Influence of developmental temperature on cold shock and chill coma recovery in Drosophila ananassae: Acclimation and latitudinal variations among Indian populations

Exposure of various Drosophila species to mild increase or decrease in temperature has consistently been shown to result in increased resistance to subsequent temperature extremes. We investigated cold tolerance in 45 Indian natural populations of Drosophila ananassae collected from all over India by monitoring the time taken by adults to recover from chill-coma after a treatment for 16 h at 4 °C. Significant latitudinal and altitudinal differentiation was observed for chill coma recovery in D. ananassae. Chill-coma recovery was closely associated with local climatic factors like average annual temperature and relative humidity of origin of populations.Role of growth temperature on chill-coma recovery was also analyzed. In all cases, recovery time decreased when growth temperature was lowered and linear reaction norms were observed. Populations from higher latitudes were more cold resistance than low latitude populations. Our results also suggest that within species cold adaptation and response may vary with latitude as a consequence of direct or indirect effects of selection. Our study extends evidence for a higher cold tolerance in north Indian populations that seems to have evolved during the colonization of D. ananassae and supports the hypothesis of an adaptive response of plasticity to the experienced environment.