Simultaneous hermaphroditism, tit-for-tat, and the evolutionary stability of social systems

Abstract

Egg trading is a kind of mating behavior occuring in simultaneously hermaphroditic coral-reef fishes in the family Serranidae. It is a form of delayed reciprocity in which individuals give up eggs to be fertilized in exchange for the opportunity to fertilize the eggs of a partner. The behavior is consistent with the Tit-for-Tat model of cooperation. Egg trading possesses three unusual but potentially important features. First, it almost certainly originated through interactions among unrelated individuals, unlike other examples of delayed reciprocity. Second, it probably originated not as cooperation but as a form of defection or cheating. Third, egg trading and related behavior can account at least in part for the maintenance of the monogamous mating systems of several serranines under ecological conditions in which such systems would not be expected to originate or persist. The reason is that the effects of such behavior patterns are positively frequency-dependent. Much social behavior probably has frequency-dependent effects, and internally generated stability may therefore be involved in the evolution of many animal social systems. However, the extent of its influence is not yet known.