1022-7954/02/3805- $27.00 © 2002 MAIK “Nauka /Interperiodica” 0538 Russian Journal of Genetics, Vol. 38, No. 5, 2002, pp. 538–547. Translated from Genetika, Vol. 38, No. 5, 2002, pp. 655–664. Original Russian Text Copyright © 2002 by Frisman, Kartavtseva, Pavlenko, Kostenko, Suzuki, Iwasa, Nakata, Chernyavskii. INTRODUCTION Red-backed voles of the genus Clethrionomys are widespread in forests of moderate and (partially) sub- tropical zones of Eurasia and North America and dwell in forest sites of forest-, meadow-, and tundra-steppes, as well as in the water-meadow forests of the steppe zone. Up to eight species are known in this genus including species with extensive or limited (confined to several small islands) ranges. The northern red-backed vole (C. rutilus Pallas, 1779) and the gray large-toothed red-backed vole (C. rufocanus Sundevall, 1846) have the most extensive ranges. In Eurasia, both species inhabit the area extending from Scandinavia to the Pacific Ocean, and the range of C. rutilus extends even to the territories of North America [1]. In the region of the Sea of Okhotsk (hereinafter, Priokhotye), the ranges of C. rutilus and C. rufocanus represent some series of isolates confined to coastal areas of land, the Kam- chatka Peninsula, and systems of islands: the Shantar Islands, the Sakhalin Island, some of the Kuril Islands, and the Hokkaido Island with adjacent small islands. In addition to the large-toothed red-backed and northern red-backed voles, the islands of Priokhotye are inhabited by two endemic taxonomic forms belong- ing to the genus Clethrionomys. C. sicotanensis Tokuda, 1935, was described in the Sakhalin Island (southern part), the Hokkaido Island, and the southern Kuril Islands. C. rex Imaizumi, 1971, was described in the Hokkaido Island and adjacent small islands. As these species only slightly differ from each other and from C. rufocanus by morphometric and color traits, is not surprising that the taxonomic interpretation of the volume of the genus Clethrionomys is far from clarity. Thus, some authors [2–4] consider C. sicotanensis to be a part of C. rufocanus, whereas others [5–8] assume that the former is an independent species. Clethrionomys rex is presented as a separate species in Corbet’s review [3]; however, other authors [4, 9] include it in C. rufocanus. Phylogenetic studies of vari- ation of nuclear (ribosomal) and mitochondrial DNA revealed that C. rex and C. rufocanus represent inde- pendent phyletic lines diverged in early Pleistocene [10], and differences that are observed between them at present time allow authors to consider them sibling spe- cies [11]. Analyzing morphological and genetic data, Kaneko et al. [12] came to conclusion that forms sico- tanensis and rex are combined into one independent species. We know only two published works on the study of allozyme differentiation in the taxonomic forms of for- est voles from Priokhotye. Regarding the elucidation of the level of differentiation of C. rufocanus and C. sico- tanensis, the results of these works are ambiguous. One group of authors think that these forms are conspecific Gene-Geographic Variation and Genetic Differentiation in Red-Backed Voles of the Genus Clethrionomys (Rodentia, Cricetidae) from the Region of the Sea of Okhotsk L. V. Frisman 1 , I. V. Kartavtseva 1 , M. V. Pavlenko 1 , V. A. Kostenko 1 , H. Suzuki 2 , M. Iwasa 2 , K. Nakata 3 , and F. B. Chernyavskii 4 1 Institute of Biology and Soil Sciences, Russian Academy of Sciences, Vladivostok, 690022 Russia; fax: (4232) 310-193, e-mail: IBSS@eastnet.febras.ru 2 Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University, Kita-ku, Sapporo, 060-0810 Japan 3 Hokkaido Forestry Research Institute, Higashiyama, Koshunai Bibai, Hokkaido, 079-01 Japan 4 Institute of Biological Problems of the North, Russian Academy of Sciences, Magadan, 685000 Russia Received May 4, 2001 Abstract—Thirteen enzyme systems and three nonenzyme proteins were electrophoretically analyzed in red- backed voles of the genus Clethrionomys. In total, 25 loci were interpreted. Gene-geographic variation was studied and indices of genetic variability and differentiation were determined. By the distribution of electro- phoretic variants of hemoglobin, C. rutilus was shown to be divided into two geographical groups (northern and southern). A low level of genetic differentiation was revealed in the island isolates of C. rutilus and C. rufoca- nus. Separation of C. rufocanus, C. rex, and C. sicotanensis into a superspecies complex was confirmed. A study of differential G- and C-banding on C. rutilus and C. rufocanus chromosomes did not reveal intraspecific vari- ation of autosomes. In these species, karyotypes of voles from Kamchatka Peninsula were studied for the first time. They appeared to be morphologically similar to the karyotypes continental voles by both autosomes and sex chromosomes. ANIMAL GENETICS