Evidence of independent climatic selection for desiccation and starvation tolerance in Indian tropical populations of Drosophila melanogaster

On the Indian subcontinent, geographical populations (8.0 degrees to 33.0 d egrees) of Drosophila melanogaster demonstrate opposite latitudinal dines f or desiccation (r = 0.83) and starvation (r = -0.88). Desiccation tolerance is significantly and positively correlated with body size and abdominal pi gmentation, whereas starvation is negatively correlated with body size and life-history characteristics. Analysis of variance and analysis of covarian ce show a substantial direct effect of body size for both traits. For the I ndian geographical populations, both latitudinal and altitudinal variations can explain the observed divergence of these two traits of ecological sign ificance. Regression analysis of climatic variables (i.e. T-max, T-min and T-average), which are not significantly correlated with latitude, are posit ively and significantly associated with starvation and can explain trait va riability (R-2 = 0.78-0.88). In contrast, T-CV (R-2 = 0.65), rainfall and p recipitation (R-2 = 0.32) are significantly but positively associated with desiccation tolerance. The observed negative correlation between climatical ly selected starvation and desiccation in Indian geographical populations i s not in line with the correlated selection response of these traits on the basis of laboratory selection experiments. For south Indian tropical popul ations, higher starvation tolerance might be selected because of temperatur e variables (T-max, T-min and T-average), higher metabolic stress in relati on to smaller body size, greater competition and involve a trade-off for li fe-history traits. In contrast, significantly higher desiccation tolerance in subtropical (northern) populations might be selected because of T-CV, ra infall and precipitation, which reflect seasonal variations. Desiccation an d starvation tolerance are independent traits that reveal rapid evolutionar y trends in tropical and subtropical climates.