Increased Rate of Fixation of Nucleotide Substitutions in the Mitochondrial DNA of Bony Fish Species (Osteichthyes) That Originated from the Arctic or Settled through It

The problem of differences in the rate of evolution among different animal or plant species has been intensely discussed in recent years, so the question of the validity of a so-called molecular clock hypothesis is very relevant. We have performed a search for publications describing median networks, which include haplotypes of mitochondrial genes for closely related boreal and arctic fish species (or those who settled through the Arctic). In all seven cases included into our analysis, the rate of nucleotide substitutions in Arctic taxa or taxa that settled through the Arctic during their evolutionary history was higher, and this difference was statistically significant. Therefore, the formation of new fish taxa in polar latitudes is accompanied by a rapid evolution of mitochondrial DNA that apparently reflects their adaptation to the new environment. In addition, speciation in Arctic fishes is usually accompanied by multiple chromosome fusions. Therefore, both our data and the data of other researchers provide solid reasons to doubt in the validity of the molecular clock hypothesis.