No suggestion of hybridization between the vulnerable black-faced impala (Aepyceros melampus petersi) and the common impala (A. m. melampus) in Etosha National Park, Namibia

Abstract

There are two recognized subspecies of impala in sub-Saharan Africa: the common impala (Aepyceros melampus melampus) -- widespread in southern and east Africa -- and the vulnerable black-faced impala (A. m. petersi) -- found naturally in only a small enclave in southwest Africa. The Etosha National Park (NP) in Namibia harbours the largest and only protected-area population of black-faced impala, numbering some 1500 individuals. Due to translocations of the exotic common impala to commercial farms in Namibia during the past decades, the black-faced impala in Etosha is faced with the potentially serious threat of hybridization posed by secondary contact with the common impala inhabiting bordering farms. Using eight microsatellite DNA markers, we analysed 127 black-faced impala individuals from the five subpopulations in Etosha NP, to determine the degree, if any, of hybridization within the park. We found that (a) the black-faced impala were highly genetically differentiated from the common impala (pairwise theta-values ranged from 0.18 to 0.39 between subspecies; overall value = 0.27) and (b) black-faced samples showed high levels of genetic variability [average expected heterozygosity (H(E)) = 0.61 +/- 0.01 SE], although not as high as that observed in the common impala (average H(E) = 0.69 +/- 0.02 SE). (c) No hybridization between the subspecies in Etosha was suggested. A Bayesian Markov Chain Monte Carlo approach revealed clear distinction of individuals into groups according to their subspecies of origin, with a zero level of 'genetic admixture' among subspecies.