Phylogeography and population genetic structure of two anuran species inhabiting the Mojave Desert

Three studies are presented that apply the principles and methodologies of phylogeography to two anuran species (a frog and a toad) that inhabit the Mojave Desert of North America. The first study evaluates the geographic distributions of mitochondrial DNA (mtDNA) lineages (clades) within the broadly distributed toad, Bufo punctatus, as these relate to vicariant events hypothesized to have structured desert biotas within North America. Phylogeographic analyses support three clades with distributions corresponding to the Peninsular Desert of Baja, California, Chihuahuan Desert - Colorado Plateau (Eastern), and Mojave - Sonoran deserts (Western). Divergence levels and congruence with postulated vicariant events indicate separation of clades during the Late Neogene. Evaluation of mtDNA diversity and nested analysis reveal likely post-Pleistocene dispersal and contact across barriers separating the Eastern and Western clades. Speculation is made as to why the observed deep phylogeographic structure has not been eroded during Pleistocene interglacials.;A second study elucidates population genetic structure of B. punctatus among aquatic sites within mountain ranges and among mountain range groups, and relates patterns to previously determined hypotheses of population structure. Results from hierarchical analysis of molecular variance show generally high levels of genetic structure among mountain ranges, but little variation among sites within most mountain ranges. In mountain ranges demonstrating significant inter-site genetic structure, pairwise FST comparisons indicate that only a few sites are responsible. A likely range expansion is inferred in two ranges. Recent convergence between two divergent lineages is indicated within one range. Bufo punctatus occurs primarily in patchy populations within mountain ranges, but populations appear to be isolated among ranges.;The third study focuses on the evolutionary distinctiveness of leopard frogs (Rana sp.) along the Colorado and Virgin River drainages within the northeastern Mojave Desert. Phylogenetic analyses of mtDNA control region sequences, restriction site variation, and congruent patterns from randomly amplified polymorphic DNA (RAPDs), indicate that these leopard frogs differ from R. yavapaiensis, a sister-taxon occurring in the Sonoran Desert. These two taxa show significant multivariate morphological differentiation. Leopard frogs from the Mojave Desert are phylogenetically distinct and recognizable as R. onca.