The impact of climate and habitat on body shape and size evolution in whip spiders (Amblypygi)

Arthropod body size responds to environmental variation at differing spatial scales. Amblypygi (whip spiders) is an ancient order of arachnids with remarkably conserved body shape, despite their global distribution. While several studies have investigated how body size evolved in spiders, virtually no study has addressed this issue in whip spiders. Here, we analysed how body size and shape of 69 species of Charontid whip spiders evolved in response to climate and habitat. We used Generalized Least Squares to test if bioclimatic variables and habitat influence the variation in body size and shape. Additionally, we fitted alternative macroevolutionary models to body size and shape using Bayesian and Maximum Likelihood approaches. Finally, we estimated phylogenetic signal and tested for differences in evolutionary rates among habitats. Body size decreased slightly with increasing mean annual temperatures and increased with increasing yearly precipitation. Body size evolved following an increasing trend, while the adaptive landscape of body shape seems to have distinct optima, but not rates, for each habitat. Our results support both Cope-Deperets and Bergmanns rule, while habitat had a lesser role. This is the first study to analyze the evolution of Amblypygi phenotypes, which helps in understanding why their morphology is so conserved.