Mode of mating preference and the direction of evolution in Drosophila

Sexual (or ethological) isolation constitutes the most important class among different means of reproductive isolation in animal species. The phenomenon of sexual isolation has been extensively studied in the genus Drosophila. The degree of sexual isolation and the mode of mating preference are often used to indicate the phylogenetic relationship between the species and also their evolutionary sequence. Asymmetrical or one-sided mating preference observed in a number of Drosophila species groups has been used to elucidate the direction of evolution. Based on the mode of mating preference, different models which are even opposite to each other have been proposed by different investigators to predict the direction of evolution among closely related species. One-sided mating preference observed among the geographical strains of the same species has also been used to predict the direction of evolution. This review documents several cases of asymmetrical mating preference (both inter- and intraspecific) including the interesting cases reported by Indian workers and in the light of these observations of asymmetry in mating preference, the general applicability of different models is discussed.