Behavioral Ecology of Mating in the Male Gila Topminnow, Poecilipsis Occidentalis (Cyprinodontiformes: Poeciliidae)

Abstract

Males of the fish family Poeciliidae cease growth upon attainment of sexual maturity. Because position in fish social hierarchies is in large part size—dependent, Poeciliopsis occidentalis ♂ ♂ which mature at a small body size may be locked into subordinate status. As an apparent consequence of disparate competitive abilities, ♂ ♂ at extremes of body size exhibited contrasting mating strategies. Females were courted by large, territorial ♂ ♂. Tiny ♂ ♂ remained at a distance prior to dashing toward ♀ ♀ for a copulatory attempt. The accuracy of sneak copulatory attempts by tiny ♂ ♂ appeared to be enhanced by a relatively longer intromittent organ. Quantitative data on territory size and rates of social encounters indicated possible costs and benefits of such alternate strategies. Possible ultimate causes of these contrasting behaviors are the cost—benefit balance of a particular strategy and underlying genes. Possible proximate factors include the growing season, sex ratio, and the competitive environment.