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Chemosignals are mediators of social interactions in mammals, providing con- and hetero-specifics with information on fixed (e.g., species, sex, group, and individual identity) and variable (e.g., social, reproductive, and health status) features of the signaler. Yet, methodological difficulties of recording and quantifying odor signals, especially in field conditions, have hampered studies of natural systems. We present the first use of the Torion® portable gas chromatography-mass spectrometry (GC-MS) instrument for in situ chemical analysis of primate scents. We collected and analyzed swab samples from the scent glands and skin from 13 groups (57 individuals) of two sympatric species of wild emperor tamarins, Saguinus imperator, and Weddell's saddleback tamarins, Leontocebus weddelli (Callitrichidae). In total, 11 compounds of interest (i.e., probably derived from the animals) could be detected in the samples, with 31 of 215 samples containing at least one compound of interest. The composition of these 31 samples varied systematically with species, group, sex, and breeding status. Moreover, we tentatively identified seven of the compounds of interest as methyl hexanoate, benzaldehyde, ethyl hexanoate, acetophenone, a branched C15 alkane, 4-methoxybenzaldehyde, and hexadecan-1-ol. As the field of primate semiochemistry continues to grow, we believe that portable GC-MS instruments have the potential to help make progress in the study of primate chemosignaling in field conditions, despite limitations that we encountered. We further provide recommendations for future use of the Torion® portable GC-MS for in situ analyses.

Cooperative breeders live in social groups in which individuals in an age–sex class vary in reproductive development due to reproductive dominance by a few individuals in each group. Among callitrichids, adult males have been implicated in driving group reproductive output, but uneven sampling efforts, the underlying effects of group size, and pseudoreplication at the group and species levels are confounding variables in these analyses. We examined the drivers of group reproductive output in callitrichids by 1) conducting a meta-analysis of published studies of callitrichid group composition; 2) assigning developmental class based on reproductive morphology; and 3) using multivariate modeling to test whether the proportion of individuals of each developmental class predicts the presence and the number of surviving offspring among free-ranging Weddell’s saddleback tamarins (Leontocebus weddelli) and emperor tamarins (Saguinus imperator) in Peru. The meta-analysis revealed that the number of adult females and group size, but not the number of adult males, are significantly correlated with group reproductive output. Statistical models of the new dataset revealed that the proportion of primary breeding males, primary breeding females, and group size predicted whether groups had surviving infants, and that only the proportion of primary breeding females and group size predicted the number of surviving infants. Thus, primary breeding males appear to be necessary for groups to raise any infants, but a higher proportion of primary breeding females and a larger group size increase group reproductive output overall.

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.

Primate long calls are high-amplitude vocalizations that can be critical in maintaining intragroup contact and intergroup spacing, and can encode abundant information about a call's producer, such as age, sex, and individual identity. Long calls of the wild emperor (Saguinus imperator) and saddleback (Leontocebus weddelli) tamarins were tested for these identity signals using artificial neural networks, machine-learning models that reduce subjectivity in vocalization classification. To assess whether modelling could be streamlined by using only factors which were responsible for the majority of variation within networks, each series of networks was re-trained after implementing two methods of feature selection. First, networks were trained and run using only the subset of variables whose weights accounted for ≥50% of each original network's variation, as identified by the networks themselves. In the second, only variables implemented by decision trees in predicting outcomes were used. Networks predicted dependent variables above chance (≥58.7% for sex, ≥69.2 for age class, and ≥38.8% for seven to eight individuals), but classification accuracy was not markedly improved by feature selection. Findings are discussed with regard to implications for future studies on identity signaling in vocalizations and streamlining of data analysis.

Parasite-host relationships are influenced by several factors intrinsic to hosts, such as social standing, group membership, sex, and age. However, in wild populations, temporal variation in parasite distributions and concomitant infections can alter these patterns. We used microscropy and molecular methods to screen for naturally occurring haemoparasitic infections in two Neotropical primate host populations, the saddleback (Leontocebus weddelli) and emperor (Saguinus imperator) tamarin, in the lowland tropical rainforests of southeastern Peru. Repeat sampling was conducted from known individuals over a three-year period to test for parasite-host and parasite-parasite associations. Three parasites were detected in L. weddelli including Trypanosoma minasense, Mansonella mariae, and Dipetalonema spp., while S. imperator only hosted the latter two. Temporal variation in prevalence was observed in T. minasense and Dipetalonema spp., confirming the necessity of a multi-year study to evaluate parasite-host relationships in this system. Although callitrichids display a distinct reproductive dominance hierarchy, characterized by single breeding females that typically mate polyandrously and can suppress the reproduction of subdominant females, logistic models did not identify sex or breeding status as determining factors in the presence of these parasites. However, age class had a positive effect on infection with M. mariae and T. minasense, and adults demonstrated higher parasite species richness than juveniles or sub-adults across both species. Body weight had a positive effect on the presence of Dipetalonema spp. The inclusion of co-infection variables in statistical models of parasite presence/absence data improved model fit for two of three parasites. This study verifies the importance and need for broad spectrum and long-term screening of parasite assemblages of natural host populations., Graphical abstract Image 1, Highlights • Co-infection data improves statistical models of parasite prevalence. • Longitudinal sampling is key to unraveling parasite-host relationships in nature. • Host specificity of blood parasites among sympatric Callitrichine primates. • Sex roles in cooperatively breeding primates may not impact parasitism.

Geophagy, or soil consumption, has been documented in diverse animal taxa, including many primates. Physiological functions such as mineral supplementation, detoxification of secondary compounds, and antacid properties are possible causes for this behavior. We report on observations of geophagy at arboreal termitaria by free-ranging Pithecia rylandsi at La Estacion Biologica Los Amigos (EBLA) in Peru between 2008 and 2015. Characteristics of geophagy events, including saki monkey behavior at the termitaria, were recorded and geochemical analyses were conducted on consumed termitaria, nearby topsoils, and unvisited termitaria. We observed 76 feeding bouts at 26 different termitaria by two groups of P. rylandsi during 1125 observational hours (0.07 bouts/obs. h). Geophagy occurred throughout the year, but rates peaked in January during the rainy season. All age and sex classes visited both active and inactive mounds. Feeding bouts were brief (171 ± SD 154 s), and no differences were observed in time spent feeding at active or inactive termitaria. Analyses showed that consumed soils contained higher concentrations of phosphorous, potassium, calcium, and magnesium than did topsoil. Consumed soils also contained a higher total cation exchange capacity than topsoil. Our analysis of consumed versus control termitaria revealed no differences in their chemical composition. We discuss these results in the context of the two primary hypotheses proposed for geophagy in pitheciins: mineral supplementation and toxin adsorption. Our data are consistent with the interpretation that P. rylandsi consume soils from arboreal termitaria to aid in adsorption of toxins found in immature seeds, which are a year-round component of their diet.