Phylogeography of Fowler's Toad, Bufo fowleri, at its Northern Range Limit.
Green, David*,1, Smith, M. 2, 1 McGill University, Montreal, Quebec, Canada2 University of Guelph, Guelph, Ontario, Canada
ABSTRACT- Many of the species of small, terrestrial animals that recolonised previously glaciated areas in the Great Lakes basin of North America over the past 10,000 to 12,000 years exhibit genetic evidence of multiple invasion routes and present-day secondary contact between deeply divergent lineages. With this in mind, we investigated the phylogeographic structure of genetic variability in Fowler's toad (Bufo fowleri) at the northern edge of its distribution where its range encircles Lake Erie. Because B. fowleri is closely tied to habitats along the Lake Erie shoreline, we would expect that the species' colonization of the northern shore would have been limited to a small number of possible dispersal routes. Thus there should remain genetic evidence of the number of invasions that took place. A 540 bp DNA sequence from the mitochondrial control region of 158 individuals from 21 populations was amplified and its variation analyzed. Inter-population sequence variation ranged from 0% to 6%. Phylogenetic analysis of p-distance using the neighbor-joining method revealed two deeply divergent (6% sequence divergence) mtDNA lineages. Additional mitochondrial (CO1) and nuclear (ITS1) markers were also sequenced and analyzed . The two major lineages discerned with this multi-gene approach may possibly have arisen due to secondary contact of populations that entered the region via separate routes. However, the phylogeographic pattern is not simple. The populations of toads at Long Point, on the north shore of Lake Erie, clustered with the population from Indiana Dunes on Lake Michigan to form Phylogroup 2 whereas all other B. fowleri populations examined from both sides of Lake Erie constituted Phylogroup 1. Furthermore, mtDNA sequences from the related species, Bufo americanus, obtained from populations outside the range of B. fowleri, clustered with mtDNA haplotypes of B. fowleri Phylogroup 1, indicating the possibility of partial introgression of mitochondria from one species to the other.
Key words: phylogeography, amphibian, postglacial recolonisation, mtDNA
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