Comparison of Temporal Cortex Cytoarchitectural Variability Across Primates

Primates with larger brains tend to possess a greater number of distinct cortical areas, but there are limited data from systematic quantita-tive analysis of cytoarchitectural variation across the cortex of different species. The current study aimed to determine if brain size covaries with cellular distributions across the cortical surface. Greater cytoarchitectural differentiation might indicate increased modularity of cortical func-tion. Our preliminary sample included coronal histological sections of the temporal lobe from Indri indri, Lagothrix lagotricha, Saguinus midas, and Saimiri sciureus. The temporal lobe contains cortical areas that function in higher-order audi-tory processing and visual object recognition. The cortex was sampled from c200 equidis-tantly-located sites in each brain from sections representing the entire rostrocaudal axis of the temporal lobe. From each site, characteristics of cellular distributions were quantiܪed using image analysis procedures to obtain data on vertical changes from the top of layer II to bottom of layer VI in: 1) the proportion of cell proܪles versus neuropil space (grey level) and 2) the size distri-bution and density of cell proܪles. Results showed that the coefܪcient of variation in cortical grey level increased with brain size (rho"0.95, P"0.05). Variation in cell proܪle sizes tended to decrease, but not signiܪcantly (rho"-0.80, P"0.20). We found no consistent rostrocaudal gradient of variation in these aspects of cytoarchitecture across temporal lobe sections in the sample. Further analyses will incorporate a greater range of primates. These studies will contribute to our understanding of developmental mechanisms in shaping primate cortical structure.Same-sex sexual behavior in wild woolly monkeys (Lagothrix lagotricha poeppigii)LAURA A. ABONDANO1, KELSEY M. ELLIS2 and ANTHONY DI FIORE1,31Department of Anthropology, University of Texas at Austin, 2Department of Anthropology, Miami University, 3Tiputini Biodiversity Station, College of Biological and Environmental Sciences, Universidad San Francisco de QuitoStudies of sexual behaviors and reproductive strat-egies have often focused on interactions between different-sex dyads, potentially underestimating the frequency of same-sex sexual behavior (SSSB) among animal species. However, SSSB is ubiquitous across the animal kingdom, and, among primates, there are a variety of species that commonly display SSSB (e.g., bonobos, macaques, capuchins). Here, we present novel data on same-sex mounting behavior, one type of SSSB, in wild woolly monkeys (Lagothrix lagotricha poeppigii) living in a pristine tropical rainforest in the Ecuadorian Amazon. Between 2014 and 2018, we recorded data on sexual behaviors among adult and subadult individuals in four neighboring social groups. Of 279 observed cases of mounting, ܪve (1.8%) were among same-sex dyads (four female-female and one male-male). Interestingly, all ܪve cases involved at least one subadult individual, suggesting that in woolly monkeys SSSB may be used as an exper-imental or learning strategy for subadults prior to reaching sexual maturity as adults. However, further investigations are needed to better under-stand the function of SSSB in woolly monkeys. With this study, we hope to grow the compara-tive data set to better understand the function of non-conceptive sexual behaviors, including SSSB, among animals including primates