Hybridisation

Liger which is bred from a male lion and a female tiger; b – Mule which is bred from a male donkey and female horse; c – Zedonk/Zonkey which is bred from a zebra and a donkey

Unfortunately, people want to manipulate and interfere with nature and in doing so have come up with a few hybrid animals which would not have formed under natural circumstances. In the Figure above, three examples of such hybrids are shown. These are unnatural hybrids which only occur through human manipulation. It is important to steer away from such practices and to protect the natural genetic integrity of every species.

For healthy population growth to occur, a genetically viable population is essential. Wild herbivores appear to be less susceptible to inbreeding than domesticated ones because they are genetically more heterogeneous. Many cases are known where large populations of wild animals have been built up from small herds or a few individual animals that were established in an area. When dealing with vulnerable or small populations, the first objective should be to increase the population size and thereby enlarge the genetic pool. However, it remains sound policy to obtain breeding males from another genetic source from time to time, especially when all the animals available are from the same local genetic stock. It will also prevent the development of numerous localised genetic species or subspecies.

Wildlife-proof fences prevent the free exchange of genetic material between large herbivores on bordering or neighbouring wildlife ranches. Therefore, it would be advantageous for the owners of neighbouring ranches to exchange healthy breeding animals from time to time to prevent inbreeding depression in their herds. A further option is to remove the fence between adjacent ranches to form conservancies where the natural genetic exchange will occur within larger and more viable populations.

Individual members of genetically poor herds may display noticeable physical defects, or the herd will not produce sufficient healthy young. Inbreeding is also harmful to the fertility of the surviving animals and the vitality of the young animals. Any irregular individuals, such as those with thin or twisted horns or other defects, should be removed from the breeding herd immediately.

A sound economic and genetic rule is rather to obtain animals from the available local stock than import them at great expense from distant places. Apart from the genetic implications, losses in animals that are kept in captivity for a long time or are transported over long distances can be unacceptably high.

A common example of hybridisation is the mule which originates from a horse and a donkey

Even hybrids of the same genus like Kobus are now known to produce fertile hybrids. Genetically, all three forms of the springbok are also of the same species, but there are three distinct subspecies. The springbok, Antidorcas marsupialis angolensis, from Angola, is generally small and light in weight. The springbok, Antidorcas marsupialis marsupialis, from the Karoo, the Free State and the south-western North West provinces are slightly larger and heavier than those from Angola, with a shoulder height of approximately 0.76 m. The springbok, Antidorcas marsupialis hofmeyri, from Limpopo, the Northern Cape, Botswana and Namibia is much larger and heavier than the rest with a shoulder height of up to 0.87 m. They also have the longest horns, especially those from the Swakopmund area. These subspecies should never be mixed in the same population on a wildlife ranch.

From left to right, top to bottom. a – Antidorcas marsupialis angolensis; b – Antidorcas marsupialis marsupialis; c – Antidorcas marsupialis hofmeyri

Black springbok and white springbok are two colour variants that may occur in any population, and they are not distinct subspecies. Nevertheless, they should be left to occur naturally and should not be produced selectively. When bred selectively, these species arise from a very limited gene pool, have less resistance to environmental pressures and are more prone to sickness or mutations. In nature, the springbok colourations are specifically designed in such a manner as to help camouflage the animal in the wild. When looking at the white springbok, stands out significantly among its natural habitat and will be more prone to predation as predators can target the individual among the group.

Black and white springbok are colour variants which can arise naturally, however specifically selecting and breeding for them are not advised

Wild animals will also hybridise on a wildlife ranch when the area is too small and minimum herd sizes are not maintained. The following are known or possible hybrids between wild animals:

• Fertile hybrids:
  • Bontebok and blesbok.
  • Blue wildebeest and black wildebeest.
  • African cat and domesticated cat.
• Infertile hybrids:
  • Tsessebe and blesbok.
  • Red hartebeest and blesbok.
  • Roan antelope and sable antelope.
  • Eland and greater Kudu.
  • Black rhinoceros and white rhinoceros.
  • Hartmann’s Mountain Zebra and donkey.
• Possible hybrids:
  • Burchell’s Zebra and Cape Mountain Zebra.
  • African savanna buffalo and Indian water buffalo.

Biologists know on scientific grounds that closely related animal species or subspecies that are separated geographically develop unique genetic, physiological and anatomical adaptations over time. The blesbok, for example, has unique alleles that do not exist in the bontebok. This is a natural process. Consequently, they should not be allowed to crossbreed to ensure that these unique characteristics may be maintained.

The bontebok is classified as a vulnerable species and is one of the rarest antelope species in South Africa. Protection of this limited gene pool is therefore of utmost importance. Genetically pure bontebok is a very valuable commodity and should be preserved as best as possible and never be allowed to be mixed with blesbok on the same wildlife reserve. The bontebok and blesbok hybrid is of little value other than for meat production.

Examples of animals that have to remain isolated from each other are:

• The black-faced Impala and the common Impala.
• The giant sable antelope and southern sable antelope.
• The West African roan antelope and the Southern roan antelope.
• The northern white rhinoceros and the southern white rhinoceros.
• The blesbok and the bontebok.
• The ostriches from northern and southern Africa.

Irresponsible crossbreeding can cause economic and ecological losses, especially for trophy hunting. The Environment Management: Biodiversity Act (Act No. 10 of 2004) prohibits the introduction of animals to areas where they did not occur historically. This should prevent the hybridisation of closely related but ecologically distinct types of wildlife.

 

Hybridisation of Ecotypes

a – Tragelaphus oryx; b – Tragelaphus oryx livingstonii with more distinct vertical stripes

Ecotypes often produce fertile offspring, and several wildlife ranchers can form a breeding group to keep certain ecotypes pure. This can be done in the same way as the sturdy groups that are functioning in agriculture. Examples are the Cape eland and Livingstone’s eland, the Karoo springbok and the Kalahari springbok. The hybridisation of ecotypes is sometimes a fad but in the case of the eland, certain wildlife producers in the Bushveld use Livingstone’s eland bulls to breed with Cape eland cows. Livingstone’s eland is more resistant to heartwater infections from the Amblyomma tick than the Cape eland. In the case of the springbok, the Kalahari springbok rams are used to breed with the smaller Karoo springbok ewes. This is a practice that is being done to improve meat production. These are just for functional reasons and the animals are usually harvested for meat. It is strongly recommended that wildlife ranchers form breeding clubs to conserve pure genetic lines. This can be achieved by selecting animals based on closely related individuals following genetically tested results. However, producers must also be aware that this practice can lead to inbreeding and the loss of genetic fitness if new genetic material is not introduced from time to time. The practice of breeding clubs will fall under extensive wildlife production and that of functional breeding for meat production or tick resistance under intensive wildlife production.

Breeding clubs can also function to breed animals with phenotypical features that represent animals that have already become extinct. For example, the breeding of quagga Equus quagga look-alikes from Burchell’s zebra has only a few stripes on the hindquarters. Researchers also recognise four distinct subspecies of the sable antelope Hippotragus niger. These are Hippotragus niger kikkii from south-eastern Kenya and eastern Tanzania, Hippotragus niger niger from southern Africa, and Hippotragus niger variani from a severely limited area of Angola. Then there is another subspecies, Hippotragus niger anselli, which is found in eastern Zambia and Malawi to south-eastern Tanzania. However, this specific classification is based generally on a restricted geographical sampling of only a few specimens and single morphological characters which are subject to extensive individual variation. Reports indicate that the giant sable antelope population in Angola is small and that can hybridise with roan antelope, therefore Zambian sable antelope with the same facial marks as the giant sable antelope can be used to breed giant sable antelope look-alikes.

Hybridisation between the black wildebeest, Connochaetes gnou, and blue wildebeest, Connochaetes taurinus, has occurred at numerous locations across South Africa and the genetic integrity of both species is at high risk. Potentially a significant percentage of the black wildebeest population carries a proportion of introgressed blue wildebeest genetic material. These hybrid species are difficult to detect based on hybrid phenotypic characteristics and become increasingly more difficult to detect with F2 and further generations.

In 1995 in the Spioenkop Nature Reserve, KwaZulu-Natal, two suspected hybrid individuals were shot to prevent further hybridisation. However, upon closer inspection, a significant proportion of the population displayed some sort of hybrid characteristics suggesting hybridisation beyond the F2 generation. To ensure genetically pure animals and the conservation of the black wildebeest species, the entire herd was culled to prevent further contamination and spread of the hybrids.

A government policy was later implemented to prevent the translocation of either species which originates from properties where both species occurred. This was done to limit the potential risk of importing hybrid animals into a new area. Sadly, even the populations which are declared to be pure black wildebeest are questionable as entire black wildebeest populations of southern Africa potentially contain a significant proportion of introgressed blue wildebeest genetic material.

The skulls of a male blue wildebeest (a) and a male black wildebeest (c), compared to a hybrid male skull (b), recovered from a private game farm in the Free State Province by SVand JSB. Although the hybrid specimen shows almost perfect intermediate morphology between black and blue wildebeest, hybrid morphology varies considerably, with pathologies commonly observed. (Source: Modified after Brink 2005)

Four male wildebeest specimens (Connochaetes taurinus x C. gnou) from South Africa, demonstrating the range of morphological variation in cranial and horn morphology of wildebeest hybrids, including both size and shape variation (South African Journal of Science Vol.106 n.11-12 Nov./Dec. 2010)

 

Practical Genetic Management of Wildlife

Wildlife ranchers are responsible for the practical genetic management of wildlife on their reserve

 

Wildlife ranchers should keep only those wild animals that are ecologically adapted to their region and that are known to have occurred historically in that region. This will ensure that competition between ecologically equivalent animals is eliminated, for example between the sable antelope and the gemsbok. The aim should also be to keep healthy breeding herds to satisfy all the social requirements of the animals. Genetic impoverishment is difficult to determine in wild animals because of the strong tendency towards natural selection. It is recommended that when wild animals are utilised commercially and there are fewer than 50 breeding animals on a wildlife ranch, the percentage of males that are removed annually or biannually should be replaced by the same number of local males, but from unrelated herds.

Wildlife ranchers should also preferably re-establish complete breeding herds instead of fragmented ones or parcels of unrelated individuals because it can take some time for new social groupings to form. In doing so, they should therefore avoid buying odd parcels at live wildlife auctions. For example, rather buy a herd of 10 sables from the same herd than buy two sable antelope each from five different sources. A single individual of any type of animal that occurs on a wildlife ranch should be removed. For example, one tsessebe bull on a ranch with 100 blesbok is a clear recipe for hybridisation, especially when the single animal is a bull of an anatomically stronger type of herbivore.

In rarer animals, such as the sable antelope, which are hunted for their trophy value, the trophies should only be taken from the bachelor or male herds, but not from herd bulls that are temporarily recuperating there. Whenever possible, the population growth of all the wild animals should be calculated during annual counts. If the rate of growth, or population increase, is inadequate, a few males should be culled from the breeding herds. For example, a growth rate of at least 5% is required for Burchell’s zebra because infertile stallions can decrease the overall population growth rate by appropriating the fertile mares without producing offspring.

Genetic management recommendations to prevent hybridisation between species:

• No property should be permitted to contain two species which could interbreed and form hybrid species. Neighbouring farms should also be considered to avoid animals possibly escaping through the fence and mating with the other species.
• Suspected hybrid herds should be adequately fenced in and regularly inspected by the authorities. Until reliable genetic testing has been completed to rule out hybrid genes, no live offtake should be permitted from such a herd.
• If a herd is confirmed to contain hybrid alleles, the owner or rancher is advised to remove the entire herd through hunting or culling. Government intervention might be available to compensate for farmers who have legally acquired both species before hybridisation potential was discovered.
• The limited pure populations should be registered and strict measures should be implemented to manage the introduction of new animals or the translocation of these animals to new areas with potential hybridisation risks. Record-keeping and permit systems need to be in place.
• In government-protected areas or locations where there is a possibility of hybridisation occurring or where hybrid animals may have been introduced, no animals may be taken out alive.
• Proper record systems need to be implemented to regulate the ownership and translocation of such species.
• The exportation of genetically tainted herds to neighbouring countries should be monitored and managed to prevent hybrid or potential hybrid species from being exported.
• There needs to be improved oversight and regulation of game capture operations which operate illegally by issuing transportation permits without making sure that the animals do not come into contact with potential hybrid species at the new location or the genetic integrity of the animals which are being moved.