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

A variety of mechanisms, including intrasexual competition,intersexualconflict, and physiological constraints, can explainpatterns of reproductionand the adaptive value of specificbehaviors. In a Mediterranean wrasse,Symphodus ocellatus (Labridae),large, nesting males occasionallyrefuse to spawn with willingfemales in the presence of small, sneaker males.We exploredthe possible adaptive significance of this behavior. Nestingmalesrefuse females despite the fact that it reduces theirimmediate matingsuccess. This nesting-male behavior also decreasesfemale and sneaker matingsuccess and occurs when sneaker malessurround the nest. Experiments thatdecreased the number ofsneakers around nests showed that nesting malesrespond immediatelyto mating opportunities when fewer sneakers are present,andthus they are not simply constrained by a lack of energy orlack of sperm.Experiments that increased the number of sneakersat the nest caused nestingmales initially to refuse spawningopportunities, followed by a subsequentdecrease in sneakerpresence and an increase in mating rate. We propose thatthisbehavior is the result of a trade-off between immediate matingsuccessand future reproduction created by competition betweenmales and conflictbetween the sexes. Males reduce their immediatemating success by reducingspawning at the nest; sneaker malessubsequently leave, and thisdecreases mate competition forthe nesting male. Unresponsiveness of nestingmales also causessexual conflict between females and nesting males overmating.We argue that this behavior and the existence of a trade-offcan onlybe understood by examining intersexual conflict andintrasexual competitionsimultaneously.