Original Investigation Geographical distribution and chromosomal study of the underground vole Microtus thomasi in Albania and Montenegro Michail Th. Rovatsos a , George P. Mitsainas a , Gligor Paspali b , Selfo Oruci b , Eva B. Giagia-Athanasopoulou a,n a Department of Biology, University of Patras, GR 26500 Patras, Greece b Department of Biology and Chemistry, University Eqrem Cabej, Gjirokaster, Albania article info Article history: Received 22 October 2009 Accepted 12 January 2010 Keywords: Microtus Asynaptic Heterochromatin Sex chromosomes Polymorphism abstract In order to better define the geographical distribution of the underground vole Microtus thomasi and the chromosomal variability, within its natural populations, we studied 77 individuals from 14 localities of Albania and Montenegro. Chromosomal preparations were obtained from bone marrow and testicular material, on which a karyological analysis, based on C-banding patterns was performed. The examined individuals belonged to the chromosomal races ‘‘thomasi’’ (2n =44, FN=44), ‘‘subalpine’’ (2n =42, FN=42) and ‘‘Rb-subalpine’’ (2n =40, FN=42), which are also distributed in Greece. However, the C-banding pattern revealed an extensive sex chromosome polymorphism, demonstrated by three different X and three different Y chromosomal variants. Taking under consideration all available chromosomal data for M. thomasi, it seems that the species could possess the highest chromosomal variability, within its genus. It is proposed that due to the limited mobility of the underground vole and the rough, mountainous terrain of the Balkan Peninsula, it is possible that several small populations were isolated, in which inbreeding and random genetic drift led to the fixation of different chromosomal mutations, giving rise to the extensive chromosomal variability, observed today. & 2010 Deutsche Gesellschaft f ¨ ur S¨ augetierkunde. Published by Elsevier Gmbh. All rights reserved. Introduction The underground vole Microtus thomasi is a Balkan endemic species, distributed in Greece, Albania and former Yugoslavia (Shenbrot and Krasnov, 2005). Its geographical distribution in Greece is well documented, and it is thus known that the species occurs on large areas of the mainland as well as on Euboia island. The vole occupies mainly grass fields and crops from sea level to 2000 m a.s.l., spending its entire life in underground tunnels and feeding almost exclusively on roots and tubers (Giagia-Athanasopoulou et al., 1995, Giagia-Athanasopoulou and Stamatopoulos, 1997; Rovatsos et al., 2008; Tryfonopoulos et al., 2008; Mitsainas et al., 2009). Considering the previous chromosomal studies on Greek populations, M. thomasi occurs with four different chromosomal races, namely ‘‘thomasi’’, ‘‘atticus’’, ‘‘subalpine’’ and ‘‘Rb-subalpine’’ (Giagia-Athanasopoulou et al., 1995; Giagia-Athanasopoulou and Stamatopoulos, 1997). The ‘‘thomasi’’ chromosomal race is considered to be the ancestral form, with 44 acrocentric chromosomes, including heterochromosomes (2n=44, FN=44), while the ‘‘atticus’’ chromosome race differs from the previous in the morphology of the sex chromosomes, with a sub-telocentric X and in some cases a metacentric Y chromosome (2n=44, FN=46). In addition, both races present several X and Y chromosomal variants, differing in the morphology and/or hetero- chromatin constitution (Mitsainas et al., 2009). The ‘‘subalpine’’ chromosomal race has 42 acrocentric chromosomes (2n=42, FN=42), while the ‘‘Rb-subalpine’’ chromosomal race has derived from ‘‘subalpine’’, through an Rb fusion between two large-sized autosomal pairs (2n =40, FN=42) (Giagia-Athanasopoulou and Stamatopoulos, 1997). On the other hand, the geographical distribution of M. thomasi in other Balkan countries is rather poorly documented, since few reports have been presented during the last 30 years. In fact, M. thomasi was initially reported from 6 localities of Montenegro and 2 localities from Bozna-Herzegovina (Petrov and Zivkovic, 1972, 1979), and only recently was it reported for the first time, through the study of owl pellets, from 13 localities of Albania (Bego et al., 2008). Based on a previous chromosomal study of Montenegro specimens, using conventional staining (Petrov and Zivkovic, 1972), it was later concluded that those specimens belonged to the ‘‘thomasi’’ chromosomal race (Giagia, 1985). However, there do not seem to exist any additional karyological data from other Balkan regions within the species’ distribution range. In this context, it was considered necessary to better define the geographical distribution of M. thomasi outside Greece and to inquire, whether the remarkable chromosomal variability that is Contents lists available at ScienceDirect journal homepage: www.elsevier.de/mambio Mammalian Biology 1616-5047/$ - see front matter & 2010 Deutsche Gesellschaft f ¨ ur S¨ augetierkunde. Published by Elsevier Gmbh. All rights reserved. doi:10.1016/j.mambio.2010.01.003 n Corresponding author. Tel.: + 30 2610969271; fax: + 30 2610969271. E-mail address: giagia@upatras.gr (E.B. Giagia-Athanasopoulou). Mamm. biol. 76 (2011) 22–27