DISRUPTIVE SELECTION ON BODY WEIGHT IN DROSOPHILA MELANOGASTER

Disruptive selection can have two consequences in a population: the rise of polymorphism or the divergence of the population. Divergence creates subpopulations which can be sexually isolated. Previous studies have shown that these consequences depend on the pattern of mate choices by the individuals. We have studied the effects of different patterns of mating (free mating, enforced random mating and enforced assortative mating) in a population of Drosophila melanogaster subjected to disruptive selection on body weight. Disruptive selection increased the weight dispersion in all mating patterns but brought about divergence within the population only when it occurred in association with enforced assortative mating (without complete sexual isolation between the subpopulations). When mating was free, the dispersion, measured by change in the coefficient of variation, was only somewhat larger than with enforced random mating: thus the principal consequence of disruptive selection was the rise of polymorphism in the population.