Pollution constrains thermal adaptation but not thermoregulation in dung beetles.

Insect heat and cold tolerance can be constrained by multiple factors, either natural, such as elevation, or anthropogenic, as pesticide exposure. Under a scenario of global change, alterations to physiological processes for tolerating thermal extremes and controlling self-temperature could make insect populations vulnerable. Therefore, this study sought to evaluate whether exposure to ivermectin, a pesticide used in livestock pastures around the world, affects thermal tolerance, thermoregulation and energetic status of several populations of the dung beetle Euoniticellus intermedius (Reiche) (Coleoptera: Scarabaeidae) sampled along an elevational gradient and reared under a common garden experiment. We detected differences in physiological function associated with elevation being evident in cold tolerance, thermoregulation and energetic status. Regarding ivermectin, it unexpectedly increased heat tolerance and improved cold tolerance at intermediate elevation, indicating a hormetic response. Contrastingly, ivermectin reduced cold tolerance at high elevation, revealing a physiological cost of colonizing high elevations. Lipid content was higher at high ivermectin concentrations, potentially resulting from selection of high-quality individuals, and was highest at low elevations, as expected from adaptation to high temperatures. Finally, ivermectin did not affect thermoregulatory capacity, a trait that was only affected by elevation. Our results indicate that ivermectin exposure affects beetle tolerance to warm and cold temperatures, posing potential risks to the persistence of specific populations and the provision of ecosystem services in contaminated areas.