Rhino genetics are characterised by small populations and genetic bottlenecks. Efforts to conserve genetic diversity aim to slow down the inevitable extinction rate of certain subspecies. Every rhino in the world is being threatened by large-scale poaching, as a result of the misconception in Asia that the animal’s horns have medicinal value.
Rhino are classified with horses and zebras under the order Perissodactyla – animals with an odd number of toes. Horses and zebras have one toe, while rhino have three. Furthermore, rhinos are classified in the family Rhinoceroses, under which five species and several subspecies are found worldwide.
Approximately 3 500 single-horned rhinos (Rhinoceros unicornis) are found in India and Nepal, while the Javanese (Rhinoceros sondaicus) and Sumatran rhino (Dicerorhinus sumatrensis) – with around 100 animals remaining each – are classified as critically endangered.
In South Africa, two rhino species are found, namely the white rhino (Ceratotherium simum) and the black rhino (Diceros bicornis). Although approximately 20 000 white rhinos are found in Southern Africa. Their Convention on International Trade in Endangered Species (Cites) status is “near threatened” as a result of large-scale poaching for their horns.
The roughly 5 000 black rhinos in Africa, however, are classified as “critically endangered”. According to fossil records, the Ceratotherium and Diceros species diverged seven million years ago. There are currently three black rhinos and two white rhino subspecies.
In 1969 there were an estimated 65 000 black rhinos in Africa. However, the population declined by 96% over the next 25 years, until there were only 2 475 left in 1993. Their numbers increased again until there were 4 880 by 2010. Currently there are only approximately 5 000 severely endangered black rhinos remaining on the continent. They are found in South Africa (±1 900), Namibia (±1 750), Kenya (±600), Zimbabwe (±400) and Tanzania (±100).
In previous years, there was uncertainty about the black rhino subspecies. Seven subspecies of black rhino were originally described, but later only four subspecies were identified. Currently there are only three subspecies left, namely the Diceros bicornis minor (mainly in South Africa), Diceros bicornis bicornis (mainly in Namibia) and Diceros bicornis michaeli (mainly in Kenya). The fourth subspecies, Diceros bicornis longipes of Cameroon, became extinct in 2006.
Almost half of the remaining black rhino in Africa belong to the subspecies D. b. minor, of which most are found in South Africa. D. b. diceros are mainly found in Namibia, while approximately 500 D. b. michaeli are found in Kenya. Around six D. b. michaeli were found in the Addo Elephant National Park in the sixties, where they form a subpopulation of approximately 60 animals. It has never been their natural habitat, but they serve as an additional source of genetics. All three subspecies are found in several countries in Africa, as well as in zoos across the world.
Table 1: Number of black rhinoceros (Diceros bicornis) subspecies populations.
|Subspecies||Ecological region||Geographical region||Status||Number*|
|D. b. minor
D. b. bicornis
D. b. michaeli
D. b. longipes
|Mainly South Africa and Zimbabwe
Namibia and South Africa
Kenya, Tanzania and South Africa
Cameroon and possibly Chad
Most of the South African black rhino (Diceros bicornis minor) are descendants of approximately 110 black rhinos in the Hluhluwe-iMfolozi and Mkhuze nature reserves in KwaZulu-Natal in the 1930s, as well as a few rhino that were moved from Zimbabwe to the Kruger National Park.
The danger of small populations is that they can easily become extinct – for instance due to a natural disaster or if they are poached, but also because of inbreeding and the loss of genetic diversity. The only way of preventing a small group from becoming extinct, is to increase their numbers as rapidly as possible and to move them to other areas with a suitable habitat.
Since the 1960s and 70s, this was done with the Hluhluwe-iMfolozi and the Mkhuze black rhino, and more black rhino populations were established in parks in KwaZulu-Natal and elsewhere in South Africa. They are being managed as a meta population, and animals are exchanged to reduce inbreeding. The risk of extinction due to inbreeding or poaching can thereby be reduced.
Currently the South African D. b. minor black rhino populations are state- or privately owned. If some of these groups are threatened by extinction as a result of inbreeding, they can be supplemented by relatively unrelated animals from other groups.
Establishing different lines
It is rather complex to manage small populations. It is most important to attempt to establish different populations or lines and monitor them closely. If some of these populations show signs of decline due to inbreeding with low levels of fertility or weak calves, animals from other populations can be brought in.
Decline as a result of inbreeding can disappear completely in one generation by merely using unrelated animals as parents. By studying the deoxyribonucleic acid (DNA) of the different populations, it can be determined which specific animals can be exchanged between groups.
Genetic studies include the study of microsatellites, which are markers on the DNA of animals. If the markers are, for instance, largely the same, it means that there is not much genetic variety between the animals and their genetic diversity is low. If the markers are largely the same within populations, it can mean that the populations should remain separate and are regarded as subspecies.
If the groups are to remain genetically separated, it can lead to inbreeding within a group, which can cause inbreeding degeneration and possible extinction. The genetics of a small population, therefore, is no exact science, and can lead to difficult issues with different answers and opinions. There are also different opinions regarding the conservation of rhino.
Although most of the remaining black rhino belong to the subspecies D. b. minor, genetic microsatellite studies have shown that they exhibit the lowest levels of genetic diversity compared to the other black rhino subspecies. These low levels of genetic diversity have possibly been caused by a genetic bottleneck (almost all of them descendants of relatively small number of animals in a rather small geographical area), or else D. b. minor has historically always been genetically homogenous.
If they have historically exhibited low levels of genetic diversity – before they entered the genetic bottleneck – it should not affect them significantly. Historically, the other two subspecies (D. b. bicornis of Namibia and D. b. michaeli of Kenya) were found over much larger areas, and the higher levels of genetic diversity could merely be a reflection thereof.
Karsten and Associates are of the opinion that the genetic diversity of D. b. minor is no reason for concern, as it is in line with, and even higher than, the values of other large mammals in the same areas. Anderson-Lederer, however, also used mitochondrial DNA studies to look at genetic diversity, and their view is that there is reason for concern, as the black rhino in the Hluhluwe-iMfolozi park may be starting to show signs of inbreeding degradation because of a lower than desired reproduction rate.
There are two subspecies of white rhino, the more common southern white rhino (Ceratotherium simum ssp. simum) and the critically endangered northern white rhino (Ceratotherium simum ssp. cottoni).
The southern white rhino was originally widespread in the bushveld regions of Southern Africa, south of the Zambezi River. However, by the end of the 19th century, they almost became extinct when only one population of approximately 20 to 50 animals were left in KwaZulu-Natal.
By the end of 2010, after many years of protecting and moving the animals several times, the population grew to more than 20 000 animals, of which more than 90% are still found in South Africa. The southern white rhino is also found in Namibia, Kenya, Zimbabwe, Botswana and Swaziland, with only a few animals in other countries. Most of South Africa’s white rhino are found in the Kruger National Park, while around 25% were estimated to be privately owned in 2010.
Just like the black rhino, the southern white rhino came through a genetic bottleneck because, in reality, the 20 000 animals are all descendants of the 20 to 50 animals in KwaZulu-Natal. They are also threatened by large-scale poaching for their horns.
Although there were a few northern white rhinos in a park in the Democratic Republic of the Congo (DRC) a few years ago, they could not be traced since then and it is generally accepted that they died of natural causes.
In an article in a leading Public Library of Science (PLoS) journal in 2010, Colin Groves tried to argue that the northern white rhino subspecies should be declared a separate species to the southern white rhino. Other scientists disagreed with him, mainly because it is technically of academic interest. The northern white rhino is critically endangered and about to become extinct.
By November 2015 only three northern white rhino (a bull and two cows) were left. They belonged to the Dvůr Králové zoo in the Czech Republic, but were moved to the Ol Pajeta Conservancy in Kenya, where they are guarded by armed guards 24 hours a day. These rhinos are practically infertile and the problem is finding ways to preserve some of these northern white rhino genetics using special techniques.
Black market for rhino horn
Although rhino numbers have been increased successfully and are increasing in general due to continued conservation, the black market for rhino horn is a huge threat to their existence. At present, the southern white rhino is the most populous subspecies, with 20 000 found mainly in different populations in South Africa and neighbouring countries. The northern white rhino, however, is about to become extinct.
Black rhino numbers are considerably lower, with a total of approximately 5 000 animals. Three subspecies are still active – one mainly in South Africa with approximately half of the animals, one in Namibia with almost half of the animal numbers and the eastern black rhino in Kenya, with around 500 animals. The fourth subspecies became extinct as recently as 2006. There are populations of all three remaining subspecies in different countries – a fact that will hopefully ensure their conservation.
There are also organisations campaigning for the conservation of rhino. The University of Pretoria (UP) has collected the data of more than 15 000 rhinos and their DNA details on their Rhino DNA Index System (RhODIS) database, and this information is being used to arrest and convict poachers.
There are low levels of genetic diversity within D. b. minor, which is mainly found in South Africa, but the advantage is that the information is out there. The situation can be managed to ensure the survival of the rhino – despite the onslaught against them. – Helena Theron, SA Stud Book
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