CompCytogen 6(3): 267-271 (2012) COMPARATIVE | rerrweretopascasinan doi: 10.3897/CompCytogen.v6i3.3019 Kas Cyto genetics www.pensoft.net/journals/compcytogen International Journal of Plant & Animal Cytogenetics, Karyosystematics, and Molecular Systematics A comparison of the chromosome G-banding pattern in two Sorex species, S. satunini and S. araneus (Mammalia, Insectivora) Yuriy M. Borisov', Victor N. Orlov' I Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii pr, Moscow, 119071 Russia Corresponding author: Yuriy M. Borisov (boris@sevin.ru) Academic editor: V. Lukhtanov | Received 27 February 2012 | Accepted 19 June 2012 | Published 20 August 2012 Citation: Borisov YM, Orlov VN (2012) A comparison of the chromosome G-banding pattern in two Sorex species, S. satunini and S. araneus (Mammalia, Insectivora). Comparative Cytogenetics 6(3): 267-271. doi: 10.3897/CompCytogen. v6i3.3019 Abstract The G-banded karyotype of S. satunini was compared with the karyotype of Sorex araneus. Extensive homology was revealed. The major chromosomal rearrangements involved in the evolutionary divergence of these species have been identified as centric fusions and centromeric shifts. From the known palaeon- tological age of S. satunini it is obvious that the vast chromosomal polymorphism of the S. araneus group originated during the middle Pleistocene. Keywords G-banding, common shrew, Sorex araneus, Sorex satunini, karyotype, phylogeny Introduction Within the genus Sorex Linnaeus, 1758, the Sorex araneus group includes eight species characterized by the sex chromosome complex XY_Y, (Zima et al. 1998). Some of them were raised to species status on a karyological basis. Two species from this group, the common shrew Sorex araneus Linnaeus, 1758 and the Caucasian shrew S. satunini Og- nev, 1922 can be defined as cryptic species that are virtually impossible to distinguish by morphological (cranial) characters (Sokolov and Tembotov 1989). The common shrew is widely distributed in Europe and Asia up to as far east as Lake Baikal, and the Caucasian shrew is known to be present in the Caucasus and in Copyright Yuriy M. Borisov,Victor N. Orlov. This is an open access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 268 Yuriy M. Borisov & Victor N. Orlov / Comparative Cytogenetics 6(3): 267-271 (2012) the northern parts of Asia Minor (Sokolov and Tembotov 1989, Bukhnikashvili and Krystufek 2008). In the North Caucasian plains, this species is contiguous with the common shrew (the chromosomal race Neroosa) (Stacheev et al. 2010). The common shrew displays phenomenal variability of the autosomal comple- ment (Wojcik et al. 2002). The Caucasian shrew is monomorphic and can be reliably identified by means of conventionally stained karyotype (Kozlovsky 1973, Sokolov and Tembotov 1989, Macholan 1996). Macholan (1996) recognized in G-banded metaphases of the S. satunini the autosomes af, bc and tu, which are invariantly present in the common shrew karyotype. The presence of these Robertsonian fusions in the S. satunini corroborates the findings of Zagorodniuk and Khazan (1996) who described the arm combinations of autosomes af, bc, gh, ik, jn, lo, and tu in the karyotype of a single female from Kobi (Georgia). From the plain between the Kuban and Don rivers we described a new subspecies of the Caucasian shrew Sorex satunini tembotovi Orlov, Balakirev, Borisov, 2010 (Or- lov et al. 2010) that differs from the subspecies S. s. armenica Sokolov et Tembotoy, 1989 and S. s. stavropolica Sokolov et Tembotov, 1989. In this study the karyotypes of S. s. tembotovi and S. araneus (chromosome race Moscow) were examined and compared. Material and methods Three females and four males of S. satunini were captured in the valley of the Beisoog River (45°40'N, 39°41'E), 90 km N of the Krasnodar city in June 2009. Two shrews of the race Moscow (male and female) were captured in Moscow vicinity. Mitotic chromosome spreads were prepared in the field conditions from bone mar- row and spleen cells using the air-drying technique after fixation with methanol and glacial acetic acid. For G-banding, the slides were treated with trypsin solution accord- ing to Seabright (1971). Chromosome nomenclature used follows Searle et al. (2010). Results and comments The karyotype of S. satunini consists of 24—25 chromosomes. The sex chromosomes are a large metacentric X, a small acrocentric Y,, and a medium-sized Y,. Of 11 au- tosomal pairs, only a single pair of small chromosomes is acrocentric, all other au- tosomes are biarmed. Such a karyotype has been described for many populations from the North Caucasian and Transcaucasian regions (Kozlovsky 1973, Sokolov and Tembotov 1989, Macholan 1996). The Caucasian shrew has the following chromosome formula: XX / XY\Y,, af, bc gh, ik, jn, lo, tu, m, p, g, 7, tu. The comparison of the G-banded metaphase chromosomes of S. satunini and of S. araneus (the race Moscow) is presented in Fig. 1. This compari- son revealed a considerable homology between individual chromosomal arms. Identical A comparison of the chromosome G-banding pattern in two Sorex species... 269 v 4 is — .) 6 § ix ‘ ‘= d ‘ . a i” | f ° f ) be af tu m A H2eH] C i} }< { 3< 3 f< P q F Figure |. The G-banded karyotype of Sorex satunini (male) in comparison with the karyotype of S. araneus (the race Moscow, male). The chromosomes of the race Moscow are given in the frameworks. Some chromosomes are identical (a), the others are different because of the arms involved in different «8D fusions (b) or because of the centromeric shift (€). Centromere position is indicated by “<”. Bar = 3 um. banding patterns and centromeric positions were found in two large biarmed autosomes af and bc, in small metacentric tu, in acrocentric pare m and in the sex chromosomes (Fig. 1a). The acrocentric m is found in the karyotypes of the chromosomal races of S. araneus either as an individual acrocentric, or in combination with other acrocentrics. Seven arms of S. araneus, namely g, i, k, j, n, 4 and 0, were also identified in the complement of S. satunini. The difference in G-banding of the arm / between S. sa- tunini and other species of the S. araneus group was observed (Fig. 1b). An identical banding pattern and a different centromeric position were found in three autosomal pairs: p, g, and 7, suggesting occurrence of centromeric shift. The chromosomes 7, 4, and r were found to be metacentric in the complement of S. satunini (Fig. 1c) and acrocentric in Sorex araneus. The large biarmed chromosome bc was also identified in the complement of S. an- tinorii Bonaparte, 1840, and only in S. coronatus Millet, 1828 it was substituted by ci (Hausser and Jammot 1974). The biarmed chromosome /o is found in the karyotypes of S. coronatus and S. antinorii, the biarmed chromosome jn - in the karyotype of S. coronatus (Briinner et al. 2002). The metacentric zk is known in five chromosomal races of S. araneus (Wéjcik et al. 2003). The metacentric gh was identified only in the complement of S. satunini (Fig. 1b). In karyotype of S. coronatus there are only two species-specific chromosome rear- rangements (Rb fusions ci and mp). In karyotype of S. antinorii there are only two spe- 270 Yuriy M. Borisov & Victor N. Orlov / Comparative Cytogenetics 6(3): 267-271 (2012) cies-specific chromosome rearrangements, too (/j and kn). In karyotype of S. satunini there are five species-specific chromosome rearrangements (Rb fusion gh, centromeric shifts in the chromosomes p, g, 7, and, probably, a paracentric inversion in the chro- mosomal arm /), i.e. S. satunini has more rearranged karyotype than the species of S. araneus group in Western Europe. A number of chromosome rearrangements shared by S. araneus, S. satunini and S. antinorii (centric fusions bc), by S. coronatus, S. satunini and S. antinorii (lo), by S. coronatus and S. satunini (jn) suggest the existence of acommon ancestral species in the Pleistocene of Europe analogous to the modern S. araneus. The known paleontological age points to an early origin of S. satunini. At present, the dating of fossils confirmed by the radiocarbohydrate analysis is known only for S. satunini. These fossils, morphologically very similar to the recent S. satunini were found in the Transcaucasian region (Kudaro caves) in all layers of the middle and late Pleistocene, beginning since 0.36 Myr BP (Osipova 2006). Acknowledgments We are grateful to V.V. Stacheev, A.E. Balakirev for the assistance during the expedition and E.V. Cherepanova for the comments on the manuscript. The study was supported by the Russian Foundation for Basic Research (grant 12-04-00551) and Program of the Russian Academy of Sciences “Dynamics and conservation of gene pools”. References Briinner H, Lugon-Moulin N, Balloux F, Fumagalli L, Hausser J (2002) A taxonomical reeval- uation of the chromosome race Valais of the common shrew, Sorex araneus (Insectivora: Soricidae), from multiple, independent characters. Acta Theriologica 47: 245-275. Bukhnikashvili A, Krystufek B (2008) Sorex satunini IUCN 2011. IUCN Red List of Threat- ened Species. Version 2011.1. www.iucnredlist.org Hausser J, Jammot D (1974) Etude biométrique des machoires chez les Sorex du groupe araneus en Europe continentale (Mammalia, Insectivora). Mammalia 38: 324-343. doi: 10.1515/ mamm.1974.38.2.324 Kozlovsky AI (1973) Somatic chromosomes of two species of the shrews in Caucasus. Zoolog- icheski Zhurnal 52: 571-576 [in Russian]. Macholan M (1996) Chromosomal and allozyme characterization of the Caucasian shrew, Sorex satunini, from north-eastern Turkey. Hereditas 125: 225-231. Orlov VN, Balakirev AE, Borisov YuM (2010) A new subspecies of the Caucasian shrew Sorex satunini (Mammalia) and phylogenetic relationships of the species inferred from mtDNA sequences and chromosomal markers. Journal of Ecology 1: 111-114. [in Russian]. Osipova VA (2006) Fossil history of shrews (Family Soricidae) in Caucasus. Ph.D. Dissertation, St. Peterburg, Russian Federation: Zoological Institute, Russian Academy of Sciences. [in Russian] A comparison of the chromosome G-banding pattern in two Sorex species... 271 Seabright MA (1971) A rapid banding technique for human chromosomes. Lancet 2 (7731): 971-972. doi: 10.1016/S0140-6736(71)90287-X Searle JB, Fedyk S, Fredga K, Hausser J, Volobouev VT (2010) Nomenclature for the chro- mosomes of the common shrew (Sorex araneus). Comparative Cytogenetics 4: 87-96. doi: 10.3897/compcytogen.v4il.28 Sokolov VE, Tembotov AK (1989) Mammals of the Caucasus. Insectivora. Nauka Press, Mos- cow, 548 pp. [in Russian] Stacheev VV, Balakirev AE, Grigoryeva OO, Shestak AG, Potapov SG, Borisov YuM, Orlov VN (2010) Distribution of cryptic shrew species of the genus Sorex (Mammalia) on the plain between the Don and Kuban rivers with molecular marker diagnostics. Povolzhskiy Journal of Ecology 4: 396-403. [in Russian] Wojcik JM, Borodin PM, Fedyk S, Fredga K, Hausser J, Mishta A, Orlov VN, Searle JB, Vo- lobouev VT, Zima J (2003) The list of the chromosome races of the common shrew Sorex araneus (updated 2002). Mammalia 68: 169-178. Wojcik JM, Ratkiewicz M, Searle JB (2002) Evolution of the common shrew Sorex araneus: chromosomal and molecular aspects. In: Gliwicz J (Ed) Theriology at the turn of a new century. Bialowieza, Polish Academy of Sciences. Acta Theriologica 47(Suppl. 1): 139-167. Zagorodniuk I, Khazan M (1996) Cladogenesis in the Sorex araneus group and its biogeo- graphic interpretation. Abstracts of the ISACC Fourth International Meeting. Norr Malma and Uppsala, August 22-26, 1996. Uppsala University, Uppsala, 38. Zima J, Luka¢ova L, Macholan M (1998) Chromosomal evolution in shrews. In: Wojcik JM, Wolsan M (Eds) Evolution of Shrews. Mammal Research Institute, Polish Academy of Sci- ences, Bialowieza: 175-218.