Factors underlying natural variation in body pigmentation of Drosophila melanogaster

Abstract

Molecular mechanisms underlying standing genetic variation of an ecologically relevant trait such as pigmentation trait variation in a model insect, Drosophila melanogaster, are relevant to our understanding of different kinds of intergenomic interactions. In this study, we focused on the association between body pigmentation and stress resistance, and on genotype-by-environment interaction, both of which are likely to contribute to the persistence of phenotypic variation in a natural population. First, we detected a significant association between pigmentation traits in females and starvation resistance (darker strains were weaker) and a weak association between pigmentation and chill coma recovery time (darker strains showed shorter recovery time) among 20 inbred strains from the Drosophila melanogaster Genetic Reference Panel (DGRP), which originated from a natural population in North America. These associations revealed a complex relationship between body pigmentation and physiological traits that may give rise to balanced selective forces acting on the traits under fluctuating environmental conditions. Second, using four of the DGRP strains, a substantial degree of genotype (strain) × environment (rearing temperature) interaction was detected among expression levels of the genes encoding effector enzymes in the melanin biosynthesis pathway. These interactions can potentially reduce the efficiency of purifying selection on the pigmentation traits over a wide range of temperature conditions. Finally, we discuss possible mechanisms that contribute to the maintenance of the standing pigmentation variation in this species.