Mitochondrial DNA evolution of tetraploids in the genus Neobatrachus (Anura: Myobatrachidae)

The Australian burrowing frog-genus Neobatrachus currently contains six diploid and four tetraploid species that are recognized by a combination of morphological, cytogenetic, and behavioral characters. Sequences of the mitochondrially encoded cytochrome oxidase I (COI) gene were used to reconstruct historical relationships among diploid and tetraploid species, Data were anal)zed by using parsimony, minimum evolution, and maximum likelihood as optimality criteria. Based on our results, we hypothesize that there have been at least two origins of tetraploids: one gave rise to an "eastern" lineage (N. sudelli from Queensland and South Australia, N. centralis from South Australia and Western Australia, and N. aquilonius from the Northern Territory); the other gave rise to a "western" lineage (N. kunapalari and N. aquilonius from Western Australia). Origins of the eastern lineage from extant diploids were not resolved. Members of the western lineage may be derived from N. albipes or N. fulvus. We conclude that tetraploid lineages may be older than previously suggested, that there have been multiple origins of tetraploidy in Neobatrachus, and that some of the tetraploids may have speciated subsequent to their origin. Our results suggest a preliminary framework in which to address further questions on the origins of tetraploids and their subsequent patterns of speciation.