Biogeographic position and body size jointly set lower thermal limits of wandering spiders

Most species encounter large variations in abiotic conditions along their distribution range. Climate, and in particular temperature, varies along clinal gradients, which determines phenotypic plasticity, local adaptations and associated physiological responses of most terrestrial ectotherms, such as insects and spiders. This study aimed to determine how the biogeographic position of populations and the body size of two wandering spiders set their limits of cold (freezing) resistance. Using an ad-hoc design, we sampled relatively large numbers of individuals from four populations of Dolomedes fimbriatus and one population of the sister species Dolomedes plantarius originating from contrasting climatic areas (temperate and continental climate), and compared their supercooling ability as an indicator of cold resistance. Results indicated that spiders from northern (continental) populations had higher cold resistance than spiders from a southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red-listed and rarest D. plantarius was slightly less cold-tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection. Keywords: Supercooling ability; fishing spiders; freezing; climate change; Dolomedes