Cold adaptation in geographical populations of<i>Drosophila melanogaster</i>: phenotypic plasticity is more important than genetic variability

TLDR

Most Drosophila species are classified as temperate or tropical, reflecting differences in thermal adaptation, particularly cold tolerance, though low‑temperature growth can also induce harmful phenotypes such as male sterility. The study examined cold tolerance in a global D. melanogaster collection by measuring chill‑coma recovery time after 0 °C exposure. Recovery time was measured after 0 °C chill, and the influence of growth temperature was examined in tropical and temperate populations.

Abstract

Summary According to their geographical distribution, most Drosophila species may be classified as either temperate or tropical, and this pattern is assumed to reflect differences in their thermal adaptation, especially in their cold tolerance. We investigated cold tolerance in a global collection of D. melanogaster by monitoring the time adults take to recover from chill coma after a treatment at 0 °C. Flies grown at an intermediate temperature (21 °C) showed a significant linear latitudinal cline: recovery was faster in populations living in colder climates. The role of growth temperature was analysed in a subset of tropical and temperate populations. In all cases, recovery time decreased when growth temperature was lowered, and linear reaction norms were observed. This adaptive phenotypic plasticity explained more than 80% of the total variation, while genetic latitudinal differences accounted for less than 4%. The beneficial effect observed in adults grown at a low temperature contrasts with other phenotypic effects which, like male sterility, appear as harmful and pathological. Our results point to the difficulty of finding a general interpretation to the diversity of plastic responses that are induced by growth temperature variations.