Low potential for sexual selection in simultaneously hermaphroditic animals

Hermaphroditic animals are poorly represented in the sexual selection liter ature. This deficiency may reflect our inability to come to grips with herm aphroditism or, alternatively; it could be due to an inherent difference be tween hermaphrodites and gonochorists. Here we provide a number of reasons why sexual selection on traits related to mate acquisition can be expected to be intrinsically weaker in hermaphrodites. We show that the 'male' fitne ss component, which can be increased by sexual selection in hermaphrodites, is only half that of pure males in a gonochorist population This component can be reduced even further when hermaphrodites self-fertilize. As a resul t, the potential for sexual selection (psi) on male characters in hermaphro dites is at most half that of gonochorists. Given a specific mate handling cost, sperm production cost and rate of encountering receptive mates, we ca lculate the optimal allocation to mate acquisition and sperm. Since both pa rtners of a hermaphroditic pair invest in mate acquisition, hermaphrodites should optimally invest less in mate acquisition. This can further reduce p si by up to one-half. A higher readiness to mate and high investment in spe rm can lead to a further systematic reduction in Ps in hermaphrodites.