Spiders bring new insight into the eco-evolutionary drivers of body size variation and sexual size dimorphism in arthropods

Body size has been used thoroughly in arthropod ecology as a reliable trait to assess fitness responses to changes in environmental factors. Among these, spiders represent a large and diverse group, colonizing almost all terrestrial habitats. Here, we propose a review on intraspecific body size variation in arthropods over two main macroecological spatial gradients—latitude and elevation—both of high interest in a global warming context. We found that more species with a direct than with an indirect development present a converse Bergmann cline along both gradients. Focusing on spiders, we propose that life history traits such as voltinism, mobility, and brood care influence intraspecific body size patterns—potentially hiding large-scale patterns. Further, we assessed interspecific sexual size dimorphism (SSD) in spider species. We found that extreme SSD—the most original feature in spider biometry—is influenced by hunting guild rather than phylogeny of spider families, suggesting that ecological factors prevail over evolutionary drivers in shaping SSD.