Phylogeny and evolution of male genitalia in Withiidae (Arachnida: Pseudoscorpiones)

The evolution of animal genitalia has been an intriguing topic of research since Darwin proposed that sexual selection is acting upon these traits. Pseudoscorpions (Arachnida) are an interesting model to test this hypothesis since they exhibit a wide array of sexual traits and sexual strategies, including the development of elaborate spermatophores. In this context, we (1) explored the phylogenetic relationships within Withiidae using somatic, sexual characters, and molecular data; (2) estimated times of diversification of the lineages within the family; and (3) explored rates of change of male genitalia characters. We found strong support for the monophyly of Withidae and for both the Neotropical and the non-Neotropical clades; as for the sister group of Withiidae, there is no conclusive evidence since molecular data suggest Atemnidae, supporting previous molecular studies, but the combined morphological and molecular data pointed to Cheliferidae instead, with high support in both cases. The dating analysis suggests that Withiidae originated in the Cretaceous and its main diversification occurred during the Eocene. We also found that sensory traits such as the position of the trichobothria isb and ist , and not genital traits such as length of the ejaculatory canal, change faster, challenging the prediction of higher change rates in the former. In conclusion, for pseudoscorpions, factors other than sexual selection may contribute to stronger selective pressures over their morphology.