C-heterochromatin variation and NOR distribution in the karyotype of water vole, Arvicola terrestris (Mammalia, Rodentia)

Abstract

A chromosomal study of populations of Arvicola terrestris from Anatolia in Turkey and from Cen- tral Europe was performed. The diploid number of 36 chromosomes was found in all the specimens examined. The autosomal complement consisted of 12 meta- and submetacentric pairs, two large or medium-sized subtelo- centric pairs, and three small acrocentric (Turkey) or subtelocentric (Central Europe) pairs (FNa = 62-68). The X chromosome was medium-sized submetacentric, the Y chromosome was small acrocentric or subtelocentric. All the chromosomes could be reliably identifi ed by their unique G-banding patterns. The C-banding analysis revealed variation in the amount of constitutive heterochromatin in centromeric regions and in short arms of certain autosomes. A unique feature of the C-banded karyotype of individuals from Anatolia was the absence of dark positive regions in most chromosomes. Populations of water vole from Anatolia resemble in their C-band pattern those studied previously in Azerbaijan, and possibly also in the Balkan peninsula, and they are different in this respect from populations in Central Europe and the other parts of the species range. The X chromosome was stained uniformly and C-negatively in populations from Anatolia, whereas a faint dark centromeric C-band was observed in individuals from Central Europe. The Y chromosome was stained C-positively. The active nu- cleolar organizer regions (NORs) were localized in one pair of small metacentric and two acrocentric autosome pairs in the karyotype of individuals from Anatolia.