Geographic variation in acclimation responses of thermal tolerance in South African diving beetles (Dytiscidae: Coleoptera).

Understanding sources of variation in animal thermal limits is critical to forecasting ecological responses to climate change. Here, we estimated upper and lower thermal limits, and their capacity to respond to thermal acclimation, in several species and populations of diving beetles (Dytiscidae) from diverse geographic regions representative of variable climate within South Africa. We also considered ecoregions and latitudinal ranges as potential predictors of thermal limits and the plasticity thereof. For upper thermal limits, species showed significant variation and limited acclimation-related plasticity. Lower thermal limits responded to acclimation in some cases and showed marked variation among species that could be explained by taxonomic affiliation and ecoregion. Limited acclimation ability in the species included in this study suggest plasticity of thermal limits will not be a likely buffer for coping with climate change. From the present results for the Dytiscidae of the region, it appears the group may be particularly susceptible to heat and/or drought and may thus serve as useful indicator species of ecosystem change. Understanding how these climate-related impacts play out at different spatial and temporal scales will have profound implications for conservation management and functional responses, especially important in a region already showing a trend for warming and drying.