Effects of social status, age, and season on androgen and cortisol levels in wild male golden lion tamarins (Leontopithecus rosalia)

Environmental and social influences on neuroendocrine puberty and behavior in macaques and other nonhuman primates

This article is part of a Special Issue "Puberty and Adolescence". Puberty is the developmental period when the hypothalamic-pituitary-gonadal (HPG) axis is activated, following a juvenile quiescent period, and reproductive capacity matures. Although pubertal events occur in a consistent sequence, there is considerable variation between individuals in the onset and timing of pubertal events, with puberty onset occurring earlier in girls than in boys. Evidence in humans demonstrates that social and environmental context influences the timing of puberty onset and may account for some of the observed variation. This review analyzes the nonhuman primate literature, focusing primarily on rhesus macaques (Macaca mulatta), to examine the social and environmental influences on puberty onset, how these factors influence puberty in males and females, and to review the relationship between puberty onset of adult neuroendocrine function and sexual behavior. Social and environmental factors influence the timing of puberty onset and pubertal events in nonhuman primates, as in humans, and the influences of these factors differ for males and females. In nonhuman primates, gonadal hormones are not required for sexual behavior, but modulate the frequency of occurrence of behavior, with social context influencing the relationship between gonadal hormones and sexual behavior. Thus, the onset of sexual behavior is independent of neuroendocrine changes at puberty; however, there are distinct behavioral changes that occur at puberty, which are modulated by social context. Puberty is possibly the developmental period when hormonal modulation of sexual behavior is organized, and thus, when social context interacts with hormonal state to strongly influence the expression of sexual behavior.

Effect of reproductive status on hypothalamic-pituitary-adrenal (HPA) activity and reactivity in male California mice (Peromyscus californicus)

Previous studies indicate that reproductive condition can alter stress response and glucocorticoid release. Although the functional significance of hypothalamic-pituitary-adrenal (HPA) axis modulation by breeding condition is not fully understood, one possible explanation is the behavior hypothesis, which states that an animal's need to express parental behavior may be driving modulation of the HPA axis. This possibility is consistent with findings of blunted activity and reactivity of the HPA axis in lactating female mammals; however, effects of reproductive status on HPA function have not been well characterized in male mammals that express parental behavior. Therefore, we tested this hypothesis in the monogamous and biparental California mouse. Several aspects of HPA activity were compared in males from three reproductive conditions: virgin males (housed with another male), non-breeding males (housed with a tubally ligated female), and first-time fathers (housed with a female and their first litter of pups). In light of the behavior hypothesis we predicted that new fathers would differ from virgin and non-breeding males in several aspects of HPA function and corticosterone (CORT) output: decreased amplitude of the diurnal rhythm in CORT, a blunted CORT increase following predator-odor stress, increased sensitivity to glucocorticoid negative feedback, and/or a blunted CORT response to pharmacological stimulation. In addition, we predicted that first-time fathers would be more resistant to CORT-induced suppression of testosterone secretion, as testosterone is important for paternal behavior in this species. We found that virgin males, non-breeding males and first-time fathers did not display any CORT differences in diurnal rhythm, response to a predator-odor stressor, or response to pharmacological suppression or stimulation. Additionally, there were no differences in circulating testosterone concentrations. Adrenal mass was, however, significantly lower in new fathers than in virgin or non-breeding males. These results suggest that the behavior hypothesis does not explain HPA function across reproductive conditions in male California mice.

The association of intergroup encounters, dominance status, and fecal androgen and glucocorticoid profiles in wild male white-faced capuchins (Cebus capucinus)

Androgens play a role in male reproductive competition, frequently via aggression, while glucocorticoids are associated with the stress response. However, the relationships of these hormones with different sources of competition (intra- vs. intergroup) and dominance status are highly variable. Here, we consider the fecal androgen (fA) and glucocorticoid (fGC) profiles of alpha and subordinate male Cebus capucinus in the context of intergroup competition during a rare period of low intragroup competition (i.e. all females were either pregnant or lactating). Intergroup encounters (IGEs) are a long-term reproductive strategy in male white-faced capuchins, enabling them to assess the composition of neighboring groups. IGEs pose a threat to resident males as these can result in injury or death, loss of dominance rank, group eviction, and group takeovers that are frequently associated with infanticide. From February to July 2007, fecal samples were collected from eight males in three groups of white-faced capuchins in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. IGE rate was positively associated with both fA and fGC levels, indicating that IGEs are perceived as reproductive challenges by resident males, and may be associated with elevated metabolic costs. Alpha males sire the majority of group offspring and, accordingly, the threat of IGEs to both future (via rank loss or eviction) and current (via infanticide) reproductive success is greater than for subordinate males. Consistent with this observation, alpha males had higher fA and fGC levels than subordinate males. Given that all females were either pregnant or lactating and pronounced overt intragroup competition was absent, we interpret the difference in hormone profiles of alpha and subordinate males as being primarily associated with variation in the perceived threats of IGEs according to dominance status. Future studies should focus on the interaction of intra- and intergroup competition by examining hormone levels in the presence of periovulatory females.

The endocrinology of male rhesus macaque social and reproductive status: a test of the challenge and social stress hypotheses

Social status primarily determines male mammalian reproductive success, and hypotheses on the endocrinology of dominance have stimulated unprecedented investigation of its costs and benefits. Under the challenge hypothesis, male testosterone levels rise according to competitive need, while the social stress hypothesis predicts glucocorticoid (GC) rises in high ranking individuals during social unrest. Periods of social instability in group-living primates, primarily in baboons, provide evidence for both hypotheses, but data on social instability in seasonally-breeding species with marked social despotism but lower reproductive skew are lacking. We tested these hypotheses in seasonally-breeding rhesus macaques on Cayo Santiago, Puerto Rico. We documented male fecal GC and androgen levels over a 10 month period in relation to rank, age, natal status and group tenure length, including during a socially unstable period in which coalitions of lower-ranked males attacked higher-ranked males. Androgen but not GC levels rose during the mating season; older males had lower birth season levels but underwent a greater inter-season rise than younger males. Neither endocrine measure was related to rank except during social instability, when higher ranked individuals had higher and more variable levels of both. High ranking male targets had the highest GC levels of all males when targeted, and also had high and variable GC and androgen levels across the instability period. Our results provide evidence for both the challenge and social stress hypotheses.

Female parity, male aggression, and the Challenge Hypothesis in wild chimpanzees

The Challenge Hypothesis proposes that testosterone mediates aggression during periods of heightened conflict between males, especially episodes that have important fitness consequences. Considerable evidence from seasonally breeding species provides support for this hypothesis, but few data exist in animals that mate year-round. We tested predictions generated by the Challenge Hypothesis in chimpanzees, a non-seasonally breeding primate, through a study of individuals living in an exceptionally large community at Ngogo, Kibale National Park, Uganda. Results indicated that dominance rank had no influence on testosterone levels. Instead of rank influencing testosterone production, additional analyses revealed an important role for reproductive competition. Male chimpanzees displayed more aggression when they were in the same party as parous estrous females than when reproductively active females were unavailable. Male chimpanzees competed more intensely for mating opportunities with parous females than with nulliparas, and as a consequence, males displayed more aggression around the former than the latter. When males accompanied parous estrous females, their urinary testosterone concentrations were significantly higher than baseline concentrations. In contrast, urinary testosterone concentrations did not exceed baseline when males associated with nulliparous estrous females. These differences in testosterone levels could not be attributed to mating per se because males copulated equally often with parous and nulliparous females. Furthermore, variation in testosterone concentrations were not due to males gathering together in large parties, as their levels in these situations did not exceed baseline. Taken together, these findings, derived from a relatively large sample of males and estrous females, replicate those from a prior study and furnish additional support for the Challenge Hypothesis. Our results suggest that the Challenge Hypothesis is likely to be broadly applicable to chimpanzees and increase our understanding of the physiological costs to males who compete for estrous females.

Social status, glucocorticoids, immune function, and health: can animal studies help us understand human socioeconomic-status-related health disparities?

For humans in developed nations, socioeconomic status (SES)--relative income, education and occupational position in a society--is a strong predictor of morbidity and mortality rates, with increasing SES predicting longer life span (e.g. Marmot et al., 1991). Mechanisms underlying this relationship have been examined, but the relative role of each mechanism still remains unknown. By understanding the relative role of specific mechanisms that underlie dramatic health disparities between high and low social status individuals we can begin to identify effective, targeted methods to alleviate health disparities. In the current paper, we take advantage of a growing number of animal studies that have quantified biological health-related correlates (glucocorticoid production and immune function) of social status and compare these studies to the current literature on human SES and health to determine if and how animal studies can further our understanding of SES-associated human health disparities. Specifically, we compared social-status related glucocorticoid production and immune function in humans and animals. From the review, we show that our present understanding of the relationships between social status and glucocorticoid production/immune function is still growing, but that there are already identifiable parallels (and non-parallels) between humans and animals. We propose timely areas of future study focused on (1) specific aspects of social status that may influence stress-related physiology, (2) mechanisms underlying long-term influences of social status on physiology and health, and (3) intervention studies to alleviate potentially negative physiological correlates of social status.

The Steroid/Peptide Theory of Social Bonds: integrating testosterone and peptide responses for classifying social behavioral contexts

Hormones, and hormone responses to social contexts, are the proximate mechanisms of evolutionary pathways to pair bonds and other social bonds. Testosterone (T) is implicated in tradeoffs relevant to pair bonding, and oxytocin (OT) and arginine vasopressin (AVP) are positively tied to social bonding in a variety of species. Here, we present the Steroid/Peptide Theory of Social Bonds (S/P Theory), which integrates T and peptides to provide a model, set of predictions, and classification system for social behavioral contexts related to social bonds. The S/P Theory also resolves several paradoxes apparent in the literature on social bonds and hormones: the Offspring Defense Paradox, Aggression Paradox, and Intimacy Paradox. In the S/P Theory, we partition aggression into antagonistic and protective aggression, which both increase T but exert distinct effects on AVP and thus social bonds. Similarly, we partition intimacy into sexual and nurturant intimacy, both of which increase OT and facilitate social bonds, but exert distinct effects on T. We describe the utility of the S/P Theory for classifying 'tricky' behavioral contexts on the basis of their hormonal responses using partner cuddling, a behavior which is assumed to be nurturant but increases T, as a test case of the S/P Theory. The S/P Theory provides a comparative basis for conceptualizing and testing evolved hormonal pathways to pair bonds with attention to species, context, and gender/sex specificities and convergences.

Social factors increase fecal testosterone levels in wild male gray-cheeked mangabeys (Lophocebus albigena)

Testosterone can be expected to play a significant role in mediating behavior and life history in social animals, but the number of species with data from the wild is still too small to make generalizations. We investigated the influence of social factors (social status, aggression, and reproductive females) and environmental variation (rainfall and temperature) on fecal testosterone concentrations in wild male gray-cheeked mangabeys (Lophocebus albigena) living in five groups in Kibale National Park, Uganda. This species is phylogenetically closely related to baboons, but is arboreal, with multi-male, multi-female groups rarely exceeding 20 individuals. We analyzed 358 fecal samples from 21 adult males. We found that the highest-ranking males had the highest testosterone concentrations while immigrant males had the lowest testosterone concentrations. Aggression was not correlated with testosterone levels. The presence of females with sexual swellings at their most tumescent stage increased testosterone concentrations in all males. Finally, individuals tended to have lower testosterone when the temperature was higher.

Social and developmental influences on urinary androgen levels in young male white-faced marmosets (Callithrix geoffroyi)

Callitrichine primates (marmosets and tamarins) often remain in their natal groups beyond the time of sexual maturity. Although studies have characterized the development of female reproductive function in callitrichine offspring, less is known about the male reproductive development. To document reproductive development in male marmosets, we monitored urinary androgen (uA) excretion in males housed in a captive colony of white-faced marmosets (Callithrix geoffroyi). Young male marmosets showed relatively low and stable rates of uA excretion early in life, with elevated production at the end of the juvenile period (9-10 months) and again at the onset of adulthood (16 months). uA levels of adult breeding males were also measured to compare to adult-aged sons. Although breeding males did have higher uA levels than their adult-aged sons, these differences did not reach conventional levels of significance. Evidence from some other reports has suggested that androgen levels of males in other species are influenced by social factors, such as the presence of a sexually receptive female or of dependent offspring. In this study, however, uA levels did not vary, based on their mothers' pregnancy status or the presence of younger siblings in the natal group. Patterns of androgen excretion in the white-faced marmoset roughly reflect those of other callitrichine species. Furthermore, unlike callitrichine daughters, gonadal activity in sons does not seem to be sensitive to within-group social cues.

Endocrinology of year-round reproduction in a highly seasonal habitat: environmental variability in testosterone and glucocorticoids in baboon males

In conditions characterized by energetic constraints, such as in periods of low food availability, some trade-offs between reproduction and self-maintenance may be necessary; even year-round breeders may then be forced to exhibit some reproductive seasonality. Prior research has largely focused on female reproduction and physiology, and few studies have evaluated the impact of environmental factors on males. Here we assessed the effects of season and ambient temperatures on fecal glucocorticoid (fGC) and testosterone (fT) levels in male baboons in Amboseli, Kenya. The Amboseli basin is a highly challenging, semiarid tropical habitat that is characterized by strongly seasonal patterns of rainfall and by high ambient temperatures. We previously reported that female baboons were impacted by these challenging environmental conditions. We ask here whether male baboons in the same environment and groups as females exhibit similar physiological effects. We found that after accounting for male age and individual variability, males exhibited higher fGC levels and lower fT levels during the dry season than during the wet season. Furthermore, fT but not fGC levels were lower in months of high average daily maximum temperatures, suggesting a direct impact of heat on testes. Our results demonstrate that male baboons, like females, experience ecological stress that alters their reproductive physiology. The impact of the environment on male reproduction deserves more attention both in its own right and because alteration in male physiology may contribute to the reduction in female fertility observed inchallenging environments.

Male competition and its hormonal correlates in Assamese macaques (Macaca assamensis)

In polygynous mammals, where males compete over access to females, the potential of males to monopolize reproductive females largely depends on the spatio-temporal distribution of reproductive females. We investigated mechanisms of male reproductive competition and its hormonal basis in a cercopithecine species with reduced contest potential owing to female reproductive synchrony and concealed ovulation. Over 16 months including two mating seasons we collected 1218 h of observational focal animal data and 1254 fecal samples of 11-12 adult and large subadult male Assamese macaques (Macaca assamensis) living in their natural habitat in Thailand. Androgen output along with aggressive behavior showed a seasonal pattern, with highest values being obtained by all males during the mating season and by those males experiencing acute social challenges, e.g. rank change and dispersal. Individual androgen levels and rates of attacks were linked across the study period, suggesting a promoting function of androgens for aggressive behavior. Dominance rank predicted neither mating success nor androgen levels consistently, indicating a reduced selective advantage of high social status for general mating access. However, high ranking males engaged in extended consortships with reproductive females. Distribution of consortships across males followed a priority of access distribution, with the two top ranking males accounting for 75% of consort activity, suggesting that high social status also carries fitness benefits in a species characterized by low contest potential.

Sources of variation in fecal cortisol levels in howler monkeys in Belize

High cortisol levels are known to cause low fecundity and increased mortality; thus, the prospect of using cortisol as a measure of population health is an exciting one. However, because so many factors can interact to influence cortisol release, it can be difficult to interpret what exactly is creating changes to cortisol levels. This study investigates variation in fecal cortisol levels in a population of black howlers (Alouatta pigra) from 350 fecal samples collected from 33 individuals in more than 4 years. A general linear mixed model revealed that cortisol varied significantly with fruit availability and contact with tourists. When fruit availability was low, cortisol increased, likely because when fruit availability is low monkeys eat less fruit, thus obtaining less sugar. This result may simply reflect cortisol's metabolic function of mobilizing glucose. It also indicates that these monkeys may be experiencing periods of food stress throughout the year, which was earlier thought to be minimal for a primarily folivorous species. Presence of tourists was the only other factor found to lead to high cortisol; with exposure to tourists increasing stress levels. These results highlight the importance of understanding how physiological factors can influence cortisol, making it easier to interpret results and determine the external social or ecological stressors that may increase cortisol.

Endocrine milieu of perioestrus in the giant panda (Ailuropoda melanoleuca), as determined by non-invasive hormone measures

The aim of the present study was to determine the efficacy of faecal hormonal measures for evaluating ovarian activity in a significant sized cohort of giant pandas during the perioestrual period. Faecal excretion of oestrogen and progestagen metabolites corresponded with urinary patterns and receptive behaviours. Longitudinal assessment of 10 females revealed that, on average, faecal oestrogen concentrations started to rise (P < 0.05) above baseline (baseline mean ± s.e.m.; 64.7 ± 6.6 ng g−1) 5 days before the preovulatory oestrogen peak (484.6 ± 126.8 ng g−1), which was followed by a gradual descent over 4 days to nadir. Mean faecal progestagen metabolite concentrations increased approximately twofold above baseline (from 186.2 ± 37.7 to 347.2 ± 75.7 ng g−1; P < 0.05) during the 20-day interval after the preovulatory oestrogen surge. Variability within and among females precluded the use of a threshold of oestrogen or progestagen metabolites to predict reproductive status, yet faeces collected 2–3 days per week provided sufficient data to recognise that an individual was in the perioestrual period. Finally, in females that were examined for at least 3 consecutive years, there was an 18–53 day variation in the onset and an 8–13 day variation in the duration of perioestrual behaviour from year to year. In summary, these findings indicate that gonadal hormone profiles associated with the period immediately before, during and after oestrus are accurately revealed by analysis of the fibrous faeces of the giant panda. This approach has potential value for providing point-in-time information on the reproductive status of free-living individuals.

Seasonal and social influences on fecal androgen and glucocorticoid excretion in wild male long-tailed macaques (Macaca fascicularis)

Whereas it is well known that in strictly seasonal breeding primates (income breeders), alike other vertebrates, males show pronounced changes in testicular and adrenal hormone levels concurrent with reproductive activity, hormonal patterns in males of non-strictly seasonal breeding primate species (capital breeders) and their relation to seasonal and social correlates remain largely unknown. In the present study, we examined the annual pattern of fecal androgen and glucocorticoid excretion and their relationship to environmental (rainfall, temperature) and social factors (number of cycling females, male aggression and copulation rates, male dominance rank) in a group of wild long-tailed macaques (Macaca fascicularis), a species with a moderate degree of reproductive seasonality and classified as capital breeder. The study was carried out in the Gunung Leuser National Park, North Sumatra, Indonesia over a period of ten months encompassing the conception and the birth season. Our results show that male long-tailed macaques exhibit a distinct annual variation in both androgen and glucocorticoid levels. Androgen (but not glucocorticoid) levels were significantly elevated during the conception period in association with elevated rates of male-male aggression and copulatory activity, both strongly related to the number of cycling females in the group. Neither glucocorticoid nor androgen levels were related to male dominance rank or to the environmental parameters investigated. Interestingly, levels of both hormones started to increase in the late birth season and thus 1-2 months prior to the mating season, suggesting that male long-tailed macaques go through pre-breeding hormonal changes in preparation for prospective challenges. Our data thus provide the first evidence that males of a non-strictly seasonal breeding species/capital breeder show endocrine patterns generally similar to those found in strictly seasonal/income breeders.

Reproductive tactics influence cortisol levels in individual male gray-cheeked mangabeys (Lophocebus albigena)

Concentration of the hormone cortisol is often used as an indicator of stress, and chronically high cortisol levels are often associated with poor health. Among group living animals that compete for resources, agonistic social interactions can be expected to contribute to variation in cortisol levels within and among individuals over time. Reproductive tactics of males can change with individual quality, relatedness, and social structure, and affect cortisol levels. In gray-cheeked mangabey (Lophocebus albigena) groups, male rank is an important factor in social interactions, and males also move between groups while actively competing for females or sneaking copulations. During a 20-month study we observed the social behavior and collected 461 fecal samples from 24 adult male gray-cheeked mangabeys from five groups in Kibale National Park, Uganda. Aggressive interactions and the presence of females at the peak of sexual swelling were associated with elevated cortisol concentrations in all males. Independently, dominant (i.e., highest-ranking) males within groups had higher cortisol concentrations than subordinate males, and immigrant males had higher cortisol concentrations than dominant males.

Adaptive genetic variation, stress and glucose regulation

Elevated glucose levels in the presence of insulin are indicative of type 2 diabetes and the more inclusive metabolic syndrome. Alleles conferring susceptibility to these and other common conditions may be adaptations to past environments. It is possible that other mammals exhibiting environmental diversity harbor similar variants; therefore, we assessed glucose regulation in two species of deer mice (Peromyscus), a diverse endemic North American group. The prairie deer mouse, P. maniculatus bairdii (BW), and the Oldfield mouse, P. polionotus subgriseus (PO) differ in sexual dimorphism, behavior and habitat. PO animals exhibit better regulatory ability than BW animals, particularly among males, although both species display equivalent insulin levels/responses and non-fasted glucose levels. Hybrid males exhibit a PO glucose challenge response and subsequent analysis of consomic animals implicates Y chromosome variation as the genetic cause. Two pieces of evidence indicate that the male glucose regulatory differences are mediated by stress response: (1) fasting and handling alone account for most of the variation; (2) an inhibitor of glucocorticoid (GC) stress hormone synthesis eliminates these differences. PO males have GC levels that are twice those of BW males, indicating the presence of alleles that attenuate the GC response. We hypothesize that the interspecific physiological and behavioral differences are interrelated and that similar human variants exist.

The Effects of Kin on Primate Life Histories

Advances in our understanding of primate life histories and dispersal patterns provide insights into the ways in which facultative responses to local ecological and demographic conditions are mediated by phylogenetic constraints. The long life spans characteristic of primates provide the necessary conditions for overlapping generations of related individuals to maintain extended kin bonds. Dispersal regimes dictate the opportunities for biological kin to interact with one another and define the range of potential reproductive and social partners within and beyond their natal groups. Dispersal patterns also affect variation in components of life histories such as female age at first reproduction, reproductive rates, and trade-offs between investment in current vs. future offspring and extended kin. Understanding these dynamics has important implications for assessing the viability of small populations and the ability of different primates to adapt.

Social correlates of fecal testosterone in male ursine colobus monkeys (Colobus vellerosus): the effect of male reproductive competition in aseasonal breeders

Male testosterone (T) levels are thought to be linked with the mating system, degree of parental care, and male-male aggression in reproductive contexts (The 'challenge hypothesis'; Wingfield et al., 1990). In many species though, T increases associated with mating behavior cannot be separated from those associated with male-male aggression. We tested the challenge hypothesis on aseasonally breeding ursine colobus (Colobus vellerosus), where male-male competition is intense outside of mating contexts. Fecal samples (N=109) were collected from >27 subadult and adult males in seven groups during 13-months of research in Ghana in 2004-2005. Fecal T (fT) levels were determined by enzyme immunosorbant assays. Behavioral data was collected using focal-animal and ad libitum sampling. The number of receptive females in each group did not positively correlate with male fT. There was a trend for adult males to have higher fT than subadult males; however there was no effect of rank on fT. The level of male-male aggression experienced was positively correlated with fT and individual males showed higher mean fT during 'challenge' than during 'non-challenge' periods. The number of male incursions experienced positively correlated with fT whereas the number of between-group encounters did not. Males attempt to gain reproductive opportunities during incursions, thus these results support the 'challenge hypothesis' in C. vellerosus. Outside of mating contexts, higher male fT levels are associated with increased aggression. Male parental investment in the form of infant defense was associated with increased fT, rather than the decline expected from other forms of paternal care.

Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus

Given the dramatic behavioral effects of winning and losing contests, and pronounced changes in stress and sex steroid hormones post-fight, it is reasonable to suppose that these hormones also dictate future behavior. We sampled water-borne cortisol, testosterone (T), and 11-ketotestosterone (KT) before and after contests in the mangrove killifish, Kryptolebias marmoratus, to determine how endogenous steroid hormone levels might predict and respond to contest dynamics or success. Pre-fight cortisol related negatively, and pre-fight T related positively to contest initiation and winning, particularly in the smaller opponent. In the pairs where a larger fish won the contest, winners with higher pre-fight T and lower pre-fight cortisol delivered more attacks to the losers. Contest duration and escalation influenced post-fight hormone concentrations primarily in losers. Escalation significantly increased post-fight cortisol, T, and KT for losers but not for winners. However, winners that attacked losers at higher rates had higher levels of post-fight cortisol. Losers also demonstrate the most consistent post-fight hormone responses, particularly to contest escalation and duration. Despite the bidirectional relationship between hormones and contest behavior, we found no overall mean differences in pre- or post-fight cortisol, T, or KT between eventual winners and losers. Thus, it is evident that the categorical states of winner and loser cannot alone reveal the complex, reciprocal associations between endocrine systems and social behavior.

Androgen and glucocorticoid levels reflect seasonally occurring social challenges in male redfronted lemurs (Eulemur fulvus rufus)

Intense reproductive competition and social instability are assumed to increase concentrations of glucocorticoids and androgens in vertebrates, as a means of coping with these challenges. In seasonally breeding redfronted lemurs (Eulemur fulvus rufus), the mating and the birth season and the associated increased male competition are predicted to pose such reproductive challenges. In this paper, we investigate seasonal variation in hormone excretion in male redfronted lemurs, and examine whether this variation is associated with social or ecological factors. Although dominance status has been shown to affect individual stress levels across many taxa, we predicted no rank-related differences in glucocorticoids for redfronted lemurs because relatively equal costs are associated with both high and low rank positions (based on patterns of rank acquisition/maintenance and threats toward subordinates). Over a 14-month period, we collected behavioral data (1843 focal hours) and 617 fecal samples from 13 redfronted lemur males in Kirindy Forest/Madagascar. We found no general rank-related pattern of testosterone or glucocorticoid excretion in this species. Both hormones were excreted at significantly higher levels during the mating and the birth season, despite social stability during both periods. The elevated mating season levels may be explained by increased within-group reproductive competition during this time and are in line with previous studies of other seasonally reproducing primates. For the birth season increase, we propose that the predictable risk of infanticide in this highly seasonal species affects male gonadal and adrenal endocrine activity. We evaluate alternative social and ecological factors influencing the production of both hormone classes and conclude based on our preliminary investigations that none of them can account for the observed pattern.

Parasite community interactions: Trypanosoma cruzi and intestinal helminths infecting wild golden lion tamarins Leontopithecus rosalia and golden-headed lion tamarins L. chrysomelas (Callitrichidae, L., 1766)

The parasite prevalence and infection intensity in primate wild populations can be affected by many variables linked to host and/or parasite ecology or either to interparasite competition/mutualism. In this study, we tested how host sex, age, and place of origin, as well parasitic concomitant infections affect the structure of golden lion and golden-headed lion tamarins parasite community, considering Trypanosoma cruzi and intestinal helminths infection in these primates. A total of 206 tamarins from two Atlantic Coastal rain forest areas in Brazil were tested during 4 years for prevalence of T. cruzi infection and helminth prevalence. Three intestinal helminth groups showed high prevalences in both tamarin species: Prosthenorchis sp., Spiruridae, and Trichostrongylidae. An association between presence of T. cruzi infection and higher intestinal helminth prevalence was found in both tamarin species. Two explanations for this association seem to be plausible: (1) lower helminth-linked mortality rates in T. cruzi-infected tamarins and (2) lower elimination rates of helminths in such tamarins. A higher frequency of T. cruzi-positive blood cultures was significantly correlated to female tamarins and to the presence of Trichostrongylidae infection. The possibility of an increase in the transmissibility of T. cruzi and the three analyzed helminths in lion tamarins with concomitant infections is discussed.