Cytogenetic relationships inRattus, Cremnomys, Millardia, Nesokia andBandicota (Rodentia: Muridae)

Abstract

The karyology was studied in different taxa ofRattus, Cremnomys, Millardia, Nesokia andBandicota. Chromosome banding patterns of 18 taxa belonging to 4 species of the genusRattus, 2 species ofCremnomys, 1 species each ofMillardia andNesokia and 2 species ofBandicota are presented. Present studies and the karyological information of different taxa available from elsewhere have revealed that the karyotypes ofMillardia, Cremnomys, Lenothrix (exceptL. canus) andMaxomys (M. bartelsii only) are unique and show little resemblance toRattus, Stenomys, Berylmys andLeopoldamys. G-band comparison has revealed the presence of 4 pairs of similar autosomes in addition to conservation of the G-band pattern of the X chromosome in divergent karyotypes ofRattus rattus, Millardia meltada andCremnomys cutchieus medius. Chromosome inversions, fusions and variations in constitutive heterochromatin have been identified. The presence of a few similar chromosomes suggests that these taxa have evolved from a common ancestral taxon. The conventional karyotype ofLenothrix canus and theNiviventer group of rats (Marshall, 1977) also reveal a pair of large subtelocentrics and a few pairs of small metacentrics similar to those observed in the subgeneraRattus, Stenomys, Berylmys andLeopoldamys. The autosomal complements of the lesser bandicoot-ratsNesokia indica andBandicota bengalensis are alike and are related to those of species in the subgenusRattus through only 2 pericentric inversions. A few pericentric inversions and a deletion may be assumed to compare the karyotype of the great bandicoot-ratB. indica indica withB. bengalensis. The other great bandicoot-rats,B. indica nemorivaga andB. indica savilei, have an additional pair of autosomes and the karyotype of the former subspecies has diversified through a few pericentric inversions also.