Selective processes and adaptive evolution of the cytochrome b gene in salamanders of the genus Salamandrella

Abstract

Sequence analysis of the cytochrome b gene fragment in the salamanders of the genus Salamandrella, Siberian salamander and Schrenk salamander was performed with the purpose to elucidate the effect of natural selection on the evolution of mitochondrial DNA (mtDNA) in these species. It was demonstrated that despite of notable influence of negative selection (expressed as very low dN/dS values), speciation and intraspecific divergence in salamanders was accompanied by the appearance of radical amino acid substitutions, caused by the influence of positive (directional) selection. To examine the evolutionary pattern of synonymous mtDNA sites, distribution of conservative and non-conservative substitutions was analyzed. The rates of conservative and non-conservative substitutions were nearly equal, pointing to neutrality of mutation process at synonymous mtDNA sites of salamanders. Analysis of conservative and non-conservative synonymous substitution distributions in different parts of phylogenetic trees showed that the differences between the synonymous groups compared were statistically significant only in one phylogenetic group of Siberian salamander (haplogroup C) (P = 0.02). In the group of single substitutions, located at terminal phylogenetic branches of Siberian salamanders from group C, increased rate of conservative substitutions was observed. Based on these findings, it was suggested that selective processes could have an influence on the formation of the synonymous substitution profile in the Siberian salamander mtDNA fragment examined.