Divergence of water balance mechanisms and acclimation potential in body color morphs of Drosophila ananassae

Drosophila ananassae is a desiccation sensitive species, but the physiological basis of its abundance in the drier subtropical areas is largely unknown. We tested the hypothesis whether body color morphs of D. ananassae differ in the mechanistic basis of water conservation as well as desiccation acclimation potential, consistent with their distribution under dry or wet habitats. We observed reduced rate of water loss consistent with the greater desiccation potential of dark morph as compared with light morph, despite lack of quantitative differences in cuticular lipid mass between them. Dark morph evidenced greater wet and dry mass (∼1.17-fold) as well as higher hemolymph content (∼1.70-fold) and (∼17%) dehydration tolerance to sustain longer survival under desiccation stress (LT50 17.5 hr) as compared with light morph (LT50 4.3 hr). We found significant differences in the storage of energy metabolites in the body color morphs of D. ananassae, that is, carbohydrate content was significantly higher (∼0.18 mg/mg dry mass) in the dark morph as compared to light morph, but greater (∼0.05 mg/mg dry mass) body lipid content was evident in the light morph. Under desiccation stress, dark and light morphs utilized mainly carbohydrates but also lipids to a lesser extent. However, the rate of utilization of energy metabolites did not vary between dark and light morphs. Further, the dark morph consumed higher energy content derived from carbohydrates under desiccation stress as compared with the light morph. Finally, we found contrasting patterns of acclimation to desiccation stress in the two body color morphs, that is, increase in desiccation survival (4.7 hr), as well as in dehydration tolerance (∼6%) due to acclimation of the dark morph but no such effects were observed in the light morph. Thus, divergence in water balance mechanisms as well as acclimation potential reflects evolved physiological adaptations of the dark morph under drier but of the light morph to wet climatic conditions. J. Exp. Zool. 321A: 13–27, 2014. © 2013 Wiley Periodicals, Inc.