IS SEXUAL SELECTION AND SPECIES RECOGNITION A CONTINUUM - MATING-BEHAVIOR OF THE STALK-EYED FLY DROSOPHILA-HETERONEURA

If behavioral isolation between species can evolve as a consequence of sexual selection within a species, then traits that are both sexually selected and used as a criterion of species recognition by females sh ould be identifiable, The broad male head of the Hawaiian picture-wing ed fly Drosophila heteroneura is a novel sexual dimorphism that may be sexually selected and involved in behavioral isolation from D. silves tris. We found that males with broad heads are more successful in sexu al selection, both through female mate choice and through aggressive i nteractions, However, female D. heteroneura do not discriminate agains t hybrids on the basis of their head width, Thus, this novel trait is sexually selected but is not a major contributor to species recognitio n, Our methods should be applicable to other species in which behavior al isolation is a factor.