Geographical restriction and body size variation in two sibling species of flower-breeding Drosophila

Abstract

Abstract Background:Variations in body size and body melanization are thought to be important features for local adaptation of environmental stresses in many insects and latitudinal clines of such variation have been found many taxa. When two species share similar resource, ecological divergence and niche partitioning may further evolve as the consequence of competition. Here, we examined the distribution, host plant usage, and body size variation of two closely-related species, Drosophila elegans, which has two discrete body color morphs, and D. gunungcola on three islands. Results:The brown morph of D. elegans has a similar distribution to D. gunungcola in Java and Sumatra, whereas the black morph of D. elegans is exclusively found in Taiwan. A significant correlation between latitudes and altitudes was found in sites where D. gunungcola was found in Sumatra south of equator. The brown morph of D. elegans was found to be smaller in body size and tends to live in warmer habitat compared to the black morph of D. elegans and D. gunungcola. A significant genetic correlation between body color and body size was found in recombinant inbred lines derived from hybrids of brown and black morph strains.Conclusions:The restricted distribution of D. gunungcola in Southern hemisphere coincides with the lack of highland habitat near the equator. Four plant species were found to be exclusively utilized by D. elegans only in Taiwan whereas the same flower species are shared by both fly species in Java and Sumatra, suggesting the presence of inter-specific competition for breeding sites in overlapping zones. Darker body coloration with larger body size appears to have evolved twice in this lineage, reflecting similar patterns of natural selection in Indonesia and postglacial Taiwan.