Coadapted changes in energy metabolites and body color phenotypes for resistance to starvation and desiccation in latitudinal populations of D. melanogaster

In D. melanogaster, resistance to starvation and desiccation vary in opposite directions across a geographical gradient in India but there is lack of such clinal variation on other continents. However, it is not clear whether these resistance traits or other correlated traits are the target of natural selection. For resistance to starvation or desiccation in D. melanogaster, we tested the hypothesis whether body color phenotypes and energy metabolites show correlated selection response. Our results are interesting in several respects. First, based on within population analysis, assorted darker and lighter flies from a given population showed that darker flies store higher amount of trehalose and confer greater desiccation resistance as compared with lighter flies. By contrast, lighter flies store higher lipids content and confer increased starvation tolerance. Thus, there is a trade-off for energy metabolites as well as body color phenotypes for starvation and desiccation stress. Further, trait associations within populations reflect similar patterns in geographical populations. Second, we found opposite clines for trehalose and body lipids. Third, coadapated phenotypes have evolved under contrasting climatic conditions i.e. drier and colder northern localities select darker flies with higher trehalose as well as desiccation resistance while hot and humid localities favor lighter flies with higher lipids level and greater starvation tolerance. Thus, the evolution of coadapated phenotypes associated with starvation and desiccation resistance might have resulted due to specific ecological conditions i.e. humidity changes on the Indian subcontinent.