Cross-species microsatellite markers for the detection of hybrids in the genus connochaetes
Black wildebeest (Connochaetes gnou), a species endemic to South Africa, experienced two bottlenecks in the last century and the number of animals ultimately decreased to approximately 300. These bottlenecks led to a decrease in the genetic diversity of black wildebeest populations across South Africa. An additional threat to the genetic integrity of the black wildebeest was discovered between the 1960s and late 1980s, when researchers noted that hybridization between blue and black wildebeest occurs and that these hybrid animals are fertile. Identification of the hybrid individuals is crucial and various molecular techniques were researched, with microsatellite markers proving to be the most successful. The aim of the current study was to investigate the effectiveness of previously identified cross-species microsatellite markers and statistical approaches for the identification of hybrid herds and individuals on various Nature Reserves in the Free State Province as well as privately owned game farms in and around the Province. Two previously identified diagnostic microsatellite markers (BM1824 and ETH10) were used to screen the populations for putative hybrids. The genetic diversity of the black wildebeest populations studied supported earlier findings showing lower genetic diversity in black wildebeest compared to blue wildebeest. The addition of new reference material in the current study revealed that some of the alleles previously assumed to be unique to a specific species were in fact shared between the two species. This reinforced the need to use more reference populations of adequate size. Nominally blue wildebeest alleles were found in five populations on different game farms and Nature Reserves. The presence of these alleles could be an indication that hybrids are present at these localities or alternatively, support the finding that the number and distribution of reference populations should be increased. Assignment of populations to specific clusters using different software programmes revealed that, due to the large amount of genetic material shared between blue and black wildebeest, no clear assignment of individuals to a specific cluster could be obtained. Molecular analysis of two known hybrid animals did indicate that the two microsatellite markers chosen were able to identify first generation hybrids and possibly even second generation hybrids. The study also investigated the persistence of introgression of blue wildebeest genetic material into black wildebeest populations using simulation software. The simulation tests revealed that introgressed alleles could still be detected after ten generations of backcrossing. This has serious implications for the management of hybrid populations. Various recommendations can be made in terms of the future management and conservation of black wildebeest on Nature Reserves and game farms. The most practical approach for dealing with hybrid animals would first be to develop additional molecular techniques for the accurate identification of populations that contain hybrid animals. Positively identified hybrid populations should be kept separate and no introductions of these animals should be made into pure populations. A more drastic approach would be to cull animals with hybrid ancestry. This would however have serious implications on the already reduced level of genetic diversity in the black wildebeest populations. The most pragmatic approach for dealing with hybrid populations would be to keep pure blue and black wildebeest in protected areas and allow black wildebeest with moderate introgression on game ranches exclusively used for sport hunting.
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