Experimental evolution under combined thermal-nutritional stress inDrosophila melanogasterresults in evolved shifts in larval thermotolerance and thermal plasticity

Abstract

AbstractAnimals are facing increasing thermal and nutritional stress under climate change. Genetic adaptation is necessary to buffer long-term stress. However, it’s unclear whether adaptation to combined stress can occur without compromising viability and thermal plasticity. We tested thermotolerance and thermal plasticity in larvalDrosophila melanogasterselected under different temperatures (18°C, 25°C, 28°C) and diets (standard, diluted, low protein:carbohydrate). Basal cold tolerance was affected by both low protein concentration and temperature; larvae evolved higher basal cold tolerance on diluted and low protein:carbohydrate diets at 18°C and 28°C. Hardening increased cold tolerance for most lines, except those selected at 18°C and 28°C on low protein:carbohydrate diets and 25°C on standard diets. Basal heat tolerance was affected by selection temperature, with higher tolerance in 25°C selection lines. An interaction between selection temperature, selection diet and hardening treatment affected plasticity in heat tolerance, with most selection lines showing reduced heat tolerance upon hardening, except for lines selected at 25°C on low protein diets and at 28°C on standard diets. Our results indicate that adaptation to combined stress allows basal cold tolerance and plasticity in cold tolerance to evolve independently, but not heat tolerance, highlighting the increased vulnerability of ectotherms to long-term climate change.