Extensive genome reorganization in the African rodent genus Otomys

Abstract

With 3 plates in the text) Two species of Otomys, 0. unisulcatus (2n = 28) and 0. irroratus (2n = 28) were karyotypically compared by G-banding, C-banding and silver staining. The genomes of the two species differ in respect to all three cytogenetic parameters examined. Although no G-band homologies were evident between 0. unisulcatus and 0 . irroratus, the former species, on comparison with the murid, Rattus norvegicus, and the New World cricetid, Peromyscus melunophrys, shows the conservation of several primitive cricetid-murid G-band sequences. The extensive changes in the 0. irroratus genome have resulted from numerous structural rearrangements to the point where neither the changed patterns nor events causing them are identifiable. It is argued that narrow habitat specificity and its susceptibility to climatic vagaries has, through population fractioning and the creation of isolated demes, facilitated rapid chromosomal evolution in 0. irroratus.

Chromosomal evolution in the vlei rat, <i>Otomys irroratus</i> (Muridae: Otomyinae): a compound chromosomal rearrangement separates two major cytogenetic groups

“…1c and 2a). In all other respects the Alice specimens had a G-banded karyotype identical to that originally published for the species by Robinson and Elder (1987) and, on comparison with Contrafatto et al (1992a), also specimens from their Alice, Port Elizabeth, Committee's Drift, and Grahamstown specimens, although in the latter instance pair 14 appears to correspond to autosomal pair 8 of the Otomys standard.…”

“…Chromosome numbering in the karyotypes presented herein follows the Otomys standard proposed by Robinson and Elder (1987).…”

“…The Uitenhage specimen had a diploid number of 2n = 28 (Fig. 1a) and, except for the absence of a heterochromatic short arm in one homologue of pair 5, it was identical to the karyotype displayed by O. irroratus from the Tsitsikama population and sampled by Robinson and Elder (1987).…”

“…In order to draw conclusions on the patterns of chromosome evolution in O. irroratus, we compared our data to the published karyotypes for specimens from Alice, Bloemfontein, and Hogsback (Contrafatto et al, 1992a, b) as well as Tsitsikama, Cape Province, (34°14)S, 23°46)E) (Robinson and Elder, 1987); Karkloof, KwaZulu Natal (29°21)S, 30°13)E) (Contrafatto et al, 1992b); Stutterheim, Eastern Cape Province (32°30)S, 27°17)E) (Contrafatto et al, 1992b); Constantia, Western Cape Province (34°02)S, 18°22)E) (Contrafatto et al, 1992a); and Port Elizabeth, Eastern Cape Province (33°55)S, 25°40)E) (Contrafatto et al, 1992b).…”

“…The A assemblage is regarded as comprising only acrocentric chromosomes (excluding one to four biarmed B chromosomes) and is further subdivided into two races, A1 and A2. The A1 race is fixed for a putative tandem fusion of chromosomes 7 and 12 (see Contrafatto et al, 1997), whereas subgroup A2 has an acrocentric cytotype (without the tandem fusion autosome) but which is thought to contain two de novo autosomal pairs (1a and 1b; Contrafatto et al, 1992a, b) which these authors were unable to assign to the standard karyotype (see Robinson and Elder, 1987). Group B specimens have at least six to eight pairs of biarmed autosomes (Taylor, 2000), the short arms of which are entirely heterochromatic (except in pair 6, which has a pericentric inversion; see Robinson and Elder, 1987).…”