Invasion and adaptation of a warm-adapted species to montane localities: effect of acclimation potential.

Drosophila ananassae has successfully invaded the cold and dry montane localities of the Western Himalayas in recent years. The ability of this desiccation- and cold-sensitive tropical species to evolve in response to seasonal changes in montane localities is largely unknown. Here, we investigated how this sensitive species adapt to seasonally varying environmental conditions that are lethal to its survival. We observed change in the frequency of dark and light morphs of D. ananassae in five mid-altitude localities during the last decade (2000-2010). We document invasion of D. ananassae to montane localities and increase in frequency of the dark morph. The stress tolerance of morphs (dark and light) remained unaffected of developmental acclimation. However, adult acclimation has shown significant effects on tolerance to various environmental stresses in morphs and effect of this acclimation persist for long durations. Desiccation and cold stress tolerance was increased after adult acclimation for respective stress in the dark morph; while tolerance of the light morph was not affected. Further, heat tolerance of the light morph was increased after adult heat acclimation with no influence on heat tolerance of the dark morph. Our results suggest a possible role of adult acclimation in successful invasion and adaptation of D. ananassae to montane localities. Future experiments should be carried out to determine whether the survival in adverse conditions of low versus high temperature and humidity during seasonal changes is assisted by different acclimation abilities of the two morphs of D. ananassae.