Corticosterone Levels In Males Research Articles

Glucocorticoid levels are linked to lifetime reproductive success and survival of adult barn owls.

Glucocorticoid hormones, such as corticosterone, are crucial in regulating daily life metabolism and energy expenditure, as well as promoting short-term physiological and behavioural responses to unpredictable environmental challenges. Therefore, glucocorticoids are considered to mediate trade-offs between survival and reproduction. Relatively little is known about how selection has shaped glucocorticoid levels. We used 15years of capture-recapture and dead recovery data combined with 13years of corticosterone and breeding success data taken on breeding barn owls (Tyto alba) to investigate such trade-offs. We found that survival was positively correlated with stress-induced corticosterone levels in both sexes, whereas annual and lifetime reproductive success (i.e. the sum of young successfully fledged during the entire reproductive career) was positively correlated with both baseline and stress-induced corticosterone levels in females only. Our results suggest that, in the barn owl, the stress-induced corticosterone response is a good proxy for adult survival and lifetime reproductive success. However, selection pressure appears to act differently on corticosterone levels of males and females.

Developmental programming of the adrenocortical stress response by yolk testosterone depends on sex and life history stage.

Developmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus-pituitary-adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific and life history stage-dependent manner. Compared with controls, males from testosterone-treated eggs had higher baseline corticosterone levels, whereas females from testosterone-treated eggs showed prolonged stress-induced corticosterone secretion during the reproductive but not the non-reproductive phase. Adult RMR was unaffected by in ovo testosterone treatment but correlated with integrated corticosterone stress secretion levels. We conclude that exposure of the embryo to testosterone programs the hypothalamus-pituitary-adrenal axis in a sex-specific manner that in females depends, in expression, on reproductive state. The modified baseline corticosterone levels in males and stress-induced corticosterone levels in females may explain some of the long-lasting effects of maternal testosterone in the egg on behavior and could be linked to previously observed reduced mortality of testosterone-treated females.

Anesthesia with sevoflurane in neonatal rats: Developmental neuroendocrine abnormalities and alleviating effects of the corticosteroid and Cl− importer antagonists

Background1.5 million children under 12 months of age are exposed to general anesthesia annually in the United States alone. Human and especially animal studies provide evidence that exposure to general anesthesia during the early postnatal period may lead to long-term neurocognitive abnormalities via poorly understood mechanisms. We investigated whether an immature stress response system and γ-aminobutyric acid (GABA) type A receptor activities are involved in mediating these abnormalities. MethodsSprague–Dawley rats at postnatal days 4, 5 or 6 were anesthetized with 2.1% sevoflurane for 6h; maternally separated and house reared rats served as controls. ResultsSevoflurane anesthesia markedly increased corticosterone levels in rat pups of both genders. In adulthood, these rats responded to stress with heightened secretion of corticosterone and a greater increase in corticosterone levels in males versus females. Only male rats, previously exposed to neonatal sevoflurane, had a higher frequency of miniature inhibitory postsynaptic currents in CA1 neurons, spent a shorter time in open arms of the elevated plus maze (EPM) and exhibited impaired prepulse inhibition (PPI) of startle. Pretreatment of male rats prior to sevoflurane with the Na+-K+-2Cl− cotransporter inhibitor, bumetanide, or the mineralocorticoid receptor antagonist, RU28318, normalized endocrine responses to stress and the EPM behavior in adulthood, while only those pretreated with bumetanide exhibited normalized PPI of startle responses. Neither bumetanide nor RU28318 altered the effect of sevoflurane on synaptic activity. ConclusionsSevoflurane-enhanced neuronal excitation and elevated corticosteroid levels at the time of anesthesia contribute to the mechanisms initiating neonatal sevoflurane-induced long-term endocrine and neurobehavioral abnormalities.

Early social deprivation impairs pair bonding and alters serum corticosterone and the NAcc dopamine system in mandarin voles

Early life stress has a long-term negative impact on emotion, learning, memory and adult sexual behavior, and these deficits most likely impair pair bonding. Here, we investigated whether early social deprivation (ED) affects the formation of pair bonds in socially monogamous mandarin voles (Microtus mandarinus). In a partner preference test (PPT), ED-reared adult females and males did not show a preference for their partner, spent more time exploring the cage of an unfamiliar animal and directed high levels of aggression toward unfamiliar animals. In social interaction test, ED increased exploring behavior only in females, but increased movement around the partner and reduced inactivity in both males and females. Three days of cohabitation did not alter serum corticosterone levels in ED-reared males, but increased corticosterone levels in males that received bi-parental care (PC). Interestingly, serum corticosterone levels in ED- and PC-reared females declined after cohabitation. ED significantly increased basal serum corticosterone levels in males, but had no effect on females. ED significantly up-regulated the levels of dopamine and the mRNA expression of dopamine 1-type receptor (D1R) in the nucleus accumbens (NAcc) in females and males. ED suppressed dopamine 2-type receptor mRNA (D2R) expression in females, but increased this in males. After three days of cohabitation, levels of D1R mRNA and D2R mRNA expression changed in opposite directions in PC-reared voles, but in the same direction in ED-reared males, and only the expression of D2R mRNA increased in ED-reared females. Our results indicate that early social deprivation inhibits pair bonding at adulthood. This inhibition is possibly associated with sex-specific alterations in serum corticosterone, levels of dopamine and mRNA expression of two types of dopamine receptors in the NAcc.

Corticosterone and brood abandonment in a passerine bird

Hormones regulate decision-making strategies, in particular by translating an individual's physiological state into decisions on major behavioural and life-history processes, such as reproduction. Corticosterone, a glucocorticoid hormone, has been gaining attention as a mediator of reproductive effort, and experimentally elevated corticosterone concentrations have been shown to disrupt reproduction in avian species. Here, we tested whether individual variation in corticosterone concentrations is related to the decision for brood abandonment in free-living great tits, Parus major. Because of harsh environmental conditions, many adults abandoned their first broods in 2010, enabling us to ask which physiological, environmental and individual characteristics increased the probability of nest desertion by both males and females. The best predictors of nest desertion were high stress-induced corticosterone levels in males and low average nestling mass. Furthermore, high stress-induced corticosterone levels in 2010 appeared to represent plastic responses to environmental conditions and reproductive investment: individual males that abandoned their nests in 2010 had higher stress-induced corticosterone concentrations and produced nestlings with lower average mass than in 2009, when nesting successfully. Females that abandoned their nests in 2010 had higher baseline corticosterone concentrations than in 2009, when nesting successfully. Also, males that renested after abandonment in 2010 had lower stress-induced corticosterone concentrations and nestlings with higher mass. Finally, pairs that abandoned but renested later in 2010 had similar fledgling success at the end of the season as those that did not abandon. These results indicate that an individual's reproductive decision is the result of a plastic modulation of the corticosterone stress response that influences reproductive decisions according to environmental conditions.

Chronic high corticosterone reduces neurogenesis in the dentate gyrus of adult male and female rats

Adult neurogenesis in the dentate gyrus of the hippocampus is altered with stress exposure and has been implicated in depression. High levels of corticosterone (CORT) suppress neurogenesis in the dentate gyrus of male rats. However both acute and chronic stress do not consistently reduce adult hippocampal neurogenesis in female rats. Therefore, this study was conducted to investigate the effect of different doses of corticosterone on hippocampal neurogenesis in male and female rats. Rats received 21 days of s.c. injections of either oil, 10 or 40 mg/kg CORT. Subjects were perfused 24 h after the last CORT injection and brains were analyzed for cell proliferation (Ki67-labeling) or immature neurons (doublecortin-labeling). Results show that in both males and females high CORT, but not low CORT, reduced both cell proliferation and the density of immature neurons in the dentate gyrus. Furthermore, high CORT males had reduced density in immature neurons in both the ventral and dorsal regions while high CORT females only showed the reduced density of immature neurons in the ventral hippocampus. The high dose of CORT disrupted the estrous cycle of females. Further, the low dose of CORT significantly reduced weight gain and increased basal CORT levels in males but not females, suggesting a greater vulnerability in males with the lower dose of CORT. Thus we find subtle sex differences in the response to chronic CORT on both body weight and on neurogenesis in the dorsal dentate gyrus that may play a role in understanding different vulnerabilities to stress-related neuropsychiatric disorders between the sexes.

Disentangling the Effects of Environment and Life‐History Stage on Corticosterone Modulation in Costa Rican Rufous‐Collared Sparrows, Zonotrichia capensis costaricensis

This study explores the factors that influence modulation of baseline corticosterone levels and the hypothalamo-pituitary-adrenal cortex (HPA) axis response to stress in Costa Rican rufous-collared sparrows (Zonotrichia capensis costaricensis). Individuals in our study population vary in their timing of breeding and molt. Thus, at multiple times of the year, we were able to investigate how the HPA axis changes with life-history stage (breeding, molt) and the interaction of season and life-history stage. Season explained most of the variation in corticosterone data. During the dry season, males had higher baseline corticosterone levels and both females and males had a higher stress response, regardless of breeding or molting condition. Breeding did not significantly affect corticosterone levels in either males or females. There was no direct effect of molt on corticosterone levels in males or in females, but there was a significant interaction between season and molt for male baseline corticosterone levels and HPA axis responsiveness. Baseline corticosterone levels were not correlated with body condition, suggesting that body condition is not an explanatory factor for HPA axis change. Our data indicate that environmental conditions may affect how the HPA axis in birds is modulated during different life-history stages. They also emphasize the importance of studying species with diverse life cycles and seasonality.

Effect of Nociceptin/Orphanin FQ (N/OFQ) and isoflurane on the corticosterone secretory response in mice lacking the N/OFQ prepropeptide (ppN/OFQ-/-)

The effects of subcutaneous Nociceptin/Orphanin FQ (N/OFQ) administration on corticosterone (CORT) secretion were determined in male and female wild-type mice and mice lacking the N/OFQ prepropeptide. Additionally the effect of pretreating animals with isoflurane anesthesia to minimize the potential stress of injection was examined. Although N/OFQ itself did not specifically increase CORT levels in males or females of either genotype, injection alone (either vehicle or N/OFQ) or isoflurane exposure both increased CORT levels in all groups. These results demonstrate that N/OFQ does not elevate circulating CORT levels; however the injection process itself results in increased CORT secretion. Pretreatment with isoflurane did not significantly diminish the CORT response to injection, except in wild-type males. In fact, isoflurane exposure alone increased CORT levels above basal values. Additionally, a gender difference was evident; females displayed a greater change of plasma CORT levels than males. Finally, because even saline injection increased CORT levels, we closely investigated another possible non-specific stress effect, i.e. the effect of transporting animals from their home environment in the animal facility to the laboratory on the day of the experiment. Although basal CORT levels were similar to values reported in other studies, circulating CORT levels were elevated in animals transported to the laboratory, even after a 30 min acclimation period. These results indicate that the experimental protocol that is followed when conducting stress experiments needs to be carefully considered.

Acute predator stress impairs the consolidation and retrieval of hippocampus-dependent memory in male and female rats

We have studied the effects of an acute predator stress experience on spatial learning and memory in adult male and female Sprague-Dawley rats. All rats were trained to learn the location of a hidden escape platform in the radial-arm water maze (RAWM), a hippocampus-dependent spatial memory task. In the control (non-stress) condition, female rats were superior to the males in the accuracy and consistency of their spatial memory performance tested over multiple days of training. In the stress condition, rats were exposed to the cat for 30 min immediately before or after learning, or before the 24-h memory test. Predator stress dramatically increased corticosterone levels in males and females, with females exhibiting greater baseline and stress-evoked responses than males. Despite these sex differences in the overall magnitudes of corticosterone levels, there were significant sex-independent correlations involving basal and stress-evoked corticosterone levels, and memory performance. Most importantly, predator stress impaired short-term memory, as well as processes involved in memory consolidation and retrieval, in male and female rats. Overall, we have found that an intense, ethologically relevant stressor produced a largely equivalent impairment of memory in male and female rats, and sex-independent corticosterone-memory correlations. These findings may provide insight into commonalities in how traumatic stress affects the brain and memory in men and women.

Pollution related effects on immune function and stress in a free‐living population of pied flycatcher Ficedula hypoleuca

We investigated whether exposure to heavy metal pollution affected the immune function of individuals in a free living population of a small insectivorous passerine bird, the pied flycatcher Ficedula hypoleuca. We measured humoral immune responses in two study areas: a polluted area in the vicinity of a copper smelter and a control area far from the smelter. Plasma corticosterone level and blood heterophil/lymphocyte ratio (H/L) were used as more general physiological measures of stress. The immune response of F. hypoleuca was not suppressed by pollution stress. In contrast, we found that F. hypoleuca males showed stronger humoral immune responses to a novel antigen (tetanus toxoid) in the polluted environment than in the unpolluted one. After the immunization of males, numbers of lymphocytes rose significantly more in the polluted area, leading to a smaller H/L ratio than in males from the control area. Females showed no pollution related effects on their immune responses. Corticosterone levels of males and nestlings were not related to pollution levels. Nestlings showed somewhat higher H/L ratios and lower fledging success in the polluted area, both factors indicating increased stress levels in a polluted area. Our results suggest that humoral immune response of male F. hypoleuca may be enhanced under moderate levels of heavy metal pollution. Enhanced immune function may, however, also be costly for birds and the higher humoral immune responses in polluted areas may thus have negative effects on the birds’ breeding performance and survival.

Feather pecking in chickens is genetically related to behavioural and developmental traits

Feather pecking (FP) is a detrimental behaviour in chickens, which is performed by only some individuals in a flock. FP was studied in 54 red junglefowl (ancestor of domestic chickens), 36 White Leghorn laying hens, and 762 birds from an F 2-intercross between these two lines. From all F 2-birds, growth and feed consumption were measured. Age at sexual maturity and egg production in females, and corticosterone levels in males were also measured. From 333 F 2-birds of both sexes, and 20 parental birds, body composition with respect to bone mineral content, muscle and fat was obtained by post-mortem examinations using Dual X-Ray Absorptiometry (DXA). In femurs of the same birds, the bone density and structure were analysed using DXA and Peripheral Quantitative Computerized Tomography (pQCT), and a biomechanical analysis of bone strength was performed. Furthermore, plumage condition was determined in all birds as a measure of being exposed to feather pecking. Using 105 DNA-markers in all F 2-birds, a genome-wide scan for Quantitative Trait Loci (QTL), associated with the behaviour in the F 2-generation was performed. FP was at least as frequent in the red junglefowl as in the White Leghorn strain studied here, and significantly more common among females both in the parental strains and in the F 2-generation. In the F 2-birds, FP was phenotypically linked to early sexual maturation, fast growth, weak bones, and, in males, also high fat accumulation, indicating that feather peckers have a different resource allocation pattern. Behaviourally, F 2 feather peckers were more active in an open field test, in a novel food/novel object test, and in a restraint test, indicating that feather pecking might be genetically linked to a proactive coping strategy. Only one suggestive QTL with a low explanatory value was found on chromosome 3, showing that many genes, each with a small effect, are probably involved in the causation of feather pecking. There were significant effects of sire and dam on the risk of being a victim of feather pecking, and victims grew faster pre- and post-hatching, had lower corticosterone levels and were less active in a restraint test. Hence, a wide array of behavioural and developmental traits were genetically linked to FP.

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 17β-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 17β-estradiol, progesterone, and testosterone throughout the year. In reproductive females, 17β-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.

Immune response of male barn swallows in relation to parental effort, corticosterone plasma levels, and sexual ornamentation

Life-history theory posits trade-offs between fitness components. Reproduction negatively affects physiology and immune system functioning, and the effect of this form of stress may be mediated by glucocorticosteroids. We manipulated brood size of barn swallows (Hirundo rustica) to study the effect of stress arising from reproductive effort on corticosterone levels of males. We also measured T-cell--mediated immunocompetence by intradermally injecting birds with phytohemagglutinin, which is mitogenic to T-lymphocytes. The results confirmed the prediction of a negative effect of parental effort on lymphoproliferative response. We found no covariation between immune response and corticosterone levels. Males with long tails, an ornament currently under directional sexual selection, had a relatively large T-cell response to the mitogen, consistent with models of parasite-mediated sexual selection predicting higher levels of immune defense in highly ornamented males. In addition, males with large sexual ornaments had relatively low corticosterone levels at the end of the parental period. These results can be reconciled with the hypothesis proposing a trade-off between parental activities and adaptive immunity and suggest that highly ornamented males are less exposed or less susceptible to stress arising from parental effort. Copyright 2002.

Sex differences in plasma corticosterone in desert tortoises,Gopherus agassizii, during the reproductive cycle

Blood samples from 30 female and 20 male adult desert tortoises, Gopherus agassizii, were collected at monthly intervals during the annual reproductive cycle (April to October). Plasma corticosterone and the sex steroids in each of the samples were analyzed by radioimmunoassay. Mean corticosterone levels in males were significantly higher than in females (P < 0.001) in every month. Male tortoises showed a marked seasonal pattern in plasma corticosterone with a highly significant peak in July, August, September, and October that corresponded with a similar peak in plasma testosterone. Testosterone and corticosterone in the male showed a highly significant correlation (P < 0.0001). The pattern of corticosterone in the female was less marked, with a significant peak in May during the mating and nesting season, but no association with the peak in estradiol in late summer was apparent. The highest levels of corticosterone in the males were associated with the peak in spermatogenesis and intense male-male combat. These results support similar data from other reptiles that suggest increased glucocorticoid secretion during periods of increased activity and metabolism.

Chronic intermittent stress does not differentially alter brain corticosteroid receptor densities in rats prenatally exposed to ethanol

Prenatal ethanol exposure produces hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness to stressors. The present study tested the hypothesis that decreased corticosteroid receptor densities at HPA feedback sites may play a role in deficient feedback inhibition and the resultant HPA hyperresponsiveness that is observed following prenatal ethanol exposure. Brains of adult Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF) and ad libitum-fed control (C) treatment groups were examined for both mineralocorticoid receptor (MR; Type I) and glucocorticoid receptor (GR; Type II) densities using a cytosolic binding assay. Experiment 1 compared the effects of chronic intermittent stress (Stress Regimen I) and corticosterone (CORT) pellet implants on hippocampal corticosteroid receptor densities in control rats. Experiment 2 determined whether exposure to Stress Regimen I would differentially downregulate and whether adrenalectomy (ADX) would differentially upregulate hippocampal corticosteroid receptors in E compared with PF and C animals. Experiment 3 examined the effects of a modified chronic intermittent stress regimen (Stress Regimen II) on corticosteroid receptor densities at several HPA feedback sites (hippocampus, prefrontal cortex, hypothalamus, and anterior pituitary) in E compared with PF and C animals. CORT pellet implants significantly downregulated hippocampal GR and MR densities in control males and females. Exposure to Stress Regimen I produced downregulation of hippocampal GRs and MRs in males comparable with that produced with CORT pellet implants, and significant downregulation of hippocampal GRs in females across all prenatal treatment groups. This stress regimen also elevated basal plasma CORT levels without concurrent changes in plasma CBG levels, and increased relative adrenal weights in both males and females. In addition, upregulation of hippocampal GRs occurred at 7 days compared with 24 h following ADX in females that had previously been exposed to this stress regimen. Following exposure to Stress Regimen II, both the downregulation of hippocampal corticosteroid receptors and the increase in basal CORT levels in males and females appear to have been abolished by the changes in housing condition during the period of chronic stress. Importantly, prenatal ethanol exposure did not differentially alter GR or MR densities at any feedback site under non-stressed conditions. Exposure to Stress Regimen II, revealed subtle effects of prenatal treatments on hippocampal GRs however it is unlikely that these changes in corticosteroid receptor densities mediated the feedback inhibition deficits observed in E animals. Together, these data demonstrate that: (1) a relatively mild intermittent stress regimen can increase basal CORT levels and downregulate hippocampal corticosteroid receptor densities (2) a seemingly small change in housing conditions during stress appears to eliminate both receptor downregulation and increase in basal CORT levels and (3) decreased corticosteroid receptor densities at HPA feedback sites in the brain do not appear to underlie the HPA hyperresponsiveness observed in E animals.

Cytokines Inhibit Sexual Behavior in Female Rats: II. Prostaglandins Mediate the Suppressive Effects of Interleukin-1β

The proinflammatory cytokine interleukin-1 (IL-1) induces several behavioral alterations that are characteristic of illness, such as anorexia and reduced locomotor and social activity. We have recently demonstrated that IL-1 inhibits sexual activity, motivation and attractivity in female, but not in male rats following either central or peripheral administration. In the present study we examined the involvement of prostaglandin (PG) synthesis in mediating IL-1-induced suppression of female sexual behavior. Administration of the cyclooxygenase blockers indomethacin or ibuprofen completely prevented IL-1-induced suppression of female sexual behavior, including the reduction in proceptive behavior, the lordosis response to a male's mounts, and the preference for a sexually active partner. In a subsequent study, ex-vivo release of hypothalamic PGE2 and the secretion of corticosterone (CS) were measured in males and estrous females following IL-1 administration. At the same time and dose of IL-1 administration that significantly reduced sexual behavior in female but not male rats, IL-1 produced a significant increase in PGE2 release in female, but not in male rats. In contrast, IL-1 induced a significant elevation of serum CS levels in males but not in females. These findings suggest that PG synthesis is involved in mediating the effects of IL-1 on female sexual behavior. Furthermore, differential secretion of PGs and CS may underlie the gender difference in the effects of IL-1 on sexual behavior.

Behavioural and hormonal responses of the pied flycatcher to environmental stressors

I investigated the effects of high plasma levels of corticosterone in male pied flycatchers,Ficedula hypoleuca, during the period of territorial establishment and the nestling period. In a second experiment males were exposed to a territorial intruder, a great spotted woodpecker model and a weasel model during the nest-building and nestling periods and their behavioural and hormonal reactions studied. Males were also exposed to handling stress (hormonal study) during these periods. During the period of territorial establishment, corticosterone-treated males, as well as control males, abandoned the territory in which they were captured; however, males in both groups very soon established new territories. During the nestling period, corticosterone-treated males, but not control males, abandoned their nests. During the nest-building period, intact males frequently attacked the territorial intruder but corticosterone-treated males never did; the woodpecker was only rarely attacked by intact males, and the weasel never. During the nestling period, the weasel was not attacked and territorial intruders only rarely; but woodpeckers were frequently attacked. With the progress of the breeding season, male flycatchers significantly reduced their sensitivity, in terms of the adrenocortical response, to all stressors tested. During the nest-building period, corticosterone levels were significantly higher in males exposed to handling, a weasel and a territorial intruder than in unmanipulated males; corticosterone levels in males exposed to a woodpecker did not differ from those in unmanipulated males; and testosterone levels were significantly elevated in males exposed to a woodpecker and to an intruder, but were reduced in males exposed to a weasel. Handling did not affect the testosterone level. During the nestling period, all groups showed low testosterone levels, and only exposure to a weasel and to handling increased corticosterone levels significantly. The results indicate that environmentally induced changes in testosterone and corticosterone secretion can be affected independently from one another, and that there are ecological bases for the differentiated hormonal responses to stress.