Sequence divergence at mitochondrial genes in animals: applicability of DNA data in genetics of speciation and molecular phylogenetics.

Nucleotide diversity estimates for the genes Cyt-b (cytochrome b) and Co-1 (cytochrome oxidase 1) are analyzed. Genetic divergence of populations (1) and taxa of different rank, such as subspecies, semispecies or/and sibling species (2), species within a genus (3), species from different genera within a family (4), and species from separate families within an order (5) have been compared using a database of p-distances and similar measures. Empirical data for 20,731 vertebrate and invertebrate animal species reveal various and increasing levels of genetic divergence of the sequences of the two genes, Cyt-b and Co-1, in the five groups compared. Mean unweighted scores of p-distances (%) for five groups are: Cyt-b (1) 1.38±0.30, (2) 5.10±0.91, (3) 10.31±0.93, (4) 17.86±1.36, (5) 26.36±3.88 and Co-1 (1) 0.89±0.16, (2) 3.78±1.18, (3) 11.06±0.53, (4) 16.60±0.69, (5) 20.57±0.40. These estimates testify to the applicability of p-distance for most intraspecies and interspecies comparisons of genetic divergence up to the order level for the two genes compared. The results of the analysis of the nucleotide divergence within species and higher taxa of animals suggest that a phyletic evolution in animals is likely to prevail at the molecular level, and speciation mainly corresponds to the geographic or divergence mode (type D1). The prevalence of the D1 speciation mode does not mean that other modes are absent. At least seven possible modes of speciation are considered. The approach suggested that allows recognize the speciation modes formally with the operational genetic criteria. Such approach may help to solve a key problem of the biological species concept, i.e. the lack of ability to monitor in most cases the reproductive isolation barriers between species.