Meeting Abstract
Toad populations of the western toad (Bufo boreas) species complex are found throughout the western U.S. from Colorado to the Pacific Ocean and from Alaska to western Mexico. The phylogeography of the several species and evolutionary significant units (ESUs) within this complex has been reconstructed from phylogenetic analyses and the paleohydrology of the Great Basin populations to estimate times in which each of the species or ESUs became separated and started on their trajectory towards significant differentiation. The Humboldt/Lahontan ESU located in most of northern Nevada, separated from the Mojave ESU approximately 1.6 million years ago when a pluvial period connected populations through what today is Mono Lake. Bufo williamsi in Dixie Valley, Nevada, separated from the Humboldt/Lahontan watershed approximately 650,000 years ago during a postpluvial period created a barrier between Lake Lahontan and Dixie Lake. Bufo monfontanus in central Nevada likely separated from populations in Lake Bonneville a dry period in the late Pliocene, and B. nevadensis separated from Nevada populations when the wet areas on Railroad Valley, NV became isolated from the White River, which drained into the Colorado River which formerly connected Colorado populations of toads with those in Railroad Valley about 5 to 20 million years ago. The Amargosa toad currently found in Oasis Valley in southern Nevada is clearly an ESU, but its differentiation from other populations in the Mojave Desert is very recent (less than 15,000 years), and all populations in the Mojave Desert should reasonably considered to be B. nelsoni. These analyses provide perspective on the natural history of an entire species complex of toads in the U.S.
