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Phylogeography of Declining Relict and Lowland Leopard Frogs in the Desert Southwest of North America
Citation:
Olah-Hemmings, V., J. R. Jaeger, M. J. Sredl, M. A. Schlaepfer, R. D. Jennings, C. A. Drost, D. F. BRADFORD, AND B. R. Riddle. Phylogeography of Declining Relict and Lowland Leopard Frogs in the Desert Southwest of North America. JOURNAL OF ZOOLOGY. Oxford University Press, Cary, NC, 280:343-354, (2010).
Impact/Purpose:
The relict leopard frog, Rana (syn. Lithobates) onca, and the lowland leopard frog, R. yavapaiensis, occupy springs, streams, and wetlands within warm-desert regions of southwestern North America. In recent years, both of these closely related frogs have experienced population declines and broad range contractions (Clarkson & Rorabaugh, 1989; Bradford, Jaeger & Jennings, 2004; Sredl, 2005). As an apparent regional endemic, R. onca has suffered the worst and is currently managed under a federally sanctioned conservation agreement and strategy. Previous phylogenetic analysis based on mitochondrial DNA (mtDNA), nuclear DNA markers, and morphology revealed that these frogs were distinct taxa but at a shallow level of divergence, which led to the speculation that this level of difference “probably” represents relatively recent, Late Pleistocene-Holocene isolation (Jaeger et al., 2001). Further evidence that these taxa are closely related was subsequently provided in a broader phylogenetic analysis of ranid frogs in which a lower than species-level distinction was implied (Hillis & Wilcox, 2005).
Description:
We investigated the phylogeography of the closely related relict leopard frog (Rana onca) and lowland leopard frog (R. yavapaiensis) – two declining anurans from the warm-desert regions of southwestern North America. We used sequence data from two mitochondrial DNA genes to assess 276 individuals representing 30 sites from across current distributions. Our analysis supports the previously determined phylogenetic break between these taxa, and we found no admixing of R. onca and R. yavapaiensis haplotypes within our extensive sampling of sites. Our assessment, however, further divided R. yavapaiensis into two distinct mtDNA lineages, one representing populations across Arizona and northern Mexico and the other a newly discovered population within the western Grand Canyon, Arizona. Estimates of sequence evolution indicate a possible Early Pleistocene divergence of R. onca and R. yavapaiensis, followed by a Middle Pleistocene separation of the western Grand Canyon population of R. yavapaiensis from the main R. yavapaiensis clade. Phylogeographic and demographic analyses indicate population or range expansion for R. yavapaiensis within its main distribution that appears to predate the latest glacial maximum. Species distribution models under current and latest glacial climatic conditions suggest that R. onca and R. yavapaiensis may not have greatly shifted ranges. Our data supports the designation of R. onca as a distinct taxon, and additionally points to the uniqueness of the isolated population of R. yavapaiensis within the western Grand Canyon.