Testosterone reactivity to facial display of emotions in men and women

Previous studies have examined testosterone's role in regulating the processing of facial displays of emotions (FDEs). However, the reciprocal process – the influence of FDEs, an evolutionarily ancient and potent class of social signals, on the secretion of testosterone – has not yet been studied. To address this gap, we examined the effects of emotional content and sex of facial stimuli in modulating endogenous testosterone fluctuations, as well as sex differences in the endocrine responses to faces. One hundred and sixty-four young healthy men and women were exposed, in a between-subjects design, to happy or angry same-sex or opposite-sex facial expressions. Results showed that in both men (n = 85) and women (n = 79), extended exposure to faces of the opposite sex, regardless of their apparent emotional content, was accompanied by an accumulation in salivary testosterone when compared to exposure to faces of the same sex. Furthermore, testosterone change in women exposed to angry expressions was greater than testosterone change in women exposed to happy expressions. These results add emotional facial stimuli to the collection of social signals that modulate endocrine status, and are discussed with regard to the evolutionary roles of testosterone.     

Psychopathic personality traits and cortisol response to stress: The role of sex, type of stressor, and menstrual phase

Previous research indicates that psychopathic personality traits are associated with lower cortisol secretion in response to stress in men but not in women. The current study explored whether prior null results for women were related to the latency of the cortisol stress response to two different types of stressors. Additionally, accuracy of self-reported menstrual phase was explored via salivary progesterone levels. A mixed-sex sample of 145 participants characterized by high (36 men, 37 women) and low (34 men, 38 women) scores on a screening measure of psychopathic personality traits were randomly assigned to either a performance-based stressor task or a social rejection stressor task. Salivary hormone samples were taken just prior to task onset (baseline) and at 0, 20, 40, and 60 min post-stressor. Results indicated that both men and women characterized by psychopathic personality traits exhibited lower stress-induced cortisol levels to the performance-based task in comparison with controls at 20 min post-stressor. The social rejection task produced a cortisol response 20 min post-stressor in the male controls only. Removal of women with low progesterone from the analyses strengthened the psychopathy group differences. Results could suggest that deficient cortisol production in response to stress might be another important neurobiological feature associated with psychopathic traits, and that biological verification of menstrual phase is an important aspect to obtaining accurate cortisol results in women.     

Rapid endocrine responses of young men to social interactions with young women

It is well-established that males of many nonhuman vertebrate species exhibit hormonal reactions to stimuli from potential mates. The present studies were designed to test replication of preliminary findings suggesting that human males may exhibit such reactions as well. In Experiment 1, young men (n=115) provided saliva samples before and after either conversing with a woman confederate or sitting alone for 15 min. Changes from baseline in salivary testosterone concentrations were significantly greater among the men exposed to women, but only among subjects tested in the afternoon. In Experiment 2, male subjects (n=99) interacted with either a male or a female confederate with saliva samples collected before and after these interactions and all experimental sessions conducted in the afternoon. Men who interacted with women exhibited significant elevations of testosterone relative to both their own baseline concentrations and to change scores among the men who interacted with other men. In addition, women confederates' ratings of men's extraversion and degree of self-disclosure were positively correlated with changes in testosterone. In both experiments, furthermore, changes in cortisol concentrations from baseline were significantly greater among men who spoke with women relative to men in the control conditions. The results provide evidence that social interactions with potential mates can in fact trigger specific patterns of endocrine responses in human males.     

Telling facial metrics: facial width is associated with testosterone levels in men

High facial width-to-height ratio (fWHR) has been associated with a cluster of behavioural traits in men, including aggression and status-striving. This association between face structure and behaviour may be caused by testosterone. Here we investigated the relationship of both baseline and reactive testosterone levels to fWHR. In addition, we investigated the link between testosterone and three well-characterised sexually dimorphic facial metrics. Testosterone was measured in one sample of males (n = 185) before and after a speed-dating event. An additional sample provided only baseline testosterone measures (n = 92). fWHR was positively associated with testosterone reactions to potential mate exposure and marginally associated with baseline testosterone in Sample 1. We found a positive association with baseline testosterone and fWHR in Sample 2. In addition, face-width-to-lower-height ratio was positively associated with testosterone in both samples, suggesting that, in particular, facial width (scaled by two measures of facial height) is associated with testosterone. Importantly, our results also indicate that there is no association between adult testosterone and the sexual dimorphism of face shape. Thus, while our findings question the status of sexual dimorphism as a proxy measure of testosterone, they do provide evidence that testosterone is linked to fWHR and might underlie the relationship between fWHR and behaviour.     

The effects of saliva collection,handling and storage on salivary testosterone measurement

Several endocrine parameters commonly measured in plasma, such as steroid hormones, can be measured in the oral fluid. However, there are several technical aspects of saliva sampling and processing that can potentially bias the validity of salivary testosterone measurement. The aim of this study was to evaluate the effects caused by repeated sampling; 5 min centrifugation (at 2000, 6000 or 10,000g); the stimulation of saliva flow by a cotton swab soaked in 2% citric acid touching the tongue; different storage times and conditions as well as the impact of blood contamination on salivary testosterone concentration measured using a commercially available ELISA kit. Fresh, unprocessed, unstimulated saliva samples served as a control. Salivary testosterone concentrations were influenced neither by repeated sampling nor by stimulation of salivary flow. Testosterone levels determined in samples stored in various laboratory conditions for time periods up to 1 month did not differ in comparison with controls. For both genders, salivary testosterone levels were substantially reduced after centrifugation (men F = 29.1; women F = 56.17, p < 0.0001). Blood contamination decreased salivary testosterone levels in a dose-dependent manner (men F = 6.54, p < 0.01, F = 5.01, p < 0.05). Salivary testosterone can be considered A robust and stable marker. However, saliva processing and blood leakage can introduce bias into measurements of salivary testoterone using ELISA. Our observations should be considered in studies focusing on salivary testosterone.     

Are optimal levels of testosterone associated with better cognitive function in healthy older women and men?

Background

Sex steroids can positively affect the brain and from this it would follow that high levels of sex steroids could be associated with better cognitive function in older men and women.

Methods

This Healthy Ageing Study sample comprised of 521 older participants (51% women) without dementia at baseline, with an age range from 64 to 94 years. Testosterone and sex hormone binding globulin were measured using the automated Immulite 2000 and analyzed in association with baseline memory, global cognitive function and decline (assessed using the Mini-Mental Status Examination or MMSE) and controlling for potential confounds such as age, education, vascular disease, smoking, diabetes, thyroid function, and body mass index.

Results

In healthy older men and women, optimal levels of testosterone were associated with better MMSE scores at baseline. Follow-up analyses indicated that in men, low testosterone levels (OR = .94, 95% CI = .88 to 1.00) were a risk factor for a sharp cognitive decline after 2 years, perhaps indicative of dementia. Associations were independent of covariates and baseline MMSE. Conversely, women at risk for a sharp drop in cognitive function showed some evidence for higher calculated free testosterone levels at baseline.

Conclusions

Results replicate earlier cross-sectional findings that high levels of sex steroids are not associated with better cognitive function in older people. In men, age accelerated endocrinological change could be associated with dementia pathology.

General significance

These data do not support increasing testosterone levels to prevent cognitive decline in men and women over 65 years of age.     

An experimental test of the testosterone mediated oxidation handicap hypothesis in a wild bird

The oxidation handicap hypothesis (OHH) proposed that honesty in sexual signals is maintained when testosterone simultaneously promotes the development of elaborate signals and imposes an oxidative cost. Although there is evidence that testosterone enhances display traits in some cases, relatively few studies have tested the prediction that testosterone generates oxidative costs. We tested this prediction experimentally by administering testosterone (n = 14) and control (n = 14) implants to free-living common yellowthroat warblers (Geothlypis trichas) and quantifying testosterone and oxidative state before and 35 ± 15 days after implantation. We interpreted our experimental results in the context of a larger database of 83 unmanipulated males observed over five breeding seasons. In our observational data, testosterone was related to aspects of the carotenoid-based bib, but these relationships were age-dependent. Bib coloration was related to testosterone only for first time breeders, while bib size was positively and negatively associated with testosterone among experienced and inexperienced breeders, respectively. Two measures of oxidative metabolism—damage to DNA and total antioxidant capacity (TAC)—were unrelated to endogenous testosterone. Despite the correlation between endogenous testosterone and plumage, our experimental results failed to support the key prediction of the OHH. Testosterone treated males had higher levels of TAC upon recapture, but oxidative damage to DNA did not differ from controls. Because antioxidants can protect against the harmful effects of oxidative stress, one interpretation of our results is that males physiologically compensated for elevated testosterone, avoiding the honesty enforcing mechanism of the OHH. Taken together, our results suggest that testosterone is not a direct mediator of honest signaling in yellowthroats via its effects on oxidative stress.     

Decreased circulating leptin and increased neuropeptide Y gene expression are implicated in food deprivation-induced hyperactivity in striped hamsters, Cricetulus barabensis

Physiological and behavioral adjustments of small mammals are important strategies in response to variations in food availability. Although numerous of studies have been carried out in rodents, behavioral patterns in response to food deprivation and re-feeding (FD–RF) are still inconsistent. Here we examined effects of a 24 h FD followed by RF on general activity, serum leptin concentrations and gene expression of orexigenic and anorexigenic hypothalamic neuropeptides in striped hamsters (Cricetulus barabensis) with/without leptin supplements. The time spent on activity was increased by 2.5 fold in FD hamsters compared with controls fed ad libitum (P < 0.01). Body mass, fat mass as well as serum leptin concentrations were significantly decreased in FD hamsters in comparison with ad libitum controls, which were in parallel with hyperactivity. During re-feeding, leptin concentrations increased rapidly to pre-deprivation levels by 12 h, but locomotor activity decreased gradually and did not return to pre-deprivation levels until 5 days after re-feeding. Leptin administration to FD hamsters significantly attenuated the increased activity. Gene expression of hypothalamic neuropeptide Y (NPY) was upregulated in FD hamsters and fell down to control levels when hamsters were re-fed ad libitum, similar to that observed in activity behavior. Leptin supplement induced increases in serum leptin concentrations (184.1%, P < 0.05) in FD hamsters and simultaneously attenuated the increase in activity (45.8%, P < 0.05) and NPY gene expression (35%, P < 0.05). This may allow us to draw a more generalized conclusion that decreased leptin concentrations function as a starvation signal in animals under food shortage; to induce an increase in activity levels, leading animals to forage and/or migrate, and consequently increasing the chance of survival. Decreased concentrations of serum leptin in animals subjected to food shortage may induce an upregulation of gene expression of hypothalamus NPY, consequently driving a significant increase in foraging behavior.     

Testosterone responses to competition in men are related to facial masculinity

Relationships between androgens and the size of sexually dimorphic male traits have been demonstrated in several non-human species. It is often assumed that a similar relationship exists for human male faces, but clear evidence of an association between circulating testosterone levels and the size of masculine facial traits in adulthood is absent. Here we demonstrate that, after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces. In participants randomly allocated to a 'winning' condition, testosterone was elevated relative to pre-task levels at 5 and 20 min post-task. In a control group of participants allocated to a 'losing' condition there were no significant differences between pre- and post-task testosterone. An index of facial masculinity based on the measurement of sexually dimorphic facial traits was not associated with pre-task (baseline) testosterone levels, but was associated with testosterone levels 5 and 20 min after success in the competitive task. These findings indicate that a man's facial structure may afford important information about the functioning of his endocrine system.     

Variation in CAG repeat length of the androgen receptor gene predicts variables associated with intrasexual competitiveness in human males

An expanding body of research suggests that circulating androgens regulate the allocation of energy between mating and survival effort in human males, with higher androgen levels promoting greater investment in mating effort. Because variations in the number of CAG codon repeats in the human androgen receptor (AR) gene appear to modulate the phenotypic effects of androgens - with shorter repeat lengths associated with greater androgenic effects per unit androgen - polymorphisms in this gene may predict trait-like individual differences in the degree to which men are calibrated toward greater mating effort. Consistent with this, men in the present study with shorter CAG repeat lengths exhibited greater upper body strength and scored higher on self-report measures of dominance and prestige, all of which are argued to be indices of mating effort. Repeat length failed to predict sociosexual orientation (i.e. pursuit of short-term mating relationships), however, suggesting that the traits correlated with this polymorphism may be primarily associated with intrasexual competitiveness in the service of long-term mating effort. None of these measures of mating effort was related to baseline testosterone concentrations (either as main effects or as interactions with CAG repeat length), implying that long-term androgen exposure associated with AR gene polymorphisms may account for more variance in some androgen-dependent traits than does current testosterone concentration. These findings provide further evidence for the importance of the CAG repeat polymorphism in the AR gene in explaining a broad range of individual differences in human males.     

Basal and dynamic relationships between implicit power motivation and estradiol in women

This study investigated basal and reciprocal relationships between implicit power motivation (n Power), a preference for having impact and dominance over others, and both salivary estradiol and testosterone in women. 49 participants completed the Picture Story Exercise, a measure of n Power. During a laboratory contest, participants competed in pairs on a cognitive task and contest outcome (win vs. loss) was experimentally varied. Estradiol and testosterone levels were determined in saliva samples collected at baseline and several times post-contest, including 1 day post-contest. n Power was positively associated with basal estradiol concentrations. The positive correlation between n Power and basal estradiol was stronger in single women, women not taking oral contraceptives, or in women with low-CV estradiol samples than in the overall sample of women. Women's estradiol responses to a dominance contest were influenced by the interaction of n Power and contest outcome: estradiol increased in power-motivated winners but decreased in power-motivated losers. For power-motivated winners, elevated levels of estradiol were still present the day after the contest. Lastly, n Power and estradiol did not correlate with self-reported dominance and correlated negatively with self-reported aggression. Self-reported dominance and aggression did not predict estradiol changes as a function of contest outcome. Overall, n Power did not predict basal testosterone levels or testosterone changes as a function of dominance contest outcome.     

The relative importance of intra- and intersexual selection on human male sexually dimorphic traits

Recent evidence suggests that in sexual selection on human males, intrasexual competition plays a larger role than female choice. In a sample of men (N?=?164), we sought to provide further evidence on the effects of men's physical dominance and sexual attractiveness on mating success and hence in sexual selection. Objective measures and subjective ratings of male sexually dimorphic traits purportedly under sexual selection (height, vocal and facial masculinity, upper body size from 3D scans, physical strength, and baseline testosterone) and observer perceptions of physical dominance and sexual attractiveness based on self-presentation video recordings were assessed and associated with mating success (sociosexual behaviour and number of potential conceptions) in a partly longitudinal design. Results from structural equation models and selection analyses revealed that physical dominance, but not sexual attractiveness, predicted mating success. Physical dominance mediated associations of upper body size, physical strength, as well as vocal and facial physical dominance and attractiveness with mating success. These findings thus suggest a greater importance of intrasexual competition than female choice in human male sexual selection.     

Chronic variable stress in fathers alters paternal and social behavior but not pup development in the biparental California mouse (Peromyscus californicus)

Stress and chronically elevated glucocorticoid levels have been shown to disrupt parental behavior in mothers; however, almost no studies have investigated corresponding effects in fathers. The present experiment tested the hypothesis that chronic variable stress inhibits paternal behavior and consequently alters pup development in the monogamous, biparental California mouse (Peromyscus californicus). First-time fathers were assigned to one of three experimental groups: chronic variable stress (CVS, n = 8), separation control (SC, n = 7), or unmanipulated control (UC, n = 8). The CVS paradigm (3 stressors per day for 7 days) successfully stressed mice, as evidenced by increased baseline plasma corticosterone concentrations, increased adrenal mass, decreased thymus mass, and a decrease in body mass over time. CVS altered paternal and social behavior of fathers, but major differences were observed only on day 6 of the 7-day paradigm. At that time point, CVS fathers spent less time with their pairmate and pups, and more time autogrooming, as compared to UC fathers; SC fathers spent more time behaving paternally and grooming the female mate than CVS and UC fathers. Thus, CVS blocked the separation-induced increase in social behaviors observed in the SC fathers. Nonetheless, chronic stress in fathers did not appear to alter survival or development of their offspring: pups from the three experimental conditions did not differ in body mass gain over time, in the day of eye opening, or in basal or post-stress corticosterone levels. These results demonstrate that chronic stress can transiently disrupt paternal and social behavior in P. californicus fathers, but does not alter pup development or survival under controlled, non-challenging laboratory conditions.     

Changes in androgen receptor, estrogen receptor alpha, and sexual behavior with aging and testosterone in male rats

Reproductive aging in males is characterized by a diminution in sexual behavior beginning in middle age. We investigated the relationships among testosterone, androgen receptor (AR) and estrogen receptor alpha (ERα) cell numbers in the hypothalamus, and their relationship to sexual performance in male rats. Young (3 months) and middle-aged (12 months) rats were given sexual behavior tests, then castrated and implanted with vehicle or testosterone capsules. Rats were tested again for sexual behavior. Numbers of AR and ERα immunoreactive cells were counted in the anteroventral periventricular nucleus and the medial preoptic nucleus, and serum hormones were measured. Middle-aged intact rats had significant impairments of all sexual behavior measures compared to young males. After castration and testosterone implantation, sexual behaviors in middle-aged males were largely comparable to those in the young males. In the hypothalamus, AR cell density was significantly (5-fold) higher, and ERα cell density significantly (6-fold) lower, in testosterone- than vehicle-treated males, with no age differences. Thus, restoration of serum testosterone to comparable levels in young and middle-aged rats resulted in similar preoptic AR and ERα cell density concomitant with a reinstatement of most behaviors. These data suggest that age-related differences in sexual behavior cannot be due to absolute levels of testosterone, and further, the middle-aged brain retains the capacity to respond to exogenous testosterone with changes in hypothalamic AR and ERα expression. Our finding that testosterone replacement in aging males has profound effects on hypothalamic receptors and behavior has potential medical implications for the treatment of age-related hypogonadism in men.     

Association between testosterone, estradiol and sex hormone binding globulin levels in men with type 1 diabetes with nephropathy

Male sex is a risk factor for development and progression of diabetic nephropathy; however, the relationship between sex hormone levels and diabetic nephropathy in type 1 diabetic men is unknown. This was a prospective follow-up study as part of the nationwide Finnish Diabetic Nephropathy (FinnDiane) Study; 297 patients were followed for 5.9 ± 1.5 years. Serum total testosterone (Tt) and estradiol (Te), calculated free testosterone (cFt) and estradiol (cFe) and sex hormone binding globulin were measured at baseline and correlated with urinary albumin excretion rate, estimated glomerular filtration rate and markers of metabolic syndrome. Diabetes without renal disease was associated with decreased Tt (p < 0.001), Te (p < 0.001) and cFt (p = 0.001) levels compared with healthy non-diabetic men. With progression of renal disease from micro- to macroalbuminuria, this decrease in serum Tt was even more pronounced. Cox regression showed that cFt and cFe were independent predictors of the progression from macroalbuminuria to end-stage renal disease. Our study shows that men with type 1 diabetes exhibit dysregulated sex hormone levels, which is most pronounced in men with progressive renal disease, suggesting that sex hormones may play a role in the pathogenesis of diabetic nephropathy associated with type 1 diabetes.     

Endogenous testosterone levels, mental rotation performance, and constituent abilities in middle-to-older aged men

Evidence from both human and animal studies suggests that gonadal steroids, such as testosterone, exert activational effects on adult spatial behavior. Endogenous testosterone levels decline gradually but variably as men age; it remains to be shown whether these decreases are associated with age-related declines in visuo-spatial performance or constituent abilities indicative of generalized age-related cognitive decline. Ninety-six healthy, community dwelling men aged between 38 and 69 years completed the Vandenberg and Kuse Mental Rotation Test (MRT) together with a battery of tests including processing speed, executive function, perceptual discrimination, working memory, and reaction time measures. Significant main effects of tertiles of calculated free testosterone levels (cEFT) were found on composite measures of processing speed, executive function, and perceptual discrimination ability in a subset of men aged over 50 years in age and crystallized intelligence controlled analyses; higher cEFT levels were associated with poorer performance. Hierarchical multiple regression and path analyses on the whole data set showed that cEFT levels negatively moderated processing speed performance, which in turn predicted both working memory and MRT performance with aging. Together these data suggest that age-related declines in endogenous testosterone levels in healthy middle-to-older aged men are not associated with generalized age-related cognitive decline.     

Tandem Androgenic and Psychological Shifts in Male Reproductive Effort Following a Manipulated “Win” or “Loss” in a Sporting Competition

Male-male competition is involved in inter- and intrasexual selection, with both endocrine and psychological factors presumably contributing to reproductive success in human males. We examined relationships among men’s naturally occurring testosterone, their self-perceived mate value (SPMV), self-esteem, sociosexuality, and expected likelihood of approaching attractive women versus situations leading to child involvement. We then monitored changes in these measures in male rowers (N?=?38) from Cambridge, UK, following a manipulated “win” or “loss” as a result of an indoor rowing contest. Baseline results revealed that men with heightened testosterone and SPMV values typically had greater inclinations toward engaging in casual sexual relationships and a higher likelihood of approaching attractive women in a hypothetical social situation. As anticipated, both testosterone and SPMV increased following a manipulated “victory” and were associated with heightened sociosexuality, and increased expectations toward approaching attractive women versus individuals who would involve them in interacting with children after the race. SPMV and self-esteem appeared to mediate some of the effects of testosterone on post-race values. These findings are considered in the broader context of individual trade-offs between mating and parental effort and a model of the concurrent and dynamic androgenic and psychological influences contributing to male reproductive effort and success.     

The effects of competition and implicit power motive on men's testosterone,emotion recognition,and aggression

A contribution to a special issue on Hormones and Human Competition.We investigated the effects of competition on men's testosterone levels and assessed whether androgen reactivity was associated with subsequent emotion recognition and reactive and proactive aggression. We also explored whether personalized power (p Power) moderated these relationships. In Study 1, 84 males competed on a number tracing task and interpreted emotions from facial expressions. In Study 2, 72 males competed on the same task and were assessed on proactive and reactive aggression. In both studies, contrary to the biosocial model of status (Mazur, 1985), winners' testosterone levels decreased significantly while losers' levels increased, albeit not significantly. Personalized power moderated the effect of competition outcome on testosterone change in both studies. Using the aggregate sample, we found that the effect of decreased testosterone levels among winners (compared to losers) was significant for individuals low in p Power but not for those with medium or high p Power. Testosterone change was positively related to emotion recognition, but unrelated to either aggression subtype. The testosterone-mediated relationship between winning and losing and emotion recognition was moderated by p Power. In addition, p Power moderated the direct (i.e., non-testosterone mediated) path between competition outcome and emotion recognition and both types of aggression: high p-Power winners were more accurate at deciphering others' emotions than high p-Power losers. Finally, among high p-Power men, winners aggressed more proactively than losers, whereas losers aggressed more reactively than winners. Collectively, these studies highlight the importance of implicit power motivation in modulating hormonal, cognitive, and behavioral outcomes arising from human competition.     

Do testosterone declines during the transition to marriage and fatherhood relate to men's sexual behavior? Evidence from the Philippines

Testosterone (T) is thought to help facilitate trade-offs between mating and parenting in humans. Across diverse cultural settings married men and fathers have lower T than other men and couples' sexual activity often declines during the first years of marriage and after having children. It is unknown whether these behavioral and hormonal changes are related. Here we use longitudinal data from a large study in the Philippines (n = 433) to test this model. We show that among unmarried non-fathers at baseline (n = 153; age: 21.5 ± 0.3 years) who became newly married new fathers by follow-up (4.5 years later), those who experienced less pronounced longitudinal declines in T reported more frequent intercourse with their partners at follow-up (p < 0.01) compared to men with larger declines in T. Controlling for duration of marriage, findings were similar for men transitioning from unmarried to married (without children) (p < 0.05). Men who remained unmarried and childless throughout the study period did not show similar T-sexual activity outcomes. Among newly married new fathers, subjects who had frequent intercourse both before and after the transition to married fatherhood had more modest declines in T compared to peers who had less frequent sex (p < 0.001). Our findings are generally consistent with theoretical expectations and cross-species empirical observations regarding the role of T in male life history trade-offs, particularly in species with bi-parental care, and add to evidence that T and sexual activity have bidirectional relationships in human males.     

Food, stress, and reproduction: Short-term fasting alters endocrine physiology and reproductive behavior in the zebra finch

Stress is thought to be a potent suppressor of reproduction. However, the vast majority of studies focus on the relationship between chronic stress and reproductive suppression, despite the fact that chronic stress is rare in the wild. We investigated the role of fasting in altering acute stress physiology, reproductive physiology, and reproductive behavior of male zebra finches (Taeniopygia guttata) with several goals in mind. First, we wanted to determine if acute fasting could stimulate an increase in plasma corticosterone and a decrease in corticosteroid binding globulin (CBG) and testosterone. We then investigated whether fasting could alter expression of undirected song and courtship behavior. After subjecting males to fasting periods ranging from 1 to 10 h, we collected plasma to measure corticosterone, CBG, and testosterone. We found that plasma corticosterone was elevated, and testosterone was decreased after 4, 6, and 10 h of fasting periods compared with samples collected from the same males during nonfasted (control) periods. CBG was lower than control levels only after 10 h of fasting. We also found that, coincident with these endocrine changes, males sang less and courted females less vigorously following short-term fasting relative to control conditions. Our data demonstrate that acute fasting resulted in rapid changes in endocrine physiology consistent with hypothalamo-pituitary-adrenal axis activation and hypothalamo-pituitary-gonadal axis deactivation. Fasting also inhibited reproductive behavior. We suggest that zebra finches exhibit physiological and behavioral flexibility that makes them an excellent model system for studying interactions of acute stress and reproduction.