摘要：The biogeographic history of aquatic organisms in relation to the Wasatch Mountains divide (which separates the eastern Great Basin and upper Colorado River basin in Utah) has been little studied aside from a large body of work on fishes. Pyrgulopsis kolobensis is a small springsnail that is distributed (in the eastern portion of its range) along the western flanks of the Wasatch Mountains, with a single population occurring just across the Wasatch divide in Strawberry Valley. Here we analyze the genetic structure of this species across the Wasatch divide (using the mtCOI gene) to discriminate between alternative hypotheses that explain this distributional pattern. The 6 P. kolobensis populations that we sampled were resolved as a single, weakly supported and shallowly structured clade in a Bayesian analysis. Specimens from Strawberry Valley shared a unique haplotype and differed from the other populations by 0.3%–0.8% sequence divergence, suggesting a geologically recent split that well postdated the Miocene inception of the Wasatch divide. This result is consistent with a hypothesis (supported by geological evidence) that the Strawberry Valley population became isolated during the late Quaternary as a result of a headwater transfer across the Wasatch divide. Our findings parallel a recent phylogeographic study of regional pebblesnails (Fluminicola coloradensis) and contrast with the prevailing pattern in fishes, which generally do not cross the Wasatch divide. The ability of these 2 snail species to penetrate into upland headwater habitats appears to be the key to their success in crossing the Wasatch (and other) drainage divides.La historia biogeográfica de los organismos acuáticos en relación con la bifurcación de las Montañas Wasatch (que separan la Great Basin este y la cuenca alta del Río Colorado en Utah) ha sido poco estudiada, además del extenso trabajo que se ha realizado con peces. Pyrgulopsis kolobensis es un pequeño caracol de agua dulce que se distribuye en la parte oriental de la cordillera, a lo largo de los flancos occidentales de las montañas Wasatch, con una sola población que emerge al otro lado de la bifurcación Wasatch en Strawberry Valley. En este estudio analizamos la estructura genética de esta especie a lo largo de la bifurcación Wasatch (utilizando el gen mtCOI) para discriminar entre las hipótesis alternativas que explican este patrón en la distribución. Las 6 poblaciones de P. kolobensis que muestreamos fueron reconocidas como un único clado, débilmente apoyado y superficialmente estructurado con un análisis bayesiano. Los especímenes de Strawberry
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