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Genetic pollution

23 November 2012

Sustainable wildlife production and use in South Africa following clear conservation principles have been recognized as legitimate forms of conservation by the IUCN and consequently have deflected pressure of animal rights groups from the South African wildlife industry. However, actions purely for financial gain have recently emerged which could jeopardise this benefit because they ignore such conservation principles. This involves breeding aberrant colour variations and hybridizing wildlife to produce animals with specific traits. Moreover, many professional hunters are not interested in hunting artificially colour variants and hybrids that are being bred artificially and this is becoming an economic factor that should be considered. The question of colour variants has already been addressed earlier and only genetic pollution by the hybridization of ecotypes, subspecies and species will be dealt with here.

A species is a basic unit of biological classification and was historically recognized when all the members of a group of organisms differed morphologically in at least one characteristic from all the members of another one. All the members of a particular species are related to a common ancestor, interbreed and produce fertile offspring. More recently, differences in the genetic frequencies of DNA, known as genetic fingerprinting, have refined the concept of a species although there is still much debate about an all-inclusive definition of it. It is now agreed that members of the same species have a high degree of genetic similarity despite having infinite minor variations which make them adaptable as ecotypes to local differences in their environment. In the wild, related species are prevented from hybridizing by social behaviour and by geographic and genetic isolation. Consequently, defining a species involves a mixture of difficult but related aspects.

Geneticists are still developing the species concept and recently micro-RNA (short molecules) have already shown new relationships between higher taxonomic groups. Through similar DNA sequencing and lack of divergence it is still possible that the members of two different species can interbreed unless their geographic isolation has already created larger genetic differences over a long time. Unless there is regular genetic interchange it is also possible for individual herds of wildlife to develop into genetic species without showing obvious morphological differences on a wildlife ranch where the herds are isolated from contact with other genetic material over a long time. It is known that genetic species occur most commonly in isolated bat and rodent communities but genetic species have already been recorded in two large herbivore genera including the genus Kobus which includes the waterbuck, puku and sitatunga.

Genetic pollution occurs when two species, subspecies or ecotypes are mixed artificially. Even on the species level it is possible that hybridization can occur when the social structure of a breeding herd is incomplete. For example, a breeding herd of the rare giant sable antelope was recently relocated to another area to establish a new breeding population in Angola. However, hybridization with a roan antelope bull occurred because the sable antelope herd did not contain at least one adult sable antelope bull. Moreover because they are closely related the offspring were fertile. Another example is hybridization between the blue and black wildebeest under similar circumstances. It is therefore essential that complete social units be involved when any wildlife ranch is to be stocked with breeding herds of new species and that existing herds which may possibly be vulnerable to hybridization must be complete social units.

When populations occur in isolation, there is always the danger of a loss of genetic heterogeneity which can cause additional problems. For example, Cape mountain zebra populations that originate from small founding herds are prone to develop sarcoid tumour-like growths which do not occur in herds with a greater genetic heterogeneity. Aberrant and genetically homogeneous melanistic animals are also more prone to develop a whole range of diseases than normally coloured ones.

Different subspecies develop over time within species when populations become geographically and consequently reproductively and genetically isolated. Historically, subspecies were recognized when 75 percent of the members of one population differed morphologically from 75 per cent of a related one. Differences in DNA sequencing are now being used to differentiate between subspecies. For example, 13 genetic markers (alleles) were recently used to differentiate between the closely related bontebok and blesbok but genetic pollution with blesbok genetic material has now already contaminated most of the bontebok herds in their historical range in the Western Cape province because the blesbok and bontebok will readily interbreed and lose their genetic differences when they are kept together. When a rare subspecies such as the bontebok is present on a wildlife ranch it makes financial and common sense to preserve its genetic integrity.

Unfortunately the indiscriminate importation of different subspecies into South Africa has already polluted much of the wildlife on wildlife ranches genetically, leaving only conservation areas as sources of pure genetic material in many cases. For example, it is now also known that at least the subspecies of our southern springbok, roan antelope, Cape eland and sable antelope are at least in part already hybridised. The springbok of the interior southern regions of South Africa has been hybridized with the Kalahari springbok which is a different subspecies in an effort to increase its size, the roan antelope with stock from West Africa and Malawi, the sable antelope with stock from East Africa and the Western Zambian ecotype, and the Cape eland with the subspecies representing Livingstone’s eland. All this was done to create herds of “better” animals for financial gain. In some cases there may be no or only a few pure herds outside conservation areas any more. Consequently, wildlife with proof of genetic purity should rather be purchased on wildlife auctions or privately.

Ecotypes represent a lower taxonomic class than subspecies and are populations that become genetically adapted to localized and often specific environments. They will lose these adaptations when they are introduced elsewhere and interbreed with other types of the same species or subspecies. The west Zambian sable antelope, for example, is of the same subspecies as our southern sable antelope yet it has already adapted genetically with resultant morphological differences to a different environment in western Zambia. It may well eventually become a separate subspecies there unless it is genetically polluted their by artificial means.

All the indications are that the indiscriminate introduction of wildlife to South Africa and the resultant genetic pollution will eventually do more harm than good. It may also well rob the South African wildlife industry of natural resources of local and even rare genetic variations that could be an exceptional benefit. Moreover, it will cause the loss of a conservation image that could expose the wildlife industry to aggressive animal rights movements in the future. The overall need for sound genetic management following conservation principles is therefore obvious.

 

References:

Anon. 2011. Die bontebok in ere herstel. News release, June. Kimberley: Northern Cape Bontebok Breeders.

Baker, R J and R D Bradley 2006. Speciation in mammals and the genetic species concept. Journal of Mammalogy 87(4): 643 - 662.

IUCN 2009. Outstanding rescue of the giant sable antelope. IUCN News, 4 September. http://www.iucn.org/about/programmes/species/about/species/specialist/group

Jansen van Vuuren, B, T J Robinson, P VazPinto, R Estes and C A Matthee 2010. Western Zambian sable: are they a geographic extension of the giant sable antelope? South African Journal of Wildlife Research 40(1): 35 - 42.

By: Prof J du P Bothma

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