Comparative chromosome banding analysis of three South American species of rice rats of the genus Oryzomys (Rodentia, Sigmodontinae)

Comparative G- and C-banding analysis in three species of rice rats, namely Oryzomys megacephalus from Peru and French Guiana, O. yunganus (Peru) and O. nitidus (Bolivia) was carried out. It revealed that Peruvian O. megacephalus (2N=52, NFa=62) and that from French Guiana (2N=54, NFa=64) differ from each other by one Rb translocation and one heterochromatic arm addition/deletion. Three further Rb translocations separate them from O. yunganus (2N=58, NFa=62). Only 16 out of 39 autosomal pairs of O. nitidus (2N=80, NFa=86) shared homologous banding patterns with O. yunganus, 4 of which were involved in tandem translocations to form the larger chromosomes in two other taxa. The study suggests that O. megacephalus, O. yunganus and O. laticeps studied previously form a monophyletic group in good agreement with earlier molecular and morphological data. By contrast, the limited homologous banding patterns found between them and O. nitidus cast doubt on its belonging to the same phylogenetic lineage. In the light of available chromosomal and molecular data, the significance of intra- and interspecies karyotypic variability within Oryzomys and its relevance to systematics and phylogeny of the genus are discussed.