A trade-off generated by sexual conflict: Mediterranean wrasse males refuse present mates to increase future success

A variety of mechanisms, including intrasexual competition, intersexual conflict, and physiological constraints, can explain patterns of reproduction and the adaptive value of specific behaviors. In a Mediterranean wrasse, Symphodus ocellatus (Labridae), large, nesting males occasionally refuse to spawn with willing females in the presence of small, sneaker males. We explored the possible adaptive significance of this behavior. Nesting males refuse females despite the fact that it reduces their immediate mating success. This nesting-male behavior also decreases female and sneaker mating success and occurs when sneaker males surround the nest. Experiments that decreased the number of sneakers around nests showed that nesting males respond immediately to mating opportunities when fewer sneakers are present, and thus they are not simply constrained by a lack of energy or lack of sperm. Experiments that increased the number of sneakers at the nest caused nesting males initially to refuse spawning opportunities, followed by a subsequent decrease in sneaker presence and an increase in mating rate. We propose that this behavior is the result of a trade-off between immediate mating success and future reproduction created by competition between males and conflict between the sexes. Males reduce their immediate mating success by reducing spawning at the nest; sneaker males subsequently leave, and this decreases mate competition for the nesting male. Unresponsiveness of nesting males also causes sexual conflict between females and nesting males over mating. We argue that this behavior and the existence of a trade-off can only be understood by examining intersexual conflict and intrasexual competition simultaneously.