Do NEWTS AT CRATER LAKE REPRESENT A DISTINCTLY EVoLVING PoPULATIoN oF RoUGH-SKINNED NEWTS?

There is abundant evidence that genetic and morphological diversity is present among widespread species. This variation results from multiple processes, such as interruptions in gene flow or local adaptation. In Crater Lake National Park, a volcanic lake formed 7,700 y ago. Rough-skinned Newts (Taricha granulosa) subsequently colonized Crater Lake, and the lake population was described as a subspecies, the Mazama Newt (T. g. mazamae), characterized by dark ventral pigmentation. The sub-specific designation is not recognized by all authorities. In this study, we used a combination of genetic, morphological, and coloration data to test whether newts within the Crater Lake caldera form a distinct population segment (DPS). We found that the ventral surfaces of Crater Lake newts were darker and that head shapes and body condition were distinguishable from Rough-skinned Newts sampled throughout Oregon. Using microsatellite loci and mitochondrial DNA sequence data, we also found genetic differentiation between the caldera population and newts sampled from locations outside the caldera. Clustering analyses of microsatellite loci segregated Crater Lake newts from newts collected outside the caldera. Moreover, newts just outside the caldera were more similar to newts hundreds of kilometers distant than to the more proximal newt population within the caldera. Genetic diversity was also lower in newts found in the caldera compared to populations outside. Combined, our integrative approach provides evidence that Crater Lake newts are a distinct population that meets criteria as a DPS. This isolated population is threatened by introduced crayfish, and therefore conservation measures designed to protect this population are warranted.