ETHOLOGICAL ISOLATION AND PHYLOGENY IN THE <i>PLANITIBIA</i> SUBGROUP OF HAWAIIAN <i>DROSOPHILA</i>

Abstract

Spieth (1966, 1968a, 1968b) reported laboratory and field observations of the bizarre courtship behavior patterns displayed by Hawaiian drosophilids and suggested the role of ethological isolation as one of the major reproductive isolating mechanisms in the endemic fauna. Additionally, Spieth (1966) showed that qualitative analyses of these courtship patterns permit one to infer the phylogenetic relationships of species sharing elements of these patterns. Although preliminary observations of courtship patterns of the four species studied in this paper have been recorded by Spieth (pers. comm.), detailed analyses of these patterns have not been reported. Nevertheless, the data presented in this paper, measuring the amount of premating reproductive isolation among the four species in malechoice experiments, provide basis for the interpretation of phylogenetic relationships of these species. The subjects of this study are four closely related picture-winged species of Hawaiian Drosophila. Drosophila differens and planitibia inhabit the rain forests of Molokai and Maui respectively, while heteroneura and silvestris are sympatric over a wide range on the Big Island of Hawaii. The chromosomal relationships of all four species have been reported by Carson and Stalker (1968) and Craddock (1974). D. differens and planitibia are monomorphic and homosequential in banding patterns of polytene chromosomes while heteroneura and silvestris share a