Flies on the rise: acclimation effect on mitochondrial oxidation capacity at normal and high temperatures in Drosophila melanogaster.

Increased average temperatures and extreme thermal events (such as heatwaves) brought forth by climate change impose important constraints on aerobic metabolism. Notably, mitochondrial metabolism, which is affected by both long- and short-term temperature changes, has been put forward as an important determinant for thermal tolerance of organisms. This study examines the influence of phenotypic plasticity on metabolic and physiological parameters in Drosophila and the link between mitochondrial functions and their upper thermal limits. We showed that Drosophila acclimated to 15 °C have a 0.65 °C lower critical thermal maximum (CTmax) compared to those acclimated to 24 °C. Drosophila acclimated to 15 °C exhibited a higher proportion of shorter saturated and monounsaturated fatty acids, concomitant with lower proportions of polyunsaturated fatty acids. No mitochondrial quantitative changes (fractional area and number) were detected between acclimation groups, but changes of mitochondrial oxidation capacities were observed. Specifically, in both 15 °C- and 24 °C-acclimated groups, complex I-induced respiration was increased when measured between 15 and 24 °C, but drastically declined when measured at 40 °C. When succinate and glycerol-3-phosphate were added, this decrease was however compensated in flies acclimated to 24 °C, suggesting an important impact of acclimation on mitochondrial functions related to thermal tolerance. Our study reveals that the use of oxidative substrates at high temperatures is influenced by acclimation temperature and strongly related to upper thermal tolerance as a difference of 0.65 °C in CTmax translates into important mitochondrial changes.