Role of the adrenal gland in early post-hatching differentiation of alternative male phenotypes in the tree lezard (Urosaurus ornatus)

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.

Sex steroid binding proteins in the plasma of hatchling Chelonia mydas

Sex steroid binding proteins were identified in hatchling female and male Chelonia mydas by dialysis and steady-state gel electrophoresis when examined at 4 degrees C. A testosterone binding protein with high binding affinity (K (a) = 0.98 +/- 0.5 x 10(8) M(-1)) and low to moderate binding capacity (B (max) = 7.58 +/- 4.2 x 10(-5) M) was observed in male hatchlings. An oestradiol binding protein with high affinity (K (a) = 0.35 +/- 1.8 x 10(8) M(-1)) and low to moderate binding capacity (B (max) = 0.16 +/- 0.5 x 10(-4) M) was identified in female hatchlings. This study confirmed that sex steroid binding proteins (SSBPs) become inactivate in both sexes at 36 degrees C, the maximum body temperature of sea turtle hatchlings at emergence. The inactivation of SSBPs at this temperature indicates that sex steroid hormones circulate freely in the body of the green turtles and are biologically available in the blood plasma. This observation is consistent with female and male hatchling C. mydas having different physiological (hormonal) and developmental requirements around the time of emergence. Moreover, concurrently conducted competition studies showed that sex steroids including testosterone and oestradiol do compete for binding sites in both male and female C. mydas hatchling plasma. Competition also occurred between testosterone and dihydrotestosterone for binding sites in the male C. mydas plasma. However, competition studies in the plasma of female hatchling C. mydas demonstrate that oestrone does not compete with oestradiol for binding sites.

Developmental and geographic variation in stress hormones in wild Belding's ground squirrels (Spermophilus beldingi)

Extensive research has been conducted on the role of glucocorticoids in regulating growth, mobilizing energy, responding to stressors and modulating learning and memory. However, little is known about the production of corticoids during early development in free-living animals, particularly during sensitive periods of acquisition of important behaviors. In a four-year study of Belding's ground squirrels, Spermophilus beldingi, a non-invasive assay of glucocorticoids was used to quantify age and population differences among juveniles from three California locations. Fecal-cortisol metabolites are elevated during a short period when juveniles first emerge aboveground from their natal burrows at about 4 weeks of age. This period of cortisol elevation coincides with when young are learning survival behaviors such as anti-predator responses and foraging strategies. Population differences in juvenile cortisol levels, which may reflect local variation in habitat quality and predator environments, were not evident until 2 weeks after emergence. Elevated cortisol at the age of emergence was also observed in juveniles born and reared in captivity without exposure to typical stressors that occur around the age of emergence. These results indicate that corticoids are regulated during early development, and the possible functions of age-related corticoid levels are discussed, including mobilization of glucose for natal emergence and later facilitation of growth and energy storage during the short summer before hibernation. In some species, elevated corticoids can also facilitate learning and memory, and current work is exploring whether the higher cortisol observed in all three S. beldingi populations just after emergence function to promote rapid acquisition of survival behaviors.

Corticosterone stimulates hatching of late-term tree lizard embryos

The regulation of hatching in oviparous animals is important for successful reproduction and survival, but is poorly understood. We unexpectedly found that RU-486, a progesterone and glucocorticoid antagonist, interferes with hatching of viable tree lizard (Urosaurus ornatus) embryos in a dose-dependent manner and hypothesized that embryonic glucocorticoids regulate hatching. To test this hypothesis, we treated eggs with corticosterone (CORT) or vehicle on Day 30 (85%) of incubation, left other eggs untreated, and observed relative hatch order and hatch time. In one study, the CORT egg hatched first in 9 of 11 clutches. In a second study, the CORT egg hatched first in 9 of 12 clutches, before vehicle-treated eggs in 10 of 12 clutches, and before untreated eggs in 7 of 9 clutches. On average, CORT eggs hatched 18.2 h before vehicle-treated eggs and 11.6 h before untreated eggs. Thus, CORT accelerates hatching of near-term embryos and RU-486 appears to block this effect. CORT may mobilize energy substrates that fuel hatching and/or accelerate lung development, and may provide a mechanism by which stressed embryos escape environmental stressors.

Females competing to reproduce: dominance matters but testosterone may not

The associations among aggression, testosterone (T), and reproductive success have been well studied, particularly in male birds. In many species, males challenged with simulated or real territorial intrusions increase T and levels of aggression, outcomes linked to higher dominance status and greater reproductive success. For females, the patterns are less clear. Females behave aggressively towards one another, and in some species, females respond to a social challenge with increases in T, but in other species they do not. Prior work on female dark-eyed juncos (Junco hyemalis) had shown that experimental elevation of T increases social status and intrasexual aggression. Here, we conducted two experiments designed to answer three questions: Are endogenous concentrations of T associated with dominance status in captive female juncos? Does dominance status influence readiness to breed in female juncos? And do captive females increase T in response to a challenge? In the first experiment, we introduced two females to a breeding aviary, allowed them to form a dominance relationship and then introduced a male. We found that dominant females were more likely to breed than subordinates, but that dominance status was not predicted by circulating T. In the second experiment, we allowed a resident male and female to establish ownership of a breeding aviary (territory) then introduced a second, intruder female. We found that resident females were aggressive towards and dominant over intruders, but T did not increase during aggressive interactions. We suggest that during the breeding season, intrasexual aggression between females may influence reproductive success, but not be dependent upon fluctuations in T. Selection may have favored independence of aggression from T because high concentrations of T could interfere with normal ovulation or produce detrimental maternal effects.

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.

Historical contributions of research on reptiles to behavioral neuroendocrinology

Some of the first experiments in behavioral endocrinology in the 1930s were conducted with lizards, but events led to a hiatus that lasted for 30 years. In the 1960s, research resumed using techniques current at the time, but it was not until the mid-1970s that behavioral neuroendocrinology "discovered" reptiles as animal model systems. This historical review summarizes this period of work, illustrating an enormous increase in research that have led to conclusions such as (1) the phenomenon of dissociated reproductive strategies and hormone-independent behaviors, which have aided our understanding of how the "memory" of sex steroid actions is maintained. (2) Progesterone plays an important role in the organization and activation of sexual behavior in males. Progesterone also synergizes with T to control male courtship much as does estrogen and progesterone to control sexual receptivity in females. Thus, progesterone is as much a "male" hormone as it is a "female" hormone. (3) Use of cytochrome oxidase histochemistry to study the role of experience over the long term in modifying brain activity. (4) Hormone manipulations as a powerful tool to test hypotheses about the evolution of behavior in free-living animals.

Evolution of neuroendocrine mechanisms that regulate sexual behavior

Whiptail lizards provide a unique system to study evolution of brain mechanisms because both ancestral (sexual) and descendant (parthenogenetic) species exist. Parthenogenetic whiptails enable us to avoid the two major confounds in sex differences research - males and females that differ both genetically and hormonally. Parthenogens are females that reproduce clonally, yet display alternately female-like and male-like pseudosexual behavior. Thus, the neural circuitry underlying male and female sexual behavior can be examined within the 'same' brain (same genome), enabling us to see how neuroendocrine mechanisms controlling mounting behavior change. In ancestral males, testicular androgens control sexual behavior, whereas male-like pseudocopulatory behavior is controlled by ovarian progesterone in parthenogens, revealing that progesterone is important in regulating sexual behavior in male vertebrates, including mammals.

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.