Scorpion phylogeography in the North American aridlands

Understanding the geographic, geologic, and climatic forces responsible for generating current patterns of biodiversity has been a central objective of phylogeography. To develop a better understanding of these processes in the North American aridlands, I used DNA sequence data and species distribution modeling to conduct three phylogeographic assessments incorporating four species of arid-adapted scorpions: Hadrurus arizonensis, H. jedediah, H. spadix, and Paruroctonus becki. In an assessment of H. arizonensis, phylogeographic patterns indicate that Pleistocene climate cycles and associated glacial refugia played a central role in structuring the genetic diversity of this species in the Mojave and Sonoran deserts, mostly supporting predictions from a recent model of historical biotic assembly for these regions. However, the phylogeography of H. arizonensis also revealed a potential glacial refugium along the Lower Colorado River Valley that had not been considered in previous evaluations. To assess the impact that Pleistocene climate fluctuations had in other North American aridlands, I then compared phylogeographic patterns from H. jedediah and H. spadix, to those from H. arizonensis. Since these three species are closely related and morphologically similar, effects from phylogenetic signal and divergent phenotypes should have been minimal, so differences in phylogeographic patterns should reflect the relative influence of Pleistocene climates in different regions. Under this assumption, comparative phylogeography of these three species suggest that the impact of glacial climates was most pronounced for the biotas of the Great Basin and Snake River Plain, over those in the Colorado Plateau, and Mohave and Sonoran deserts. Finally, I conducted a phylogeography of P. becki, an unrelated species that spans the Mojave Desert and western Great Basin. Phylogenetic analyses identified five mitochondrial lineages in P. becki. The timing and geographic arrangement of these lineages supports a vicariant origin associated with the tectonically dynamic Eastern California Shear Zone. In association with these deeper patterns, demographic analyses indicated that a lineage in the Great Basin had undergone a recent post-glacial expansion, which according to predictions from climate-based models and a landscape interpolation of genetic distances, probably occurred from refugial areas in the northwest Great Basin. In general, phylogeographic assessments of North American aridland scorpions support phylogeographic inferences from co-distributed organisms, but add a novel glacial refugium in the Mojave Desert and a unique pattern of post-glacial expansions from an area within the Great Basin.