In some species habitual same-sex sexual behavior co-occurs with high levels of intra-sexual alliance formation, suggesting that these behaviors may be linked. We tested for such a link by comparing behavioral and physiological outcomes of sex with unrelated same- and opposite-sex partners in female bonobos (Pan paniscus). We analyzed behavioral outcomes following 971 sexual events involving n = 19 female and n = 8 male adult and sub-adult members of a wild, habituated bonobo community. We additionally collected n = 143 urine samples before and after sexual interactions to non-invasively measure oxytocin (OT), which modulates female sexual behavior and facilitates cooperation in other species. The majority of sexual events (65%) consisted of female same-sex genito-genital rubbing (or GG-rubbing). Female dyads engaged in significantly more sexual interactions than did inter-sexual dyads, and females were more likely to remain within close proximity to their partners following GG-rubbing. Females also exhibited greater increases in urinary OT following GG-rubbing compared with copulations, indicating a physiological basis for increased motivation to cooperate among females. The frequency of coalitionary support among non-kin was positively predicted by the frequency of sexual interactions for female as well opposite-sex dyads, although coalitionary support tended to be more frequent among females. The emergence of habitual same-sex sexual behavior may have been an important step in the evolution of cooperation outside of kinship and pair-bonds in one of our closest phylogenetic relatives.

Evolutionary models consider hunting and food sharing to be milestones that paved the way from primate to human societies. Because fossil evidence is scarce, hominoid primates serve as referential models to assess our common ancestors’ capacity in terms of communal use of resources, food sharing, and other forms of cooperation. Whereas chimpanzees form male-male bonds exhibiting resource-defense polygyny with intolerance and aggression toward nonresidents, bonobos form male-female and female-female bonds resulting in relaxed relations with neighboring groups. Here we report the first known case of meat sharing between members of two bonobo communities, revealing a new dimension of social tolerance in this species. This observation testifies to the behavioral plasticity that exists in the two Pan species and contributes to scenarios concerning the traits of the last common ancestor of Pan and Homo. It also contributes to the discussion of physiological triggers of in-group/out-group behavior and allows reconsideration of the emergence of social norms in prehuman societies.

With animal species disappearing at unprecedented rates, we need an efficient monitoring method providing reliable estimates of population density and abundance, critical for the assessment of population status and trend. We deployed 160 camera traps (CTs) systematically over 743 locations covering 17,127 km²of evergreen lowland rainforest of Salonga National Park, block South, Democratic Republic of the Congo. We evaluated the applicability of CT distance sampling (CTDS) to species different in size and behaviour. To improve precision of estimates, we evaluated two methods estimating species' availability (‘A’) for detection by CTs. We recorded 16,700 video clips, revealing 43 different animal taxa. We estimated densities of 14 species differing in physical, behavioural and ecological traits, and extracted species‐specific availability from available video footage using two methods (a)‘ACa’(Cappelle et al. [2019]Am.J.Primatol., 81, e22962) and (b)‘ARo’(Rowcliffe et al. [2014]MethodsEcol.Evol. 5, 1170). With sample sizes being large enough, we found minor differences betweenACaandARoin estimated densities. In contrast, low detectability and reactivity to the camera were main sources of bias. CTDS proved efficient for estimating density of homogenously rather than patchily distributed species. Synthesis and applications.Our application of camera trap distance sampling (CTDS) to a diverse vertebrate community demonstrates the enormous potential of this methodology for surveys of terrestrial wildlife, allowing rapid assessments of species' status and trends that can translate into effective conservation strategies. By providing the first estimates of understudied species such as the Congo peafowl, the giant ground pangolin and the cusimanses, CTDS may be used as a tool to revise these species' conservation status in the IUCN Red List of Threatened Species. Based on the constraints we encountered, we identify improvements to the current application, enhancing the general applicability of this method.

Strontium isotope (⁸⁷Sr/⁸⁶Sr) analysis with reference to strontium isotope landscapes (Sr isoscapes) allows reconstructing mobility and migration in archaeology, ecology, and forensics. However, despite the vast potential of research involving ⁸⁷Sr/⁸⁶Sr analysis particularly in Africa, Sr isoscapes remain unavailable for the largest parts of the continent. Here, we measure the ⁸⁷Sr/⁸⁶Sr ratios in 778 environmental samples from 24 African countries and combine this data with published data to model a bioavailable Sr isoscape for sub-Saharan Africa using random forest regression. We demonstrate the efficacy of this Sr isoscape, in combination with other lines of evidence, to trace the African roots of individuals from historic slavery contexts, particularly those with highly radiogenic ⁸⁷Sr/⁸⁶Sr ratios uncommon in the African Diaspora. Our study provides an extensive African ⁸⁷Sr/⁸⁶Sr dataset which includes scientifically marginalized regions of Africa, with significant implications for the archaeology of the transatlantic slave trade, wildlife ecology, conservation, and forensics.

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from ‘despotic’ to ‘tolerant’). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships.