Molecular and Ecological Characterization of Extralimital Populations of Red-Legged Frogs from Western North America

Abstract

Extralimital populations of red-legged frogs have recently been found on Graham Island (Queen Charlotte Islands), British Columbia, and on Chichagof Island, Alaska. Both islands are well north of the traditionally understood (or core) range of red-legged frogs in western North America. The Chichagof Island frogs are known to be introduced, and the Graham Island frogs are suspected to be introduced. However, species-level identification of these populations remains uncertain. Recent phylogeographic analyses have demonstrated that there are two species of red-legged frogs, Rana aurora and Rana draytonii, and R. aurora is more closely related to the Cascades Frog, Rana cascadae (i.e., (aurora + draytonii) is not monophyletic). Here, we compare new mtDNA sequence data from these extralimital populations to available sequences from 50 populations from the core range of red-legged frogs. These results demonstrate that both extralimital populations are the Northern Red-Legged Frog, R. aurora, and are most closely related to haplotypes found in the most northern clade of R. aurora. Further, we conduct ecological niche modeling under current conditions and future conditions that assume a global warming scenario to assess habitat suitability in southeastern Alaska and the Queen Charlotte Islands and the potential for the persistence and expansion of the extralimital populations. These analyses suggest that the extralimital populations occur in the most suitable habitat on Graham and Chichagof Islands and that suitability will increase on Graham and decrease on Chichagof Island in the future. These results are used to discuss several management options for the extralimital R. aurora.