We studied intergroup social play (IGSP) among immatures in wild black and gold howler monkeys (Alouatta caraya) in northeastern Argentina. IGSP events are one form of affiliative interaction that can occur during intergroup encounters. The main goal of this study was to analyze IGSP in A. caraya immatures and assess how intrinsic (e.g., age and sex) and extrinsic (e.g., seasonality) factors can influence the development of this type of social behavior. We followed 12 groups between 2008 and 2015 and recorded 182 encounters and 61 events of IGSP. Considering the composition of play partners, most IGSP events occurred among juveniles of both sexes (33%), followed by juveniles that were only-male (31%), and finally between mixed-sex juveniles and infants (20%) interactions. Additionally, most IGSP events occurred mainly in summer (56%), followed by spring (29%), with fewer events occurring in autumn (15%) and no IGSP events recorded in winter. Our results suggest that IGSP constitutes a beneficial activity in wild A. caraya that promotes behavioral flexibility, where immatures acquire social skills, such as tolerance, by interacting with unknown individuals. Moreover, the higher participation of young males in IGSP is consistent with the fact that adult black and gold howler males tend to be more actively involved in group encounters than females, supporting the hypothesis that social play provides benefits in the development of motor and social skills. Finally, seasonality in the frequencies of IGSP might be related to availability of foods with high and easily mobilized energy content in summer and spring.
Studies have shown that as age increases, parasitism could also be more frequent, on the other hand, the lack of immunity can increase the risk of infection in younger individuals. Regarding sex, there is a general tendency for males to be more parasitized than females, in the case of primates, this is related to the effort made by males into attaining and maintain a high rank, implying high levels of testosterone, a hormone with immunosuppressive effects. Immunosuppressive effects of stress hormones can also increase susceptibility in dominant or subordinate individuals, nevertheless, in a study, the level of exposure to parasites seems to be more important than the immunosuppressive effects of stress in explaining why dominant females have more infections from directly transmitted parasites. In this study, we investigated the relationship between the prevalence of Giardia spp. and Blastocystis spp. and the categories of age and sex in black and golden howler monkeys (Alouatta caraya) of Argentina. We analyzed 375 fecal samples from 27 individuals (juveniles and adults of both sexes), using microscopy and techniques of flotation and sedimentation. To analyze the relationship between age, sex, and infection prevalence, a Generalized Linear Mixed Model was used. In adults, the prevalence of infection was 78.5 % while in juveniles, all individuals (100 %) were infected with both protozoa. Males had a infection prevalence 84.6%, in females it was 92.8 %. When comparing infection prevalence between ages and between sexes, no significant differences were found (P > 0.05). Research suggests that parasite infection rates may be influenced by specific form of transmission, in this sense, these protozoa, are transmitted through ingestion of cysts which are infectious immediately after defecation has occurred. On the other hand, all members of the group tend to defecate simultaneously, leaving all the members of the group exposed to infection. Therefore, we suggest that physiological or behavioral factors do not appear to be important in the risk of protozoan infection.
The expansion of human populations associated with urbanization results in extensive modification of natural habitats. While many species cannot persist in these highly modified environments, some species adopt new strategies, which contribute to their survival. Several primate species have persisted in altered habitats, including members of the genus <i>Alouatta</i>. To improve our understanding of this interplay, we compared glucocorticoid (GCC) levels in male and female black and gold howler monkeys (<i>Alouatta caraya</i>) in urban and rural areas in northeastern Argentina. Fecal samples (<i>n</i> = 60) were collected from adults and hormone extracts were analyzed by enzyme immunoassays (EIA). Monkeys living in urban areas (females: 109.15 ± 18.83; males: 106.15 ± 10.48) had lower GCC<i></i>levels than monkeys living in rural areas (females: 152.01 ± 19.50; males:139,82 ± 10.85). Interestingly, males living in urban areas had lower GCC levels compared to those living in rural areas, whereas no differences were observed in GCC levels between females living in urban and rural areas. While these results suggest that urban areas may provide a release from intergroup competition for male howler monkeys, future work is needed to better understand the dynamics of this association to best inform management and conservation of this vulnerable species.
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