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

Physiological plasticity in elephants: highly dynamic glucocorticoids in African and Asian elephants

Slowly reproducing and long-lived terrestrial mammals are often more at risk from challenges that influence fitness and survival. It is, therefore, important to understand how animals cope with such challenges and how coping mechanisms translate over generations and affect phenotypic plasticity. Rapidly escalating anthropogenic challenges may further diminish an animal's ability to reinstate homeostasis. Research to advance insights on elephant stress physiology has predominantly focused on relative or comparative analyses of a major stress response marker, glucocorticoids (GCs), across different ecological, anthropogenic, and reproductive contexts. This paper presents an extensive review of published findings on Asian and African elephants from 1980 to 2023 (May) and reveals that stress responses, as measured by alterations in GCs in different sample matrices, often are highly dynamic and vary within and across individuals exposed to similar stimuli, and not always in a predictable fashion. Such dynamicity in physiological reactivity may be mediated by individual differences in personality traits or coping styles, ecological conditions, and technical factors that often are not considered in study designs. We describe probable causations under the 'Physiological Dynamicity Model', which considers context-experience-individuality effects. Highly variable adrenal responses may affect physiological plasticity with potential fitness and survival consequences. This review also addresses the significance of cautious interpretations of GCs data in the context of normal adaptive stress versus distress. We emphasize the need for long-term assessments of GCs that incorporate multiple markers of 'stress' and 'well-being' to decipher the probable fitness consequences of highly dynamic physiological adrenal responses in elephants. Ultimately, we propose that assessing GC responses to current and future challenges is one of the most valuable and informative conservation tools we have for guiding conservation strategies.

Hormonal responses to mating competition in male Tonkean macaques

Glucocorticoid and androgen hormones play a prominent role in male reproductive effort. Their production usually increases in non-human primates during mating competition, which may include rivalry for access to receptive females, struggles for high dominance rank, or social pressure on low-ranking individuals. It is generally assumed that glucocorticoids and androgens are associated with mating challenges rather than dominance status, but the involvement of multiple factors makes it difficult to disentangle the two. In this regard, Tonkean macaques provide a suitable model because they are characterized by relaxed dominance and year-round breeding, meaning that there is typically no more than one receptive female in a group, and thus first-ranking males can easily monopolize her. We studied two captive groups of Tonkean macaques over an 80-month period, recording the reproductive status of females, collecting urine from males and sampling behaviors in both sexes. Male urinary hormone concentrations could be affected by increased competition caused by the mating period, the number of males and the degree of female attractiveness. The highest increases in androgens were recorded in males performing female mate-guarding. Despite the importance of dominance status in determining which males can mate, we found no significant effect of male rank on glucocorticoids and only a marginal effect on androgens during mate-guarding. Both types of hormones were more directly involved in the mating effort of males than in their dominance status. Our results show that their function can be understood in light of the particular competitive needs generated by the species-specific social system.

Laissez-Faire Stallions? Males' Fecal Cortisol Metabolite Concentrations Do Not Vary with Increased Female Turnover in Feral Horses (Equus caballus)

Stress responses can be triggered by several physical and social factors, prompting physiological reactions including increases in glucocorticoid concentrations. In a population of feral horses (Equus caballus) on Shackleford Banks, North Carolina, females previously immunized with the immunocontraceptive agent porcine zona pellucida (PZP) change social groups (bands) more often than unimmunized females, disrupting the social stability within the population. We assessed the effects of increased female group changing behavior (or female turnover) on individual male stress by comparing fecal cortisol metabolite (FCM) concentrations among stallions experiencing varying amounts of female group changing behavior. FCM concentrations did not significantly correlate with female turnover. Similarly, FCM concentrations were not dependent upon the timing of female group changing behavior. These findings suggest that female turnover rate has little influence on physiological measures of stress in associated stallions. That said, Shackleford stallions experiencing increased female turnover do engage in behaviors typically associated with stress (increased vigilance, highly escalated male-male conflicts). Future work should compare FCM concentrations across time within populations and among populations managed under different strategies to better isolate factors influencing stallion stress physiology. Such studies are especially important if we are to determine how changes in female behavior related to immunocontraception impact physiological and behavioral indicators of stress for non-target animals. Finally, our study highlights the importance of considering both physiological and behavioral measures when investigating animal responses to potentially challenging situations.

Season and reproductive activity influence cortisol levels in the Malagasy primate Lepilemur edwardsi

Throughout the year, wild animals are exposed to a variety of challenges such as changing environmental conditions and reproductive activity. These challenges may affect their stress hormone levels for varying durations and in varying intensities and impacts. Measurements of the glucocorticoid hormone cortisol in the hair of mammals are considered a good biomarker for measuring physiological stress and are increasingly used to evaluate stress hormone levels of wild animals. Here, we examined the influence of season, reproductive activity, sex, as well as body condition on hair cortisol concentrations (HCC) in Lepilemur edwardsi, a small Malagasy primate species. L. edwardsi lives in the seasonal dry forests of western Madagascar, which are characterized by a strongly changing resource availability throughout the year. We hypothesized that these seasonal changes of resource availability and additionally the reproductive cycle of this species would influence HCC of L. edwardsi. Results revealed that hair cortisol concentration of females did not change seasonally or with the reproductive cycle. However, we found a significant increase of hair cortisol levels in males from the early wet season during the early dry season (mating season). This increase is presumably due to changed behavior during the mating season, as sportive lemurs travel more and show aggressive behavior during this time of the year. This behavior is energy-costly and stressful, and presumably leads to elevated HCC. As elevated cortisol levels may impair immune function, L. edwardsi males might also be more susceptible to parasites and diseases, which is unfavorable in particular during a period of low resource availability (dry season).

Hormonal correlates of male dominance rank, age, and genital colouration in vervet monkey (Chlorocebus pygerythrus)

Primates are the most colourful members of the Mammalian clade. In vervet monkeys (Chlorocebus pygerythrus), males are characterized by their red penis and blue scrotum. Such colour signals are often used in conspecific communication, and thus could be used to convey signaller condition. We quantified scrotal and penile colour characteristics using digital photographs between May-June 2016 from males in two neighboring groups along the shores of Lake Nabugabo, Uganda. We examined the relationship between fecal hormones, male dominance rank, age (adult vs. immature), and colour. Adult males were higher ranking than immatures, but there were no rank or age differences in fecal hormone levels. Glucocorticoids and androgens were positively correlated in immature, but not adult males. All scrotal characteristics were predicted by age, with adult males having more teal (i.e., less blue, more green) and more luminant scrota. Within adult males, those with higher androgens levels had more saturated blue scrotal colouration and higher-ranking males were more luminant. Penile colouration was also associated with age and rank. High-ranking males had a more saturated red penis, and adult male penile colour was more luminant and bluer than in immature males. Our findings are consistent with previous reports that scrotal colouration advertises sexual or reproductive maturity (i.e., age), but we also find that within adult males, colour also advertises dominance rank and may be mediated by androgen levels. Penile colouration also appears to signal information about male age and dominance rank but does not appear to be mediated by hormones.

Interactions between reproductive biology and microbiomes in wild animal species

Many parts of the animal body harbor microbial communities, known as animal-associated microbiomes, that affect the regulation of physiological functions. Studies in human and animal models have demonstrated that the reproductive biology and such microbiomes also interact. However, this concept is poorly studied in wild animal species and little is known about the implications to fertility, parental/offspring health, and survival in natural habitats. The objective of this review is to (1) specify the interactions between animals' reproductive biology, including reproductive signaling, pregnancy, and offspring development, and their microbiomes, with an emphasis on wild species and (2) identify important research gaps as well as areas for further studies. While microbiomes present in the reproductive tract play the most direct role, other bodily microbiomes may also contribute to facilitating reproduction. In fish, amphibians, reptiles, birds, and mammals, endogenous processes related to the host physiology and behavior (visual and olfactory reproductive signals, copulation) can both influence and be influenced by the structure and function of microbial communities. In addition, exposures to maternal microbiomes in mammals (through vagina, skin, and milk) shape the offspring microbiomes, which, in turn, affects health later in life. Importantly, for all wild animal species, host-associated microbiomes are also influenced by environmental variations. There is still limited literature on wild animals compared to the large body of research on model species and humans. However, the few studies in wild species clearly highlight the necessity of increased research in rare and endangered animals to optimize conservation efforts in situ and ex situ. Thus, the link between microbiomes and reproduction is an emerging and critical component in wild animal conservation.

Aggression, glucocorticoids, and the chronic costs of status competition for wild male chimpanzees

Across vertebrates, high social status affords preferential access to resources, and is expected to correlate positively with health and longevity. Increasing evidence, however, suggests that although dominant females generally enjoy reduced exposure to physiological and psychosocial stressors, dominant males do not. Here we test the hypothesis that costly mating competition by high-ranking males results in chronic, potentially harmful elevations in glucocorticoid production. We examined urinary glucocorticoids (n = 8029 samples) in a 20-year longitudinal study of wild male chimpanzees (n = 20 adults) in the Kanyawara community of Kibale National Park, Uganda. We tested whether glucocorticoid production was associated with dominance rank in the long term, and with mating competition and dominance instability in the short term. Using mixed models, we found that both male aggression and glucocorticoid excretion increased when the dominance hierarchy was unstable, and when parous females were sexually available. Glucocorticoid excretion was positively associated with male rank in stable and unstable hierarchies, and in mating and non-mating contexts. Glucorticoids increased with both giving and receiving aggression, but giving aggression was the primary mechanism linking elevated glucocorticoids with high rank. Glucocorticoids also increased with age. Together these results show that investment in male-male competition increases cumulative exposure to glucocorticoids, suggesting a long-term tradeoff with health that may constrain the ability to maintain high status across the life course. Our data suggest that the relationship between social rank and glucocorticoid production often differs in males and females owing to sex differences in the operation of sexual selection.

Behavioral and physiological responses to instability in group membership in wild male woolly monkeys (Lagothrix lagotricha poeppigii)

In group-living species, integrating into a new social group after dispersal is an important life history milestone associated with physical and social challenges. Generally, this process seems to be accompanied by heightened glucocorticoid (GC) concentrations; however, most studies of physiological responses to group transfer have been conducted on species with despotic social relationships, where integrating individuals are often targets of frequent aggression. Here we present data on fecal glucocorticoid (fGC) concentrations during periods of unstable group membership for male woolly monkeys (Lagothrix lagotricha poeppigii), a species with extremely low rates of male-male aggression and generally tolerant male-male associations. We collected data on males in four study groups at the Tiputini Biodiversity Station, Ecuador, and observed three attempted transfer events, involving a total of four adult males, in one study group. We observed only three instances of overt aggression (chases) between males across the entire study period, though male display behaviors were more frequent. We tested whether rates of displays were higher during periods of unstable group membership using a generalized linear mixed model (LMM). We also examined whether male status, group stability, and the occurrence of intergroup encounters affected fGC concentrations using LMMs. Contrary to our predictions, rates of display behaviors were not higher during periods of unstable group membership. However, both transient/integrating males and those who were already group members showed elevated fGC concentrations during these unstable periods. Our results suggest that even in species with tolerant male-male relationships, the integration of unfamiliar individuals can provoke an increase in GCs.

Assessment and preservation of liquid and frozen-thawed Black crested mangabey (Lophocebus aterrimus) spermatozoa obtained by transrectal ultrasonic-guided massage of the accessory sex glands and electroejaculation

The Black Crested Mangabey (Lophocebus aterrimus) is an African monkey listed as Near Threatened by the IUCN and in captivity the population is limited to 34 males. The aim of this study was to evaluate two Black Crested Mangabey males, maintained in captivity in a zoological garden and suspected of infertility, with a complete examination of their genital tract using ultrasonography, followed by recovery of semen using transrectal ultrasonic massage of the accessory sexual glands (TUMASG) and electroejaculation. One male had small testicular and accessory sex gland sizes indicative of senile hypoplasia. The other male was suspected of infertility. Four semen samples were obtained. Fresh semen was initially evaluated, diluted in Refrigeration Medium Test Yolk buffer, cooled at 15 °C and cryopreserved. Endocrine profiles (testosterone, oestradiol, FSH, LH, cortisol), prostatic specific antigen and semen variables (volume, concentration, motility by CASA, viability and acrosome status using flow cytometry, morphology, morphometry utilising TEM) were evaluated in raw, cooled and cryopreserved samples. There was no detrimental effect of cooling or cryopreservation on sperm viability and acrosomal integrity. Similar percentages of viable and acrosome-intact spermatozoa were present in cooled (for 6 h) and frozen-thawed semen samples (75.1% compared with 69.0%, P > 0.05), while progressive motility was greater in cooled, compared with frozen-thawed samples (81.5% compared with 67.3%). This study was the first in which there was evaluation of sperm variables in this species and, although this study is limited by the number of animals it provides background information for further studies using assisted reproductive technologies.

The presence of females induces elevated cortisol levels in an alpha male: Experimental evidence in chimpanzees

OBJECTIVES

In group-living primates, it has been reported that the alpha male exhibits high concentrations of cortisol and testosterone in the context of mating competition. We investigated how the presence of females affected salivary cortisol and testosterone levels in males from a small captive group of chimpanzees (Pan troglodytes). Specifically, we assessed whether the presence of females resulted in a rapid increase in salivary cortisol and testosterone levels in the alpha male.

MATERIALS AND METHODS

We compared the social behavior and salivary hormone concentrations of four males before and after the presentation of receptive females. Three times a day, we collected saliva samples, a useful matrix for investigating short-term hormonal changes, and measured cortisol and testosterone concentration by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

The frequency of inter-male aggression increased in the presence of females, indicating intense competition among males. Salivary cortisol levels increased in all males in the presence of females; however, the increase was significantly more pronounced in the alpha male. We found a complex three-way interaction among the presence of females, sampling timings, and male dominance rank in the analysis of salivary testosterone. Contrary to our prediction, a post hoc analysis revealed that salivary testosterone levels decreased after female introduction and that the alpha male did not show a higher level of salivary testosterone.

CONCLUSIONS

Our study provides experimental evidence suggesting that the presence of females plays a significant role in the rank-related variation in the cortisol levels in male chimpanzees. Furthermore, our findings demonstrate the usefulness of salivary hormones for detecting short-term physiological changes in studies of socioendocrinology.

Alpha male status and availability of conceptive females are associated with high glucocorticoid concentrations in high-ranking male rhesus macaques (Macaca mulatta) during the mating season

The relationship between male mating opportunities, stress, and glucocorticoid concentrations is complicated by the fact that physiological stress and glucocorticoid concentrations can be influenced by dominance rank, group size, and the stability of the male dominance hierarchy, along with ecological factors. We studied the three highest-ranking males in nine different social groups within the same free-ranging population of rhesus macaques on Cayo Santiago, Puerto Rico, during the mating season, to examine variation in glucocorticoid concentrations in relation to number of females that conceived each month, alpha status, number of adult males in a group, and male rank hierarchy stability. We found that glucocorticoid concentrations were highest in the early mating season period when more females conceived in each group and declined linearly as the mating season progressed and the number of conceptive females decreased. Alpha males had significantly higher mean monthly glucocorticoid concentrations than other high-ranking males throughout the study period. Male age, number of adult males in a group, and hierarchy stability were not significantly associated with glucocorticoid concentrations. Our findings suggest that alpha males may experience significantly higher levels of physiological stress than their immediate subordinates and that this stress coincides with the period of the mating season when most conceptions occur.

Hormonal correlates of natal dispersal and rank attainment in wild male baboons

In many mammals, maturational milestones such as dispersal and the attainment of adult dominance rank mark stages in the onset of reproductive activity and depend on a coordinated set of hormonal and socio-behavioral changes. Studies that focus on the link between hormones and maturational milestones are uncommon in wild mammals because of the challenges of obtaining adequate sample sizes of maturing animals and of tracking the movements of dispersing animals. We examined two maturational milestones in wild male baboons-adult dominance rank attainment and natal dispersal-and measured their association with variation in glucocorticoids (fGC) and fecal testosterone (fT). We found that rank attainment is associated with an increase in fGC levels but not fT levels: males that have achieved any adult rank have higher fGC than males that have not yet attained an adult rank. This indicates that once males have attained an adult rank they experience greater energetic and/or psychosocial demands than they did prior to attaining this milestone, most likely because of the resulting participation in both agonistic and sexual behaviors that accompany rank attainment. In contrast, natal dispersal does not produce sustained increases in either fGC or fT levels, suggesting that individuals are either well adapted to face the challenges associated with dispersal or that the effects of dispersal on hormone levels are ephemeral for male baboons.

The next step for stress research in primates: To identify relationships between glucocorticoid secretion and fitness

Glucocorticoids are hormones that mediate the energetic demands that accompany environmental challenges. It is therefore not surprising that these metabolic hormones have come to dominate endocrine research on the health and fitness of wild populations. Yet, several problems have been identified in the vertebrate research that also apply to the non-human primate research. First, glucocorticoids should not be used as a proxy for fitness (unless a link has previously been established between glucocorticoids and fitness for a particular population). Second, stress research in behavioral ecology has been overly focused on "chronic stress" despite little evidence that chronic stress hampers fitness in wild animals. Third, research effort has been disproportionately focused on the causes of glucocorticoid variation rather than the fitness consequences. With these problems in mind, we have three objectives for this review. We describe the conceptual framework behind the "stress concept", emphasizing that high glucocorticoids do not necessarily indicate a stress response, and that a stress response does not necessarily indicate an animal is in poor health. Then, we conduct a comprehensive review of all studies on "stress" in wild primates, including any study that examined environmental factors, the stress response, and/or fitness (or proxies for fitness). Remarkably, not a single primate study establishes a connection between all three. Finally, we provide several recommendations for future research in the field of primate behavioral endocrinology, primarily the need to move beyond identifying the factors that cause glucocorticoid secretion to additionally focus on the relationship between glucocorticoids and fitness. We believe that this is an important next step for research on stress physiology in primates.

Testosterone and reproductive effort in male primates

Considerable evidence suggests that the steroid hormone testosterone mediates major life-history trade-offs in vertebrates, promoting mating effort at the expense of parenting effort or survival. Observations from a range of wild primates support the "Challenge Hypothesis," which posits that variation in male testosterone is more closely associated with aggressive mating competition than with reproductive physiology. In both seasonally and non-seasonally breeding species, males increase testosterone production primarily when competing for fecund females. In species where males compete to maintain long-term access to females, testosterone increases when males are threatened with losing access to females, rather than during mating periods. And when male status is linked to mating success, and dependent on aggression, high-ranking males normally maintain higher testosterone levels than subordinates, particularly when dominance hierarchies are unstable. Trade-offs between parenting effort and mating effort appear to be weak in most primates, because direct investment in the form of infant transport and provisioning is rare. Instead, infant protection is the primary form of paternal investment in the order. Testosterone does not inhibit this form of investment, which relies on male aggression. Testosterone has a wide range of effects in primates that plausibly function to support male competitive behavior. These include psychological effects related to dominance striving, analgesic effects, and effects on the development and maintenance of the armaments and adornments that males employ in mating competition.

Is social dispersal stressful? A study in male crested macaques (Macaca nigra)

In gregarious species, dispersal events represent one of the most dramatic changes in social life and environment an animal will experience during life due to increased predation risk, aggression from unfamiliar conspecifics and the lack of social support. However, little is known about how individuals respond physiologically to dispersal and whether this process is stressful for the individuals involved. We therefore studied the physiological stress response during dispersal in the crested macaque, a primate species in which males often change groups. Over a period of 14months and 14 dispersal events in 4 groups, we determined faecal glucocorticoid metabolite (FGCM) levels during the process of immigration into a new group and examined a variety of factors (e.g. male age, rank achieved, number of males in the group) potentially affecting FGCM levels during this process. We found that FGCM levels were significantly elevated in the first few days upon immigration, after which levels returned quickly to baseline. FGCM response levels upon immigration were significantly and positively influenced by the number of males in the group. The rank a male achieved upon immigration, aggression received, as well as the proximity to other males did not significantly influence FGCM levels. Our data confirm previous findings on other species demonstrating that in crested macaques immigration into a new social group is associated with an acute endocrine stress response. However, given that stress hormone levels remained elevated only for a short period of time, we do not expect males to experience high physiological costs during immigration. Given our limited knowledge on the physiological responses to dispersal in animals, this study contributes to our understanding of dispersal more generally, and particularly inter-individual differences in the stress response and the potential physiological costs associated with these.

Call rates of mothers change with maternal experience and with infant characteristics in free-ranging gray-cheeked mangabeys

Studies have shown that becoming a mother triggers important social changes within females, according to both social experience and infant characteristics, showing different maternal concerns. But how this impacts call usage has been far less studied. Based on 6 months of observations of five free-ranging groups of gray-cheeked mangabeys, we investigated variations in the production of three call types (contact, excitement, and alarm calls) in 29 females of different ages, dominance ranks, and infant rearing experiences: 15 females with infants of different ages and sexes, and 14 females without infants. We found that in females with infants-both maternal and infant characteristics influenced call production in a call type-dependent way. Females produced contact calls at a higher rate during the first month of infant age and after weaning when infants start to move away. Mothers of daughters produced more contact calls than mothers of sons. More excitement calls were recorded for first-time and young mothers and for females with young infants, while alarm call rates were not influenced by any of these factors. Increased mother-infant spatial separation enhanced only contact and excitement call rates. Finally, we found that females with infants vocalized much more than females without infants. Our results contribute to the current debate about the social factors responsible for the flexibility of call usage in nonhuman primates and open new lines for research on mothering behavior in forest-dwelling species. Am. J. Primatol. 78:983-991, 2016. © 2016 Wiley Periodicals, Inc.

Male endocrine response to seasonally varying environmental and social factors in a neotropical primate, Cebus capucinus

OBJECTIVE

Circannual variation in reproduction is pervasive in birds and mammals. In primates, breeding seasonality is variable, with seasonal birth peaks occurring even in year-round breeders. Environmental seasonality is reportedly an important contributor to the observed variation in reproductive seasonality. Given that food availability is the primary factor constraining female reproduction, predictions concerning responsiveness to environmental seasonality focus on females, with studies of males focusing primarily on social factors. We examined the influence of both environmental and social factors on male fecal testosterone (fT) and glucocorticoids (fGC) in moderately seasonally breeding white-faced capuchin monkeys (Cebus capucinus) in Costa Rica.

METHODS

Over 17 months, we collected 993 fecal samples from 14 males in three groups. We used LMM to simultaneously examine the relative effects of photoperiod, fruit biomass, rainfall, temperature, female reproductive status (i.e., number of periovulatory periods, POPs), and male age and dominance rank on monthly fT and fGC levels.

RESULTS

Male age and rank had large effects on fT and fGC. Additionally, some hormone variation was explained by environmental factors: photoperiod in the previous month (i.e., lagged photoperiod) was the best environmental predictor of monthly fT levels, whereas fGC levels were best explained by lagged photoperiod, fruit biomass, and rainfall. POPs predicted monthly fT and fGC, but this effect was reduced when all variables were considered simultaneously, possibly because lagged photoperiod and POP were highly correlated.

CONCLUSIONS

Males may use photoperiod as a cue predicting circannual trends in the temporal distribution of fertile females, while also fine-tuning short-term hormone increases to the actual presence of ovulatory females, which may occur at any time during the year.

Redtail and red colobus monkeys show intersite urinary cortisol concentration variation in Kibale National Park, Uganda

Non-invasive measurement of urinary cortisol is a proven method of evaluating the impact of environmental stressors on wild primates. Variation in cortisol concentrations can reflect physiological stress, and prolonged elevation of circulating cortisol can significantly affect individual and population-level health. In a previous study, we found that urinary cortisol concentrations in grey-cheeked mangabeys (Lophocebus albigena) were higher at a highly disturbed site (Mainaro) in Kibale National Park, Uganda compared with a minimally disturbed site (Ngogo) in the same habitat. Here, we expand on this research, reporting on cortisol concentrations in two other cercopithecid monkeys (Cercopithecus ascanius and Piliocolobus rufomitratus) at the same two sites. We hypothesized that C. ascanius would show no difference between sites, given its preference for secondary forests, while P. rufomitratus would have higher cortisol concentrations at the disturbed site. Contrary to expectations, both species exhibited significantly higher cortisol concentrations at Ngogo (minimally disturbed) compared with Mainaro (disturbed). We suggest that these results may be caused by inter- or intragroup social dynamics, intersite differences in predation rate, fruit/food availability and chemistry, or a combination of these factors. These initial evaluations of urinary cortisol concentrations provide testable hypotheses on habitat disturbance and Kibale primate ecophysiology.

Costs of mate-guarding in wild male long-tailed macaques (Macaca fascicularis): physiological stress and aggression

Mate-guarding is an important determinant of male reproductive success in a number of species. However, it is known to potentially incur costs. The aim of the present study was to assess the effect of mate-guarding on male physiological stress and aggression in long-tailed macaques, a species in which males mate-guard females to a lesser extent than predicted by the Priority of Access model (PoA). The study was carried out during two mating periods on three groups of wild long-tailed macaques in Indonesia by combining behavioral observations with non-invasive measurements of fecal glucocorticoid (fGC) levels. Mate-guarding was associated with a general rise in male stress hormone levels but, from a certain threshold of mate-guarding onwards, increased vigilance time was associated with a decrease in stress hormone output. Mate-guarding also increased male-male aggression rate and male vigilance time. Overall, alpha males were more physiologically stressed than other males independently of mating competition. Increased glucocorticoid levels during mate-guarding are most likely adaptive since it may help males to mobilize extra-energy required for mate-guarding and ultimately maintain a balanced energetic status. However, repeated exposure to high levels of stress over an extended period is potentially deleterious to the immune system and thus may carry costs. This potential physiological cost together with the cost of increased aggression mate-guarding male face may limit the male's ability to mate-guard females, explaining the deviance from the PoA model observed in long-tailed macaques. Comparing our results to previous findings we discuss how ecological factors, reproductive seasonality and rank achievement may modulate the extent to which costs of mate-guarding limit male monopolization abilities.

Hormonal correlates of male life history stages in wild white-faced capuchin monkeys (Cebus capucinus)

Much attention has been paid to hormonal variation in relation to male dominance status and reproductive seasonality, but we know relatively little about how hormones vary across life history stages. Here we examine fecal testosterone (fT), dihydrotestosterone (fDHT), and glucocorticoid (fGC) profiles across male life history stages in wild white-faced capuchins (Cebus capucinus). Study subjects included 37 males residing in three habituated social groups in the Área de Conservacíon Guanacaste, Costa Rica. Male life history stages included infant (0 to <12months; N=3), early juvenile (1 to <3years; N=10), late juvenile (3 to <6years; N=9), subadult (6 to <10years; N=8), subordinate adult (⩾10years; N=3), and alpha adult (⩾10years; N=4, including one recently deposed alpha). Life history stage was a significant predictor of fT; levels were low throughout the infant and juvenile phases, doubled in subadult and subordinate adults, and were highest for alpha males. Life history stage was not a significant predictor of fDHT, fDHT:fT, or fGC levels. Puberty in white-faced capuchins appears to begin in earnest during the subadult male phase, indicated by the first significant rise in fT. Given their high fT levels and exaggerated secondary sexual characteristics, we argue that alpha adult males represent a distinctive life history stage not experienced by all male capuchins. This study is the first to physiologically validate observable male life history stages using patterns of hormone excretion in wild Neotropical primates, with evidence for a strong association between fT levels and life history stage.

Associations between social behaviour and adrenal activity in female Barbary macaques: consequences of study design

Faecal glucocorticoid metabolite (fGCM) concentrations have been used to evaluate adrenal activity in a variety of species; including as an indicator of the physiological response to social stress. However, across studies, the relationships between dominance rank, social behaviours and adrenal responses can be inconsistent. Differences in the relationship between rank and glucocorticoids may be due to the relative costs of social status, and the relative frequencies of social stressors and potential coping mechanisms. However, the differences in observed relationships between specific social behaviours and glucocorticoids may be partly explained by sampling frequency, as studies often use average fGCM concentrations collected over a period of weeks or months, rather than fGCM concentrations that are temporally-matched with behavioural data. In this study, we directly compared long-term average and temporally-matched data to determine whether particular social behaviours were related to adrenal activity in female Barbary macaques (Macaca sylvanus) at Trentham Monkey Forest, UK; and whether observed relationships were consistent using these two approaches. Average rates of autogrooming were positively correlated with average fGCM; however, this relationship was not robust in temporally-matched samples. Instead, specific social behaviours associated with agonism were associated with fGCM in temporally-matched samples within individuals. These results indicate that analyses of relationships using long-term average fGCM and temporally-matched samples do not necessarily provide comparable results, highlighting that study design is critical in determining associations between an individual's social behaviour and the relative physiological costs involved.

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.

Social behavior, foraging strategies, and fecal glucocorticoids in female blue monkeys (Cercopithecus mitis): potential fitness benefits of high rank in a forest guenon

Socioecological theory predicts that aggressive feeding competition is associated with linear dominance hierarchies and reproductive advantages for high-ranking females. Female blue monkeys contest fruits and have a linear dominance hierarchy, yet previous research has shown no evidence that high-ranking females benefit from greater feeding success or fertility. Here, we assess whether individuals differ in fecal glucocorticoid (fGC) excretion and examine proximate determinants of such differences to infer potential fitness correlates of rank, using data collected from two study groups in the Kakamega Forest, Kenya. We found that higher ranking females had preferential access to fruits in both groups, although the behavioral mechanisms leading to this effect varied between groups. Despite a consistent rank difference in feeding on fruits, an overall rank effect on fGCs emerged in only one group; females of this group spent comparatively more time feeding on fruits, fruits accounted for a greater proportion of the diet, and females engaged in more frequent food-related agonism. In addition, more females in this group were lactating during a period of low fruit availability, when rank effects on fGCs were particularly strong. Regardless of fruit availability, among lactating females of both groups higher rank was associated with lower fGC levels, indicating lower energetic stress in higher ranking females when energy demands were particularly high. Individual rates of agonism, a potential psychological stressor, were unrelated to fGCs at all times. After we accounted for rates of agonism and feeding on fruits, females of one group who groomed others more had lower fGCs, suggesting that variable social coping behavior can contribute to fGC variation in some groups. This study provides the first empirical evidence that high-ranking female blue monkeys may obtain fitness benefits from their social status, by gaining priority of access to fruits during critical times in the reproductive cycle.

Do Dispersing Monkeys Follow Kin? Evidence from Gray-cheeked Mangabeys (Lophocebus albigena)

Among social vertebrates, immigrants may incur a substantial fitness cost when they attempt to join a new group. Dispersers could reduce that cost, or increase their probability of mating via coalition formation, by immigrating into groups containing first- or second-degree relatives. We here examine whether dispersing males tend to move into groups containing fathers or brothers in gray-cheeked mangabeys (Lophocebus albigena) in Kibale National Park, Uganda. We sampled blood from 21 subadult and adult male mangabeys in 7 social groups and genotyped them at 17 microsatellite loci. Twelve genotyped males dispersed to groups containing other genotyped adult males during the study; in only 1 case did the group contain a probable male relative. Contrary to the prediction that dispersing males would follow kin, relatively few adult male dyads were likely first- or second-degree relatives; opportunities for kin-biased dispersal by mangabeys appear to be rare. During 4 yr of observation, adult brothers shared a group only once, and for only 6 wk. Mean relatedness among adult males sharing a group was lower than that among males in different groups. Randomization tests indicate that closely related males share groups no more often than expected by chance, although these tests had limited power. We suggest that the demographic conditions that allow kin-biased dispersal to evolve do not occur in mangabeys, may be unusual among primates, and are worth further attention.

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.

Stress, social behaviour, and secondary sexual traits in a male primate

We examined variation in glucocorticoid levels in the mandrill, a brightly coloured primate species, to identify major social influences on stress hormones, and investigate relationships among glucocorticoid levels, testosterone and secondary sexual ornamentation. We collected a total of 317 fecal samples for 16 adult male mandrills over 13 months, including mating and non-mating periods and periods of both dominance rank stability and instability, and compared fecal glucocorticoid levels with dominance rank, rank stability, presence of receptive females, gastro-intestinal parasite infection, fecal testosterone and facial red coloration. Glucocorticoid levels did not vary systematically with dominance rank, but increased when the dominance hierarchy was unstable, and increased in the presence of receptive females. The relationship between dominance rank and glucocorticoid levels changed direction according to the stability of the dominance hierarchy: glucocorticoid levels were higher in subordinate males under stable conditions, but under conditions of instability higher ranking males had higher glucocorticoid levels. The influence of dominance rank also interacted with the presence of receptive females: glucocorticoids were higher in dominant males than in subordinates, but only during mating periods, suggesting that dominant males are more stressed than subordinates during such periods. These findings support previous studies showing that the relationship between glucocorticoids and dominance rank in male baboons is dependent on the social environment. We also found that males with higher glucocorticoids suffered a higher diversity of gastrointestinal parasite infection, in line with evidence that glucocorticoids suppress the immune system in other species. However, we found no support for the stress-mediated immunocompetence handicap hypothesis for the evolution of condition-dependent ornaments: glucocorticoid and testosterone levels were positively related, rather than the negative relationship predicted by the hypothesis, and we found no relationship between red colour and glucocorticoid levels, suggesting that glucocorticoids do not play a role in translating social conditions or physical health into ornament expression in this species.

Cortisol levels and aggression in neutered and intact free-roaming female cats living in urban social groups

Free-roaming domestic cats in urban areas often live in defined social groups, and the breeding females in these groups tend to form structures of a matrilineal nature. In recent years, resulting from the growing populations of free-roaming cats in many cities worldwide, these cats are being managed using the Trap-Neuter-Return (TNR) method. The aims of this study were to explore the hypotheses that (a) neutering reduces aggression in the females living in such social groups; and (b) if such reduction does occur, that it might be accompanied by a reduction in cortisol levels. The study was conducted on eight cat feeding groups in residential neighbourhoods in Tel Aviv, Israel. The municipal veterinary department offers TNR services upon request. Cats are collected from the feeding group and returned to their original group after neutering. We found that neutered females showed reduced aggressiveness as well as reduced cortisol levels compared to the intact females. In addition, those intact females that displayed more aggression had higher cortisol levels compared to the less aggressive intact females. Based on the results of this study it is possible to suggest for the first time a possible relationship between cortisol levels and aggression in free-roaming female domestic cats. This study is an initial step in assessing the long-term effects of Trap-Neuter-Return (TNR) on the welfare of the individual cat. If cortisol levels in female cats are reduced after neutering, partly as a result of reduced social and reproductive pressures (as expressed by lower aggression of the neutered females), it is possible that TNR has an added beneficial role in cat welfare in addition to that of control of population size.

Social and hormonal mechanisms underlying male reproductive strategies in black howler monkeys (Alouatta pigra)

We investigated the social and hormonal mechanisms underlying male reproductive strategies in two multimale-multifemale groups of black howler monkeys (Alouatta pigra) during a 14-month study in Palenque National Park, Mexico. Fecal glucocorticoid (fGC) and androgen (fA) levels were analyzed for 343 fecal samples collected from 14 males during their presence in the study groups. Neither immigrating males nor resident males that remained in the group had elevated fGC and fA levels during 11 observed male migration events, suggesting that competition over group membership was not associated with variation in the fecal hormonal levels of males. Instead, fGC and fA levels were significantly higher in males who maintained a central position in the group and had almost exclusive access to fertile females than in other resident males. These "central" males were responsible for maintaining close spatial associations and cultivating strong affiliative relationships with cycling, sexually active females but not with noncycling, sexually inactive females. "Noncentral" males did not form strong social relationships with either cycling or noncycling females and had no or very few mating opportunities. Our findings suggest that male black howler monkeys compete nonaggressively by fostering relationships with cycling females and that the elevated fGC levels of central males may be indicative of the social challenges involved in their indirect competition.