PHYLOGEOGRAPHY OF BUFO-MARINUS FROM ITS NATURAL AND INTRODUCED RANGES

The marine toad, Bufo marinus, has a broad natural distribution extend ing from the south-west of the USA to southern Peru and the central Am azon. It was introduced to several localities in the Caribbean and Pac ific Oceans to control sugar cane pests. Mie sequenced 468 bp of mitoc hondrial DNA (mtDNA) containing the ND3 gene, and flanking tRNA genes from toads spanning the broad natural and introduced ranges. Consisten t with the known history of introductions and expected effects of seri al bottlenecks, mtDNA within introduced populations in Hawaii and Aust ralia was uniform and most closely related to samples from eastern Ven ezuela and French Guiana. However, mtDNA nucleotide diversity in the g eographic region spanning the source areas is also relatively low (0.1 8-0.46%) and the absence of variation in the introduced populations pr ecludes quantitative assessment of the reduction in genetic diversity. Unexpectedly, there was a large phylogeographic break (5.4% sequence divergence) within the natural range separating populations east and w est of the Venezuelan Andes. We hypothesize that the two major lineage s of B. marinus were isolated by the uplift of the eastern Andean cord illera which was completed approximately 2.7 Ma. Another species of th e marinus group, B. paracnemis, had mtDNA paraphyletic, with marinus, being nested within the eastern lineage. Thus, at least one speciation event within the marinus group postdates the split within marinus. Th ese findings suggest that the taxonomy of B. marinus should be re-eval uated and that the search for pathogens to control Australian populati ons should be conducted in populations from both lineages in the natur al range.