Searching for Variables Representing the Response to Cold Stress in Mediterranean Geotrupinae Reveals an Association Between Heat and Cold Tolerances

The study of cold tolerance is imperative for understanding insect activity across spatial and temporal gradients. Here, we assessed various physiological variables to discern the response to cold stress in Mediterranean earth-boring dung beetles, utilizing an infrared thermography protocol initially developed for detecting heat stress variables. Subsequently, we conducted a joint analysis of heat and cold stress variables to explore the extent of congruence between their responses. Our findings indicate that the temperatures at which activity ceases and resumes are the most effective variables for distinguishing between the cold thermal strategies of the studied species. Moreover, our analyses revealed a positive association between the variables representing heat and cold tolerances, wherein species with higher upper limits of heat tolerance also exhibit higher temperatures at which they become immobilized by cold. This result suggest that adaptations to endure heat may compromise resistance to cold in these insects. We hypothesize about the main factors (loss of wings, fusion of the elytra, and accumulation of haemolymph) that could have represented radical modifications in the Mediterranean clades of Geotrupinae. These factors may have reshaped their life history and thermal physiology, potentially impairing thermogenesis, reducing cold hardiness and freezing resistance.