Identifying Pleistocene refugia in North American cold deserts using phylogeographic analyses and ecological niche modelling

Aim: We analysed phylogeographic patterns and ecological niche models (ENMs) of the widespread velvet ant (Hymenoptera: Mutillidae) Sphaeorpthalma difficilis to understand the history of diversification in the Nearctic deserts and to identify areas that may have been cold-desert refugia during the Pleistocene. These areas should be targeted for conservation because of their climatic stability throughout historical climate change events. Location: North American arid regions. Methods: The two internal transcribed spacer regions (ITS1 and ITS2) were sequenced and analysed using Bayesian techniques to uncover phylogeographic patterns of relatedness among S. difficilis populations. History of diversification was estimated using parsimony-based and maximum likelihood character reconstructions. Molecular dating analyses were implemented in the program r8s and were calibrated with Dominican amber fossils. ENMs were developed based on current climate data and projected onto Pleistocene climate surfaces. Results: The analyses suggest that S. difficilis had a complex history of Pleistocene range expansion and contraction that led to the formation of genetically distinct populations inhabiting distinct arid regions. ENMs and phylogeographic patterns indicate that several cold-desert refugia existed in North America, particularly in the Colorado Plateau and parts of the Great Basin Desert. Main conclusions: Analyses of S. difficilis are used to identify potential Pleistocene refugia in the North American cold deserts. Because these areas represent climatically stable locations, they are critical for the long-term persistence of biodiversity. This research provides evidence that in addition to desert-like conditions persisting through the ice age in parts of the Nearctic warm deserts, many areas maintained desert-like characteristics in the regional cold deserts. Further work is needed to elucidate options for preserving biodiversity in these cold-desert refugia.