Divergent mechanisms for water conservation in Drosophila species

The role of melanization and cuticular lipids in water conservation has been studied in many Drosophila species (Diptera: Drosophilidae). Nevertheless, a comparative approach to larval and adult stages of ecologically diverse, wild Drosophila species is still required. Based upon abdominal cuticular melanization patterns, wild-caught Drosophila species were categorized as (1) melanic, (2) fixed-melanic, or (3) non-melanic. At the interspecific level, the ecological significance of melanization and cuticular lipids was determined by the inverse association of melanization and cuticular water loss in melanic species, and of cuticular lipids and cuticular water loss in fixed-melanic and non-melanic species. Interestingly, higher amounts of cuticular lipids were also evident in fixed as well as non-melanic species, as compared to melanic species at larval stages, which is consistent with their differences in reduced water loss rates. Moreover, fixed-melanic and non-melanic species exhibited comparatively higher (ca. 1.8–2.0 fold) desiccation resistance. Thus, cuticular lipids provide a better waterproofing mechanism than melanization. Furthermore, acclimation to dehydration stress in adults improved desiccation resistance in melanic species, whereas such effects were lacking in fixed-melanic and non-melanic species. However, there were no changes in cuticular components as a consequence of desiccation acclimation. Thus, our results indicate that melanic, fixed-melanic, and non-melanic Drosophila species differ in the evolved physiological mechanisms of water conservation to adapt to dry conditions.