Food competition in a semi-free-ranging Cebus apella group

The competitive regime faced by individuals is fundamental to modelling the evolution of social organisation. In this paper, we assess the relative importance of contest and scramble food competition on the social dynamics of a provisioned semifree-ranging Cebus apella group (n= 18). Individuals competed directly for provisioned and clumped foods. Effects of indirect competition were apparent with individuals foraging in different areas and with increased group dispersion during periods of low food abundance. We suggest that both forms of competition can act simultaneously and to some extent synergistically in their influence on social dynamics; the combination of social and ecological opportunities for competition and how those opportunities are exploited both influence the nature of the relationships within social groups of primates as well as underlying the evolved social structure

Signatures of adaptive evolution in platyrrhine primate genomes.

The platyrrhine family Cebidae (capuchin and squirrel monkeys) exhibit among the largest primate encephalization quotients. Each cebid lineage is also characterized by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae such as high sensorimotor intelligence with tool use, advanced cognitive abilities, and behavioral flexibility. Here, we take a comparative genomics approach, performing genome-wide tests for positive selection across five cebid branches, to gain insight into major periods of cebid adaptive evolution. We uncover candidate targets of selection across cebid evolutionary history that may underlie the emergence of lineage-specific traits. Our analyses highlight shifting and sustained selective pressures on genes related to brain development, longevity, reproduction, and morphology, including evidence for cumulative and diversifying neurobiological adaptations across cebid evolution. In addition to generating a high-quality reference genome assembly for robust capuchins, our results lend to a better understanding of the adaptive diversification of this distinctive primate clade

Characterization of Stone Tool Use in Wild Groups of Critically Endangered Yellow-Breasted Capuchin Monkeys (Sapajus xanthosternos).

OBJECTIVES: A hallmark of hominin evolution is the advent and diversification of stone tool use, and biological anthropologists have a particular interest in characterizing tool use behaviors in different hominin species. Robust capuchins, the genus Sapajus, are an excellent convergent model system for understanding tool use evolution, principally in the context of foraging, in terms of how they use stones to process hard fruits. However, most published studies of capuchin tool use in the wild focus on the species Sapajus libidinosus. In order to strengthen comparative analyses, it is important to do research across robust capuchin species to understand tool use capacities and variation across the genus. The first indirect evidence that reported tool use in wild S. xanthosternos was in 2009, but since that time no additional publications have described this behavior for this species. In this study we provide the first complete characterization of tool use in wild S. xanthosternos for two areas within Montes Claros, Minas Gerais state, Brazil: Santa Rosa de Lima district, and Lapa Grande State Park. We compare our findings to the stone tool use characteristics reported in wild Sapajus libidinosus and other capuchin monkey species. MATERIALS AND METHODS: In monthly surveys from January to September 2018, we walked trails through the two study areas and categorized tool use site characteristics, including anvil area, height, and perimeter; hammer stone weight; and species of fruit utilized. Additionally, we utilized camera traps at high-use sites. RESULTS: We describe the tools used by S. xanthosternos at 169 sites clustered in seven Nutcracking Areas, for processing three different species of encased fruit: Macaúba (Acrocomia aculeata), Cansaçao (Cnidoscolus pubescens), and Guariroba (Syagrus oleracea). With camera traps, we directly observed tool use behavior for the first time in this species. DISCUSSION: Sapajus xanthosternos displayed tool use patterns very similar to those of S. libidinosus. The main difference was in regards to physical force; in our study, the mean weight of stones used by S. xanthosternos was higher than the mean reported for S. libidinosus at most field sites; however, there was no difference in hammer weight between S. libidinosus and S. xanthosternos when hammering Macaúba. We also registered the heaviest hammer stone for tool use (7.675 kg) known for the robust capuchin genus. It is clear from our study that tool use capacity and characteristics are conserved across the radiation of extant Sapajus, suggesting a possible stone tool use cognitive capacity spanning up to 3.3 million years of diversification within this genus. Unlike stone tool use occurring throughout the year for S. libidinosus, at our study sites S. xanthosternos used nutcracking tools only during the dry season

Female emancipation in a male dominant, sexually dimorphic primate under natural conditions

In most group-living animals, a dominance hierarchy reduces the costs of competition for limited resources. Dominance ranks may reflect prior attributes, such as body size, related to fighting ability or reflect the history of self-reinforcing effects of winning and losing a conflict (the winner-loser effect), or both. As to prior attributes, in sexually dimorphic species, where males are larger than females, males are assumed to be dominant over females. As to the winner-loser effect, the computational model DomWorld has shown that despite the female’s lower initial fighting ability, females achieve some degree of dominance of females over males. In the model, this degree of female dominance increases with the proportion of males in a group. This increase was supposed to emerge from the higher fraction of fights of males among themselves. These correlations were confirmed in despotic macaques, vervet monkeys, and in humans. Here, we first investigate this hypothesis in DomWorld and next in long-term data of 9,300 observation hours on six wild groups of robust capuchin monkeys (Sapajus libidinosus; S. nigritus, and S. xanthosternos) in three Brazilian sites. We test whether both the proportion of males and degree of female dominance over males are indeed associated with a higher relative frequency of aggression among males and a higher relative frequency of aggression of females to males. We confirm these correlations in DomWorld. Next, we confirm in empirical data of capuchin monkeys that with the proportion of males in the group there is indeed an increase in female dominance over males, and in the relative frequency of both male-male aggression and aggression of females to males and that the female dominance index is significantly positively associated with male male aggression. Our results reveal that adult sex ratio influences the power relation between the sexes beyond predictions from socioecological models.</p

News and Perspectives: Words matter in primatology

Postings on social media on Twitter (now X), BioAnthropology News (Facebook), and other venues, as well as recent publications in prominent journals, show that primatologists, ecologists, and other researchers are questioning the terms “Old World” and “New World” due to their colonial implications and history. The terms are offensive if they result in erasing Indigenous voices and history, ignoring the fact that Indigenous peoples were in the Americas long before European colonization. Language use is not without context, but alternative terminology is not always obvious and available. In this perspective, we share opinions expressed by an international group of primatologists who considered questions about the use of these terms, whether primatologists should adjust language use, and how to move forward. The diversity of opinions provides insight into how conventional terms used in primatological research and conservation may impact our effectiveness in these domains

News and Perspectives: Words matter in primatology

Postings on social media on Twitter (now X), BioAnthropology News (Facebook), and other venues, as well as recent publications in prominent journals, show that primatologists, ecologists, and other researchers are questioning the terms “Old World” and “New World” due to their colonial implications and history. The terms are offensive if they result in erasing Indigenous voices and history, ignoring the fact that Indigenous peoples were in the Americas long before European colonization. Language use is not without context, but alternative terminology is not always obvious and available. In this perspective, we share opinions expressed by an international group of primatologists who considered questions about the use of these terms, whether primatologists should adjust language use, and how to move forward. The diversity of opinions provides insight into how conventional terms used in primatological research and conservation may impact our effectiveness in these domains

Tropical field stations yield high conservation return on investment

Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km 2 than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly