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Infant adoption is an association that occurs between an adult individual and a dependent infant and occurs most often when lactating females care for a nutritionally dependent infant that is not her offspring. Adult females are often involved in adoption; while, direct infant care by males occurs in less than 5% of all mammalian species. We report the first record of adoption by wild male adults of Alouatta caraya, a platyrrhine primate species that does not typically participate in parental care. We observed two independent cases of adoption, in two different groups (G1, G2) at the Corrientes Biological Station, Argentina. After the death of two adult females with dependent infants, one adult male adopted an orphan in each group. We recorded the activity of the adoptive males and the two infants. During this period, adoptive males expressed parental care behaviors toward infants. However, after 38 days in G1 and 53 days in G2, both infants died. Based on our continuous monitoring of study groups, we suggest that adoptive males are the biological parents of the orphaned infants. As such, kin selection may explain the care of the infants. However, another explanation could be group familiarity, which refers to the social bonds and cohesion that develop among individuals within a group, even if they are not genetically related. An adult male, although not genetically related to the infants, may take care of them due to the cohesion and relationships established within the group during his period of residence. The study of these rare parental behaviors taken by A. caraya adult males provide insights into the knowledge of group social cohesion and structure., Competing Interests: Declarations. Conflict of interest: The authors declare none. Ethical approval: The study complied with the current laws and permission of Argentina., (© 2024. The Author(s), under exclusive licence to Japan Monkey Centre.)

Fruit ingestion by frugivores and the subsequent passage of seeds through their digestive tract can influence seed germination patterns. The removal of germination inhibitors contained in the fruit pulp (deinhibition effect), and/or the abrasion of the seed coat (scarification effect), can modify the probability and speed of seed germination. We followed seven groups of black-and-gold howler monkeys (Alouatta caraya) in northeastern Argentina between November 2012 and January 2013 to study the effect of seed passage through the howler monkeys' gut on seed germination. For three native and one exotic species, we compared the proportion of germination and germination times among seeds in three different treatments: gut-passed seeds (GP), manually extracted seeds from fruits (ME), and seeds in intact fruits (IF). Paired comparisons between treatments allowed us to assess the overall effect of seed passage (total effect without distinguishing individual effects, GP vs. IF), deinhibition effect (ME vs. IF), and scarification effect (GP vs. ME). Our results suggest that passage through the howler monkeys' gut enhances seed germination by an increase in the proportion of germinated seeds and/or by a reduction in germination times. We found that deinhibition enhanced germination in three out of the four studied species, while scarification enhanced germination in one and decreased germination in another species. Our work highlights that gut passage may affect seed germination by different mechanisms, and all of these mechanisms should be considered in germination studies. It also emphasizes the importance of A. caraya as a seed disperser in northeastern Argentina, showing the high quality of the treatment provided to seeds.

Several primates show sex-based differences in activity patterns and social interactions during infancy. These differences have been associated with adult social and reproductive functions of males and females and are related to male-male competition. Our goal was to describe behavioral patterns of wild Alouatta caraya male and female infants, a species with sexual dimorphism in body size and behavioral strategies during adulthood. We also examined the relationship between life history variables, infant sex and age, activity patterns, and social interactions in order to determine whether males and females follow different trajectories during early growth. Over a 27-month study, we observed 21 male infants and 14 female infants across two similar sites in northern Argentina. Data were analyzed using generalized linear mixed model (GLMM) tests. We found no differences in suckling time or weaning age between males and females (9.7 vs. 9.4 months), but male infants spent more time feeding on solid food and resting than female infants. Males also invested more time in contact with their mothers than did female infants, and mothers rejected and broke contact with males more frequently than with females. Other behavioral categories did not differ between the sexes. Our results suggest that higher nutritional demands of males compared with females may affect some behaviors. However, mothers of sons did not experience immediate trade-offs between current and future reproduction. Other behaviors, similarly expressed by the two sexes, suggest a similar developmental trajectory between male and female A. caraya infants, meaning that most differences emerge following the infant period.

Parent-offspring conflict has been scarcely studied in Neotropical primates. In this study, we explored mother-offspring conflict in a group of wild black and gold howler monkeys (Alouatta caraya) in northeastern Argentina. We used the all-occurrences technique to record behaviors, completing 712 h of observation. The results showed that all immature individuals between 2 and 23 months expressed conflict with regard to suckling or traveling with their mothers. Successful suckling attempts negatively correlated with the age of the immatures, occurring least frequently with the presence of newborns. In the juvenile period, the decline in successful attempts was a consequence of juveniles reducing suckling attempts and mother rejection.