The capacity of Drosophila to heat harden associates with low rates of heat-shocked protein synthesis

The thermotolerance of a species or of an ecotype is important for determining its habitat range and vigour, and considerable research has focused on identifying underlying physiological, biochemical and genetic bases of thermotolerance traits. Rates of protein synthesis in tissues when organisms experience a sudden heat stress as occurs on rare hot days may be important to avoid heat-induced paralysis and to survive. While natural variation in Drosophila melanogaster thermotolerance has been associated with heat-shock gene expression, little attention has been given to examining the thermo-protective role of protein synthesis generally. Using two independently derived sets of single-pair mating lines, we characterised variation in rates of protein synthesis in dissected ovarian tissues, both before and after a heat shock applied at different severities in the two sets. In both sets of lines heat-shocked protein synthesis rates were negatively associated with the increase in heat knockdown tolerance after hardening. These associations occurred in a different sex in each set. Variation in rates of Hsp70 synthesis failed to associate with levels of heat tolerance or general protein synthesis. Our results suggest heritable variation in the rate of protein synthesis following heat stress, independently of Hsp70 variation, contributes to heat tolerance variation in this species.