Evolution of Secondary Sexual Characters and Sexual Behavior Patterns in a Family of Viviparous Fishes (Cyprinodontiformes: Poeciliidae)

Aronson and Clark (1952) and Clark, Aronson and Gordon (1954) summarized the extensive behavioral work on these fishes, and they and Clark and Kamrin (1951) and Hubbs and Reynolds (1957) specifically studied the behavioral significance of fin and genitalic structure in Poeciliidae. Rosen and Gordon (1953) reviewed the mechanics of poeciliid genitalic and fin action in relation to copulatory motor patterns and provided an evolutionary interpretation of their findings. The present paper takes its origin from two separate reports, one behavioral and the other systematic3. It concerns the integration of structure and behavior in the evolution of the highly specialized, viviparous poeciliid fishes from a generalized, probably oviparous ancestor. The results of this study show, not unexpectedly, that the combination of comparative studies of behavior and functional anatomy may furnish insights on questions of evolution that do not emerge from either alone. The demonstrable effec-