Evolutionary potential of multiple measures of upper thermal tolerance in Drosophila melanogaster

Abstract

Summary Thermal tolerance influences the distribution and abundance of many species, but the adaptive capacity of species to increase upper thermal tolerance is poorly understood. Given that patterns of heat tolerance can strongly depend on assay method, it is crucial to get a better understanding of genetic variances and correlations among different heat tolerance components. This study tests for correlated responses in different heat tolerance assays in Drosophila melanogaster lines selected for increased heat tolerance following exposure to a static high temperature. Traits tested included heat tolerance measured under static (basal and hardened) and ramping assays (using different starting temperatures and ramping rates), with lines exposed to fluctuating conditions (3 days of a cycling temperature regime) and a variable food treatment. Selected lines had higher heat tolerance than control lines in all static and ramping assays. The upper thermal tolerance was up to 0·5 °C higher in the selected compared to control lines after ten generations of strong selection. Selection using a static assay therefore leads to correlated responses in other heat‐resistant components, suggesting that traits are genetically correlated and not influenced strongly by assay conditions. While the D. melanogaster population we studied harboured additive genetic variation to evolve increased upper thermal tolerance, the level detected may be insufficient to keep up with temperature increases predicted under climate change.