Sex differences have been identified in the nervous systems of all vertebrate classes. In mammals, these sex differences can often be traced to developmental actions of gonadal steroid hormones. However, the study of sexual differentiation of the mammalian nervous system has focused on a limited number of relatively non-social species where reproductive success is largely obtained through direct reproductive efforts (i.e., for males, insemination of a female; for females, mating and the rearing of young). In social species, reproduction may depend upon status within the group, with members ranking lower in the hierarchy forgoing reproduction as well as sex-specific roles associated with reproduction. Naked mole-rats exhibit the strictest reproductive hierarchy known to mammals. These small rodents are native to Africa and live in underground colonies averaging 60-80 individuals. Colonies include a single breeding female (the queen), one to three breeding males, and numerous non-reproductive adults, known as subordinates. Subordinates assist in foraging, colony defense, maintenance of the tunnel system, and care of the young, but do not exhibit mating behavior. Subordinates can become breeders, however, if a breeding member of the colony dies, or if they are removed from their colony and housed with a mate. A change in status from subordinate to breeder was recently shown to trigger several increases in the size of cell groups in the brain and spinal cord. This project will determine how the change in social status causes these neural alterations, in particular by identifying the social and hormonal conditions required for the changes in brain morphology. The work is relevant to understanding brain plasticity in adulthood, sex differences in the brain, and the influence of social factors on the brain. The project will provide excellent training opportunities for undergraduates, graduate students and postdocs interested in behavioral neuroscience.
