Genetic diversity of the Rattus complex (Rodentia: Muridae) in KwaZulu-Natal.

Abstract

The rodent genus Rattus is considered to be the single largest genus of mammals in the world. One species of Rattus is usually more dominant than another within a specific geographical area; however within the province of KwaZulu-Natal South Africa current observations indicate that Norway rats (R. norvegicus), black rats (R. rattus) and the indistinct Asian house rat (R. tanezumi) exist sympatrically. DNA sequencing of the cytochrome b and D-loop regions of the mitochondrion were used in conjunction with karyotyping of bone marrow and tissue culture cells to analyse the genetic diversity of selected Rattus populations from KwaZulu-Natal. Comparison of sequence data obtained during the study to reference sequences obtained from the NCBI GenBank revealed three well-supported monophyletic groups in maximum parsimony and Bayesian analyses. These three monophyletic groups indicated the existence of three species of the Rattus complex within KwaZulu-Natal, namely Rattus rattus, Rattus norvegicus and Rattus tanezumi. Analysis of cytochrome b sequence data revealed the presence of 6, 3 and 2 haplotypes in 20 R. norvegicus, 8 R. rattus and 5 R. tanezumi specimens, respectively. The R. norvegicus haplotypes were separated from R. rattus and R. tanezumi haplotypes by 60 mutational steps, while R. rattus haplotypes were separated from R. tanezumi haplotypes by 24 mutational steps. Analysis of D-loop sequence data revealed the presence of 6, 2 and 1 haplotypes in 14 R. norvegicus, 4 R. rattus and 3 R. tanezumi specimens, respectively. R. norvegicus haplotypes were separated from R. rattus and R. tanezumi haplotypes by 15 mutational steps, while R. rattus haplotypes were separated from R. tanezumi haplotypes by 11 mutational steps. Karyotype analysis of specimens revealed that: (1) R. rattus specimens sampled presented with a karyotype of either 2n = 38 or 2n = 40; (2) R. tanezumi specimens sampled presented with a karyotype of 2n = 42 and (3) R. norvegicus specimens sampled presented with a karyotype of 2n = 42 which was very distinct from that of R. tanezumi.