Variation for aggression and response in the competitive interactions of Drosophila melanogaster

Abstract

The competitive interactions which take place in genetically heterogeneous cultures of Drosophila melanogaster consist of both intra-genotypic and inter-genotypic effects. If these parameters are quantified separately they can be used to describe the way in which a particular genotype exerts competitive pressure on the one hand and responds to such competitive pressure on the other. The results presented in this paper show that a distinction can be made between the aggression and the response of a series of genotypes derived from the Texas population of Drosophila melanogaster. For most of the mixtures involved in this experiment the deviations from the mean competitive value attributable to aggression (a) and response (r) were quantified and shown to combine additively in their effect on the character p_a (the proportion of eggs developing successfully into adult flies, transformed into angles) with no evidence of any interaction. The components (a) and (r) show substantial variation but the lack of any correlation in their distribution suggests that they are separately adjustable by selection. The implications of this result with respect to the action of natural selection within the Texas population is considered.