|The Rosy Boa, Lichanura trivirgata.|
Wood et al. (2012) investigate the phylogeographic history of the Mojave and Sonoran Deserts using a comparative approach. They examining spatial and temporal patterns of DNA sequence variation in 12 species, and evaluate the concordance of phylogeographic breaks and lineage diversification for both Pleistocene climate fluctuation hypotheses and pre-Pleistocene vicariance hypotheses. And, they used visualization methods to assess the spatial pattern of genetic diversity and divergence across species and identify regional evolutionary hotspots.
In seven of the 12 species, lineage divergence substantially predated the Pleistocene. Historical population expansion was found in eight species, but expansion events postdated the Last Glacial Maximum in only four lineages. For all species assessed, six hotspots of high genetic divergence and diversity were concentrated in the Colorado Desert, along the Colorado River and in the Mojave/Sonoran ecotone. At least some proportion of the land within each recovered hotspot was categorized as protected, yet four of the six also overlapped with major areas of human development.
Eight of the 12 species used were members of the herpetofauna (the red spotted toad, Anaxyrus punctatus the shovel-nosed snake, Chionactus occipitalis; the collared lizard, Crotaphytus bicinctores; the sidewinder, Crotalus cerastes; the rosy boa, Licanura trivirgata; and the horned lizard, Phryanosoma platyrhinos; the spiny lizard, Scleroporus magister; and the night lizard, Xantusia vigilis).
Most of the species examined in this study diversified into distinct Mojave and Sonoran lineages prior to the LGM – supporting the older diversification hypotheses. Several evolutionary hotspots were recovered but are not strategically paired with areas of protected land. Long-term preservation of species-level biodiversity would entail selecting areas for protection in Mojave and Sonoran deeserts to retain divergent genetic diversity and ensure connectedness across environmental gradients.
The entire article is available on-line.