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

Stable Isotopes Analysis of Black Lion Tamarins Reveals Increasing Arthropod Consumption When Fruit Productivity Decreases in Forest Fragments

Given the cryptic and elusive nature of prey consumption, quantifying its contribution to the diet of free-ranging primates using behavioral methods is challenging. In this context, the use of carbon and nitrogen-stable isotopes represents a promising alternative approach. Here, we used stable isotope analysis to estimate the proportion of arthropods and fruits in the diet of black lion tamarins (Leontopithecus chrysopygus), an endangered primate endemic to the Brazilian Atlantic Forest. To do so, we ran stable isotope mixing models using isotopic data from hair samples of black lion tamarins living in six forest fragments showing different levels of habitat quality. Furthermore, we ran linear mixed models to assess the influence of habitat quality-fruit productivity (estimated by tree total basal area) and arthropod biomass - and individual characteristics (sex and body mass) on tamarins' δ15N values (a proxy for trophic position). Our results revealed that arthropods contributed more to black lion tamarins' diet than reported in previous behavioral studies, suggesting that behavioral observations may considerably underestimate the importance of arthropodivory in the diet of arboreal primates. The degree of arthropodivory and frugivory was similar within groups, in line with the strong group cohesion and synchronization of feeding behaviors of this species and supporting the role of site-specific habitat characteristics on dietary choice. Arthropod consumption was higher in areas with lower fruit productivity and did not increase when arthropod biomass increased, suggesting that fruits represent a limiting but preferred resource for this species. These results demonstrate the dietary plasticity of black lion tamarins in areas of lower forest quality, where they manage to compensate low fruit productivity by shifting to a diet richer in arthropods. Considering that this species occurs within a highly fragmented landscape, preserving and protecting small forest patches remains crucial for the conservation of this species.

Glucocorticoids and behavior in non-human primates: A meta-analytic approach to unveil potential coping mechanisms

Glucocorticoids (GCs) mediate responses to energetic and psychosocial challenges and are associated with behavioral adjustments that form part of an adaptive vertebrate stress response. GCs and behavior can indirectly influence each other, leading to either an intensification or attenuation of stress responses. Exploring these GC-behavior relationships may offer insights into the beneficial aspects of behavior and help identify coping mechanisms that potentially enhance individual fitness. We conducted a systematic review of the relationship between GCs and several behavioral traits, as described in the literature on captive and wild primates, and evaluated the effect of different categorical factors on these relationships using a meta-analytic approach. According to the type of behavior, we grouped statistical measures into affiliative, agonistic, anxiety-like, and foraging domains which were further differentiated into behavioral subgroups. We also categorized measures based on setting, method, sex and age of individuals, and sample matrix involved in each primary study. Overall, we found that some affiliative and foraging behaviors are associated with lower GC levels, while agonistic and anxiety-like behaviors are linked to higher GC levels. Specifically, non-sexual affiliation and energetically inexpensive activities were negatively related to GCs. In contrast, inter- and intragroup aggression, noncommunicative and self-directed behaviors, and energetically expensive activities were positively related to GCs. By demonstrating how certain social, ecological and intrinsic factors affect the GC-behavior relationships, our study helps elucidate the contexts that may alleviate or intensify the stress responses in non-human primates.

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.