Climatic selection of starvation and desiccation resistance in populationsof some tropical drosophilids

Geographical populations of six Indian tropical drosophilids exhibited sign ificant positive latitudinal correlations for body size (r = 0.92-0.99) and desiccation tolerance (r = 0.86-0.99): and for starvation tolerance there were significant negative correlations (r = -0.93 to -0.99). The extent of starvation as well as desiccation tolerance is significantly higher for spe cies characterized by large body size (Drosophila repleta and Zapriomus ind ianus) in comparison with other Sophophoran species. For both traits. all t he six species demonstrate significantly variable positive slope values for desiccation tolerance and negative slope values for starvation tolerance. Regression analysis of climatic data demonstrated a major role of coefficie nt of variation of mean monthly temperature (T-CV) and rainfall for higher desiccation tolerance of northern subtropical populations. For south Indian populations of ail six drosophilids, higher starvation tolerance could be selected due to T-min, higher metabolic stress in relation with smaller bod y size and higher population density and competition under tropical climati c conditions. Thr present data contrast with correlated selection response between these traits on the basis of laboratory selections. However, starva tion and desiccation tolerance evolve as independent traits in geographical populations of these six tropical drosophilids; and such traits are signif icantly correlated with body size although in opposite directions. Furtherm ore, laboratory selection experiments demonstrated no change in body size w hereas, under wild conditions, significant correlated body size changes are evident across populations as well as species. Present data suggest correl ated selection pressure on body size and traits conferring resistance to cl imatic stress.