Thermal variability and diet interaction as driver of developmental overwintering in Drosophila buzzatii

Global warming influences organisms through direct and indirect effects on abiotic and biotic factors, such as temperature and food availability. This study examines how developmental diet and thermal regime influence fitness and thermal tolerance in Drosophila buzzatii, a cactophilic fly with a broad thermal tolerance, and a model organism in evolutionary ecology. Using a factorial design, we reared flies at 10 °C and 25 °C, with and without daily thermal fluctuations, on two natural cactus-based diets and a standard lab diet. We measured viability, development time, wing length, ovariole number, chill coma recovery time and fatty acid composition. We found synergistic effects between cactus diet and thermal daily fluctuations, overcoming the complete loss of viability observed at 10 °C and mitigating the negative effects shown at 25 °C. In addition, flies reared at a low fluctuating temperature had greater cold tolerance and a higher unsaturated-to-saturated fatty acid ratio, supporting the homeoviscous adaptation hypothesis. These findings suggest D. buzzatii may overwinter as larvae and pupae in temperate areas and highlight the importance of diet-thermal interactions in shaping insect responses to climate change.