Karyotypic evolution of Apodemus (Muridae, Rodentia) inferred from comparative FISH analyses.

We conducted comparative FISH analyses to investigate the chromosomal rearrangements that have occurred during the evolution of the rodent genus Apodemus, which inhabits broadleaf forests in the temperate zone of the Palaearctic region. Chromosome-specific painting probes of the laboratory mouse were hybridized to chromosomes of seven Apodemus species, A. agrarius, A. argenteus, A. gurkha, A. peninsulae, A. semotus, A. speciosus and A. sylvaticus, and homologous chromosomal regions were determined in the species for the study of karyotypic evolution. Differences in the hybridization patterns were found in nine pairs of autosomes among the seven species. The chromosomal location of the 5S rRNA genes on the telomeric region of chromosome 20 was highly conserved in all the species. In contrast, there was much wider variation in the location of the 18S-28S rRNA genes, although they were predominantly located on chromosomes 7, 8 and 12. Phylogenetic relationships of the seven Apodemus species were inferred from the chromosome rearrangements and the chromosomal distribution patterns of the 18S-28S rRNA genes. The karyotypic relationships correlated well with the molecular phylogeny, and A. semotus had the most highly conserved karyotype among the seven species.