Tandem Fusions in Evolution of Ethiopian Endemic Rodents

The species number has been strikingly increasing in recent current works on Ethiopian endemic rodents, which to a great extent is due to genomic studies including the karyotype discoveries. Here, the diploid number 2 N = 52 is defined anew for the genus Stenocephalemys , endemic to the Ethiopian Highlands, where four karyotypes with 2 N values of 54, 50 and 46 were so far described for four taxa. The new karyotype ( S . “ pseudogriseicauda ”) combines into a nearly full series with other 2 N s (except the not yet found 2 N = 48) within the genus and shows one interspecific chromosome rearrangement associated with the tandem fusion, in the direction 2 N = 54 to 2 N = 52. Together with the earlier detection of tandem fusions between karyotypes with 2 N = 46 ( S. albipes ) and 2 N = 54 ( S. albocaudatus , S. griseicauda ), this rodent taxonomic group presents an interesting case for the phenomenon of karyotypic orthoselection in an intrageneric phyletic line via the reoccurence of such characteristic chromosomal rearrangements as tandem fusions.