Genetic variation of heat tolerance in a model ectotherm: an approach using thermal death time curves

The assessment of thermal tolerance holds significant importance in predicting the physiological responses of ectotherms, particularly in elucidating their capacity for evolutionary adaptation in the context of global warming. Current approaches to assessing thermal tolerance have limitations that can lead to misleading results, especially with regard to the heritability of thermal limits. In this study, we examined twenty isogenic lines of Drosophila melanogaster from the DGRP panel to characterize their thermal death time (TDT) curves, which account for the duration and intensity of heat stress. Furthermore, we examined the extent of genetic variation in the two parameters that characterize TDT curves, namely CTmax and thermal sensitivity z. Our analysis revealed evidence of genetic (co)variation for both parameters. Results from simulations of the evolutionary consequences of selection on CTmax and z suggest that directional selection to increase CTmax will also increase z as a correlated response. However, directional selection to increase z may have the opposite effect. We conclude that the evolution of thermosensitive or thermotolerant strategies is better achieved by directional selection to decrease or increase CTmax, which may aid in mitigating the effects of global warming on ectotherms.