Comparative Neuroanatomy and Neuroendocrinology of Strepsirrhines

Abstract

Primates have evolved both large brains and prolific social lives when compared with other mammalian species; understanding specifically how the brain has evolved to regulate social behavior is thus a key problem in both biological anthropology and social neuroscience. Many studies in this area focus on total brain size, but action of neuromodulators in the brain, such as oxytocin and vasopressin, affect a wide variety of social behavior and are key in understanding the neural underpinnings of sociality. Furthermore, the classically used model species do not capture the breadth of socioecological diversity seen across the primate order, and largely neglect the most socioecologically diverse primate taxon: strepsirrhines. Here, I investigate how the distribution of oxytocin and vasopressin receptors in the brain are related to: intersexual dominance structure, sensory specialization, social organization, and mating systems in 13 species of lemurs, and how these relationships compare to those of other primate and rodent species with similar socioecological traits. For these analyses, I re-analyzed data from seven previously studied species from the genus Eulemur (E. collaris, E. rufus, E. rufifrons, E. mongoz, E. rubriventer, E. macaco, E. flavifrons), contributed neural oxytocin and vasopressin receptor distributions for six new, previously unstudied lemur species (Lemur catta, Hapalemur griseus griseus, Varecia variegata, Propithecus coquereli, Microcebus murinus, Daubentonia madagascariensis), and then used phylogenetic comparative methods to examine common mechanisms for sociality across 42 species of rodents and primates. I found that intersexual dominance, the shift from solitary to social living, and sensory specialization predict oxytocin and vasopressin receptor distributions in lemurs, and find minimal evidence for shared mechanisms of sociality across rodents and primates. These results shed light on the evolution of primate and mammalian sociality and highlight the value of phylogenetic comparative methods to neuroscience and of neurochemical studies to biological anthropology.