Molecular phylogeography and evolutionary history of the greater kudu (Tragelaphus strepsiceros)

Abstract

The greater kudu (Tragelaphus strepsiceros) is a large spiral-horned antelope that occurs in sub-Saharan Africa. The species is predominantly a browser and inhabits a diverse range of habitats including savanna woodland, scrub and open forests. The geographical distribution extends from south-eastern Chad, northern Central African Republic (CAR), through eastern Africa, to southern Africa. Throughout its range the species is threatened by habitat loss, fragmentation, diseases and hunting for trophy. Consequently, many populations have reduced numbers and are at great risk of local extinction. In the absence of evidence from comprehensive studies, strategies for conservation and management of many species are often based on subspecies designations despite the fact that the original descriptions were based on few samples and morphological characters that vary extensively. To develop appropriate conservation and management measures, it is imperative to obtain information on population structure, historical demography and evolutionary history of the species. The information generated is used to define units for conservation of the species. In this study, the objective was to investigate population structure and evolutionary history of the greater kudu by analysing mitochondrial DNA (mtDNA) control region sequences and examining size variation in eight microsatellite loci. The mtDNA control region sequences were examined using a combined approach that included phylogeographic, nested clade and mismatch frequency distribution analyses. It was anticipated that use of the two types of genetic markers with contrasting patterns of inheritance and mutation would enhance the understanding and interpretation of the evolutionary history of the species throughout its range. The results were used to evaluate subspecies taxonomy, draw inferences on historical demography and provide information relevant for conservation and management of T. strepsiceros. Intraspecific variation in the mtDNA was examined in 94 samples from 12 locations and revealed low to medium levels of nucleotide diversity. The average nucleotide diversity was 2.7% (0.3% to 2.9%). The average sequence divergence between populations was 2.3% (0.0% to 5.7%). Eight microsatellite loci were analysed in 203 samples representing 13 locations. The number of alleles scored from these loci was 7-12 while the mean heterozygosity was 70.4% (66% to 76%). Microsatellite data showed shallow phylogeographic structure and the average measure of genetic differentiation <1>ST was 0.046. Comparisons of allelic variation across all populations revealed that the Eastern Cape had lower allelic diversity and showed significant differences in allele frequency distribution suggesting a genetic bottleneck in the population's evolutionary past. The combined analyses suggest that the greater kudu originated from Namibia and spread southwards before colonising other parts of its modern range. The results revealed weak geographic partitioning at the regional level, but showed two genetically distinct groups at the continental level. The first group comprised of populations from Namibia, Kimberley and the Eastern Cape from South Africa, while the second comprised of the remaining populations. The results suggest a single evolutionary significant unit (ESU) with two management units (MUs). In the long term, conservation efforts should focus on maintaining demographic connectivity over broad geographical areas within each MU in order to approximate the natural dispersal patterns of the species.