Sex-ratio and mating propensity in Drosophila biarmipes.

Mating success between purple eye colour mutant and wild type D. biarmipes was observed in Elens-Wattiaux mating chamber. Multiple-, female-, male- and no-choice techniques were used. The values of isolation estimate in different experiments are above one which provides no evidence for preferential mating between females and males of the same type. The comparison of sexual behaviour of mutant and wild flies clearly indicates that wild type males are more successful in mating than mutant males, and mutant females are more receptive than wild type females. Thus purple eye colour mutation affects mating propensity of both sexes in D. biarmipes. However, the difference in the number of matings of wild and mutant flies is highly significant in multipe- and no-choice experiments in which sex-ratio was 1:1 (equal number of males and females). But the difference is not significant when mating success was scored by female- and male-choice methods in which sex-ratio was 1:2 (one female and two males; one male:two females). Thus it is suggested that mating propensity in D. biarmipes is influenced by sex-ratio.