The Avian Song System: Relating Sex Differences in Behavior to Dimorphism in the Central Nervous System

Abstract

Publisher Summary Most bird species show sex differences in the pattern or frequency of vocalizations, and males either use unique vocalizations or use particular vocalizations more frequently than do females. This chapter discusses the canaries and zebra finches, because most of the neurobiological research to date has been done on these species. It also describes the steroid influences on behavior, neurochemistry, and neuroanatomy of these species and focuses on those aspects of the neurobiology of the song system that have been related to sex dimorphisms or hormone action. Any hormone action in a tissue is contingent on that tissue being able to detect the presence of the hormone. The song system appears to be characterized by steroid receptors and by particular neurotransmitters and neuromodulators. The distribution of these receptors and chemicals is very similar between the sexes, but their levels are often dimorphic. Testosterone can cause increased levels of androgen receptors, thus increasing the sensitivity of the system, and also can cause increased acetyl choline (Ach) receptors, so as to magnify the effects of any activity within the system. The actions of gonadal steroids on the avian song system are multifaceted. Hormone induced dimorphisms appear at every nucleus in this system. They appear at every level of analysis used to date, from brain volume involved in song to estimates of hormone receptors per cell. However, research on the neurochemistry of the avian song system is just beginning.