Effect of isolation and conspecific presence in a novel environment on corticosterone concentrations in a social avian species, the zebra finch (Taeniopygia guttata)

Zebra finches are a highly social and monogamous avian species. In the present study, we sought to determine the effect of social isolation (separation from the flock) in a novel environment with and without a conspecific present on the adrenocortical activity of paired and unpaired individuals of this species. With regard to paired birds, we hypothesized that the presence of the mate during isolation from the group would act as a social buffer against the stressful effects of isolation. We observed that 10 but not 30 minutes of social isolation resulted in elevated concentrations of corticosterone in unpaired and paired male zebra finches in comparison to baseline concentrations of corticosterone. Furthermore, the presence of a mate during isolation in a novel environment did not have a buffering effect against increases in corticosterone concentrations. Additionally, to compare concentrations of corticosterone in response to isolation (in a novel environment) to a previously well-established stressor, we subjected groups of birds to restraint. We observed that 10 or 30 minutes of restraint led to significantly higher concentrations of corticosterone as compared to baseline. Finally, to rule out the possibility that merely handling a bird would result in significantly elevated concentrations of corticosterone as compared to baseline samples, we measured corticosterone concentrations 10 or 30 minutes after handling involving capture and release only. Our results suggest that handling alone might have contributed to the elevation of corticosterone in birds exposed to 10 minutes but not 30 minutes of restraint. Handling by itself did not account, however, for the elevated corticosterone in birds socially isolated for 10 minutes.     

Effects of housing condition and early corticosterone treatment on learned features of song in adult male zebra finches

Early developmental stress can have long-term physiological and behavioral effects on an animal. Developmental stress and early corticosterone (Cort) exposure affect song quality in many songbirds. Early housing condition can act as a stressor and affect the growth of nestlings and adult song, and improvements in housing condition can reverse adverse effects of early stress exposure in rodents. However, little is known about this effect in songbirds. Therefore, we took a novel approach to investigate if housing condition can modify the effects of early Cort exposure on adult song in male zebra finches. We manipulated early housing conditions to include breeding in large communal flight cages (FC; standard housing condition; with mixed-sex and mix-aged birds) versus individual breeding cages (IBC, one male–female pair with small, IBC-S, or large clutches, IBC-L) in post-hatch Cort treated male birds. We found that Cort treated birds from IBC-S have higher overall song learning scores (between tutor and pupil) than from FC but there is no difference between these groups in the No-Cort treated birds. When examining the effects of Cort within each housing condition, overall song learning scores decreased in Cort treated birds from flight cages but increased in birds from IBC-S compared to controls. Likewise, the total number of syllables and syllable types increased significantly in Cort treated birds from IBC-S, but decreased in FC-reared birds though this effect was not statistically significant. These findings suggest that the effects of early Cort treatment on learned features of song depend on housing condition.     

Testosterone implants alter the frequency range of zebra finch songs

To investigate whether changes in testosterone alter the frequency range in which a zebra finch produces song, we assigned male zebra finches to two groups, one of which received testosterone implants and the other empty silastic capsule implants. We then recorded songs up to 52 weeks after the surgery and measured frequency changes in the fundamental frequencies of arbitrarily chosen harmonic stacks in the songs of birds in either group. We found statistically significant decreases after 5 weeks in the songs of the testosterone-treated birds. No changes were found in the fundamental frequencies of the control group. The frequency change remained after the apparent effects of the testosterone implants ended. These data show that high levels of testosterone can lower the frequencies of elements in zebra finch songs.     

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.     

Social facilitation of male song by male and female conspecifics in the zebra finch, Taeniopygia guttata

Zebra finches are a ubiquitous model system for the study of vocal learning in animal communication. Their song has been well described, but its possible function(s) in social communication are only partly understood. The so-called ‘directed song’ is a high-intensity, high-performance song given during courtship in close proximity to the female, which is known to mediate mate choice and mating. However, this singing mode constitutes only a fraction of zebra finch males’ prolific song output. Potential communicative functions of their second, ‘undirected’ singing mode remain unresolved in the face of contradicting reports of both facilitating and inhibiting effects of social company on singing. We addressed this issue by experimentally manipulating social contexts in a within-subject design, comparing a solo versus male or female only company condition, each lasting for 24 h. Males’ total song output was significantly higher when a conspecific was in audible and visible distance than when they were alone. Male and female company had an equally facilitating effect on song output. Our findings thus indicate that singing motivation is facilitated rather than inhibited by social company, suggesting that singing in zebra finches might function both in inter- and intrasexual communication.     

Energetic reserves, leptin and testosterone: a refinement of the immunocompetence handicap hypothesis

The immunocompetence handicap hypothesis (ICHH) assumes that testosterone (T), required for the expression of sexual traits, can also incur a cost due to its immunosuppressive properties. However, T-dependent immunosuppression could also arise as an indirect consequence of energy reallocation from the immune system to other metabolic demands. Leptin is mostly produced in lipogenic tissues and its circulating level is positively correlated with the amount of lipid reserves. Leptin also has an important role as immunoenhancer and we suggest that this hormone could play a role as a mediator of the immunosuppressive effect of testosterone. In particular, we propose that only the individuals able to maintain large lipid reserves (with high leptin levels), while sustaining high testosterone levels, might be able to develop sexual displays without an impairment of their immune defences. Here, we tested one of the assumptions underlying this extension of the ICHH: leptin administration should attenuate testosterone-induced immunosuppression. T-implanted and control male zebra finches (Taeniopygia guttata) received daily injections of leptin or phosphate buffered saline. T-implants initially depressed the phytohaemagglutinin-induced immune response. However, T-birds injected with leptin enhanced their immune response to the level of control birds. These results open a new perspective on the study of the ICHH.     

Mate recognition by female zebra finch: analysis of individuality in male call and first investigations on female decoding process

Zebra finches are monogamous birds living in large assemblies, which represent a source of confusion for recognition between mates. Because the members of a pair use distance calls to remain in contact, call-based mate recognition is highly probable in this species. Whereas it had been previously demonstrated in males [Vignal, C., Mathevon, N., Mottin, S., 2004. Audience drives male songbird response to mate's voice. Nature 430, 448-451], call-based mate recognition remained to be shown in females. By analysing the acoustic structure of male calls, we investigated the existence of an individual signature and identified the involved acoustic cues. We tested to see if females can identify their mates on the basis of their calls alone, and performed preliminary experiments using modified signals to investigate the acoustic basis of this recognition. Playback tests carried on six individuals showed that a female zebra finch is able to perform the call-based recognition of its mate. Our experiments suggested that the female uses both the energy spectrum and the frequency modulation of the male signal. More experiments are now needed to decipher precisely which acoustic cues are used by females for recognition.     

Cues to sex- and stress-hormones in the human male face: functions of glucocorticoids in the immunocompetence handicap hypothesis

The stress-linked version of the immunocompetence handicap hypothesis has been proposed to account for inconsistencies in relationships between testosterone and immune response. The model has received some support from studies demonstrating roles of stress hormones in relationships between testosterone, immune function and secondary sexual ornamentation. Such work, however, has relied on artificial elevation of testosterone so may not reflect relationships in natural populations. We created human male facial stimuli on the basis of naturally co-occurring levels of salivary testosterone and the stress hormone cortisol. In Study 1 we tested female preferences for male faces with cues to combinations of the hormones across the menstrual cycle, and in Study 2 we tested perceptions of health and dominance in a novel set of facial stimuli. Females preferred cues to low cortisol, a preference that was strongest during the fertile phase of the menstrual cycle. The effects of cortisol on attractiveness and perceived health and dominance were contingent upon level of testosterone: the effects of the stress hormone were reduced when testosterone was high. We propose explanations for our results, including low cortisol as a cue to a heritable component of health, attractiveness as a predictor of low social-evaluative threat (and, therefore, low baseline cortisol) and testosterone as a proxy of male ability to cope efficiently with stressors.     

Distribution of parvalbumin,cytochrome oxidase activity and 14C-2-deoxyglucose uptake in the brain of the zebra finch

Summary The visual system of adult zebra finches was investigated 1) immunocytochemically for the distribution of the Ca²⁺-binding protein parvalbumin, 2) for the activity of the respiratory enzyme cytochrome oxidase, and 3) for the uptake of 2-deoxyglucose. In the visual system, only nuclei of the tecto-fugal pathway and related nuclei were labeled by the parvalbumin antiserum (ectostriatum, nucleus rotundus, tectum opticum, nucleus postero-ventralis, nucleus praetectalis, nucleus subpraetectalis, nucleus isthmipars parvocellularis and-magnocellularis, nucleus isthmoopticus). Additionally, parvalbumin-positive nuclei such as area entorhinalis, area a in the hyperstriatum accessorium, nucleus septalis medialis and nucleus habenularis are described. With few exceptions there was a striking correlation of parvalbumin-positive and cytochrome oxidase-positive nuclei of the visual system. Most of the areas with high levels of parvalbumin and cytochrome oxidase were labeled with 2-deoxyglucose as well. Nucleus posteroventralis showed labeling below background intensity. 2-Deoxyglucose uptake primarily reflects energy demands of actual electrical activity, i.e., of the Na⁺-K⁺ pump, while cytochrome oxidase supposedly indicates the long-term energy demands of various metabolic pathways. Consequently, high cytochrome oxidase activity together with large 2-deoxyglucose uptake in the tecto-fugal pathway might be due to the high spontaneous and evoked electrical activity. Parvalbumin concentrations in the same areas (and in auditory areas, see Braun et al. 1985I) suggest as one possibility that special Ca²⁺ mechanisms are present in neuronal systems that can reach high levels of electrical activity.     

Testosterone decreases the potential for song plasticity in adult male zebra finches

Zebra finches are age-limited learners; males crystallize their songs at 90 days and do not subsequently alter those songs. However, a variety of interventions, including deafening and syringeal denervation, result in long-term changes to the crystallized song. These changes can be prevented by lesioning nucleus LMAN. As different social contexts for song production result in differential activation of LMAN, we asked whether the social context experienced by adult males would affect their ability to alter their songs in response to syringeal denervation. Males able to see and direct their songs to females made fewer changes to their songs than did males that could hear but not see females, but this trend was not significant. The volume of a male's HVc, a forebrain song control nucleus, also failed to predict the degree to which a male would change his song. However, testis mass was significantly correlated with the number of changes made to the song, indicating that variations in testosterone modulate adult song plasticity. We directly tested the effect of circulating testosterone on adult song plasticity by implanting adult males with either testosterone or flutamide, a testosterone receptor blocker, and tracking song changes triggered by ts nerve injury. As predicted, males implanted with testosterone changed their songs less than did males that received flutamide implants. These results suggest that the high testosterone concentrations associated with sexual maturity and song crystallization in zebra finches continue to act in adult males to reduce the potential for vocal plasticity.     

Speed of exploration and risk-taking behavior are linked to corticosterone titres in zebra finches

The existence of consistent individual differences in behavioral strategies ("personalities" or coping styles) has been reported in several animal species. Recent work in great tits has shown that such traits are heritable and exhibit significant genetic variation. Free-living birds respond to environmental stresses by up-regulating corticosterone production. Behavior during mild stress can occur in accordance to two types of coping styles, i.e. active and passive. Using artificially selected lines of zebra finches that vary in the amount of corticosterone produced in response to a manual restraint stressor we ran three "personality" experiments. We show that birds in the different corticosterone lines differ in their exploratory and risk-taking behaviors. There was an increase in exploratory behavior as corticosterone titre increased but only in the low corticosterone line. Birds in high corticosterone line showed greater risk-taking behavior than birds in the other lines. Thus, in general, higher levels of circulating corticosterone following a mild stress result in greater exploratory behavior and greater risk taking. This study shows that lines of animals selected for endocrine hormonal responses differ in their "coping" styles or "personalities".     

Heritability of corticosterone response and changes in life history traits during selection in the zebra finch

Vertebrates respond to environmental stressors through the neuro-endocrine stress response, which involves the production of glucocorticoids. We have selected independent, duplicate divergent lines of zebra finches for high, low and control corticosterone responses to a mild stressor. This experiment has shown that over the first four generations, the high lines have demonstrated a significant realized heritability of about 20%. However, the low lines have apparently not changed significantly from controls. This asymmetry in response is potentially because of the fact that all birds appear to be showing increased adaptation to the environment in which they are housed, with significant declines in corticosterone response in control lines as well as low lines. Despite the existence of two- to threefold difference in mean corticosterone titre between high and low lines, there were no observed differences in testosterone titre in adult male birds from the different groups. In addition, there were no consistent, significant differences between the lines in any of the life history variables measured--number of eggs laid per clutch, number of clutches or broods produced per pair, number of fledglings produced per breeding attempt, nor in any of egg, nestling and fledgling mortality. These results highlight the fact that the mechanisms that underlie variation in the avian physiological system can be modified to respond to differences between environments through selection. This adds an additional level of flexibility to the avian physiological system, which will allow it to respond to environmental circumstances.     

Energy metabolism, testosterone and corticosterone in white-crowned sparrows

The influence of the steroid hormones testosterone and corticosterone on energy metabolism and activity of birds is largely enigmatic. We measured resting metabolic rate during night and day in 12 long-term castrated and 12 intact male white-crowned sparrows (Zonotrichia leucophrys gambelii) under short-day (8:16 SD), long-day (20:4 LD), LD+testosterone implant and LD−testosterone implant conditions. Each male was sequentially measured under all four conditions. Photostimulation increased testosterone, resting metabolic rate, food intake, hopping activity and body mass in castrates and intact males. Surprisingly, testosterone levels and metabolic rates did not differ between intact and castrated males. Testosterone implantation increased activity and food intake, but decreased body mass and resting metabolic rate in both groups. Removing testosterone implants reversed the effects on resting metabolic rate, activity and food intake. Corticosterone levels, measured immediately at the end of metabolism measurements, showed birds were not stressed. Corticosterone had no apparent relationship with resting metabolic rate and there was no interaction between corticosterone and testosterone. Overall, positive changes in testosterone levels resulted in a decrease of resting metabolic rate. We speculate that testosterone increases activity, and birds compensate for increased activity metabolism by reducing resting metabolic rate. Accepted: 18 July 1999     

Direct effects of corticosterone on ATP production by mitochondria from immortalized hypothalamic GT1-7 neurons

Glucocorticoids are known to decrease intracellular ATP levels in the brain. This study was performed to investigate whether corticosterone at physiological levels depresses mitochondrial ATP production by directly acting on mitochondria. Mitochondria were isolated from immortalized hypothalamic GT1-7 neurons. ATP levels were determined using a luciferase–luciferin assay. When malate, α-ketoglutarate or pyruvate was used as a respiration substrate, corticosterone at ≥100 nM decreased ATP production by 10%. In contrast, corticosterone did not affect ATP production when succinate or N,N,N′,N′-tetramethyl-p-phenylenediamine + ascorbate were used. To investigate the specificity of corticosterone inhibition, we examined several steroids. All steroids tested suppressed mitochondrial ATP production by 10% at a concentration of 100 nM, in a manner similar to that of corticosterone. To examine the effects of corticosterone on GT1-7 cell physiology, we incubated GT1-7 cells with t-butyl hydroperoxide (t-BuOOH) with corticosterone. Corticosterone largely enhanced t-BuOOH-induced cell death. These results indicate that corticosterone non-specifically inhibits mitochondrial ATP production by suppressing electron transfer from NADH to the electron transfer chain through complex I. Partial inhibition of mitochondrial ATP production by corticosterone may contribute to oxidative stress-induced cell death.     

Impact of season and social challenge on testosterone and corticosterone levels in a year-round territorial bird

Plasma testosterone increases during breeding in many male vertebrates and has long been implicated in the promotion of aggressive behaviors relating to territory and mate defense. Males of some species also defend territories outside of the breeding period. For example, the European nuthatch (Sitta europaea) defends an all-purpose territory throughout the year. To contribute to the growing literature regarding the hormonal correlates of non-breeding territoriality, we investigated the seasonal testosterone and corticosterone profile of male (and female) nuthatches and determined how observed hormone patterns relate to expression of territorial aggression. Given that non-breeding territoriality in the nuthatch relates to the reproductive context (i.e., defense of a future breeding site), we predicted that males would exhibit surges in plasma testosterone throughout the year. However, we found that males showed elevated testosterone levels only during breeding. Thus, testosterone of gonadal origin does not appear to be involved in the expression of non-breeding territoriality. Interestingly, territorial behaviors of male nuthatches were stronger in spring than in autumn, suggesting that in year-round territorial species, breeding-related testosterone elevations may upregulate male-male aggression above non-breeding levels. In females, plasma testosterone was largely undetectable. We also examined effects of simulated territorial intrusions (STIs) on testosterone and corticosterone levels of breeding males. We found that STIs did not elicit a testosterone response, but caused a dramatic increase in plasma corticosterone. These data support the hypothesis that corticosterone rather than testosterone may play a role in the support of behavior and/or physiology during acute territorial encounters in single-brooded species.     

Relationships between hormones, physiological performance and immunocompetence in a color-polymorphic lizard species, Podarcis melisellensis

Species with alternative phenotypes offer unique opportunities to investigate hormone-behavior relationships. We investigated the relationships between testosterone, corticosterone, morphology, performance, and immunity in a population of lizards (Podarcis melisellensis) which exhibits a color polymorphism. Males occur in three different color morphs (white, yellow, orange), providing an opportunity to test the idea of morphs being alternative solutions to the evolutionary challenges posed on the link between hormones, morphology, performance, and immunity. Morphs differed in bite force capacity, with orange males biting harder, and in corticosterone levels, with yellow males having lower levels than orange. However, morphs did not differ in testosterone levels or in the immunological parameters tested. At the individual level, across morphs, testosterone levels predicted size-corrected bite force capacity, but no relation was found between hormone levels and immunity. Our results do not support the testosterone-based polymorphism hypothesis and reject the hypothesis of a trade-off between testosterone and immunity in this species, but provide a mechanistic link between testosterone and a sexually selected performance trait.     

Effects of 17-β-estradiol treatment of female zebra finches on offspring sex ratio and survival

Treatment of female zebra finches (Taeniopygia guttata) with 17-beta-estradiol leads to a female-biased sex ratio in their offspring at the age of independence [Horm. Behav. 35 (1999) 135]. It is unclear whether this is due to a bias of the primary sex ratio or to sex-specific survival. We replicated this experiment and found again a significantly higher total number of daughters than sons at independence in the estradiol-treated group. This was due to higher embryonic survival of daughters compared with sons in the estradiol-treated group and the reverse in the control group. There was no effect of the hormone treatment on the primary sex ratio. Treatment with 17-beta-estradiol led to a significantly shorter hatching time and to heavier offspring at day 7 after hatching. This weight was correlated with maternal plasma estradiol levels on the day of the first egg, which were significantly higher in the estradiol-treated group than in the control group. The results do not support the idea that maternal estradiol levels influence the primary sex ratio. They indicate that maternal estradiol differentially affects survival of sons and daughters via an influence on the embryonic environment, possibly enhancing offspring growth.     

The response of the hypothalamo-gonadal system to environmental factors in the zebra finch,Poephila guttata castanotis

Summary Studies of the hypothalamo-gonadal response of the zebra finch (Poephila guttata castanotis) to environmental factors were conducted by the use of adult birds captured in arid regions of South Australia. In these birds breeding activity is not photoperiodically induced but follows rainfall. The hypothalamo-hypophysial system participating in this response involves centres of the rostral and mediobasal (tuberal) hypothalamus. Parvocellular neurones in both hypothalamic portions are arranged in clusters. In the rostral hypothalamus magnocellular neurosecretory perikarya are spatially closely associated with the clusters which contain different types of parvocellular peptidergic neurones. Extended, complex neuropile formations, rich in synapses, encompass the neuronal clusters and provide important loci of neural-neuroendocrine interaction.Experiments were undertaken to correlate indicators of breeding activity, such as increased size and mass of testes, spermatogenesis, and plasma levels of androgens and luteinizing hormone, with a greater availability of drinking water, increased air humidity, and green vegetation, all of which follow rainfall. Birds maintained in male/female pairs in controlled-environment rooms at 27° C on 14L10D received a diet of seeds (containing 10% water). Thirty-two birds were given drinking water at a basal level of 1 ml/week and one of eight different treatments, consisting of different combinations of drinking water, relative air humidity, and green grass, for two weeks (4 males/treatment). The size of the left testis was estimated at laparotomy and blood samples were taken from a wing vein before and after treatment. The observations suggest that, in moisture-deprived (1 ml water/week) adult zebra finches, an increase in testicular size is associated with a free supply of water; synergistic effects of supplying both water and green grass, or water and high humidity, were also observed. However, in six other groups (8–16 males/treatment), receiving a higher basal level of water (access for 3 min/day), an increase in testicular mass was associated with high humidity, while smaller non-significant increases followed the provision of free water or green grass. Spermatogenic activity was not significantly correlated with testicular size or mass. Leydig cells were sparse in all groups. Plasma androgen levels and luteinizing hormone levels were not obviously correlated with the treatments and were lower than values in zebra finches breeding in outdoor aviaries.According to K.C. Parkes; see Note on Taxonomy, p. XVII, Avian Biology, Vol. IV (D.S. Farner, J.R. King, eds.), Academic Press, New York/London, 1974. Taeniopygia guttata castanotis is widely used for this subspecies in non-taxonomic literature.     

Changes in masculine sexual behavior, corticosterone and testosterone in response to acute and chronic stress in male rats

Chronic exposure to stressors increases HPA axis activity and concomitantly reduces HPG axis activity. This antagonistic relationship between both these axes has been proposed to underlie the inhibition of reproductive function due to stress. Sexual behavior in males may be the most vulnerable aspect of male reproduction to acute and chronic stress and it has been suggested that alterations in sexual behavior during stress are due to the antagonistic relationship between testosterone and corticosteroids. However, only in a few studies has a correlation between the levels of testosterone and corticosterone, and sexual behavior been made. In this study, we evaluated the effects of different stressors, applied both acute and chronically, on masculine sexual behavior and whether or not these effects on sexual behavior are accompanied by changes in plasma levels of corticosterone and testosterone. Additionally, we evaluated the effect of testosterone treatment on the effects of stress on sexual behavior. Sexually experienced male rats were exposed to one of the following stressors: immobilization (IMB), electric foot shocks (EFS) or immersion in cold water (ICW). Sexual behavior and plasma levels of testosterone and corticosterone were assessed on days 1, 5, 10, 15, and 20 of stress. In a second experiment, males were castrated, treated with 3 different doses of testosterone propionate (TP) and exposed to ICW for 20 consecutive days. Sexual behavior was assessed on days 1, 5, 10, 15, and 20 and steroids were evaluated on day 20. Parameters of masculine sexual behavior were modified depending on the characteristics of each stressor. Mount, intromission and ejaculation latencies increased significantly, the number of mounts increased, and ejaculations decreased significantly in males exposed to EFS and to ICW but not in males exposed to IMB. Associated with these effects, testosterone decreased in the EFS and ICW groups on days 1, 15, and 20. However, corticosterone increased only in males exposed to ICW. In castrated males, TP treatment failed to block the effects of stress by ICW on sexual behavior and corticosterone. These results indicate that the effects of stress on sexual behavior depend on the characteristics of each stressor, and these effects, as well as the decrease in testosterone are not necessarily associated with the increase in corticosterone. The fact that testosterone treatment did not prevent the effects of stress on sexual behavior suggests that other mediators could be involved in the alterations of sexual behavior caused by stress.