Rachel Petersen

RACHEL PETERSEN, then a graduate student at New York University, New York, New York, received a grant in October 2019 to aid research on ‘Mechanisms of Pre- and Post-copulatory Choice in Female Olive Baboons, A Model for Human Evolution’ supervised by Dr. James Higham. Throughout much of human and primate evolution, large male body size and sexual coercion may have restricted females’ ability to directly choose their mating partners, and instead, females may engage in indirect or cryptic processes of mate choice. This study explored vaginal gene expression as a means to better understand how females might engage in cryptic post-copulatory mate choice by physiologically discriminating between sperm from different males within their reproductive tract. This study was conducted in olive baboons, which are a particularly suitable model for human evolution due to their high degree of body size dimorphism (similar to early hominins), and sperm competition. Female baboons were trained to present their hindquarters for vaginal swabbing, and vaginal gene expression was characterized across the ovarian cycle in the absence of copulation, and in response to mating with different males. Genes relevant to immune function were highly expressed following copulation, and post-copulatory expression of two genes were found to be influenced by the genetic makeup of the mating male. These results suggest that the female reproductive tract may respond differently to sperm from different males, and that cryptic processes of female mate choice could be an important evolutionary mechanism operating throughout human evolution.