Genetic Structure of Hartebeest Populations Straddling a Transition Zone between Morphotypes

Variation in mitochondrial and microsatellite DNA was used to define the genetic structure of hartebeest populations straddling a transition zone between two morphotypes (Alcelaphus buselaphus cokei and A. b. lelwel) in Kenya. Previous analyses of mtDNA from hartebeest populations across Africa supported the refugium hypothesis; that present day hartebeest morphotypes diverged in allopatry, due to climatic changes. In this analysis of morphologically distinct populations in close geographical proximity, majority of genetic variation was found within populations, with relatively little distinction, and varying levels of subdivision, among populations. Patterns of shared alleles, and reduced tendency for mtDNA haplotypes to cluster phylogenetically according to morphotype, depicted gene flow between populations. There was sharp disparity between apparently seamless genetic transition between populations and marked disjunction in gross morphology over short distances (<100km). Hartebeest in the transitional zone between A. b. lelwel and A. b. cokei, including populations in Ruma, Meru National Parks and Laikipia, are the only remaining examples, each genetically and morphologically different from the other, of what appears to be resumed contact between two lineages that diverged in allopatry. Our results underscore the importance of using genetic and morphological information to explicitly define evolutionary processes as targets for conservation in Africa