The genetic bases of divergence in desiccation and starvation resistance among tropical and temperate populations of Drosophila melanogaster

Desiccation and starvation resistance are two stress-related traits which vary geographically with climate in Drosophila melanogaster. To investigate the contribution of epistasis to population divergence for these traits, we crossed tropical and temperate populations from two different geographical regions to produce F-1, F-2 and first backcross generations. Line-cross analysis of generation means revealed that genetic bases of divergence for both traits were complex and remarkably similar in a number of respects. Strong additive and dominance effects were present in most of the models, whereas epistatic and maternal effects were less common. The presence of epistatic effects in approximately half of the models presented in this study is consistent with line-cross studies of diverged traits in other animals, and does not support the view that epistasis is the predominant means by which populations diverge. In addition, evidence of maternal effects in both traits adds to a growing body of recent evidence that suggests maternal contributions to population differentiation are more widespread than previously thought. This finding undermines the accuracy of studies inferring epistasis directly from the magnitude of F-2 breakdown. More line-cross analysis studies of naturally diverged populations that take into account maternal effects will shed further light on the true incidence of epistasis and its importance in the evolutionary process.