Evolution of Vertebrate Olfactory Subsystems

Abstract: In this article, we describe the basic aspects of the structure and function of the olfactory system in the major groups of vertebrates. For each group, we discuss the behavioral significance of olfactory cues, as well as the means by which odorants are drawn across the sensory epithelium. We also describe the morphology of the receptor cell types that are present, and summarize the state of knowledge concerning the odorant receptor gene repertoire. The cell types and organization of the olfactory bulbs are described, as are the major central projections from the olfactory bulbs. In addition, the olfactory system proper and vomeronasal system are compared in taxa that possess both systems. Finally, the structure of the terminal nerve is described, and information concerning its function is summarized. Patterns of evolutionary change in each of these features are then analyzed.