Divergent strategy for adaptation to drought stress in two sibling species of montium species subgroup: Drosophila kikkawai and Drosophila leontia

Drosophila leontia (warm adapted) has been considered as a sister species of Drosophila kikkawai (sub-cosmopolitan) with a very similar morphology. We found divergent strategies for coping with desiccation stress in these two species of montium subgroup. Interestingly, in contrast to clinal variation for body melanization in D. kikkawai, cuticular lipid mass showed a positive cline in D. leontia across a latitudinal transect. On the basis of isofemale line analysis, within population trait variability in cuticular lipid mass per fly is positively correlated with desiccation resistance and negatively correlated with cuticular water loss in D. leontia. A comparative analysis of water budget of these two species showed that higher abdominal melanization, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. kikkawai while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. leontia. The use of organic solvents has supported water proofing role of cuticular lipids in D. leontia but not in D. kikkawai. Thus, we may suggest that body melanization and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. In both these species, carbohydrates were utilized under desiccation stress but a higher level of stored carbohydrates was evident in D. kikkawai. Further, we found increase desiccation resistance in D. kikkawai through acclimation while D. leontia lacks such a response. Thus, species specific divergence in water balance related traits in these species are consistent with their adaptations to wet and dry habitats.