averse than their first‐litter siblings. Heritability for all traits did not differ from zero (0.001–0.018); however, we found moderate support for repeatability in all observed traits (r = 0.085–0.421). Lastly, we found evidence of positive phenotypic and cohort correlations among pup traits, implying that cohort identity (i.e., common environment) contributes to the development of phenotypic syndromes in coyote pups. Our results suggest that parental habituation may be an ecological cue for offspring to reduce their fear response, thus emphasizing the role of parental plasticity in shaping their pups’ behavioral and hormonal responses toward humans.

Evidence of embryonic regulation of maternally derived yolk corticosterone

In recent years, the potential for maternal stress effects to adaptively alter offspring phenotype has received considerable attention. This research has identified offspring traits that are labile in response to maternal stress; however, an understanding of the mechanisms underlying these effects is lagging and is crucial to appreciating the significance of this maternal effect. In the present study, we sought to better understand maternal stress effects by examining the potential for embryonic regulation of corticosterone exposure, determining the phenotypic consequences of elevated corticosterone during development, and characterizing the levels of maternally transferred corticosterone in unmanipulated eggs using Trachemys scripta By dosing eggs with tritiated corticosterone and tracking the steroid throughout development, we found that most corticosterone is metabolized, and less than 1% of the corticosterone dose reaches the embryo as free corticosterone. We also found that exogenous dosing of corticosterone, in concentrations sufficient to overwhelm embryonic metabolism, reduces embryonic survival and negatively impacts hatchling traits important to fitness. Our results demonstrate that concentrations of maternal corticosterone in the yolks of unmanipulated eggs are low and are significantly lower than the doses of corticosterone required to elicit phenotypic effects in hatchlings. Taken together, these results provide evidence that both the embryo and the female may minimize corticosterone accumulation in the embryo to avoid reductions in embryonic survival and negative impacts on offspring phenotype and fitness.

Pre- and postnatal effects of experimentally manipulated maternal corticosterone on growth, stress reactivity and survival of nestling house wrens

Corticosterone plays a central role in maintaining homeostasis, promoting energy acquisition, and regulating the stress response in birds. Exposure to elevated levels of corticosterone during development can profoundly alter offspring behaviour and physiology, but the effects of elevated maternal corticosterone on offspring development remain poorly understood.We tested two competing hypotheses concerning the effect of maternally derived corticosterone on growth and development of free-living house wrens: (i) elevated maternal corticosterone causes damaging effects on nestling phenotype and fitness (collateral damage hypothesis) and (ii) increased maternal corticosterone enhances offspring fitness by preparing nestlings for the environment experienced by their mother (environmental/maternal-matching hypothesis).We used a non-invasive means to increase maternal corticosterone by providing females with corticosterone-injected mealworms prior to and during egg production in the absence of any overt pre-natal maternal stress. To disentangle pre- and post-natal effects of this elevation in maternal corticosterone, we cross-fostered young in two experiments: (i) nestlings of control and experimental females were reared by unmanipulated, natural females in a uniform maternal environment; (ii) a split-brood design that enabled us to assess the interaction between the mother's corticosterone treatment and that of the nestlings.There were significant pre-natal effects of increased maternal corticosterone on nestling growth and survival. Offspring of females experiencing experimentally increased corticosterone were heavier and larger than offspring of control females. There also was a significant interaction between maternal corticosterone treatment and the corticosterone treatment to which young were exposed within the egg in their effect on nestling survival while in the nest; experimental young exhibited greater survival than control young, but only when reared by control mothers. There was also a significant effect of maternal corticosterone treatment on nestling stress reactivity and, in both experiments, on the eventual recruitment of offspring as breeding adults in the local population.These patterns are broadly consistent with the environmental/maternal-matching hypothesis, and highlight the importance of disentangling pre- and post-natal effects of manipulations of maternal hormone levels on offspring phenotype.

Effects of augmented corticosterone in painted turtle eggs on offspring development and behavior

Maternal stressors can play an integral role in offspring development and ultimate behaviors in many vertebrates. Increased circulating stress avoidance hormones can be reflected in elevated concentrations in ova, thus providing a potential mechanism for maternal stress to be transmitted to offspring even in taxa without parental care. In this study, we assessed the potential impacts of augmented stress avoidance hormones on offspring development and anti-predator behaviors in a freshwater turtle, Chrysemys picta. We exposed C. picta eggs to biologically relevant amounts of the stress avoidance hormone, corticosterone, as a proxy for maternal stressors. We allowed the eggs to incubate in the field, then measured offspring phenotypes, conducted performance trials, and simulated nest emergence in a field experiment. Exogenous corticosterone reduced survivorship to hatch, but did not affect incubation duration, offspring size, overwinter survival, or size after hibernation. In performance trials, this hormone treatment reduced the frequency of righting, yet enhanced the righting speed of neonates. Regardless, these performance differences did not detectably alter survivorship in the nest emergence experiment. These results lend insight into the potential effects of maternal stress levels on offspring phenotypes, as well as the robustness of offspring fitness to altered levels of maternal stress in freshwater turtles.

Development of behavioural profile in the Northern common boa (Boa imperator): Repeatable independent traits or personality?

Recent studies of animal personality have focused on its proximate causation and ecological and evolutionary significance in particular, but the question of its development was largely overlooked. The attributes of personality are defined as between-individual differences in behaviour, which are consistent over time (differential consistency) and contexts (contextual generality) and both can be affected by development. We assessed several candidates for personality variables measured in various tests with different contexts over several life-stages (juveniles, older juveniles, subadults and adults) in the Northern common boa. Variables describing foraging/feeding decision and some of the defensive behaviours expressed as individual average values are highly repeatable and consistent. We found two main personality axes-one associated with foraging/feeding and the speed of decision, the other reflecting agonistic behaviour. Intensity of behaviour in the feeding context changes during development, but the level of agonistic behaviour remains the same. The juveniles and adults have a similar personality structure, but there is a period of structural change of behaviour during the second year of life (subadults). These results require a new theoretical model to explain the selection pressures resulting in this developmental pattern of personality. We also studied the proximate factors and their relationship to behavioural characteristics. Physiological parameters (heart and breath rate stress response) measured in adults clustered with variables concerning the agonistic behavioural profile, while no relationship between the juvenile/adult body size and personality concerning feeding/foraging and the agonistic behavioural profile was found. Our study suggests that it is important for studies of personality development to focus on both the structural and differential consistency, because even though behaviour is differentially consistent, the structure can change.

Seasonal shifts in sex ratios are mediated by maternal effects and fluctuating incubation temperatures

Sex-specific maternal effects can be adaptive sources of phenotypic plasticity. Reptiles with temperature-dependent sex determination (TSD) are a powerful system to investigate such maternal effects because offspring phenotype, including sex, can be sensitive to maternal influences such as oestrogens and incubation temperatures.In red-eared slider turtles (Trachemys scripta), concentrations of maternally derived oestrogens and incubation temperatures increase across the nesting season; we wanted to determine if sex ratios shift in a seasonally concordant manner, creating the potential for sex-specific maternal effects, and to define the sex ratio reaction norms under fluctuating temperatures across the nesting season.Eggs from early and late season clutches were incubated under a range of thermally fluctuating temperatures, maternally derived oestradiol concentrations were quantified via radioimmunoassay, and hatchling sex was identified. We found that late season eggs had higher maternal oestrogen concentrations and were more likely to produce female hatchlings. The sex ratio reaction norm curves systematically varied with season, such that with even a slight increase in temperature (0.5°C), late season eggs produced up to 49% more females than early season eggs.We found a seasonal shift in sex ratios which creates the potential for sex-specific phenotypic matches across the nesting season driven by maternal effects. We also describe, for the first time, systematic variation in the sex ratio reaction norm curve within a single population in a species with TSD.

The effect of environmental temperature on reptilian peripheral blood B cell functions

Recent studies have identified phagocytic B cells in a variety of species, yet little is understood about their function and how it is influenced by natural environmental variation, such as temperature. Phagocytic B-cells are present in red-eared slider turtles, Trachemys scripta, and the wide range of temperatures experienced by these ectotherms may have an effect on immunity, including B cell antibody secretion and phagocytosis. We examined the impact of environmental temperature on B cell function in vitro using phagocytic and ELISpot assays conducted at biologically relevant temperatures. We found a significant effect of temperature on antibody secretion, with maximal antibody secretion occurring at intermediate temperatures (estimated maximum of 28.8°C). There was no effect of temperature on phagocytosis. We also noted a difference in the efficiency of phagocytosis in this assay between B cells and non-B cells. Interestingly, in our in vitro assay, phagocytic B cells engulfed more foreign fluorescent beads per cell than phagocytes lacking surface immunoglobulin. This work sheds light on our understanding of phagocytic B cells and the importance of environmental temperature on the behavior of reptilian immune cells, which may have relevance for organismal fitness.

Stress response to handling is short lived but may reflect personalities in a wild, Critically Endangered tortoise species

We investigated the acute stress response associated with animal personalities by measuring plasma glucocorticoids throughout handling and collected ~2 years of movement and behavioural data in a wild, Critically Endangered animal, Astrochelys radiata (radiated tortoise). To determine whether our standard, brief conscientious handling procedures induce a stress response in our target species, we applied a stressor by way of initial animal processing and deployment of telemetry equipment. During surveys and processing, we sampled animals immediately upon detection, again after completing transmitter attachment and processing, and a final time the following day. We then used radiotelemetry to follow a subset of the animals for 22 months while collecting behavioural, climatic and location data. We found that brief and conscientious handling did not illicit consistent changes in plasma concentrations of the stress hormone corticosterone (CORT) but did reveal tremendous individual variation in response. The CORT concentration ranged more than 200-fold after imposing the stressor and returned to near-baseline values by the following day. When we accounted for the wide variation by calculating the degree of each individual's stress response relative to its baseline over its processing time, we discovered two non-overlapping physiological response types; those in which CORT concentrations increased dramatically in response to handling (219 ± 89.8 pg/ml/min) and those in which CORT varied only slightly (5.3 ± 8.9 pg/ml/min). The response types (strong vs. mild) also predicted body condition, home range size, activity, and behavioural tendencies. The degree of the individual's stress response in this species may be one component of correlated physiological and behavioural traits (animal personalities), which have previously been obscured in other chelonian studies by the use of mean values and should be considered in future conservation management applications for chelonian species.

Neuroendocrine disruption of organizational and activational hormone programming in poikilothermic vertebrates

In vertebrates, sexual differentiation of the reproductive system and brain is tightly orchestrated by organizational and activational effects of endogenous hormones. In mammals and birds, the organizational period is typified by a surge of sex hormones during differentiation of specific neural circuits; whereas activational effects are dependent upon later increases in these same hormones at sexual maturation. Depending on the reproductive organ or brain region, initial programming events may be modulated by androgens or require conversion of androgens to estrogens. The prevailing notion based upon findings in mammalian models is that male brain is sculpted to undergo masculinization and defeminization. In absence of these responses, the female brain develops. While timing of organizational and activational events vary across taxa, there are shared features. Further, exposure of different animal models to environmental chemicals such as xenoestrogens such as bisphenol A-BPA and ethinylestradiol-EE2, gestagens, and thyroid hormone disruptors, broadly classified as neuroendocrine disrupting chemicals (NED), during these critical periods may result in similar alterations in brain structure, function, and consequently, behaviors. Organizational effects of neuroendocrine systems in mammals and birds appear to be permanent, whereas teleost fish neuroendocrine systems exhibit plasticity. While there are fewer NED studies in amphibians and reptiles, data suggest that NED disrupt normal organizational-activational effects of endogenous hormones, although it remains to be determined if these disturbances are reversible. The aim of this review is to examine how various environmental chemicals may interrupt normal organizational and activational events in poikilothermic vertebrates. By altering such processes, these chemicals may affect reproductive health of an animal and result in compromised populations and ecosystem-level effects.

Effects of developmental exposure to bisphenol A and ethinyl estradiol on spatial navigational learning and memory in painted turtles (Chrysemys picta)

Developmental exposure of turtles and other reptiles to endocrine disrupting chemicals (EDCs), including bisphenol A (BPA) and ethinyl estradiol (EE2, estrogen present in birth control pills), can induce partial to full gonadal sex-reversal in males. No prior studies have considered whether in ovo exposure to EDCs disrupts normal brain sexual differentiation. Yet, rodent model studies indicate early exposure to these chemicals disturbs sexually selected behavioral traits, including spatial navigational learning and memory. Thus, we sought to determine whether developmental exposure of painted turtles (Chrysemys picta) to BPA and EE2 results in sex-dependent behavioral changes. At developmental stage 17, turtles incubated at 26⁰C (male-inducing temperature) were treated with 1) BPA High (100μg /mL), 2) BPA Low (0.01μg/mL), 3) EE2 (0.2μg/mL), or 4) vehicle or no vehicle control groups. Five months after hatching, turtles were tested with a spatial navigational test that included four food containers, only one of which was baited with food. Each turtle was randomly assigned one container that did not change over the trial period. Each individual was tested for 14 consecutive days. Results show developmental exposure to BPA High and EE2 improved spatial navigational learning and memory, as evidenced by increased number of times spent in the correct target zone and greater likelihood of solving the maze compared to control turtles. This study is the first to show that in addition to overriding temperature sex determination (TSD) of the male gonad, these EDCs may induce sex-dependent behavioral changes in turtles.

Temperature experienced during incubation affects antioxidant capacity but not oxidative damage in hatchling red-eared slider turtles (Trachemys scripta elegans)

Our understanding of how oxidative stress resistance phenotypes are affected by the developmental environment is limited. One component of the developmental environment, which is likely central to early life oxidative stress among ectothermic and oviparous species, is that of temperature. We investigated how incubation temperature manipulations affect oxidative damage and total antioxidant capacity (TAC) in red-eared slider turtle (Trachemys scripta elegans) hatchlings. First, to determine if temperature fluctuations elicit oxidative stress, eggs from clutches were randomly assigned to either a constant (29.5°C) or daily fluctuating temperature incubation (28.7±3°C) treatment. Second, to assess the effect of temperature fluctuation frequency on oxidative stress, eggs were incubated in one of three fluctuating incubation regimes; 28.7±3°C fluctuations every 12 (Hyper), 24 (Normal), or 48 hours (Hypo). Third, we tested the influence of average incubation temperature by incubating eggs in a daily fluctuating incubation temperature regime with a mean temperature of 26.5°C (Low), 27.1°C (Medium), or 27.7°C (High). Although the accumulation of oxidative damage in hatchlings was unaffected by any thermal manipulation, TAC was affected by both temperature fluctuation frequency and average incubation temperature. Individuals incubated with a low frequency of temperature fluctuations had reduced TAC, while incubation at a lower average temperature was associated with enhanced TAC. These results indicate that while sufficient to prevent oxidative damage, TAC is influenced by developmental thermal environments, potentially due to temperature mediated changes in metabolic rate. The observed differences in TAC may have important future consequences for hatchling fitness and overwinter survival.