Species realities and numbers in sexual vertebrates: Perspectives from an asexually transmitted genome

A literature review is conducted on the phylogenetic discontinuities in mtD NA sequences of 252 taxonomic species of vertebrates. About 140 of these sp ecies (56%) were subdivided clearly into two or more highly distinctive mat rilineal phylogroups, the vast majority of which were localized geographica lly. However, only a small number (two to six) of salient phylogeographic s ubdivisions (those that stand out against mean within-group divergences) ch aracterized individual species. A previous literature summary showed that v ertebrate sister species and other congeners also usually have pronounced p hylogenetic distinctions in mtDNA sequence. These observations, taken toget her, suggest that current taxonomic species often agree reasonably well in number (certainly within an order-of-magnitude) and composition with biotic entities registered in mtDNA genealogies alone. In other words, mtDNA data and traditional taxonomic assignments tend to converge on what therefore m ay be "real" biotic units in nature. All branches in mtDNA phylogenies are nonanastomose, connected strictly via historical genealogy. Thus, patterns of historical phylogenetic connection may be at least as important as conte mporary reproductive relationships per se in accounting for microevolutiona ry unities and discontinuities in sexually reproducing vertebrates. Finding s are discussed in the context of the biological and phylogenetic species c oncepts.