Adrenal activity in the female lizard Lacerta vivipara jacquin associated with breeding activities

In your CORT: Corticosterone and its receptors in the brain underlie mate choosiness in female Cope's gray treefrogs (Hyla chrysoscelis)

Selecting an attractive mate can involve trade-offs related to investment in sampling effort. Glucocorticoids like corticosterone (CORT) are involved in resolving energetic trade-offs. However, CORT is rarely studied in the context of mate choice, despite its elevated levels during reproductive readiness and the energetic transitions that characterize reproduction. Few systems are as well suited as anuran amphibians to evaluate how females resolve energetic trade-offs during mate choice. Phonotaxis tests provide a robust bioassay of mate choice that permit the precise measurement of inter-individual variation in traits such as choosiness-the willingness to pursue the most attractive mate despite costs. In Cope's gray treefrogs (Hyla chrysoscelis), females exhibit remarkable variation in circulating CORT as well as choosiness during mate choice, and a moderate dose of exogenous CORT rapidly (<1 h) and reliably induce large increases in choosiness. Here we measured the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors in the brains of females previously treated with exogenous CORT and tested for mate choosiness. We report a large decrease in GR expression in the hindbrain and midbrain of females that were treated with the moderate dosage of CORT-the same treatment group that exhibited a dramatic increase in choosiness following CORT treatment. This association, however, does not appear to be causal, as only forebrain GR levels, which are not affected by CORT injection, are positively associated with variation in choosiness. No strong effects were found for MR. We discuss these findings and suggest future studies to test the influence of glucocorticoids on mate choice.

Fecal adrenal hormone patterns during ovulatory and non-ovulatory reproductive cycles in female veiled chameleons (Chamaeleo calyptratus)

The relationship between the reproductive (hypothalamic-pituitary-gonadal; HPG) and adrenal (hypothalamic-pituitary-adrenal; HPA) hormone axes is complex and can vary depending on the species and environmental factors affecting an individual. In an effort to understand this relationship in female veiled chameleons (Chamaeleo calyptratus), the patterns of fecal metabolites of corticosterone (C), estradiol (E), testosterone (T), and progesterone (P) were analyzed by enzyme immunoassay (EIA) during ovulatory (OC; eggs laid) and non-ovulatory cycles (NOC; no eggs laid). Glucocorticoid (GC) metabolites in the fecal extracts were characterized by HPLC and corticosterone EIA performance was assessed by parallelism, accuracy and precision tests. The results indicated that the assay chosen reliably measured the hormone metabolites present in the fecal extracts. Regular, cyclical hormone metabolite patterns consisting of an E peak followed by peaks of T, P and C in close succession were observed during both ovulatory and non-ovulatory cycles; relative levels of P and C, however, were higher during ovulatory cycles. Corticosterone metabolite levels, in particular, increased throughout vitellogenesis and peaked in late vitellogenesis (in non-ovulatory cycles) or around the time of ovulation, and remained elevated throughout the gravid period, falling just prior to oviposition. The results provide evidence of variation in glucocorticoid production throughout different stages of the reproductive cycle, including a role in the ovulatory process; the physiology, however, remains unclear.

Moderately elevated glucocorticoids increase mate choosiness but do not affect sexual proceptivity or preferences in female gray treefrogs

Glucocorticoids (GCs) are rarely studied in the context of female mate choice, despite the expression of receptors for these products in sexual, sensory and decision-making brain areas. Here we investigated the effects of GC concentrations on three aspects of female sexual behavior in breeding Cope's gray treefrogs (Hyla chrysoscelis): proceptivity-a measure of sexual motivation, intraspecific mate preferences, and mate choosiness. To our knowledge this is the first experimental study on the endocrine basis of mate choosiness. We predicted that mate choosiness-forfeiting an initial mate preference to pursue a suddenly more attractive mate-would be particularly impacted by elevated GCs with moderate GC levels associated with greater choosiness. We found support for this predicted inverted-U relationship. Females in the control group (no injection) showed no change in choosiness across timepoints. In contrast, females in the vehicle, Low (20 ng g^-1) and High (180 ng g^-1) corticosterone groups exhibited a nominal decline in choosiness after injection, suggesting that the experience of injection has little or perhaps slightly suppressive effects on female choosiness. Females in the moderate dose group (60 ng g^-1), however, exhibited a significant increase (>100%) in choosiness. Further, we found no effect of elevated GCs on sexual proceptivity or the species-typical preference for longer calls. These findings may reflect a buffering of primary sensory areas in the brain against elevated GCs. The recruitment of other cognitive processes during active decision-making, however, may facilitate GC modulation of mate choosiness, thereby promoting tactical plasticity at this critical life history juncture.

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.

Does the conceptus of the viviparous lizard Barisia imbricata imbricata participates in the regulation of progesterone production and the control of luteolysis?

It is generally accepted that progesterone is necessary to maintain gestation; however, the mechanisms that control the production of this steroid remain unknown. The corpus luteum has been assigned a central role in the maintenance of gestation based on its capacity to produce progesterone. A pseudopregnancy model was performed in a viviparous lizard, Barisia imbricata imbricata, to determine whether the absence of embryos would affect the pattern of progesterone production or the corpus luteum histology. Blood samples were obtained prior to ovulation and at 8, 16, and 24 weeks after ovulation (pseudopregnant and pregnant lizards), as well as one day after parturition (pregnant lizards) or 32 weeks after ovulation (pseudopregnant lizards). The corpus luteum was surgically removed one day after blood samples were obtained. Blood aliquots from nongravid females were obtained at similar timepoints. We found a significant reduction in plasma progesterone concentrations at 24 and 32 weeks post-ovulation in pseudopregnant lizards compared with those observed at similar times in intact pregnant lizards, whereas the progesterone levels in non-gestant lizards remained significantly lower than in either pseudopregnant or pregnant lizards. Moreover, we observed that the histological appearance of the corpus luteum from pseudogestational females (obtained 24 and 32 weeks post-ovulation) differed from the corpora lutea from lizards in late gestation and intact parturient lizards. These observations suggest that the conceptus participates in the regulation of progesterone production in late gestation and also in luteolysis control.

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.

Effects of food restriction on steroidogenesis in dispersed adrenocortical cells from Yarrow's Spiny Lizard (Sceloporus jarrovii)

Changes in energy balance can lead to functional alterations at all levels of the hypothalamic-pituitary-adrenal (HPA) axis. However, relatively little is known about how energy balance affects functional properties of adrenocortical cells themselves. We investigated effects of restricted food intake on sensitivity to ACTH and rates of steroidogenesis in adrenocortical cells isolated from growing female and male Yarrow's Spiny Lizards (Sceloporus jarrovii). At the end of the feeding regimen, we assayed acute (3h) progesterone (P(4)), corticosterone (B), and aldosterone (ALDO) production in response to ACTH in dispersed adrenocortical cells. Food restriction depressed growth rate by about 50% in both males and females but did not alter baseline plasma B measured at 10 weeks in either sex. At the cellular level, food restriction had the following effects: (1) increased basal B production in both sexes and basal ALDO production in males, (2) increased net maximal rates of production of P(4), B, and ALDO in response to ACTH, and (3) no overall effect on adrenocortical cellular sensitivity to ACTH. There were modest sex differences: overall rates of P(4) production were 46% greater in cells from females than from males, and in response to food restriction, the net maximal rate of ALDO production was 50% greater in cells from males than from females. Our results demonstrate that food restriction in S. jarrovii increases adrenocortical cellular rates of steroid production without affecting overall cellular sensitivity to ACTH.

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.

Diurnal and nocturnal differences in hypothalamic-pituitary-adrenal axis function in Galápagos marine iguanas

Temporal modulation of the stress response is a ubiquitous characteristic of animals. Here, we investigate possible mechanisms underlying daily changes in corticosterone release in an ectotherm model system. Earlier work indicated that free-living Galápagos marine iguanas (Amblyrhynchus cristatus) have lower corticosterone concentrations during the night than during the day. This could result from: (i) a lower circadian secretion of adrenocorticotropic hormone (ACTH) as seen in mammals; (ii) from an increase in corticosterone negative feedback; or (iii) reflect lower metabolic activity during the night when core body temperature falls (from 35 degrees C during the day to as low as 21 degrees C during the night). To begin to distinguish between these three possibilities, exogenous ACTH was used to compare diel differences in adrenocortical tissue responsiveness, and dexamethasone was used to compare diel differences in the efficacy of corticosterone negative feedback. Low levels of exogenous ACTH (30 IU/kg body weight) potently stimulated both daytime and nighttime corticosterone release. Dexamethasone (1 mg/kg) inhibited only daytime, but not nighttime endogenous corticosterone release. Because the response to ACTH was similar between day and night we suggest that a simple lowering of core body temperature cannot explain the nighttime reduction in corticosterone release. However, the failure of negative feedback at night suggests that the response is not equivalent to the controlled downregulation seen in mammals.

Steroid hormones and aggression in female Galápagos marine iguanas

We studied steroid hormone patterns and aggression during breeding in female Galápagos marine iguanas (Amblyrhynchus cristatus). Females display vigorously towards courting males after copulating (female-male aggression), as well as fight for and defend nest sites against other females (female-female aggression). To understand the neuroendocrine basis of this aggressive behavior, we examined changes in testosterone (T), estradiol (E2), corticosterone (CORT), and progesterone (P4) during the mating and nesting periods, and then measured levels in nesting females captured during aggressive interactions. Testosterone reached maximal levels during the mating stage when female-male aggression was most common, and increased slightly, but significantly, during the nesting stage when female-female aggression was most common. However, fighting females had significantly lower T, but higher E2 and P4, than non-fighting females. It remains unclear whether these changes in hormone levels during aggressive interactions are a cause or a consequence of a change in behavior. Our results support the "challenge hypothesis", but suggest that E2 and/or P4 may increase in response to aggressive challenges in females just as T does in males. Females may be rapidly aromatizing T to elevate circulating levels of E2 during aggressive interactions. This hypothesis could explain why non-fighting females had slightly elevated baseline T, but extremely low E2, during stages when aggressive interactions were most common. Although P4 increased rapidly during aggressive encounters, it is unclear whether it acts directly to affect behavior, or indirectly via conversion to E2. The rapid production and conversion of E2 and P4 may be an important mechanism underlying female aggression in vertebrates.

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.

Seasonal steroid hormone levels and their relation to reproduction in the Western Diamond-backed Rattlesnake, Crotalus atrox (Serpentes: Viperidae)

We report seasonal variation in steroid hormone levels in blood samples from free-ranging Western Diamond-backed Rattlesnakes (Crotalus atrox), and the relationship between these hormones and events in the reproductive cycle. At a field site in the Sonoran Desert of south-central Arizona, we collected monthly blood samples over the course of two active seasons from 17 radiotelemetered females, and over three active seasons from 103 randomly encountered males. We used radioimmunoassay to measure plasma levels of 17beta-estradiol, progesterone, corticosterone, and testosterone in samples from females, and corticosterone and testosterone in samples from males. Non-reproductive females have consistently low levels of circulating 17beta-estradiol, progesterone, and testosterone throughout the year. In reproductive females, 17beta-estradiol levels increase dramatically and testosterone levels increase modestly during vitellogenesis in April and May, while progesterone levels increase dramatically at ovulation in June and then steadily decline until parturition in August. Corticosterone levels appear relatively constant in non-reproductive females, whereas reproductive females show increased levels at the end of gestation. Plasma testosterone levels in males are low in early summer and are elevated during spring and late summer, corresponding to the two mating periods of C. atrox. Plasma corticosterone levels in males did not vary seasonally and were not related to testosterone levels.

Maternal Effects on Offspring Locomotion: Influence of Density and Corticosterone Elevation in the Lizard Lacerta vivipara

Offspring phenotype can be affected by maternal history before and during gestation. Offspring sensitivity to maternal conditions is believed to have evolved to favor preadaptation of offspring to environmental factors they are likely to encounter. Because the locomotor capacity of an individual is likely to have important fitness consequences, we examined the role of long-term and short-term prenatal conditions on offspring's locomotor performance in the lizard Lacerta vivipara. To examine long-term prenatal effects, we manipulated the density of two populations, leaving two additional populations as unmanipulated. We then collected pregnant females within these four populations (Cévennes, Massif Central, France) and kept them in the laboratory until parturition. To examine short-term prenatal effects, we manipulated the corticosterone level of half the females within each population. We took two different measurements of offspring locomotion: sprint speed and endurance. As already documented, sprint speed was positively correlated with offspring body size. Although population density significantly affected female fecundity, neither the density manipulation nor the population of origin influenced offspring phenotype. Corticosterone administered during gestation decreased juvenile sprint speed but did not affect juvenile endurance. Furthermore, we observed that the motivation to run was influenced by maternal hormonal treatment. Juveniles born from corticosterone-treated mothers needed more stimuli than those born from control mothers. We conclude, therefore, that the action of corticosterone on sprint speed could be more behavioral than physiological. Offspring phenotype as measured by endurance and sprint speed appeared partly under maternal control.

Protecting embryos from stress: corticosterone effects and the corticosterone response to capture and confinement during pregnancy in a live-bearing lizard (Hoplodactylus maculatus)

Hormones in the embryonic environment, including those of the hypothalamo-pituitary-adrenal (HPA) axis, have profound effects on development in eutherian mammals. However, little is known about their effects in reptiles that have independently evolved viviparity. We investigated whether exogenous corticosterone affected embryonic development in the viviparous gecko Hoplodactylus maculatus, and whether pregnant geckos have a corticosterone response to capture and confinement that is suppressed relative to that in non-pregnant (vitellogenic) females and males. Corticosterone implants (5 mg, slow-release) administered to females in mid-pregnancy caused a large elevation of corticosterone in maternal plasma (P<0.001), probable reductions in embryonic growth and development (P=0.069-0.073), developmental abnormalities and eventual abortions. Cool temperature produced similar reductions in embryonic growth and development (P< or =0.036 cf. warm controls), but pregnancies were eventually successful. Despite the potentially harmful effects of elevated plasma corticosterone, pregnant females did not suppress their corticosterone response to capture and confinement relative to vitellogenic females, and both groups of females had higher responses than males. Future research should address whether lower maternal doses of corticosterone produce non-lethal effects on development that could contribute to phenotypic plasticity. Corticosterone implants also led to increased basking in pregnant females (P<0.001), and basal corticosterone in wild geckos (independent of reproductive condition) was positively correlated with body temperature (P<0.001). Interactions between temperature and corticosterone may have broad significance to other terrestrial ectotherms, and body temperature should be considered as a variable influencing plasma corticosterone concentrations in all future studies on reptiles.

Stress and body condition as prenatal and postnatal determinants of dispersal in the common lizard (Lacerta vivipara)

Dispersal is a complex phenomenon affected by multiple factors. Among the factors that influence dispersal in the common lizard (Lacerta vivipara), poor maternal body condition and stress are known to decrease dispersal propensity of juveniles. But the effect of individual factors on dispersal could change when several of them act concurrently or at different developmental stages. Prenatal factors can affect clutch and/or juvenile characteristics that later affect dispersal. Postnatal influences are mainly exerted on juvenile dispersal behavior. We investigated the role of body condition and stress on dispersal at a prenatal and a postnatal stage. Stress was mimicked by experimentally increasing corticosterone levels in pregnant females and recently born juveniles. We considered (1). the influence of maternal body condition and prenatal corticosterone treatment on clutch, juvenile characteristics and on dispersal behavior and (2). the influence of juvenile body condition and postnatal corticosterone treatment on juvenile dispersal behavior. There was an interaction between maternal condition and prenatal corticosterone treatment on juvenile dispersal. Dispersal decreased with maternal corticosterone increase only in juveniles from the more corpulent females, while it increased with juvenile body condition. Good maternal body condition affected clutch and juvenile characteristics favoring dispersal, while elevation of corticosterone level (stress) exerted the opposite effect. Juvenile body condition favored dispersal, while there was no effect of postnatal corticosterone treatment on juvenile dispersal propensity.

Induction of parturition in snow skinks: can low temperatures inhibit the actions of AVT?

The influence of environmental factors on the timing of parturition has not been investigated in viviparous squamates. We investigated the interaction between temperature and parturition in two viviparous skink species, the southern snow skink (Niveoscincus microlepidotus) and the metallic skink (N. metallicus). In these species, the timing of parturition is separated from the completion of embryonic development; the delay is attributed to their cool and variable habitats. We examined whether the neurohypophyseal hormone arginine vasotocin (AVT) stimulated parturition in southern snow skinks with late stage embryos in autumn (approximately 6-7 months prior to parturition) and in metallic skinks with late stage embryos in summer (approximately 2-3 weeks prior to parturition). The experiments were conducted at a range of environmentally relevant temperatures (6 degrees C, 15 degrees C, 22 degrees C, and 28 degrees C). AVT induced parturition in both species at all temperatures; time until birth, however, occurred more quickly at warmer temperatures (22 degrees and 28 degrees C), whereas cooler temperatures delayed parturition. We hypothesize that if cool temperatures are preventing parturition, then temperature must act at some level within the brain to prevent or slow the secretion of AVT. Future experiments will need to determine how temperature influences AVT production. Further research is also required to determine how the timing of parturition is influenced by interactions between temperature, photoperiod, and seasonal hormone patterns.

Seasonal changes in plasma glucocorticoid concentrations in free-living vertebrates

The vertebrate stress response helps animals respond to environmental dangers such as predators or storms. An important component of the stress response is glucocorticoid (GC) release, resulting from activation of the hypothalamic-pituitary-adrenal axis. After release, GCs induce a variety of behavioral and physiological changes that presumably help the animal respond appropriately to the situation. Consequently, GC secretion is often considered an obligatory response to stressful situations. Evidence now indicates, however, that free-living species from many taxa can seasonally modulate GC release. In other words, the magnitudes of both unstressed and stressed GC concentrations change depending upon the time of year. This review examines the growing evidence that GC concentrations in free-living reptiles, amphibians, and birds, but not mammals, are commonly elevated during the breeding season. This evidence is then used to test three hypotheses with different focuses on GC's energetic or behavioral effects, as well as on GC's role in preparing the animal for subsequent stressors. These hypotheses attempt to place annual GC rhythms into a physiological or behavioral context. Integrating seasonal differences in GC concentrations with either different physiological states or different life history stages provides clues to a new understanding of how GCs actually help in survival during stress. Consequently, understanding seasonal modulation of GC release has far-reaching importance for both the physiology of the stress response and the short-term survival of individual animals.

Influence of corticosterone on FSH-induced ovarian recrudescence in the lizard Mabuya carinata

Administration of bovine FSH (10 IU/lizard/alternate day for 30 days) in the postbreeding quiescent phase of the ovarian cycle caused a significant increase in the mean number of oogonia and oocytes, the relative weight of the oviduct, and the liver and serum estradiol levels compared to those of controls. In addition, the FSH-treated lizards showed a vitellogenic growth of follicles and development through to preovulatory follicles. However, the administration of corticosterone simultaneously with FSH (10 IU FSH + 40 microgram corticosterone/lizard/alternate day for 30 days) did not result in these changes and the ovaries resembled those of controls. The results indicate the absence of ovarian refractoriness to gonadotropic stimulation during the quiescent phase of the reproductive cycle and inhibition of FSH-induced ovarian recrudescence by corticosterone. It is suggested that corticosterone treatment reduces FSH-induced steroidogenic activity of the ovary, leads to impairment in vitellogenin secretion by the liver, and results as well in the failure of vitellogenic follicular growth in Mabuya carinata.

The reproductive cycle of the female American alligator (Alligator mississippiensis)

We examined ovarian and oviducal gross morphology and collected blood samples from wild female alligators in central Florida during most of the year. Females with vitellogenic follicles were observed throughout the year, although ovaries containing follicles larger than 15 mm were seen only during the spring and early summer (March-June). We detected a poor relationship between female body size and the number of vitellogenic follicles whereas body size was significantly correlated with clutch size. Plasma samples were analyzed for (1) estradiol-17beta (E2), testosterone (T), and corticosterone by specific radioimmunoassays; (2) vitellogenin by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis; and (3) total protein, phosphorus, and calcium by spectrophotometric assays. Reproductively active females showed elevated plasma concentrations of E2 during the fall (September-November) and spring (March-May) whereas non-reproductively active females exhibited basal levels with no apparent peaks. Vitellogenin was detected in the plasma during the same months that plasma E2 concentrations were elevated. Elevated plasma vitellogenin and E2 were not correlated with plasma total protein but were correlated with plasma calcium concentration. During late vitellogenesis, plasma T concentrations were elevated in reproductively active females coincident with a period of intense courtship and mating. Corticosterone plasma concentrations exhibit no significant monthly variation, nor apparent changes during various stages of reproductive activity although plasma concentrations were elevated during late gravidity. Our data suggest that female reproductive activity begins in the fall with an increase in plasma E2 concentration in September or October and vitellogenesis in October. Ovarian activity slows during winter and reactivates with the onset of spring.

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: I. Seasonal variation in the field

In order to document sex differences in adrenal function and how this relates to gonadal function during the period of seasonal activity, blood samples from male and female six-lined racerunners, Cnemidophorus sexlineatus, were taken immediately after capture in the field for determination of plasma corticosterone and gonadal steroid concentrations. Plasma testosterone and dihydrotestosterone levels for males, and 17 beta-estradiol and progesterone levels for females, were measured. Trends in the concentration of plasma corticosterone differed significantly between males and females. In males the highest concentrations of corticosterone were measured in late spring and the lowest concentrations were measured in late summer. Whereas half of the variation in corticosterone levels among males could be explained as seasonal change, less than 1% of the variation among females could be explained as seasonal change. In males plasma corticosterone and androgens exhibited similar seasonal decreases. Corticosterone levels for females were not correlated with progesterone or 17 beta-estradiol levels. Sex differences in seasonal variation in plasma corticosterone concentrations suggest that corticosterone may be involved in the different reproductive strategies and energy requirements of males and females during the seasonal period of activity.

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory

Circulating concentrations of plasma corticosterone and gonadal steroids were measured in intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season.

In vitro uterine contractions in the viviparous lizard Tiliqua rugosa: effects of gestation and steroid pretreatment in vivo

Uterine contractility was investigated in the viviparous lizard Tiliqua rugosa. Arginine vasotocin (AVT) induces rhythmic contractions in vitro in strips of uterine tissue from ovariectomized female T. rugosa. The strength of these contractions was related to the dosage of AVT and reduced by pretreatment in vivo with both progesterone and estradiol-17 beta. The frequency of spontaneous and AVT-induced contractions was enhanced by estradiol-17 beta pretreatment. The strength of AVT-induced contractions in pregnant females was not significantly different from that recorded in nonpregnant females. Spontaneous rhythmic contractions were present only in pregnant females. Ovariectomy did not affect either spontaneous or AVT-induced contractions in pregnant females. The data indicate that ovarian steroids modulate uterine contractility in T. rugosa. It is suggested that, following a decline in plasma progesterone levels, estrogen may be involved in the onset of parturition.