Biogeography of scorpions in the Pseudouroctonus minimus complex (Vaejovidae) from south-western North America: implications of ecological specialization for pre-Quaternary diversification

Aim The aim of this study was to assess the impact of pre-Quaternary tectonics and orogeny relative to that of Pleistocene climate change on diversification within the Pseudouroctonus minimus complex, a group of vaejovid scorpions with stenotopic habitat requirements. Location South-western North America (United States and Mexico). Methods Multilocus sequence data (1899 base pairs from two mitochondrial and two nuclear genes) were generated from 65 samples of scorpions in the minimus complex. Phylogeographical structure within the minimus complex was explored using model-based phylogenetic methods and a general mixed Yule coalescent model to identify independent geographical clusters. A time-calibrated multilocus species tree was reconstructed using a multispecies coalescent approach. Ancestral areas were estimated at divergence events across the tree using a probabilistic Bayesian approach. Results Extensive geographical structure was evident within two well-supported clades. These clades probably diverged over 25 million years ago (Ma), based on estimated mean divergence dates, followed by 14 divergences in the Miocene (25–5 Ma) and 4 divergences in the Pliocene and Pleistocene (< 5 Ma). The ancestral origin of the minimus complex was reconstructed to be across California and the Mexican Highlands. The Chihuahuan Desert was colonized twice from the Mexican Highlands, and one dispersal event occurred from the Mexican Highlands back to California. Main conclusions Spatial and temporal patterns of evolution in the minimus complex support predictions that stenotopy promoted pre-Quaternary diversification. Miocene and Pliocene geomorphology, perhaps in concert with climate change, induced allopatric divergence across the heterogeneous landscape of south-western North America. Stenotopic scorpions such as the minimus complex provide a model for exploring correlations between Earth history and biological diversification.