Sex-specific divergence for body size and desiccation-related traits in Drosophila hydei from the western Himalayas

Sex-specific-differences are a widespread source of genetic variation in various Drosophila species. In the present study, we have examined desiccation survival in males and females of Drosophila hydei from colder and drier montane conditions of the western Himalayas (altitudinal populations; 600-2202 m). In contrast with most other studies in drosophilids, D. hydei males exhibited comparatively higher desiccation resistance despite smaller body size compared to females. Accordingly, we tested the physiological basis of such adaptations in both sexes of D. hydei. Body size traits (wing length, wet weight and dry weight) were ~ 1.2 fold higher in females than males. However, desiccation resistance was 10 to 13 h higher in males than females. These differences matched enhanced storage of trehalose content (~ 1.2 fold), higher hemolymph content (~ 1.2 fold) and enhanced cuticular lipid mass (~ 1.5 fold) in males than females. Water loss before succumbing to death (dehydration tolerance) was much higher in males (~ 81%) than females (~ 64%). A greater loss of hemolymph water until death under desiccation stress was associated with higher desiccation resistance in males. Further, there were lacks of differences in the rate of water loss, rate of trehalose utilization and rate of hemolymph depletion between the sexes in D. hydei. Therefore, sex-specific differences in desiccation resistance of D. hydei were independent of body size as well as the exhaustion of metabolite reserves and rather were caused by the higher dehydration tolerance as well as higher acquisition of hemolymph and trehalose contents.