Seasonal and altitudinal effects on glucocorticoid metabolites in a wild primate (Theropithecus gelada)

Consumption of underground storage organs is associated with improved energetic status in a graminivorous primate

Early hominin species likely had access to open, grassy habitats where periodic reliance on underground storage organs (USOs) is hypothesized to have played a crucial dietary role. As the only living graminivorous primate today, geladas (Theropithecus gelada) provide a unique perspective for understanding the energetic consequences of seasonal consumption of USOs. Geladas rely heavily on above-ground grasses throughout the year, but when grass is seasonally less available, they feed more on USOs. To assess whether USOs fit the definition of fallback foods (i.e., foods that are difficult to access, less preferred, or both), we examined how foraging effort (measured via time spent feeding and moving) and energetic status (measured via urinary C-peptide) fluctuated during seasonal dietary changes in a population of wild geladas in the Simien Mountains National Park, Ethiopia. If, indeed, USOs are fallback foods, we predicted an increase in foraging effort and a decline in energetic status during the dry season, when geladas rely more heavily on USOs. We collected behavioral and physiological data from 13 adult gelada males across a 13-month period. As expected, we found that male geladas spent more time moving during drier months. However, counter to the hypothesis that USOs are fallback foods in geladas, urinary C-peptide concentrations were significantly higher during the dry season. We suggest that USOs may represent an energy-rich food item for geladas, but it remains unclear why USOs are not consumed year-round. Future work is needed to better understand seasonal variation in the availability, nutrient content, and digestibility of USOs. However, results indicate that exploiting USOs seasonally could have been a valuable dietary strategy for the evolutionary success of early hominins.

The paradox of spring: Thyroid and glucocorticoid responses to cold temperatures and food availability in free living Carneddau ponies

In seasonal environments, maintaining a constant body temperature poses challenges for endotherms. Cold winters at high latitudes, with limited food availability, create opposing demands on metabolism: upregulation preserves body temperature but depletes energy reserves. Examining endocrine profiles, such as thyroid hormone triiodothyronine (T3) and glucocorticoids (GCs), proxies for changes in metabolic rate and acute stressors, offer insights into physiological trade-offs. We evaluated how environmental conditions and gestation impact on faecal hormone metabolites (fT3Ms and fGCMs) from late winter to spring in a free-living population of Carneddau ponies. Faecal T3Ms were highest in late February and March, when temperatures were lowest. Then, fT3Ms concentrations decreased throughout April and were at the lowest in May before increasing towards the end of the study. The decline in fT3M levels in April and May was associated with warmer weather but poor food availability, diet diversity and diet composition. On the other hand, fGCM levels did not display a clear temporal pattern but were associated with reproductive status, where pregnant and lactating females had higher fGCM levels as compared to adult males and non-reproductive females. The temporal profile of fT3Ms levels highlights metabolic trade-offs in a changing environment. In contrast, the ephemeral but synchronous increase in fGCM concentrations across the population suggest a shared experience of acute stressors (i.e., weather, disturbance or social). This multi-biomarker approach can evaluate the role of acute stressors versus energy budgets in the context of interventions, reproduction, seasonality and environmental change, or across multiple scales from individuals to populations.

Analytical and biological validation of a noninvasive measurement of glucocorticoid metabolites in feces of Geoffroy's spider monkeys (Ateles geoffroyi)

We report on an analytical and biological validation of a commercial cortisol enzyme immunoassay (EIA) to measure glucocorticoids (GC) in feces of Geoffroy's spider monkeys (Ateles geoffroyi). Validation of endocrinological methods for each sample matrix and study species is crucial to establish that the methods produce reliable results. For the analytical validation of the EIA, we assessed parallelism, accuracy, and precision. We carried out a biological validation based on three well-studied GC patterns with the following predictions: (1) increased fecal GC metabolite (fGCM) concentrations after veterinary intervention; (2) increased fGCM concentrations during early morning hours; and (3) higher fGCM concentrations during gestation than in other female reproductive states. For the first prediction, we sampled feces of two zoo-housed females 2 days before, the day of, and 2 days after a veterinary intervention. For the second prediction, we analyzed 284 fecal samples collected from 12 wild males using a linear mixed model (LMM). For the third prediction, we analyzed 269 fecal samples of eight wild females using an LMM. Analytical validation revealed that the EIA showed parallelism, was accurate, and precise within each assay. However, there was elevated variation in between-assay precision. The biological validation supported all predictions: (1) the two zoo-housed females showed a substantial increase in fGCM concentrations 2.5 and 11 h after veterinary intervention; (2) there was a negative effect of sample collection time on fGCM concentrations (i.e., higher concentrations during early morning); (3) gestating females had significantly higher fGCM concentrations than lactating females. Thus, we analytically validated the commercial EIA and, despite between-assay variation, we were able to find three biologically relevant GC signals in captive and wild settings, and in males and females. We are therefore confident that the method can be used to noninvasively address behavioral endocrinology questions in Geoffroy's spider monkeys.

Linking glucocorticoid variations to monthly and daily behavior in a wild endangered neotropical primate

Identifying the factors swaying physiological stress levels in wild animals can help depict how they cope with environmental and social stressors, shedding light on their feeding ecology, behavioral plasticity, and adaptability. Here, we used noninvasive methods to explore the link between glucocorticoid levels and behavior in an endangered neotropical primate facing habitat fragmentation pressure, the black lion tamarin (Leontopithecus chrysopygus). We investigated monthly and day-to-day glucocorticoid variations independently to attempt to disentangle the complex nature of the adrenocortical activity. Between May 2019 to March 2020, we followed two groups of black lion tamarins in two different areas, a continuous forest and a small fragment, and gathered behavioral data (over 95 days in total; 8.6 ± 3.9 days/month) and fecal samples (N_samples  = 468; 4.93 ± 3.5 samples/day) simultaneously. Preliminary analyses enabled us to identify circadian variations linked to the biological rhythm, which were taken into account in subsequent models. Monthly analyses revealed that black lion tamarin fecal glucocorticoid metabolite levels vary according to changes in activity budget associated with the fruit consumption, movement, and resting time of the groups. At a day-to-day level, while intergroup encounters led to increases in fecal glucocorticoid metabolite concentrations, we found that changes in food intake or activity level did not trigger physiological stress responses. These findings suggest that diet and ranging patterns, driven by food availability and distribution, influence physiological stress at a seasonal scale, while acute stressors such as interspecific competition trigger short-term stress responses. Exploring fecal glucocorticoid metabolite variations over different timescales can help uncover the predictive and reactive facets of physiological stress in wild species. Moreover, having a comprehensive understanding of the physiological state of species is a valuable conservation tool for evaluating how they cope in changing environments.

Using an on-site laboratory for fecal steroid analysis in wild white-faced capuchins

Hormone laboratories located "on-site" where field studies are being conducted have a number of advantages. On-site laboratories allow hormone analyses to proceed in near-real-time, minimize logistics of sample permits/shipping, contribute to in-country capacity-building, and (our focus here) facilitate cross-site collaboration through shared methods and a shared laboratory. Here we provide proof-of-concept that an on-site hormone laboratory (the Taboga Field Laboratory, located in the Taboga Forest Reserve, Costa Rica) can successfully run endocrine analyses in a remote location. Using fecal samples from wild white-faced capuchins (Cebus imitator) from three Costa Rican forests, we validate the extraction and analysis of four steroid hormones (glucocorticoids, testosterone, estradiol, progesterone) across six assays (DetectX® and ISWE, all from Arbor Assays). Additionally, as the first collaboration across three long-term, wild capuchin field sites (Lomas Barbudal, Santa Rosa, Taboga) involving local Costa Rican collaborators, this laboratory can serve as a future hub for collaborative exchange.

Social correlates of androgen levels and dispersal age in juvenile male geladas

Androgens offer a window into the timing of important male life history events such as maturation. However, when males are the dispersing sex, piecing together normative androgen profiles across development is challenging because dispersing males are difficult to track. Here, we examined the conditions that may be associated with male androgen status (via fecal androgen metabolites, fAMs) and age at dispersal in wild male geladas (Theropithecus gelada). Gelada male life histories are highly variable - dispersal may occur before sexual maturation, dispersal itself can be immediate or drawn out, and, due to their multi-leveled society, social conditions affecting dispersal can vary for juveniles living in different reproductive units within the same band. Using longitudinal data from known natal males, we examined how androgen levels and age at dispersal were associated with: (1) access to maternal resources (i.e., maternal rank, birth of a younger sibling, experiencing maternal loss), and (2) access to male peers (i.e., number of similar-aged males in their unit). We found that androgens were significantly lower in males with high-ranking mothers (in males >2.5 years of age; infant androgens were unrelated) and that having more male peers in their social group and larger groups overall predicted an earlier age at dispersal. Moreover, dispersal in geladas was not preceded or followed by a surge in androgen levels. Taken together, results suggest that social environments can cause individual variation in androgens and dispersal age. Whether this variation leads to differences in male fitness in later life remains to be determined.

Cortisol metabolites vary with environmental conditions, predation risk, and human shields in a wild primate, Cercopithecus albogularis

Environmental challenges are often associated with physiological changes in wildlife that allow animals to maintain homeostasis. Among these, scarcity in resources, and risks from predators, competitors, and humans can all result in psychological and physiological stress. Yet, for habituated species, it is not clear whether this relationship with humans still holds to a lesser degree or is outweighed by the benefits of human presence - such as serving as a buffer from competitors or predators. We investigated how human presence and environmental challenges such as resource availability, weather, predation, and competition may be associated with variation in fecal cortisol metabolite levels (FCMs) in a group of samango monkeys (Cercopithecus albogularis) in the Soutpansberg Mountains, South Africa. FCMs can often broadly track environmental challenges and perturbations. Initially, we employed an exploratory analysis comparing candidate models representing biological hypotheses and found that those incorporating information on human presence had less weight than models for food availability, thermoregulation, and water scarcity. When we examined a subset of the data that included information on intergroup competition and predator alarm calls, we found that FCMs were higher on the day following potential predator encounters but not competitive interactions. As observer numbers increased, responses to predators flattened, indicating that the presence of several humans might deter predators and/or affect samangos' perception of danger - yet we could not distinguish between these possibilities. Together, these results suggest that ecological perturbations track with FCMs in this study population and challenge long-held assumptions that human presence has negligible effects on habituated study animals.

OUP accepted manuscript

Female reproductive maturation is a critical life-history milestone, initiating an individual's reproductive career. Studies in social mammals have often focused on how variables related to nutrition influence maturation age in females. However, parallel investigations have identified conspicuous male-mediated effects in which female maturation is sensitive to the presence and relatedness of males. Here, we evaluated whether the more "classic" socioecological variables (i.e., maternal rank, group size) predict maturation age in wild geladas-a primate species with known male-mediated effects on maturation and a grassy diet that is not expected to generate intense female competition. Females delayed maturation in the presence of their fathers and quickly matured when unrelated, dominant males arrived. Controlling for these male effects, however, higher-ranking daughters matured at earlier ages than lower-ranking daughters, suggesting an effect of within-group contest competition. However, contrary to predictions related to within-group scramble competition, females matured earliest in larger groups. We attribute this result to either: 1) a shift to "faster" development in response to the high infant mortality risk posed by larger groups; or 2) accelerated maturation triggered by brief, unobserved male visits. While earlier ages at maturation were indeed associated with earlier ages at first birth, these benefits were occasionally offset by male takeovers, which can delay successful reproduction via spontaneous abortion. In sum, rank-related effects on reproduction can still occur even when socioecological theory would predict otherwise, and males (and the risks they pose) may prompt female maturation even outside of successful takeovers.

Seasonal drivers of faecal glucocorticoid metabolite concentrations in an African strepsirrhine primate, the thick-tailed greater galago (Otolemur crassicaudatus)

As global non-human primate populations show dramatic declines due to climate change, land transformation and other anthropogenic stressors, it has become imperative to study physiological responses to environmental change in order to understand primate adaptability and enhance species conservation strategies. We examined the effects of seasonality on faecal glucocorticoid metabolite (fGCM) concentrations of free-ranging male and female thick-tailed greater galagos (Otolemur crassicaudatus) in an Afromontane habitat. To do so, we established an enzyme immunoassay (EIA) for monitoring fGCM concentrations in the species using a biological validation. Following this, faecal samples were collected each month over the course of a year from free-ranging males and females situated in the Soutpansberg Mountains, Limpopo, South Africa. Multivariate analyses revealed lactation period was a driver of fGCM levels, whereas sex and food availability mostly influenced seasonal fGCM concentrations in the total population. Thus far, the results of this study show that drivers of fGCM levels, an indication of increased adrenocortical activity, in O. crassicaudatus are numerous and complex within the natural environment. The species may be adapted to such conditions and an extreme change to any one component may result in elevated fGCM levels. This increases our understanding of strepsirrhine primate physiology and offers initial insights into species adaptability to a challenging environment.

Bridging Captive and Wild Studies: Behavioral Plasticity and Social Complexity in Theropithecus gelada

Cognitive ethology explores the ability of animals to flexibly adapt their behavior to rapid physical and social environment fluctuations. Although there is a historical dichotomy between field and captive studies, recently, a growing interest in questions that sit at the intersection of cognitive and adaptive perspectives has helped bridge this divide. By focusing on Theropithecus gelada, we discuss the three main reasons why this hybrid approach is extremely successful. First, captive and wild studies provide data at different social, spatial, and temporal scales that can be synthesized to give a fuller picture of the behavior. Secondly, apparently conflicting results from captive and wild settings are powerful tools to explore behavioral flexibility and latent behavioral tendencies. Third, the different settings provide ways of validating and exploring behaviors that are noticed in the other setting. Although we were able to bring together our captive and wild research to demonstrate these ideas, we could have obtained a more integrated vision on the proximate and ultimate gelada behavioral and cognitive strategies if we had considered this hybrid approach from the beginning. We hope that this manuscript stimulates scholars in designing their studies by taking into account the incredible potential of a complementary captive-wild research approach.

Costs of seasonality at a southern latitude: Behavioral endocrinology of female baboons in the Cape Peninsula of South Africa

Environmental challenges in the form of temperature extremes and unusual precipitation, which may lead to prolonged periods outside the thermoneutral zone, can be detrimental to animal physiology. Chacma baboons in the Cape Peninsula of South Africa, one of the highest latitudes at which nonhuman primates are found, experience extremes of both temperature and rainfall, as well as seasonal differences in day length that require animals to condense their daily routine into dramatically reduced daylight hours. Here we examine the effects of these climatic factors on the behavior (activity budgets and foraging patterns) and physiology (fecal glucocorticoid concentrations) of adult females (N = 33) in three groups of chacma baboons (Papio ursinus) inhabiting the Cape Peninsula, where temperatures ranged from 7 to 39 °C, monthly rainfall ranged from 2 to 158 mm, and day length varied by 4.5 h across seasons. Climatic variables showed a clear relationship to female baboon glucocorticoid concentrations, which significantly increased with lower temperatures, higher rainfall and shorter day lengths. Activity budgets also differed between summer and winter, with females generally spending less time socializing, moving and resting in the winter compared to summer, with some differences between troops in their feeding-related activities. Cold temperatures accompanied by rainfall and short day lengths may thus represent an ecological constraint for this population. This study highlights the potential impact of anthropogenic climate change on the physiology, behavior, and, ultimately, survival of wildlife populations.

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.

Seasonal shifts in the gut microbiome indicate plastic responses to diet in wild geladas

BACKGROUND

Adaptive shifts in gut microbiome composition are one route by which animals adapt to seasonal changes in food availability and diet. However, outside of dietary shifts, other potential environmental drivers of gut microbial composition have rarely been investigated, particularly in organisms living in their natural environments.

RESULTS

Here, we generated the largest wild nonhuman primate gut microbiome dataset to date to identify the environmental drivers of gut microbial diversity and function in 758 samples collected from wild Ethiopian geladas (Theropithecus gelada). Because geladas live in a cold, high-altitude environment and have a low-quality grass-based diet, they face extreme thermoregulatory and energetic constraints. We tested how proxies of food availability (rainfall) and thermoregulatory stress (temperature) predicted gut microbiome composition of geladas. The gelada gut microbiome composition covaried with rainfall and temperature in a pattern that suggests distinct responses to dietary and thermoregulatory challenges. Microbial changes were driven by differences in the main components of the diet across seasons: in rainier periods, the gut was dominated by cellulolytic/fermentative bacteria that specialized in digesting grass, while during dry periods the gut was dominated by bacteria that break down starches found in underground plant parts. Temperature had a comparatively smaller, but detectable, effect on the gut microbiome. During cold and dry periods, bacterial genes involved in energy, amino acid, and lipid metabolism increased, suggesting a stimulation of fermentation activity in the gut when thermoregulatory and nutritional stress co-occurred, and potentially helping geladas to maintain energy balance during challenging periods.

CONCLUSION

Together, these results shed light on the extent to which gut microbiota plasticity provides dietary and metabolic flexibility to the host, and might be a key factor to thriving in changing environments. On a longer evolutionary timescale, such metabolic flexibility provided by the gut microbiome may have also allowed members of Theropithecus to adopt a specialized diet, and colonize new high-altitude grassland habitats in East Africa. Video abstract.

Monitoring glucocorticoid metabolite concentrations as a proxy of environmental stress across important life-history stages in captive African penguins

Due to considerable global decline in wildlife population numbers and species diversity, because of various anthropogenic activities, conservationists increasingly rely on captive and managed populations as important reservoirs to ensure the survival of endangered and vulnerable species. However, very few of these facilities implement robust, non-invasive monitoring techniques to confirm the effectiveness of their management practices to address animal welfare challenges. This study assessed adrenocortical activity as an indication of environmental stress by investigating the effects of both natural (climate, life-history stages) and anthropogenic (visitor presence) factors on captive-housed African penguins. Seven male-female African penguin breeding pairs were housed in a large, naturalistic outside enclosure at the National Zoological Garden (NZG), South Africa. Weekly urofaecal samples were collected from all individuals over one-year to measure urofaecal glucocorticoid metabolite (ufGCM) concentrations. General linear mixed model analysis determined that visitor presence (for males) and rainfall (for females) were the two factors which best explained the variation in ufGCM concentrations of the study population; however, none of the environmental and anthropogenic factors monitored were found to be significant. A posthoc graphical analysis showed considerable individual variation in terms of ufGCM concentrations within and between sexes when comparing life-history stages. This study confirms that non-invasive steroid monitoring can be an effective tool set for defining and assessing environmental stressors for African penguins and potentially other captive seabirds. However, conservationists and wildlife managers should also consider that individual-, sex-, and population-specific differences in the response to environmental stressors can exist. As such, a generalized management protocol for a specific species may not be sufficient and should be customized according to the specific captive population and/or individual.

Dynamics and determinants of glucocorticoid metabolite concentrations in wild Verreaux's sifakas

Glucocorticoids have wide-ranging effects on animals' behaviour, but many of these effects remain poorly understood because numerous confounding factors have often been neglected in previous studies. Here, we present data from a 2-year study of 7 groups of wild Verreaux's sifakas (Propithecus verreauxi), in which we examined concentrations of faecal glucocorticoid metabolites (fGCMs, n = 2350 samples) simultaneously in relation to ambient temperatures, food intake, rank, reproduction, adult sex ratios, social interactions, vigilance and self-scratching. Multi-variate analyses revealed that fGCM concentrations were positively correlated with increases in daily temperature fluctuations and tended to decrease with increasing fruit intake. fGCM concentrations increased when males were sexually mature and began to disperse, and dominant males had higher fGCM concentrations than subordinate males. In contrast to males, older females showed a non-significant trend to have lower fGCM levels, potentially reflecting differences in male and female life-history strategies. Reproducing females had the highest fGCM concentrations during late gestation and had higher fGCM levels than non-reproducing females, except during early lactation. Variation in fGCM concentrations was not associated with variation in social interactions, adult sex ratios, vigilance and self-scratching. Altogether, we show that measures of glucocorticoid output constitute appropriate tools for studying energetic burdens of ecological and reproductive challenges. However, they seem to be insufficient indicators for immediate endocrinological responses to social and nonsocial behaviours that are not directly linked to energy metabolism.

Low rank and primiparity increase fecal glucocorticoid metabolites across gestation in wild geladas

Integrative behavioral ecology requires accurate and non-invasive measures of hormone mediators for the study of wild animal populations. Biologically sensitive assay systems for the measurement of hormones and their metabolites need to be validated for the species and sample medium (e.g. urine, feces, saliva) of interest. Where more than one assay is available for hormone (metabolite) measurement, antibody selection is useful in identifying the assay that tracks changes in an individuaĺs endocrine activity best, i.e., the most biologically sensitive assay. This is particularly important when measuring how glucocorticoids (GCs) respond to the subtle, additive effects of acute stressors during a predictable metabolic challenge, such as gestation. Here, we validate a group-specific enzyme immunoassay, measuring immunoreactive 11β-hydroxyetiocholanolone, for use in a wild primate, geladas (Theropithecus gelada). This group-specific assay produced values correlated with those from a previously validated double-antibody, corticosterone ¹²⁵I radioimmunoassay. However, the results with the group-specific assay showed a stronger response to an ACTH challenge and identified greater variation in gelada immunoreactive fecal glucocorticoid metabolites (iGCMs) compared with the corticosterone assay, indicating a higher biological sensitivity for assessing adrenocortical activity. We then used the group-specific assay to: (1) determine the normative pattern of iGCM levels across gelada gestation, and (2) identify the ecological, social, and individual factors that influence GC output for pregnant females. Using a general additive mixed model, we found that higher iGCM levels were associated with low rank (compared to high rank) and first time mothers (compared to multiparous mothers). This study highlights the importance of assay selection and the efficacy of group-specific assays for hormonal research in non-invasively collected samples. Additionally, in geladas, our results identify some of the factors that increase GC output over and above the already-elevated GC concentrations associated with gestation. In the burgeoning field of maternal stress, these factors can be examined to identify the effects that GC elevations may have on offspring development.

Detection of neopterin in the urine of captive and wild platyrrhines

Background

Non-invasive biomarkers can facilitate health assessments in wild primate populations by reducing the need for direct access to animals. Neopterin is a biomarker that is a product of the cell-mediated immune response, with high levels being indicative of poor survival expectations in some cases. The measurement of urinary neopterin concentration (UNC) has been validated as a method for monitoring cell-mediated immune system activation in multiple catarrhine species, but to date there is no study testing its utility in the urine of platyrrhine species. In this study, we collected urine samples across three platyrrhine families including small captive populations of Leontopithecus rosalia and Pithecia pithecia, and larger wild populations of Leontocebus weddelli, Saguinus imperator, Alouatta seniculus, and Plecturocebus toppini, to evaluate a commercial enzyme-linked immunosorbent assay (ELISA) for the measurement of urinary neopterin in platyrrhines.

Results

Our results revealed measured UNC fell within the sensitivity range of the assay in all urine samples collected from captive and wild platyrrhine study species via commercial ELISA, and results from several dilutions met expectations. We found significant differences in the mean UNC across all study species. Most notably, we observed higher UNC in the wild population of L. weddelli which is known to have two filarial nematode infections compared to S. imperator, which only have one.

Conclusion

Our study confirms that neopterin is measurable via commercial ELISA in urine collected from captive and wild individuals of six genera of platyrrhines across three different families. These findings promote the future utility of UNC as a promising biomarker for field primatologists conducting research in Latin America to non-invasively evaluate cell-mediated immune system activation from urine.

Social and ecological factors alter stress physiology of Virunga mountain gorillas (Gorilla beringei beringei)

Living in a rapidly changing environment can alter stress physiology at the population level, with negative impacts on health, reproductive rates, and mortality that may ultimately result in species decline. Small, isolated animal populations where genetic diversity is low are at particular risks, such as endangered Virunga mountain gorillas (Gorilla beringei beringei). Along with climate change-associated environmental shifts that are affecting the entire population, subpopulations of the Virunga gorillas have recently experienced extreme changes in their social environment. As the growing population moves closer to the forest's carrying capacity, the gorillas are coping with rising population density, increased frequencies of interactions between social units, and changing habitat use (e.g., more overlapping home ranges and routine ranging at higher elevations). Using noninvasive monitoring of fecal glucocorticoid metabolites (FGM) on 115 habituated Virunga gorillas, we investigated how social and ecological variation are related to baseline FGM levels, to better understand the adaptive capacity of mountain gorillas and monitor potential physiological indicators of population decline risks. Generalized linear mixed models revealed elevated mean monthly baseline FGM levels in months with higher rainfall and higher mean maximum and minimum temperature, suggesting that Virunga gorillas might be sensitive to predicted warming and rainfall trends involving longer, warmer dry seasons and more concentrated and extreme rainfall occurrences. Exclusive use of smaller home range areas was linked to elevated baseline FGM levels, which may reflect reduced feeding efficiency and increased travel efforts to actively avoid neighboring groups. The potential for additive effects of stress-inducing factors could have short- and long-term impacts on the reproduction, health, and ultimately survival of the Virunga gorilla population. The ongoing effects of environmental changes and population dynamics must be closely monitored and used to develop effective long-term conservation strategies that can help address these risk factors.

Faecal glucocorticoid metabolite profiles in diademed sifakas increase during seasonal fruit scarcity with interactive effects of age/sex class and habitat degradation

Glucocorticoids are metabolic byproducts of animals' physiological responses to ecological or social challenges and are thought to represent an adaptive response allowing beneficial responses to short-term challenges. Glucocorticoid metabolites (GCs) can be assayed non-invasively through faeces and therefore can be a useful tool to gauge the health of populations experiencing natural and/or anthropogenic stressors. However, the response of GCs to anthropogenic stressors varies, with both higher and lower GC levels reported. Here, we describe variation in GC secretion within eight diademed sifaka (Propithecus diadema) groups across 1 year. These groups span a gradient of anthropogenic habitat disturbance, including groups in continuous forest ('CONT') and disturbed fragments ('FRAG'), and indicators of health suggest that FRAG groups are negatively impacted by habitat disturbance. We monitored phenology, used focal animal follows to quantify diet and collected faeces (n = 547) from which we quantified GC content using enzyme immunoassay. All groups showed elevated lean-season GCs, but with a single, brief peak. GCs were inversely correlated with feeding time. No overall effect of habitat (CONT vs. FRAG) was found, but the lean-season peak was significantly higher in CONT groups. There was a significant season*age-sex interaction; adult females had an attenuated lean-season response compared with groupmates. The observed lean-season 'challenge' is consistent with previous lemur studies, as well as mammals in general. Low and largely invariable GC levels in FRAG, within the context of observed health and nutritional declines, suggest that FRAG groups employ a strategy whereby the adrenal response to stressors is downregulated. More research is needed to contextualize our observations of GC variation and health on an individual level, both in terms of corroborating evidence for ecological and social stressors, and longer-term quantification of reproductive success and fitness.

The role of glucocorticoids in the vertebrate response to weather

Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vertebrate coping mechanisms to weather. This review attempts to determine if there is a consensus response of glucocorticoids to exposure to weather-related stimuli, including food availability, precipitation, temperature and barometric pressure. The included studies cover field and laboratory studies for all vertebrate taxa, and are separated into four exposure periods, e.g., hours, days, weeks and months. Each reported result was assigned a score based on the glucocorticoid response, e.g., increased, no change, or decreased. Short-term exposure to weather-related stimuli, of up to 24 h, is generally associated with increased glucocorticoids (79% of studies), suggesting that these stimuli are perceived as stressors by most animals. In contrast, the pattern for exposures longer than 24 h shows more variation, even though a majority of studies still report an increase (64%). Lack of glucocorticoid increases appeared to result from instances where: (1) prolonged exposure was a predictable part of the life history of an animal; (2) environmental context was important for the ultimate effect of a stimulus (e.g., precipitation limited food availability in one environment, but increased food in another); (3) prolonged exposure induced chronic stress; and (4) long-term responses appeared to reflect adaptations to seasonal shifts, instead of to short-term weather. However, there is a strong bias towards studies in domesticated laboratory species and wild animals held in captivity, indicating a need for field studies, especially in reptiles and amphibians. In conclusion, the accumulated literature supports the hypothesis that glucocorticoids can serve as the physiological mechanism promoting fitness during inclement weather.

Social and ecological drivers of reproductive seasonality in geladas

Many nonseasonally breeding mammals demonstrate some degree of synchrony in births, which is generally associated with ecological factors that mediate fecundity. However, disruptive social events, such as alpha male replacements, also have the potential to affect the timing of female reproduction. Here, we examined reproductive seasonality in a wild population of geladas (Theropithecus gelada) living at high altitudes in an afro-alpine ecosystem in Ethiopia. Using 9 years of demographic data (2006-2014), we determined that, while females gave birth year-round, a seasonal peak in births coincided with peak green grass availability (their staple food source). This post-rainy season "ecological peak" in births meant that estimated conceptions for these births occurred when temperatures were at their highest and mean female fecal glucocorticoid concentrations were at their lowest. In addition to this ecological birth peak, we also found a separate birth peak that occurred only for females in groups that had experienced a recent replacement of the dominant male (i.e., a takeover). Because new dominant males cause abortions in pregnant females and kill the infants of lactating females, takeovers effectively "reset" the reproductive cycles of females in the group. This "social birth peak" was distinct from the ecological peak and was associated with higher rates of cycling and conceptions overall and higher glucocorticoid levels immediately following a takeover as compared to females that did not experience a takeover. These data demonstrate that social factors (in this case, male takeovers) can contribute to population-level reproductive seasonality above and beyond group-level reproductive synchrony.

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 energetic condition in mantled howler monkeys

Hormones have a key role in energy allocation, so their study allows understanding individual metabolic strategies. Because different hormones convey different information on the responses of individuals to energetic demands, a simultaneous analysis of variation in multiple hormones may offer a more reliable picture of metabolic strategies than single hormone assessments. In this study we focused on determining which factors were related to variation in fecal glucocorticoid and thyroid hormone metabolites in wild mantled howler monkeys (Alouatta palliata). Over 12months, we determined fecal glucocorticoid and thyroid hormone metabolite levels of 11 adults belonging to two groups, and examined the relationship between hormone metabolites and a variety of behavioral, physiological, and ecological factors (e.g., food intake, sex/reproductive state, activity, participation in agonistic interactions). We found that glucocorticoids were elevated in gestating and lactating females compared to males and cycling females, and were also higher when individuals were more active and participated in agonistic interactions. Thyroid hormone levels were also related to sex/reproductive state and activity, but were additionally positively related to fruit intake and negatively related to young leaf intake. Our study demonstrates that the non-invasive measurement of glucocorticoid and thyroid hormones of howler monkeys allows assessing different underlying physiological processes. By combining different biomarkers, which has seldom been done with wildlife, we could also parse the influence of psychological vs. metabolic challenges for individual energetic condition, which may be instrumental for deciding which factors should be accounted for when studying different hormone-behavior interactions.

Female Spider Monkeys (Ateles geoffroyi) Cope with Anthropogenic Disturbance Through Fission-Fusion Dynamics

Most primates live in habitats with some level of anthropogenic disturbance, and such disturbances have a larger impact on frugivorous primates that are more sensitive to ecological disruptions than folivores. Fecal glucocorticoid metabolites provide insight into how the external environment affects internal physiological state, and thus provide information on how anthropogenic pressures become embodied. Here, I examine how subgroup size and glucocorticoids vary with high and low fruit abundance, and how fruit abundance, subgroup size, and activity budget affect fecal glucocorticoid metabolites in female spider monkeys (Ateles geoffroyi) living in an anthropogenically disturbed habitat. I measured these variables via behavioral, ecological, and fecal sampling for 15 months in 17 female spider monkeys at El Zota Biological Field Station. Subgroup size was significantly larger during periods of high fruit abundance, but glucocorticoids did not differ between periods of low and high fruit abundance. Monthly fruit abundance predicted subgroup sizes significantly, but did not predict fecal glucocorticoid concentrations. Increased resting time and reproductive state predicted fecal glucocorticoid concentrations significantly, but travel and foraging time had no significant effect on glucocorticoid concentrations. Individual resting time over the study period correlated negatively with glucocorticoid concentrations. These results suggest that spider monkeys cope with variation in fruit abundance by adjusting subgroup size, and that these adjustments may mitigate environmental stress in this mildly seasonal environment. The large, relatively productive forest size at this site, and the availability of anthropogenic food sources, enable this population of spider monkeys to cope with human-induced habitat disturbance.

Energetics of feeding, social behavior, and life history in non-human primates

Energy is a variable of key importance to a wide range of research in primate behavioral ecology, life history, and conservation. However, obtaining detailed data on variation in energetic condition, and its biological consequences, has been a considerable challenge. In the past 20years, tremendous strides have been made towards non-invasive methods for monitoring the physiology of animals in their natural environment. These methods provide detailed, individualized data about energetic condition, as well as energy allocations to growth, reproduction, and somatic health. In doing so, they add much-needed resolution by which to move beyond correlative studies to research programs that can discriminate causes from effects and disaggregate multiple correlated features of the social and physical environment. In this review, I describe the conceptual and methodological approaches for studying primate energetics. I then discuss the core questions about primate feeding ecology, social behavior, and life history that can benefit from physiological studies, highlighting the ways in which recent research has done so. Among these are studies that test, and often refute, common assumptions about how feeding ecology shapes primate biology, and those that reveal proximate associations between energetics and reproductive strategies.

Energetics of feeding, social behavior, and life history in non-human primates

Energy is a variable of key importance to a wide range of research in primate behavioral ecology, life history, and conservation. However, obtaining detailed data on variation in energetic condition, and its biological consequences, has been a considerable challenge. In the past 20years, tremendous strides have been made towards non-invasive methods for monitoring the physiology of animals in their natural environment. These methods provide detailed, individualized data about energetic condition, as well as energy allocations to growth, reproduction, and somatic health. In doing so, they add much-needed resolution by which to move beyond correlative studies to research programs that can discriminate causes from effects and disaggregate multiple correlated features of the social and physical environment. In this review, I describe the conceptual and methodological approaches for studying primate energetics. I then discuss the core questions about primate feeding ecology, social behavior, and life history that can benefit from physiological studies, highlighting the ways in which recent research has done so. Among these are studies that test, and often refute, common assumptions about how feeding ecology shapes primate biology, and those that reveal proximate associations between energetics and reproductive strategies.

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.

Seasonality of reproductive events and early mortality in a colony of hamadryas baboons (Papio hamadryas hamadryas) over a 30-year period: Capital breeding and life history patterns in a food-provisioned population seasonally thermally stressed

In environments where energy demands and resource availability vary seasonally, individuals are expected to time the optimal allocation of resources to support survival and reproduction. Although female baboons are regarded as all year round, capital breeders, we wondered how they would respond in an ecological scenario where food were not limiting, foraging effort were negligible, and they were thermally stressed during the cold winter. This study analyzes a 30-year database of conceptions, births, resumptions of postlactational ovarian activity, menarches, and prenatal and early postnatal reproductive failures recorded in a food-provisioned colony of hamadryas baboons located in a temperate zone (40°25'N) to search for seasonal patterns in their life-history patterns and explore its fitness consequences. The results show that the study females exhibited moderate seasonality and behaved like capital breeders; ovarian activity peaked during the period of benign weather conditions (spring and early summer) and births and lactation peaked during the period when they were thermally stressed and faced a negative energy balance (winter). Mistimed conceptions were more likely to fail than timed conceptions were, although this association could be artefactual due to the difficulty to accurately detect prenatal losses. Insolation and, to a lesser extent, temperature were positively associated with conceptions, resumptions of postlactational ovarian activity and onsets of menarche, and negatively associated with births. These findings highlight the extent of plasticity (width of peaks) and resiliency (retention of a capital breeding tactic even under highly seasonally thermally stressful cold conditions) in how primates can adjust their life history patterns and solve tradeoffs in a scenario of strong seasonal variation. Am. J. Primatol. 78:1149-1164, 2016. © 2016 Wiley Periodicals, Inc.

Validating faecal glucocorticoid metabolite analysis in the Virunga mountain gorilla using a natural biological stressor

The continued degradation of primate habitat worldwide is forcing many primate populations into small protected forest islands surrounded by high-density human populations. One well-studied example is the critically endangered mountain gorilla (Gorilla beringei beringei). Decades of monitoring and research on Rwanda's mountain gorillas offer a unique opportunity to use non-invasive endocrine analysis to address pressing questions about the conservation of this endangered population. The aims of our study were as follows: (i) to validate field and laboratory methods for assessing stress through faecal glucocorticoid metabolite (FGM) analysis using inter-social unit interactions as a natural stressor; (ii) to determine the excretion lag times between interactions and detectable stress response in faeces; and (iii) to determine whether there are circadian patterns of FGM excretion. We collected ~6000 faecal samples from 127 known gorillas in 10 habituated groups, monitored by the Dian Fossey Gorilla Fund's Karisoke Research Center over 21 months in 2011 and 2012. Extracted FGMs were measured using a cortisol enzyme immunoassay (R4866; C. J. Munro). Results revealed cause-effect relationships between inter-unit interactions and increased FGMs (relative to individual pre-event samples) between 20 and 140 h after interactions, with the peak most often occurring on day 3. There was no evidence of circadian patterns in FGM concentrations, as previously shown in many species with long gut passage times. However, baseline FGM concentrations were lower in adult males than in adult females, and variation was associated with the collection month, indicating possible seasonal variation. This study provides a biologically validated, field-friendly faecal hormone metabolite extraction and laboratory enzyme immunoassay analysis method for non-invasive monitoring of adrenocortical activity in Virunga mountain gorillas. The methods are useful for future evaluation of a variety of environmental and human-induced potential stressors in this critically endangered population.

Field endocrinology of nonhuman primates: past, present, and future

In the past few decades, research on nonhuman primate endocrinology has moved from the lab to the field, leading to a huge increase in both the breadth and depth of primate field studies. Here, I discuss the past, present, and future of primate field endocrinology. I review the history of the field, and go on to discuss methodological developments and the issues that they sometimes entail. Next, I consider ways in which we might conceptualize the role of hormones, and focus on the need to distinguish proximate from ultimate levels of explanation. Current potentially problematic issues in the field include: 1) an inability to obtain noninvasive measurements of Central Nervous System (CNS) rather than peripheral hormone concentrations; 2) research questions that become stuck (e.g., questions regarding sexual swelling expression mechanisms); 3) data dredging and post-hoc linking of hormones to any plausible variable, leading to a lack of clarity on their role in animal ecology and behavior. I finish by discussing several unanswered questions that might benefit from further research. These are how we might: 1) best obtain measurements for CNS hormone concentrations non-invasively; 2) measure hormone receptor expression alongside hormone concentrations; 3) consider the human endocrinology literature more thoroughly and perhaps take more multimarker approaches; 4) better consider the social environment, including audience and dyadic familiarity effects; and 5) apply our findings to conservation issues.

Validation of a Fecal Glucocorticoid Assay to Assess Adrenocortical Activity in Meerkats Using Physiological and Biological Stimuli

In mammals, glucocorticoid (i.e. GC) levels have been associated with specific life-history stages and transitions, reproductive strategies, and a plethora of behaviors. Assessment of adrenocortical activity via measurement of glucocorticoid metabolites in feces (FGCM) has greatly facilitated data collection from wild animals, due to its non-invasive nature, and thus has become an established tool in behavioral ecology and conservation biology. The aim of our study was to validate a fecal glucocorticoid assay for assessing adrenocortical activity in meerkats (Suricata suricatta), by comparing the suitability of three GC enzyme immunoassays (corticosterone, 11β-hydroxyetiocholanolone and 11oxo-etiocholanolone) in detecting FGCM increases in adult males and females following a pharmacological challenge with adrenocorticotropic hormone (ACTH) and biological stimuli. In addition, we investigated the time course characterizing FGCM excretion, the effect of age, sex and time of day on FGCM levels and assessed the potential effects of soil contamination (sand) on FGCM patterns. Our results show that the group specific 11β-hydroxyetiocholanolone assay was most sensitive to FGCM alterations, detecting significant and most distinctive elevations in FGCM levels around 25 h after ACTH administration. We found no age and sex differences in basal FGCM or on peak response levels to ACTH, but a marked diurnal pattern, with FGCM levels being substantially higher in the morning than later during the day. Soil contamination did not significantly affect FGCM patterns. Our results emphasize the importance of conducting assay validations to characterize species-specific endocrine excretion patterns, a crucial step to all animal endocrinology studies using a non-invasive approach.

Effects of population density on corticosterone levels of prairie voles in the field

High population density is often associated with increased levels of stress-related hormones, such as corticosterone (CORT). Prairie voles (Microtus ochrogaster) are a socially monogamous species known for their large population density fluctuations in the wild. Although CORT influences the social behavior of prairie voles in the lab, the effect of population density on CORT has not previously been quantified in this species in the field. We validated a non-invasive hormone assay for measuring CORT metabolites in prairie vole feces. We then used semi-natural enclosures to experimentally manipulate population density, and measured density effects on male space use and fecal CORT levels. Our enclosures generated patterns of space use and social interaction that were consistent with previous prairie vole field studies. Contrary to the positive relationship between CORT and density typical of other taxa, we found that lower population densities (80 animals/ha) produced higher fecal CORT than higher densities (240/ha). Combined with prior work in the lab and field, the data suggest that high prairie vole population densities indicate favorable environments, perhaps through reduced predation risk. Lastly, we found that field animals had lower fecal CORT levels than laboratory-living animals. The data emphasize the usefulness of prairie voles as models for integrating ecological, evolutionary, and mechanistic questions in social behavior.

Assessing adaptability and reactive scope: Introducing a new measure and illustrating its use through a case study of environmental stress in forest-living baboons

In order to maintain regulatory processes, animals are expected to be adapted to the range of environmental stressors usually encountered in their environmental niche. The available capacity of their stress responses is termed their reactive scope, which is utilised to a greater or lesser extent to deal with different stressors. Typically, non-invasive hormone assessment is used to measure the physiological stress responses of wild animals, but, for methodological reasons, such measurements are not directly comparable across studies, limiting interpretation. To overcome this constraint, we propose a new measure of the relative strength of stress responses, 'demonstrated reactive scope', and illustrate its use in a study of ecological correlates (climate, food availability) of faecal glucocorticoid (fGC) levels in two forest-living troops of baboons. Results suggest the wild-feeding troop experiences both thermoregulatory and nutritional stress, while the crop-raiding troop experiences only thermoregulatory stress. This difference, together with the crop-raiding troop's lower overall physiological stress levels and lower demonstrated fGC reactive scope, may reflect nutritional stress-buffering in this troop. The relatively high demonstrated fGC reactive scope levels of both troops compared with other baboons and primate species, may reflect their extreme habitat, on the edge of the geographic range for baboons. Demonstrated reactive scope provides a means of gauging the relative strengths of stress responses of individuals, populations, or species under different conditions, enhancing the interpretive capacity of non-invasive studies of stress hormone levels in wild populations, e.g. in terms of animals' adaptive flexibility, the magnitude of their response to anthropogenic change, or the severity of impact of environmental conditions.

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.

Responses to social and environmental stress are attenuated by strong male bonds in wild macaques

In humans and obligatory social animals, individuals with weak social ties experience negative health and fitness consequences. The social buffering hypothesis conceptualizes one possible mediating mechanism: During stressful situations the presence of close social partners buffers against the adverse effects of increased physiological stress levels. We tested this hypothesis using data on social (rate of aggression received) and environmental (low temperatures) stressors in wild male Barbary macaques (Macaca sylvanus) in Morocco. These males form strong, enduring, and equitable affiliative relationships similar to human friendships. We tested the effect of the strength of a male's top three social bonds on his fecal glucocorticoid metabolite (fGCM) levels as a function of the stressors' intensity. The attenuating effect of stronger social bonds on physiological stress increased both with increasing rates of aggression received and with decreasing minimum daily temperature. Ruling out thermoregulatory and immediate effects of social interactions on fGCM levels, our results indicate that male Barbary macaques employ a tend-and-befriend coping strategy in the face of increased environmental as well as social day-to-day stressors. This evidence of a stress-ameliorating effect of social bonding among males under natural conditions and beyond the mother-offspring, kin or pair bond broadens the generality of the social buffering hypothesis.

Harem-holding males do not rise to the challenge: androgens respond to social but not to seasonal challenges in wild geladas

The challenge hypothesis has been enormously successful in predicting interspecific androgen profiles for vertebrate males. Nevertheless, in the absence of another theoretical framework, many researchers 'retrofit' the challenge hypothesis, so that its predictions also apply to intraspecific androgen comparisons. We use a wild primate, geladas (Theropithecus gelada), to illustrate several considerations for androgen research surrounding male contests that do not necessarily fit within the challenge hypothesis framework. Gelada society comprises harem-holding males (that can mate with females) and bachelor males (that cannot mate with females until they take over a harem). Using 6 years of data from known males, we measured androgens (i.e. faecal testosterone (fT) metabolites) both seasonally and across specific male contests. Seasonal androgen variation exhibited a very different pattern than variation resulting from male contests. Although harem-holding males had higher testosterone levels than bachelors across the year, bachelors had higher testosterone during the annual 'takeover season'. Thus, harem-holding males did not 'rise to the challenge' exactly when needed most. Yet, androgen profiles across male contests indicated that both sets of males exhibit the expected fT rise in response to challenges. Results from male geladas also support the idea that the context before (e.g. male condition) and after (e.g. contest outcome) a contest are critical variables for predicting hormones and behaviour.

Seasonal variations of basal cortisol and high stress response to captivity in Octodon degus, a mammalian model species

Across vertebrates, the hypothalamic-pituitary-adrenal axis is a conserved neuroendocrine network that responds to changing environments and involves the release of glucocorticoids into the blood. Few studies have been carried out concerning mammalian adrenal regulation in wild species either in the laboratory or field, and even fewer have been able to determine true glucocorticoid baselines. We studied the South-American caviomorph rodent Octodon degus, a diurnal and social mammal that has become an important species in the biological research. First, we determined the plasma cortisol baseline and the acute stress concentrations during the non-reproductive and mating seasons in free-living individuals. Second, using the same protocol we assessed the impact of long-term captivity on the adrenal function in wild-caught degus and degus born in laboratory. Third, we examined laboratory groups formed with degus taken from two distant natural populations; one of them originally occurs at the Andes Mountains in high altitude conditions. The data revealed seasonal modulation of basal cortisol in the wild associated with mating. In laboratory, degus presented higher cortisol stress responses, with greater magnitudes shown in degus born and reared in captivity. No differences between populations were found. The results suggest differential regulatory mechanisms between basal and stress-induced cortisol levels, and context dependence of cortisol modulation in a mammalian species.

Physiological stress in koala populations near the arid edge of their distribution

Recent research has shown that the ecology of stress has hitherto been neglected, but it is in fact an important influence on the distribution and numbers of wild vertebrates. Environmental changes have the potential to cause physiological stress that can affect population dynamics. Detailed information on the influence of environmental variables on glucocorticoid levels (a measure of stress) at the trailing edge of a species' distribution can highlight stressors that potentially threaten species and thereby help explain how environmental challenges, such as climate change, will affect the survival of these populations. Rainfall determines leaf moisture and/or nutritional content, which in turn impacts on cortisol concentrations. We show that higher faecal cortisol metabolite (FCM) levels in koala populations at the trailing arid edge of their range in southwestern Queensland are associated with lower rainfall levels (especially rainfall from the previous two months), indicating an increase in physiological stress when moisture levels are low. These results show that koalas at the semi-arid, inland edge of their geographic range, will fail to cope with increasing aridity from climate change. The results demonstrate the importance of integrating physiological assessments into ecological studies to identify stressors that have the potential to compromise the long-term survival of threatened species. This finding points to the need for research to link these stressors to demographic decline to ensure a more comprehensive understanding of species' responses to climate change.

Validation of a field technique and characterization of fecal glucocorticoid metabolite analysis in wild chimpanzees (Pan troglodytes)

Monitoring adrenocortical activity in wild primate populations is critical, given the well-documented relationship between stress, health, and reproduction. Although many primate studies have quantified fecal glucocorticoid metabolite (FGM) concentrations, it is imperative that researchers validate their method for each species. Here, we describe and validate a technique for field extraction and storage of FGMs in wild chimpanzees (Pan troglodytes). Our method circumvents many of the logistical challenges associated with field studies while yielding similar results to a commonly used laboratory method. We further validate that our method accurately reflects stress physiology using an adrenocorticotropic hormone challenge in a captive chimpanzee and an FGM peak at parturition in a wild subject. Finally, we quantify circadian patterns for FGMs for the first time in this species. Understanding these patterns may allow researchers to directly link specific events with the stress response.