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Aim The biogeography of western North American freshwater molluscs has traditionally been attributed to vicariance associated with late Tertiary rearrangement of landscape based on distributional evidence and the putatively limited dispersal ability of these organisms. We examined the phylogeography of a widely ranging western springsnail ( Pyrgulopsis wongi Hershler, 1989) to test this hypothesis and evaluate the relative importance of vicariance and dispersal in structuring the distribution of this species. Location Southwestern Great Basin (California and Nevada), United States of America. Method Two mitochondrial genes (COI, NDI) were sequenced for 28 populations of P. wongi spanning its entire geographic range, which consists of 10 topographically closed drainage basins. We also sequenced eight closely related congeners, as well as the type species of the closely related eastern North American genus Floridobia Hershler & Thompson, 2002, which was used as the outgroup. Phylogenies based on the combined data set were obtained using several methods, and networks for each gene were generated as an additional means of examining relationships among haplotypes. Partitioning of haplotype variation was studied usingamova, migration between populations was estimated using a coalescent-based method (mdiv), and divergence times were inferred using a locally calibrated molecular clock andmdiv. Results Pyrgulopsis wongi is subdivided into narrowly localized and widely distributed lineages that diverged in the Pleistocene, well after the inception of the contemporary regional landscape. While large ΦST values and the localized geographic distributions of most haplotypes imply absence or negligible contemporary dispersal of this spring-dwelling snail, the pattern of phylogeographic structuring, presence of a few widespread haplotypes, and results of themdiv analyses suggest geologically recent dispersal across drainage divides. Main conclusions Phylogeography of P. wongi conflicts with the traditional vicariance model as it is not structured by the contemporary landscape and is instead indicative of geologically recent dispersal. In the absence of evidence that dispersal of this species occurred through surface water connections during the relevant (Quaternary) time frame, we conjecture that spread may have instead been mediated by transport on waterfowl or via upland stream capture. The non-concordance between phylogeography and landscape reported in this and other recent studies of Pyrgulopsis suggests that members of this diverse and imperiled genus should not be managed using an a priori, ‘watershed as conservation unit’ approach. [ABSTRACT FROM AUTHOR]

Topography is a fundamental geophysical observable that contains valuable information about the geodynamic, tectonic and climatic history of a region. Here, we extend the traditional uses of topographic analysis to evaluate the role played by topography in the distribution of regional-scale biodiversity in the south-western USA. An important aspect of our study is its ability to provide a way to quantify characteristics of the topographic fabric and to construct predictive models that can be used to test hypotheses that relate topography and biodiversity. South-western USA region of the North American Cordillera. Our approach begins with a quantitative analysis of the topography and the construction of a predicted biodiversity map based on measurable topographic quantities: organization, roughness, slope aspect, grain orientation and mean elevation. We then make a quantitative comparison between the predicted and observed biodiversity, based on the assumption that land-cover diversity is a plausible measure of regional-scale biodiversity. Land-cover information used for this study was collected as part of the U.S.G.S. global land cover characteristics (GLCC) project and is derived from satellite (AVHRR) imagery. To a first order, the predicted regional-scale biodiversity based on our topographic model shows a good correlation with the observed biodiversity (as estimated from the land-cover diversity). Our model overestimates the biodiversity in many parts of the Colorado Plateau, Rio Grande Rift, and the low desert regions of the Southern Basin and Range, suggesting that in these provinces a biodiversity estimate based solely on topography is an over-simplification. However, much of the Madrean Archipelago and Sierra Madre provinces, which are centres of high biodiversity in this region, show excellent agreement between the observed and predicted biodiversity. While we acknowledge that many other factors in addition to topography have an important influence on biodiversity (particularly on a local scale), we conclude that topography plays a primary role in the regional to continental-scale biodiversity, particularly in regions characterized by insular mountain fabrics. [ABSTRACT FROM AUTHOR]