Project description:The coastal tailed frog (Ascaphus truei) is endemic to the Pacific Northwest of North America and is listed as a species of Special Concern under the Canadian Species at Risk Act. Its range is limited to British Columbia where it occurs widely west of the Coast Mountain Ranges extending north almost to the Alaskan Panhandle. The present study focused on surveying within the Cayoosh, Bridge (Shulaps), Seton, Anderson, Carpenter, and Downton Lake drainages. Four years of previous inventory efforts using conventional time-constrained search (TCS) methods detected tailed frog at 23/292 discrete sites (7.9% detection rate) in seven watersheds. Non-invasive environmental DNA (eDNA) methods hold promise for cryptic and low-abundance species detection. We rigorously validated a quantitative real-time polymerase chain reaction (qPCR)-based tool for detecting coastal tailed frog eDNA in water samples. This eASTR4 test is highly specific and sensitive. We applied a two-step targeted eDNA analysis approach on duplicate filtered water samples from a total of 72 sites collected over five days. The first IntegritE-DNA step mitigates false negative results and tests all DNA samples for the ability to support amplification from endogenous plant chloroplast DNA as a measure of sample viability. Three DNA samples failed this step even after inhibitor clean up suggesting that these samples were poor quality and not reliable for targeted species' DNA analyses. All other DNA samples were deemed viable and were then tested for species-specific DNA. Coastal tailed frog eDNA was detected in 55/72 (76%) discrete stream reaches; nine sites with historical known occurrence were all eDNA positive. The false negative rate for TCS compared to eDNA methods was 58%. The results expand known coastal tailed frog distribution to 24 watersheds effectively more than tripling extant occurrences and confirm a previously suspected, apparently isolated coastal tailed frog metapopulation in the Shulaps drainage.
Project description: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.