Phenotypic variability and divergence in disruptive selection.

Two types of disruptive selection (HL and LH) were performed on three lines (M, F and K) which had reached different plateaus, following a previous directional selection applied independently on the two sexes. Increase in phenotypic variability and the appearance of a bimodal frequency distribution of wing length measurements were considered as responses to disruptive selection.These responses are shown not to be linearly related; moreover both responses seem not to be related to the genetic and phenotypic variability present in the population when disruptive selection was started.These results and the persistent differences between LH and HL selections are interpreted as to suggest that the effects of disruptive selection are mainly dependent on changes in the developmental patterns of the genes involved and of their connections.The suggestion is advanced that the results presented are inconsistent with the assumption that the effects of disruptive selection be explained by genetic or developmental switch mechanisms or by chromosomal polymorphism.