Social connections predict brain structure in a multidimensional free-ranging primate society

This is the final version. Available on open access from the American Association for the Advancement of Science via the DOI in this recordData and materials availability: All data, code, and materials used in this study are available on the Open Science Framework platform (osf.io). Link: https://osf.io/xfz3r/?view_only=66633a9490e649038330a98788a0cca3. Original brain tissue samples can be provided by the University of Pennsylvania pending scientific review and a completed material transfer agreement. Requests for brain tissues should be submitted to: [email protected] and survival in most primate species reflects management of both competitive and cooperative relationships. Here, we investigated the links between neuroanatomy and sociality in free-ranging rhesus macaques. In adults, the number of social partners predicted the volume of the mid-superior temporal sulcus and ventral-dysgranular insula, implicated in social decision-making and empathy, respectively. We found no link between brain structure and other key social variables such as social status or indirect connectedness in adults, nor between maternal social networks or status and dependent infant brain structure. Our findings demonstrate that the size of specific brain structures varies with the number of direct affiliative social connections and suggest that this relationship may arise during development. These results reinforce proposed links between social network size, biological success, and the expansion of specific brain circuits

Cognitive performance is linked to group size and affects fitness in Australian magpies

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordThe social intelligence hypothesis states that the demands of social life drive cognitive evolution. This idea receives support from comparative studies that link variation in group size or mating systems with cognitive and neuroanatomical differences across species, but findings are contradictory and contentious. To understand the cognitive consequences of sociality, it is also important to investigate social variation within species. Here we show that in wild, cooperatively breeding Australian magpies, individuals that live in large groups show increased cognitive performance, which is linked to increased reproductive success. Individual performance was highly correlated across four cognitive tasks, indicating a 'general intelligence factor' that underlies cognitive performance. Repeated cognitive testing of juveniles at different ages showed that the correlation between group size and cognition emerged in early life, suggesting that living in larger groups promotes cognitive development. Furthermore, we found a positive association between the task performance of females and three indicators of reproductive success, thus identifying a selective benefit of greater cognitive performance. Together, these results provide intraspecific evidence that sociality can shape cognitive development and evolution.This work was funded by an ARC Discovery grant awarded to A.R.R., A.T. and M. B. V. Bell, and a University of Western Australia International Postgraduate Research Scholarship and Endeavour Research Fellowship awarded to B.J.A. A.T. received additional support from a BBSRC David Phillips Fellowship (BB/H021817/1)