Sexual differentiation is the process by which males and females become different. A large number of sex differences have been described in the brains of mammals and many of them are the result of hormones acting during fetal or neonatal life. However, most of what we know about the development of sex differences comes from studying relatively non-social animals, such as laboratory rats and mice. This proposal will investigate the development of sex differences in the brain and spinal cord of a highly social species, the naked mole-rat. Naked mole-rats are small, mostly hairless rodents that live in underground tunnels in groups of 60-80 individuals. They have been described as "eusocial" because of their very unusual, rigid reproductive hierarchy: only one female breeds and she mates with only 1 to 3 of the males. All of the other animals in the colony are 'subordinates,' which never breed and instead help in maintaining the burrow system and caring for the young. Subordinates can become breeders, however, if the breeding animals die, or if subordinates are removed from the colony and housed with an opposite sex mate. Male and female subordinates show no sex differences in behavior or body size, and even their genitalia are remarkable similar. Preliminary data suggest that the nervous systems of subordinate naked mole-rats may also lack sex differences common to other mammals. In this project anatomical and biochemical approaches will be used to examine three different neural areas in subordinates and breeders. The hypothesis will be tested that naked mole-rats do not undergo sexual differentiation during early life, but only upon attaining breeding status. This work will provide a novel model for study of the evolution of sex differences, and the endocrine and developmental mechanisms of sexual differentiation. The project will promote collaborative interactions between the University of Massachusetts, University of Connecticut, and Michigan State University, thus allowing students exposure to a diverse array of approaches to neuroendocrine research.
