Genetic Structure Formation of Reed Vole Populations at the Northern Periphery of Their Distribution (Alexandromys fortis, Rodentia, Arvicolinae)

The genetic structure of the reed vole ( Alexandromys fortis (Büchner 1889)) from the northern periphery of its distribution area was studied using the variability of the mtDNA control region. A high haplotype and nucleotide diversity has been shown in the northern part of the species range. The diversity is due to the presence of two lineages that form phylogenetic subclades within the NORTH lineage on dendrograms. The MAIN haplotypes have a wide geographic distribution. Basically, the distribution of the ISL haplotypes is confined to the islands of the Rimsky-Korsakov Archipelago (Bolshoy Pelis and Matveev) in the Sea of Japan and in the Barguzin Depression in Buryatia. They are also found in mainland populations, albeit with low frequencies, only in the south of the Russian Far East. The ISL haplotypes are noted to be close to those previously identified based on fossil material from cave deposits in the south of Primorsky Krai. Several alternative hypotheses concerning the ways of the formation of such a phylogeographic structure are considered. Small areas with local favorable environmental features are suggested to have persisted at the northern periphery of the reed vole distribution, where the species could have survived the Pleistocene and retained the ISL haplotypes that might have appeared earlier than the MAIN haplotypes. Those local areas can be considered as microrefugia, which could have played important roles in maintaining the high genetic diversity of the species in the southern part of the Russian Far East. Secondary colonization events by individuals with the MAIN haplotypes could have occurred already after the completion of the climatic minimum and the wide expansion of the species to the north from a southern macrorefugium. The existence of two macrorefugia, in which two subclades, MAIN and ISL, were formed, followed by random fixations of rarer ISL haplotypes in small isolated populations, is also hypothesized.