A chromosomal study on Greek populations of the genusApodemus (Rodentia, Murinae) reveals new data on B chromosome distribution

During this study, 94 specimens (51 males, 43 females) of the wood mouseApodemus sylvaticus (Linnaeus, 1758), the yellow-necked mouseA. flavicollis (Melchior, 1834) and the western broad-toothed mouseA. epimelas (Nehring, 1902) from 20 localities of Greece were karyologically examined. The first two species were found to be widely distributed and their otherwise very similar karyotype (2n=48, FN=48) could be clearly distinguished, based on C-banding pattern. The third species appeared to have a more limited geographical distribution and its karyotype was distinguished from that of the previous two species, since it contained two pairs of small metacentric autosomes (2n=48, FN=52). The chromosomal study further revealed that nine individuals ofA. flavicollis possessed supernumerary B chromosomes (2n=49–50, FN=49–50). Meiotic chromosome preparations revealed that in contrast to sex chromosomes and autosomes, B chromosomes do not participate in bivalent formation. On the other hand, no supernumerary chromosomes were found in the studiedA. sylvaticus andA. epimelas material.