Department of Genetics, Maharshi Dayanand University, Rohtak, India.
J Exp Biol. 2013 Sep 1;216(Pt 17):3301-13. doi: 10.1242/jeb.087650.
Several studies on diverse Drosophila species have reported higher desiccation resistance of females, but the physiological basis of such sex-specific differences has received less attention. We tested whether sex-specific differences in cuticular traits (melanic females and non-melanic males) of Drosophila kikkawai correspond with divergence in their water balance mechanisms. Our results are interesting in several respects. First, positive clinal variation in desiccation resistance was correlated with cuticular melanisation in females but with changes in cuticular lipid mass in males, despite a lack of differences between the sexes for the rate of water loss. Second, a comparative analysis of water budget showed that females of the northern population stored more body water as well as hemolymph content and exhibited greater dehydration tolerance than flies from the southern tropics. In contrast, we found no geographical variation in the males for water content and dehydration tolerance. Third, an ~10-fold increase in the rate of water loss after organic solvent treatment of male D. kikkawai suggested a role of cuticular lipids in cuticular transpiration, but had no effect in the females. Fourth, geographical differences in the storage of carbohydrate content (metabolic fuel) were observed in females but not in males. Interestingly, in females, the rate of utilization of carbohydrates did not vary geographically, but males from drier localities showed a 50% reduction compared with wetter localities. Thus, body melanisation, increased body water, hemolymph, carbohydrate content and greater dehydration tolerance confer greater desiccation resistance in females, but a reduced rate of water loss is the only possible mechanism to cope with drought stress in males. Finally, acclimated females showed a significant increase in drought resistance associated with higher trehalose content as well as dehydration tolerance, while males showed no acclimation response. Thus, sex-specific differences in desiccation resistance of D. kikkawai are associated with divergence in some water balance strategies, despite a lack of differences in the rate of water loss between the two sexes.
几项关于不同果蝇物种的研究报告称，雌性的脱水耐性更高，但这种性别特异性差异的生理基础受到的关注较少。我们测试了 Drosophila kikkawai 的表皮特征（雌性黑素化和雄性非黑素化）是否存在性别特异性差异，以及它们的水分平衡机制是否存在差异。我们的研究结果在几个方面都很有趣。首先，脱水耐性的正趋异与雌性的表皮黑化有关，但与雄性表皮脂质质量的变化有关，尽管两性之间的失水率没有差异。其次，对水分预算的比较分析表明，北部种群的雌性比南部热带种群的雌性储存更多的体水和血淋巴含量，并表现出更强的脱水耐性。相比之下，我们没有发现雄性在含水量和脱水耐性方面存在地理变异。第三，有机溶剂处理后雄性 Drosophila kikkawai 的失水率增加了约 10 倍，这表明表皮脂质在表皮蒸腾中起作用，但对雌性没有影响。第四，在雌性中观察到碳水化合物含量（代谢燃料）的储存存在地理差异，但在雄性中没有。有趣的是，在雌性中，碳水化合物的利用速率没有地理差异，但来自较干燥地区的雄性与较湿润地区的雄性相比，减少了 50%。因此，身体黑化、增加的体水、血淋巴、碳水化合物含量和更高的脱水耐性赋予了雌性更高的脱水耐性，但减少的失水率是雄性应对干旱胁迫的唯一可能机制。最后，适应干旱的雌性表现出与较高海藻糖含量和脱水耐性相关的显著增强的抗旱性，而雄性则没有适应反应。因此，尽管两性之间的失水率没有差异，但 Drosophila kikkawai 的脱水耐性的性别特异性差异与某些水分平衡策略的差异有关。
