Restriction patterns of mitochondrial DNA in natural populations of the murid species Otomys irroratus.

Abstract

Mitochondrial DNA (mtDNA) was isolated from 8 different natural populations of the rodent species Otomys irroratus (Muridae: Otomyinae) and from one population of the species 0. angoniensis occurring in South Africa. MtDNA samples were cleaved with five different restriction endonucleases, end-labelled with phosphorous-32, separated by electrophoresis on horizontal 1 % agarose gels and the resulting fragment bands were detected by autoradiography. The individual-specific fragment banding patterns were analysed and compared among the various populations. The percent sequence divergence among and between the populations was calculated using the formula of Nei (1979). A matrix of sequence divergence values for all intergenomic pairwise comparisons was subjected to a clustering analysis by the unweighted pair group method with arithmetic means (UPGMA, Sneath and Sokal, 1973), using the computer programme NTSYS (Rohlf: 1988). The results of these analyses allowed for a preliminary identification of phenetic groupings in the data set. A matrix generated by scoring the restriction endonuclease fragments as present or absent was used to generate a phylogenetic dendogram using the BIOSYS (Swofford and Selander, 1989) programme. The overall restriction fragment variation uncovered in this study revealed 15 different mtDNA haplotypes within the 20 individuals examined. This corresponded to a high degree of polymorphism in the populations where more than one specimen was available, as well as within the species 0. irroratus. There were no clones that were shared between any of the populations sampled. The intrapopulation sequence divergence values uncovered in this study were high (range 0.35 % to 5.08 %), but also consistent with some other reports in the literature for intrapopulation variation. The outgroup, 0. angoniensis revealed the highest divergence values when compared to the mtDNA clones found in 0. irroratus. The phenetic and cladistic cluster diagrams revealed overall similarity with one another. There appeared to be little correlation between the topology of the mtDNA haplotype phenograms and the geographic distance of the sample localities. There was, however, a marked congruence between the distribution of mtDNA haplotypes and the distribution of three distinct cytotypes occurring over the species range. A possible polyphyletic evolution of populations of 0. irroratus was inferred from the cladistic analysis.