Mitochondrial DNA divergence in southern African bufonids: are species equivalent entities?

Abstract

African bufonids differ greatly in the extent of DNA diversity within species, and divergence among species. Here we address two aspects of DNA sequence variation. First, we explore levels of diversity at several mitochondrial and nuclear genes, and their potential as systematic tools in frogs. Second, we compare divergences among twenty-eight species of African bufonids, at the mitochondrial ribosomal genes 12S and 16S. Nineteen lineages are identified, each separated by a minimum of 3.4 % sequence divergence at these genes. Maximum divergence within lineages is uniformly low (<2.3 %), irrespective of whether these include multiple described species or a single-species. This jump in divergence implies that species within the same mitochondrial lineage are not equivalent entities to single-species lineages. We suggest that low among species divergences within the B. maculatus, B. garmani, B. pardalis, and B. angusticeps groups reflect different causes, including taxonomic artefacts, and that these have the effect of distorting assessments of conservation value and biogeographic history. Comprehensive analyses of geographic variation within these groups are required, and are likely to reduce the number of recognised species.