Altitudinal variation in the ecophysiological limits of a carabid beetle depends on temperature and aridity

Abstract

1. Global warming is expected to strongly impact insect populations, particularly in montaneenvironments where elevational gradients impose steep climatic variation. Insectsin these systems are thought to be especially vulnerable because upward range shiftsreduce available habitat. However, few studies have considered the combined influenceof temperature and aridity on thermal tolerance at the intraspecific level.2. Here, we examined physiological and morphological variation in populations of the carabidbeetle (Coleoptera) Baripus nevado along an altitudinal gradient (2380, 2644 and2959 m) in Cerro Nevado, Argentina, an arid mountain system. We measured upperthermal limits (CTmax and upper lethal temperature [ULT]), body size and water loss.3. Our results revealed significant intraspecific variation: CTmax, ULT, body size andwater loss/body size all declined with elevation. Low-elevation populations exhibitedthe highest thermal limits and body mass, consistent with adaptations toendure greater aridity and desiccation stress.4. These patterns contrast with previous studies reporting conserved upper thermallimits within species across elevations, highlighting the role of water availability asan additional selective pressure. Our findings suggest that physiological and morphologicaldiversity within species can buffer climate change impacts, but also indicatethat increasing aridity may pose critical challenges even for heat-tolerantpopulations. Overall, we demonstrate that intraspecific variation in thermal physiologyis shaped by the interaction between temperature and aridity, and that this variationcould be key for the persistence of montane insects under climate change.