Molecular Biology and Genetics
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The white rhinoceros or square-lipped rhinoceros (Ceratotherium simum) is the largest and most numerous species of rhinoceros that exists. It has a wide mouth used for grazing and is the most social of all rhino species. The white rhinoceros consists of two subspecies: the southern white rhinoceros, with an estimated 17,460 wild-living animals at the end of 2007 (IUCN 2008), and the much rarer northern white rhinoceros. The northern subspecies has very few remaining, with seven confirmed individuals left, with only four still able to reproduce (Including those in captivity).
A popular theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English. The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English. The word "wide" refers to the width of the rhinoceros' mouth. So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino. This suggests the origin of the word was before codification by Dutch writers. A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word wijd was ever used to describe the rhino outside of oral use. Other popular theories suggest the name comes from its wide appearance throughout Africa, its color due to wallowing in calcareous soil or bird droppings or because of the lighter colour of its horn.
An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros. The white rhinoceros' generic name, Ceratotherium, given by the zoologist John Edward Gray in 1868, is derived from the Greek terms keras (κερας) "horn" and therion (θηριον) "beast". Simum, is derived from the Greek term simus (σιμος), meaning "flat nosed".
Taxonomy and evolution
The white rhinoceros of today was said to be likely descended from Ceratotherium praecox which lived around 7 million years ago. Remains of this white rhino have been found at Langebaanweg near Cape Town. A review of fossil rhinos in Africa by Denis Geraads has however suggested that the species from Langebaanweg is of the genus Ceratotherium, but not Ceratotherium praecox as the type specimen of Ceratotherium praecox should, in fact, be Diceros praecox, as it shows closer affinities with the black rhinoceros Diceros bicornis. It has been suggested that the modern white rhino has a longer skull than Ceratotherium praecox to facilitate consumption of shorter grasses which resulted from the long term trend to drier conditions in Africa. However, if Ceratotherium praecox is in fact Diceros praecox, then the shorter skull could indicate a browsing species. Teeth of fossils assigned to Ceratotherium found at Makapansgat in South Africa were analysed for carbon isotopes and the researchers concluded that these animals consumed more than 30% browse in their diet, suggesting that these are not the fossils of the extant Ceratotherium simum which only eats grass. It is suggested that the real lineage of the white rhino should be; Ceratotherium neumayri → Ceratotherium mauritanicum → C. simum with the Langebaanweg rhinos being Ceratotherium sp. (as yet unnamed), with black rhinos being descended from C. neumayri via Diceros praecox.
Recently, an alternative scenario has been proposed under which the earliest African Ceratotherium is considered to be Ceratotherium efficax, known from the Late Pliocene of Ethiopia and the Early Pleistocene of Tanzania. This species is proposed to have been diversified into the Middle Pleistocene species C. mauritanicum in northern Africa, C. germanoafricanum in East Africa, and the extant C. simum. The first two of these are extinct, however, C. germanoafricanum is very similar to C. simum and has often been considered a fossil and ancestral subspecies to the latter. The study also doubts the ancestry of C. neumayri from the Miocene of southern Europe to the African species. It is likely that the ancestor of both the Black and the White rhinos was a mixed feeder, with the two lineages then specialising in browse and graze, respectively.
Southern white rhinoceros
There are two subspecies of white rhinos; the southern white rhinoceros (Ceratotherium simum simum) and the northern white rhinoceros. As of 31 December 2007, there were an estimated 17,460 southern white rhino in the wild (IUCN 2008), making them by far the most abundant subspecies of rhino in the world; the number of southern white rhinos outnumbers all other rhino species combined. South Africa is the stronghold for this subspecies (93.0%), conserving 16,255 individuals in the wild in 2007 (IUCN 2008). There are smaller reintroduced populations within the historical range of the species in Namibia, Botswana, Zimbabwe and Swaziland, while a small population survives in Mozambique. Populations have also been introduced outside of the former range of the species to Kenya, Uganda and Zambia.
Wild-caught southern whites will readily breed in captivity given appropriate amounts of space and food, as well as the presence of other female rhinos of breeding age. For instance, 91 calves have been born at the San Diego Zoo Safari Park since 1972. However, for reasons that are not currently understood, the rate of reproduction is extremely low among captive-born southern white females.
Northern white rhinoceros
The northern white rhinoceros, or northern square-lipped rhinoceros (Ceratotherium simum cottoni) is considered Critically Endangered or Extinct in the Wild. Formerly found in several countries in East and Central Africa south of the Sahara, this subspecies is a grazer in grasslands and savanna woodlands. In the world, there are currently only three rhinos of this subspecies left in captivity and four have been returned to a conservancy in Kenya.
Initially, six northern white rhinoceros lived in the Dvůr Králové Zoo in the Czech Republic. Four of the six rhinos (which are also the only reproductive animals of this subspecies) were transported to Ol Pejeta Conservancy in Kenya, Africa, where scientists hope they will successfully breed and save this subspecies from extinction. One of two remaining in the Czech Republic died in late May 2011. The two other rhinos presently live at the San Diego Zoo's Safari Park in California.
Following the phylogenetic species concept, recent research has suggested the northern white rhinoceros may be an altogether different species, rather than a subspecies of white rhinoceros, in which case the correct scientific name for the former is Ceratotherium cottoni. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years.
The white rhinoceros is the largest of the five species of rhinoceros and the world's largest land mammal after the three species of elephant. It has a massive body and large head, a short neck and broad chest. The head and body length is 3.7 to 4 m (12 to 13 ft) in males and 3.4 to 3.65 m (11.2 to 12.0 ft) in females, with the tail adding another 70 cm (28 in) and the shoulder height is 1.7 to 1.85 m (5 ft 7 in to 6 ft 1 in) in the male and 1.6 to 1.77 m (5 ft 3 in to 5 ft 10 in) in the female. Weight in this animal typically ranges from 1,360 to 3,630 kg (3,000 to 8,000 lb). The male, averaging 2,300 kg (5,100 lb) is heavier than the female, at an average of 1,700 kg (3,700 lb). The largest recorded white rhinoceros was about 4,500 kg (9,900 lb). On its snout it has two horn-like growths, one behind the other. These are made of solid keratin, in which they differ from the horns of bovids (cattle and their relatives), which are keratin with a bony core, and deer antlers, which are solid bone. The front horn is larger and averages 90 cm (35 in) in length, reaching as much as 150 cm (59 in). The white rhinoceros also has a noticeable hump on the back of its neck. Each of the four stumpy feet has three toes. The color of the body ranges from yellowish brown to slate grey. Its only hair is the ear fringes and tail bristles. White rhinos have a distinctive broad, straight mouth which is used for grazing. Its ears can move independently to pick up sounds but it depends most of all on smell. The olfactory passages which are responsible for smell are larger than their entire brain. The white rhinoceros has the widest set nostrils of any land based animal.
Behavior and ecology
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (August 2009)|
White rhinoceroses are found in grassland and savannah habitat. Herbivore grazers that eat grass, preferring the shortest grains, the white rhinoceros is one of the largest pure grazers. It drinks twice a day if water is available, but if conditions are dry it can live four or five days without water. It spends about half of the day eating, one third resting, and the rest of the day doing various other things. White rhinoceroses, like all species of rhinoceros, love wallowing in mudholes to cool down.
White rhinoceroses produce sounds which include a panting contact call, grunts and snorts during courtship, squeals of distress, and deep bellows or growls when threatened. Threat displays (in males mostly) include wiping its horn on the ground and a head-low posture with ears back, combined with snarl threats and shrieking if attacked. The white rhinoceros is quick and agile and can run 50 km/h (31 mph).
White rhinoceroses live in crashes or herds of up to 14 animals (usually mostly female). Sub-adult males will congregate, often in association with an adult female. Most adult bulls are solitary. Dominant bulls mark their territory with excrement and urine. The dung is laid in well defined piles. It may have 20 to 30 of these piles to alert passing rhinoceroses that it is his territory. Another way of marking their territory is wiping their horns on bushes or the ground and scrapes with its feet before urine spraying. They do this around 10 times an hour while patrolling territory. The same ritual as urine marking except without spraying is also commonly used. The territorial male will scrape-mark every 30 m (98 ft) or so around its territory boundary. Subordinate males do not mark territory. The most serious fights break out over mating rights to do with a female. Female territory is overlapped extensively and they do not defend it.
Females reach sexual maturity at 6–7 years of age while males reach sexual maturity between 10–12 years of age. Courtship is often a difficult affair. The male stays beyond the point where the female acts aggressively and will give out a call when approaching her. The male chases and or blocks the way of the female while squealing or wailing loudly if the female tries to leave his territory. When ready to mate the female curls her tail and gets into a stiff stance during the half hour copulation. Breeding pairs stay together between 5–20 days before they part their separate ways. Gestation occurs around 16–18 months. A single calf is born and usually weighs between 40 and 65 kg (88 and 143 lb). Calves are unsteady for their first 2 to 3 days of life. When threatened the baby will run in front of the mother, who is very protective of her calf and will fight for it vigorously. Weaning starts at 2 months, but the calf may continue suckling for over 12 months. The birth interval for the white rhino is between 2 and 3 years. Before giving birth the mother will chase off her current calf. White rhinos can live to be up to 40–50 years old. Adult white rhinos have no natural predators (other than humans) due to their size, and even young rhinos are rarely attacked or preyed on due to the mother's presence and their tough skin.
The southern subspecies or majority of White rhino live in southern Africa. About 98.5% of white rhino occur in just five countries (South Africa, Namibia, Zimbabwe, Kenya and Uganda). Almost at the edge of extinction in the early 20th century, the southern subspecies has made a tremendous comeback. In 2001 it was estimated that there were 11,670 white rhinos in the wild with a further 777 in captivity worldwide, making it the most common Rhino in the world. By the end of 2007 wild-living southern white rhino had increased to an estimated 17,480 animals (IUCN 2008).
The northern white rhino (Ceratotherium simum cottoni) formerly ranged over parts of north-western Uganda, southern Chad, south-western Sudan, the eastern part of Central African Republic, and north-eastern Democratic Republic of the Congo (DRC). The last surviving population of wild northern white rhinos are located in Garamba National Park, Democratic Republic of the Congo (DRC) but in August 2005, ground and aerial surveys conducted under the direction of African Parks Foundation and the African Rhino Specialist Group (ARSG) have only found four animals: a solitary adult male and a group of one adult male and two adult females. In June 2008 it was reported that the subspecies may have gone extinct in the wild.
Like the black rhino, the white rhino is under threat from habitat loss and poaching, most recently by Janjaweed. The horn is mostly used for traditional medicine although there are no health benefits from the horn; the horn is also used for traditional necklaces.
Most white rhinos in zoos are southern white rhinos; in 2001 it was estimated that there were 777 white rhinos in captivity worldwide.
The fully captive northern white rhino population consists of only three animals, and is maintained in two zoological institutions in the U.S.A. and the Czech Republic. The San Diego Zoo Safari Park in San Diego, California, has two northern white rhinos, both of which were wild-caught. They are a female named Nola (b. 1974, on loan from 1989 from ZOO Dvůr Králové) and a male named Angalifu (b. 1974, on loan from 1990 from Khartoum Zoo in Khartoum). As of 2012, in Dvůr Králové Zoo, Dvůr Králové nad Labem, Czech Republic there is one hybrid female Nabire, born at Dvůr Králové Zoo on 15 November 1983. Her mother was a northern white rhino (C. s. cottoni), but her father was a southern white rhino (C. s. simum) named Arthur.
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