Genevieve Metzger, Anahi Espindola, Lisette P. Waits, Jack Sullivan

Contemporary and historical processes interact to structure genetic variation, however discerning between these can be difficult. Here, we analyze range-wide variation at 13 microsatellite loci in 2098 Rocky Mountain tailed frogs, Ascaphus montanus, collected from 117 streams across the species distribution in the Inland Northwest (INW) and interpret that variation in light of historical phylogeography, contemporary landscape genetics, and the reconstructed paleodistribution of the species. Further, we project species distribution models (SDMs) to predict future changes in the range as a function of changing climate. Genetic structure has a strong spatial signature that is precisely congruent with a deep (~1.8 MY) phylogeographic split in mtDNA when we partition populations into 2 clusters (K = 2), and is congruent with refugia areas inferred from our paleorange reconstructions. There is a hierarchical pattern of geographic structure as we permit additional clusters, with populations clustering following mountain ranges. Nevertheless, genetic diversity is the highest in populations at the center of the range and is attenuated in populations closer to the range edges. Similarly, geographic distance is the single best predictor of pairwise genetic differentiation, but connectivity also is an important predictor. At intermediate and local geographic scales, deviations from isolation-by-distance are more apparent, at least in the northern portion of the distribution. These results indicate that both historical and landscape factors are contributing to the genetic structure and diversity of tailed frogs in the Inland Northwest.