Correlations between measures of heat resistance and acclimation in two species of Drosophila and their hybrids

Associations between traits may differ at the interspecific and intraspecific levels, making it difficult to predict long term evolutionary constraints. In this study we used replicate hybrid lines generated from crosses between Drosophila serrata and D. birchii to investigate correlations between measures of heat resistance and acclimation responses. Within each species, knockdown heat resistance was uncorrelated with heat resistance as measured by mortality. In contrast, D. serrata was more resistant than D. birchii for both measures of heat resistance. Thus, inter- and intraspecific correlations between measures of heat resistance differ. In the hybrids, there was no evidence for a correlation between knockdown time and heat induced mortality. Hybrid data did suggest a trade-off between acclimation for knockdown heat resistance and heat resistance as measured by mortality. We argue that hybrids between species are a potentially useful tool for studying traits such as acclimation responses that show litde genetic variation within species.