Genetic response to environmental heterogeneity

Abstract

ONE of the major problems of contemporary population genetics is how to account for the large amount of genetic variation occurring in natural populations. Considerable controversy exists between those people proposing that the variation is adaptively neutral, and those arguing that most of the variation is maintained by balancing selection. One of the processes of balancing selection postulated, is based on the idea that different genetic variants are favoured in different environmental niches. We report results from an experiment designed to test this hypothesis in which populations of Drosophila were exposed to experimental environments of various degrees of heterogeneity. The rationale is simple—if genetic variation is adaptively neutral, all populations should maintain about the same amount of genetic variation; if the ‘environmental heterogeneity’ hypothesis is correct, the degree of genetic variation in a population should be correlated with the degree of heterogeneity of its environment.