Comparative population genetics of the German shepherd dog in South Africa

Introduction Mitochondrial (mt) DNA analyses have suggested that dogs and wolves diverged in multiple events over 100 000 years ago, with a possible east Asian origin. The movement of humans and their dogs resulted in extensive gene flow between domestic dog populations for many thousands of years with further mtDNA analysis revealing that dogs display a high degree of polymorphism that is neither breed-specific nor defined by geographical distribution. Modern breeding practices, however, strive to achieve distinctive phenotypic uniformity with purebred dogs becoming essentially closed gene pools. In spite of these practices, unexpectedly high levels of variability have been reported within several breeds of dogs, probably due to the heterogeneous outbred nature of the founding individuals, the relatively recent origin of many breeds of dogs or possible crossbreeding events, as occurred during the formation of different coat types in the Dachshund. The ancestors of the German shepherd dog can be traced back to an assorted collection of dogs used to herd and guard flocks of sheep in 19th century Germany. The breed received official recognition in 1899 with the establishment of the Verein für Deutsche Schäferhunde (S.V. or Club for German Shepherd dogs). The first dog registered with this organisation, Horand von Grafrath, was the founding sire of the breed and bitches were sought that would ‘complement his conformation, temperament and utilitarian type’ in order to achieve the characteristics specific to the breed. The S.V. controlled and directed breeding by exercising authority over which dogs and bitches could be bred and which offspring could be kept and raised from each litter, with extensive inbreeding utilised during the formation of the breed. German shepherd dogs were used by both the German military and the Red Cross during World War I, and at the end of the war servicemen from America and Europe returned home with stories of these dogs, popularising the breed in many countries. During the last 100 years, Breed Clubs affiliated to the S.V. have been established in more than 67 countries and over two million dogs have been registered to date in Germany alone, with 20 000 puppies being registered every year (Verein für Deutsche Schäferhunde; online at: https://www. schaeferhunde.de/site/index.php?id=431 (accessed 25 January 2007)). The German shepherd dog has remained one of the most popular breeds of dog, both as a companion dog and for the socio-economic function it fulfils as a versatile working dog. German shepherd dogs were introduced to South Africa with the first dog registered with the Kennel Union of Southern Africa in 1913; the population remained relatively small, with just 43 dogs registered between 1916 and 1919 (pers. comm. M. Darwin, Kennel Union of Southern Africa). We have investigated the impact that this founder event, and the subsequent population bottleneck with its associated inbreeding and genetic drift, has had on the genetic diversity exhibited by South African-bred German shepherd dogs. We have also addressed whether there has been sufficient gene flow, resulting from the recent extensive importation of breeding stock from the ancestral German population, to mitigate these detrimental effects on genetic diversity. Low levels of genetic diversity and minimal gene flow between isolated populations are considered to be significant factors contributing towards the many genetic diseases commonly expressed in purebred dogs and these data have been quantified by comparison with typically outbred mongrel or crossbred dogs that rarely express such traits.