Evolution of temperature preference behaviour among Drosophila larvae.

Small-bodied ectotherms are acutely vulnerable to temperature changes, but diverse thermotactic behaviors have contributed to their ability to inhabit broad climatic niches. Understanding how -and how frequently- these behaviors evolve are outstanding biological questions that are also relevant to conservation. Among insects, Drosophila melanogaster is a preeminent ectothermic model for temperature sensing and thermotaxis. However, little is known about how its temperature-related behaviors have evolved in comparison to its closely related species. We have thermo-profiled over 2400 larvae from eight species of Drosophila from different thermal habitats. Consistent with local adaptation, we found substantial variation in temperature preference and fine-scale navigational behaviors among these species. Agent-based modeling of the larval thermotaxis circuit suggests that it is the balance between cool and warm avoidance circuits, rather than changes in temperature sensitivity, that drive differences in temperature preference. Our findings highlight the recurrent evolution of temperature-related behaviors in an experimentally tractable cross-species system.