Regional differences in thermoregulation between two European butterfly communities

1. Understanding how different organisms cope with changing temperatures is vital for predicting future species’ distributions and highlighting those at risk from climate change. As ectotherms, butterflies are sensitive to temperature changes, but the factors affecting butterfly thermoregulation are not fully understood. 2. We investigated which factors influence thermoregulatory ability in a subset of a Mediterranean butterfly community. We measured adult thoracic temperature and environmental temperature (787 butterflies; 23 species) and compared buffering ability (defined as the ability to maintain a consistent body temperature across a range of air temperatures) and buffering mechanisms to previously published results from Great Britain. Finally, we tested whether thermoregulatory ability could explain species’ demographic trends in Catalonia. 3. The sampled sites in each region differ climatically, with higher temperatures and solar radiation but lower wind speeds in the Catalan sites. Both butterfly communities show nonlinear responses to temperature, suggesting a change in behaviour, from heat-seeking to heat avoidance, at approximately 22 °C. However, the communities differ in the use of buffering mechanisms, with British populations depending more on microclimates for thermoregulation compared to Catalan populations. 4. Contrary to the results from British populations, we did not find a relationship between region-wide demographic trends and butterfly thermoregulation, which may be due to the interplay between thermoregulation and the habitat changes occurring in each region. Thus, although Catalan butterfly populations seem to be able to thermoregulate successfully at present, evidence of heat avoidance suggests this situation may change in the future.This work was funded by the Spanish National Research Council (CSIC) with a JAE-Intro fellowship for the introduction to research (reference numbers JAEINT_20_00248 and JAEINT20_EX_0638) and by a Joan Oró fellowship by the Department of Research and Universities of Generalitat de Catalunya and the European Social Fund Plus (grant 2023 FI-1 00556) to ETD; the grant PID2020-117739GA-I00 MCIN / AEI / 10.13039/501100011033 to GT; the Isaac Newton Trust/Wellcome Trust ISSF/University of Cambridge Joint Research Grants Scheme (RG89529) to ECT and AJB; and the NERC Highlight topic GLiTRS project NE/V007173/1 to AJB