Clinal variation in fitness related traits in tropical drosophilids of the Indian subcontinent

In the last two decades a considerable number of studies have described geographic variation in morphometric, physiological and behavioral traits of over a dozen species of wild south-Asian drosophild fruit flies. Due to strong latitudinal and altitudinal gradients this region is highly diverse with respect to climatic conditions, making it important for studies in evolutionary ecology. In this review, we examine spatial heterogeneity across the Indian subcontinent in almost all of the traits previously investigated (body weight, desiccation tolerance, pigmentation, copulation duration, fecundity, ovariole number, wing length, alcohol dehydrogenase fast allele frequency, rate of water loss and starvation resistance). We find a linear correlation between trait variation and latitude. Our data suggest that a single climatic component, the coefficient of variance of monthly temperature averages, which is strongly correlated with latitude, explains a large proportion of variation in the traits investigated.