55 - Sexual Differentiation of Brain and Behavior in Birds

Abstract

The brains of some birds contain the most striking structural sex differences yet observed in any vertebrates. Birds are also famous for sex differences in behavior, including differences in sexual behavior and singing. Some of these differences result from a differential activation by sex steroids in adulthood. Other differences are due to long-lasting (permanent) organizational effects of estrogens secreted by the embryonic ovary. Finally, recent research demonstrates that a substantial number of genes are differentially expressed in the male and female brain and are likely responsible for sex differences in brain and behavior. This chapter reviews the different mechanisms that produce this diversity of sex differences in birds. A variety of avian behaviors are easily observable both in natural environments and in captivity. Multiple discoveries of general interest were made on birds and their behavior. Techniques for manipulating avian gene expression in vivo and even during ontogeny are currently being developed and it can thus be expected that in the relatively near future, direct manipulation of the avian genome will be routine so that avian species will remain, in the foreseeable future, the source of important discoveries that will affect major concepts in biology and even in biomedical sciences.