Mitochondrial DNA variability and geographic population structure in Pronolagus rupestris and P. randensis (Mammalia: Lagomorpha)

Abstract

Phylogeographic mitochondrial DNA (mtDNA) population structure was determined for Pronolagus rupestris and P. randensis, two species of red rock rabbit occurring in South Africa. The study revealed that P. randensis mtDNA patterns reflect phylogenetic continuity with partial spatial separation between populations, although this should be viewed with caution given the limited distributional range covered by the investigation. Eleven composite haplotypes were found in the 27 P. randensis specimens sampled. The relatively low sequence diversity of 0.74% (±0.21 %) was interpreted as reflecting limited intraspecific variation within the taxon, and is thought to be indicative of fairly recent range expansion. In the eastern Transvaal (Blyderivierspoort Nature Reserve) P. rupestris and P. randensis are found approximately 15 kilometers apart. No distributional overlap was detected even though extensive geographic sampling was undertaken in the presumed contact zone, a pattern which is thought to reflect competitive exclusion. An interesting observation was that previously documented mtDNA phylogeographic patterns recorded in the rock hyrax, Procavia capensis, coincide with the observed zone of contact between P. rupestris and P. randensis. The rock hyrax is a mammalian species of comparable body size which occurs sympatrically with Prono/agus and is similarly limited to outcrops of rock in the form of krantzes, rocky koppies or rocky hillsides. It is argued that similar vicariant events may have been implicated in shaping the evolutionary processes in these independent lineages. This hypothesis may hold for not only the taxa surveyed in this investigation, but for other mammal species with similar habitat and dispersal capabilities. The 55 P. rupestris specimens sampled showed pronounced intraspecific genetic structure with two well defined, virtually geographically contiguous clades; one situated in the north western Cape Province while the other follows the Great Escarpment extending along the southern and eastern seaboard of South Africa. These mitochondrially distinct clades were separated by 7.94% (±1 .40%) sequence divergence, a relatively high value which is thought to reflect inaccuracies in the currently accepted taxonomy of P. rupestris. The phylogeographic profiles of the two P. rupestris clades differ markedly from each other. The north western clades' matrilines are separated by few mutational steps between isolated populations, while those of the south eastern clade are characterized by deep divisions. Disruptive extrinsic factors between the two assemblages could not be identified and the clade specificity of the mtDNA haplotypes is thought to be due to competitive habitat exclusion and possibly the inability of the representatives of the two clades to interbreed.