شتر یک‌کوهانه

از ویکی‌پدیا، دانشنامهٔ آزاد
پرش به: ناوبری، جستجو
فارسی English
شتر یک‌کوهانه
طبقه‌بندی علمی
فرمانرو: جانوران
شاخه: طنابداران
رده: پستانداران
راسته: جفت‌سمان
تیره: شترسانان
سرده: شتر
گونه: C. dromedarius
نام علمی
Camelus dromedarius
کارل لینه٬ ۱۷۵۸
محدوده پراکندگی

شتر یک کوهانه گونه‌ایی از شترسانان است که در آفریقای شمالی و خاورمیانه زندگی می‌کند.

Dromadaire.jpg

پانویس[ویرایش]

منابع[ویرایش]

پیوند به بیرون[ویرایش]


For the world music group, see Dromedary (band).
Dromedary camel
07. Camel Profile, near Silverton, NSW, 07.07.2007.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Order: Artiodactyla
Family: Camelidae
Genus: Camelus
Species: C. dromedarius
Binomial name
Camelus dromedarius
Linnaeus, 1758
Dromedary Range.png
Range of the dromedary
Synonyms[1]

The dromedary (/ˈdrɒmədɛri/ or /-ədri/), also called the Arabian camel (Camelus dromedarius), is a large, even-toed ungulate with one hump on its back. One of the three species of camel, it was given its current binomial name by Carl Linnaeus in 1758. The dromedary is the largest camel after the Bactrian camel. Adult male dromedaries stand 1.8–2 m (5.9–6.6 ft) at the shoulder, while females are 1.7–1.9 m (5.6–6.2 ft) tall. The weight typically ranges from 400–600 kg (880–1,320 lb) in males and 300–540 kg (660–1,190 lb) in females. The distinctive features of this camel include its long curved neck, narrow chest, a single hump (compared to the two on the Bactrian camel), and long hairs on the throat, shoulders and hump. The coat is generally a shade of brown. The hump, 20 cm (7.9 in) tall or more, is made of fat bound together by fibrous tissue.

Active mainly during the day, the dromedaries form herds of about 20 individuals, led by a dominant male. This camel feeds on foliage and desert vegetation. The dromedary exhibits several adaptations to thrive in its desert habitat, such as the ability to tolerate greater than 30% of the water content of the body. Mating occurs once a year, and peaks in the rainy season. A single calf is born after a pregnancy of 15 months.

The dromedary has not occurred naturally in the wild for nearly 2000 years. It was first domesticated probably in Somalia or the Arabian Peninsula about 4000 years ago. In the wild, the dromedary inhabited arid regions, notably the Sahara Desert in Africa. In the present day, the domesticated dromedary is generally found in the semi-arid to arid regions of the Old World, mainly in Africa. A significant feral population occurs in Australia. The dromedary supports several north Arabian tribes through its products, such as milk and meat; it is also common as a riding and baggage animal.

Etymology

The common name "dromedary" comes from the Old French dromedaire, or the Latin dromedarius, both of which mean "swift". It is based on the Greek dromas, δρομάς (ο, η) (GEN (γενική) dromados, δρομάδος), meaning "runner".[2][3] The first recorded use of the name dates back to the 14th century AD.[4] The dromedary possibly had its origins in Arabia and is therefore sometimes referred to as the Arabian camel.[5] The term "camel" generally refers either to the dromedary or the congeneric Bactrian camel. It could have been derived from the Latin camelus, the Greek kamēlos,[6] or an old Semitic language such as the Hebrew gāmāl or the Arabic ǧamal.[7] The scientific name of the dromedary is Camelus dromedarius, which could be based on the Greek δρομὰς κάμηλος (dromas kamelos), which means "running camel".[8]

Taxonomy and classification



Lamini

Alpaca




Vicuña




Llama



Guanaco





Camelini

Dromedary



Bactrian camel





Phylogenetic relationships of the dromedary from combined analysis of all molecular data.[9]

The dromedary shares the genus Camelus with the Bactrian camel (C. bactrianus) and the wild Bactrian camel (C. ferus, sometimes considered a subspecies of the Bactrian camel). The dromedary belongs to the family Camelidae.[1][10] The ancient Greek philosopher Aristotle (4th century BC) was the first to describe the species of Camelus. He named two species in his History of Animals: the one-humped Arabian camel and the two-humped Bactrian camel.[11][12] The dromedary was given its current binomial name Camelus dromedarius by Swedish zoologist Carl Linnaeus in his 1758 publication Systema Naturae.[13] In 1927, British veterinarian Arnold Leese classified dromedaries by their basic habitats: the hill camels, small muscular animals and efficient beasts of burden; the larger plains camels, that could be further divided into the desert type (that can bear light burden and are apt for riding) and the riverine type (slow animals that can bear heavy burden); and those intermediate between these two types.[14]

In 2007, Peng Cui (of the Chinese Academy of Sciences) and colleagues carried out a phylogenetic study of the evolutionary relationships between the two tribes of Camelidae: Camelini – consisting of the three Camelus species (the study considered the wild Bactrian camel as a subspecies of the Bactrian camel) – and Lamini – consisting of the alpaca (Vicugna pacos), the guanaco (Lama guanicoe), the llama (L. glama) and the vicuña (V. vicugna). The study revealed that the two tribes had diverged 25 million years ago (early Miocene), notably earlier than what had been previously estimated from North American fossils. Speciation began first in Lamini as the alpaca came into existence 10 million years ago (late Pleistocene). Nearly two million years later, the dromedary and the Bactrian camel emerged as two independent species.[9]

The dromedary and the Bactrian camel often interbreed to produce fertile offspring. Where the ranges of the two species overlap, such as in northern Punjab, Persia and Afghanistan, the phenotypic differences between them tend to decrease as a result of extensive crossbreeding between them. The fertility of their hybrid has given rise to speculation that the dromedary and the Bactrian camel should be merged into a single species with two varieties.[14] However, a 1994 analysis of the mitochondrial cytochrome b gene revealed that the species display 10.3% divergence in their sequences.[15]

Genetics and hybrids

Main article: Hybrid camel

The diploid number of chromosomes in the dromedary is 74, the same as in any other camelid. The autosomes consist of five pairs of small to medium-sized metacentrics and submetacentrics.[16] The X chromosome is the largest in the metacentric and submetacentric group.[17] There are 31 pairs of acrocentrics.[16] The dromedary has a karyotype similar to that of the Bactrian camel.[18]

The origin of camel hybridisation dates back to the first millennium BC.[19] For about a thousand years, Bactrian camels and dromedaries have been successfully bred in regions where they are sympatric to form hybrids characterised by either a long, slightly lopsided hump, or two humps – one small and one large. These hybrids are larger and stronger than their parents – they can bear a greater load.[17][19] A cross between a first generation female hybrid and a male Bactrian camel can also produce a hybrid. Hybrids from other combinations, however, tend to be bad-tempered or runts.[20]

Evolution

The extinct Protylopus, which occurred in the upper Eocene in North America, is the oldest as well as the smallest known camel.[21] During the transition from Pliocene to Pleistocene, several mammals faced extinction. On the contrary, this period marked the successful radiation of the Camelus species; they migrated over the Bering Strait and dispersed widely into Asia, eastern Europe and Africa.[22][23] By the Pleistocene, ancestors of the dromedary came to be known from the Middle East and northern Africa.[24]

The modern dromedary probably evolved in the hotter and arid regions of western Asia from the Bactrian camel, which in turn was closely related to the earliest Old World camels.[23] This hypothesis is supported by the fact that the dromedary foetus actually has two humps, while in the adult an anterior vestigial hump is present on an adult male.[14] A jawbone of a dromedary, dated back to 8200 BC, was found on the southern coast of the Red Sea in Saudi Arabia.[25][5]

In 1975, Richard Bulliet of Columbia University observed that the dromedary exists in large numbers in those areas from where the Bactrian camel has disappeared; the converse is also true to a great extent. He suggested that this substitution could have taken place due to the heavy dependence of the Syrian and Arabian nomads on the dromedary for milk, meat and wool, while the Asiatic people domesticated the Bactrian camel but did not have to depend primarily upon it for its products.[26]

Characteristics

Note the long curved neck, single hump and the long hair on the throat, shoulders and hump of the dromedary.

The dromedary is the largest camel after the Bactrian camel. Adult male dromedaries stand 1.8–2 m (5.9–6.6 ft) at the shoulder, while females are 1.7–1.9 m (5.6–6.2 ft) tall. The weight typically ranges from 400–600 kg (880–1,320 lb) in males and 300–540 kg (660–1,190 lb) in females. The distinctive features of this camel are its long curved neck, narrow chest and a single hump (compared to the two on the Bactrian camel), thick double-layered eyelashes and bushy eyebrows.[17] These camels have a sharp vision and a good sense of smell.[5] The male has a soft palate (dulaa in Arabic), nearly 18 cm (7.1 in) long, which he inflates to produce a deep pink sac. Often mistaken for the tongue, the palate dangles out from a side of the male's mouth to attract females during the mating season.[27]

The coat is generally a shade of brown, but can range from black to nearly white.[17] Leese reported piebald dromedaries from Kordofan and Darfur in Sudan.[28] The hair is long and concentrated on the throat, shoulders and the hump. The eyes are large and protected by prominent supraorbital ridges; the ears are small and rounded. The hump is at least 20 cm (7.9 in) high.[17] The dromedary has long and powerful legs with two toes on either feet. The feet resemble flat, leathery pads.[29] This camel moves both legs on one side of the body at the same time, like the giraffe.[30]

Unlike the Bactrian camel, the dromedary has a lighter build, longer limbs, shorter hairs, a harder palate, and an insigificant or absent ethmoidal fissure.[31] The dromedary differs from the camelids of the genus Lama in possessing a hump, a longer tail, smaller ears, squarer feet and reaching a greater height at the shoulder. Moreover, the dromedary has four teats instead of the two in the Lama species.[17]



Anatomy

Body
Body for comparison with skeleton

The cranium of the dromedary consists of a postorbital bar, a tympanic bulla (filled with spongiosa), a well-defined sagittal crest, a long facial part and an indented nasal bone.[32] Typically, there are eight sternal and four non-sternal pairs of ribs.[28] The spinal cord, nearly 214 cm (84 in) long, terminates in the second and third sacral vertebra.[33] The fibula is reduced to a malleolar bone. A digitigrade animal, the dromedary walks on its toes or digits. It lacks the second and fifth digits.[34] The front feet, 19 cm (7.5 in) wide and 18 cm (7.1 in) long, are larger than the hind feet, 17 cm (6.7 in) wide and 16 cm (6.3 in) long.[29]

The dromedary has 22 milk teeth, which are eventually replaced by 34 permanent teeth. The dental formula for permanent dentition is 1.1.3.33.1.2.3, and 1.1.33.1.2 for milk dentition.[35] The juvenile develops the lower first molars by 12 to 15 months, but the permanent lower incisors appear only at 4.5 to 6.5 years of age. All teeth are in use by the age of 8 years.[36] The lenses of the eyes contain crystallin, which constitutes 8 to 13% of the total protein present there.[37]

The skin is basically black; the epidermis is 0.038–0.064 mm (0.0015–0.0025 in) thick, while the dermis is 2.2–4.7 mm (0.087–0.185 in) thick.[38] The hump is composed of fat bound together by fibrous tissue.[17] Though glands are absent on the face, males have glands on either side of the midline of the neck. These appear to be modified apocrine sweat glands which secrete a pungent, coffee-coloured fluid during the rut. The weight of these glands generally increases during the rut, and ranges from 20 to 115 g (0.71 to 4.06 oz).[39] Each cover hair is associated with an arrector pilli muscle, a hair follicle, a ring of sebaceous glands and a sweat gland.[27][40] Females have cone-shaped, four-chambered mammary glands, 2.4 cm (0.94 in) long with a base diameter of 1.5 cm (0.59 in).[41] An interesting feature of these glands is that they can produce milk with the water content as high as 90% even if the mother is at risk of dehydration.[17]

The heart, 5 kg (11 lb) heavy, has two ventricles with the tip curving to the left. The pulse rate is 50 beats per minute. The normal blood volume of the dromedary is 0.093 l (0.020 imp gal).[42] The dromedary is the only mammal with oval red blood corpuscles.[43] The pH of the blood varies from 7.1 to 7.6 (slightly alkaline). The state of hydration and the sex of the animal and the season can influence blood values.[44] The lungs lack lobes.[28] A dehydrated camel has a lower breathing rate.[45] Either kidney has a volume of 858 cm3 (52.4 cu in), and can produce urine with high chloride concentrations. Like the horse, the dromedary lacks a gall bladder. The grayish violet, crescent-like spleen weighs less than 500 g (18 oz).[43] The triangular, four-chambered liver weighs 6.5 kg (14 lb); its dimensions are: 60×42×18 cm (23.6×16.5×7.1 in).[17]

The ovaries, present in females, are reddish, circular and flattened.[46] They are enclosed in a conical bursa, and have the dimensions 4×2.5×0.5 cm (1.57×0.98×0.20 in) during anestrus. The oviducts are 25–28 cm (9.8–11.0 in) long. The uterus is bicornuate. The vagina, 3–3.5 cm (1.2–1.4 in) long, has well-developed Bartholin's glands.[22] The vulva is 3–5 cm (1.2–2.0 in) deep with a small clitoris.[35] The placenta is diffuse and epitheliochorial, with a crescent-like chorion.[47] The penis, covered by a triangular penile sheath that opens backward, is about 60 cm (24 in) long.[48] The scrotum, present in males, is located high in the perineum with the testicles in separate sacs. Testicles are 7–10 cm (2.8–3.9 in) long, 4.5 cm (1.8 in) deep and 5 cm (2.0 in) wide.[17] The right testicle is often smaller than the left.[14] The typical mass of either testicle is less than 140 g (0.31 lb); however, the mass increases during the rut, ranging from 165 to 253 g (0.364 to 0.558 lb).[17] The Cowper's gland is white, shaped like an almond, and lacks seminal vesicles; the prostate gland is dark yellow, disc-shaped and divided into two lobes.[48]

Health and diseases

3D image of MERS-CoV, of which the dromedary is possibly the animal source

The dromedary generally suffers from fewer diseases than do other domestic livestock such as goats and cattle.[49] Temperature fluctuations occur throughout the day in a healthy dromedary – the temperature reaches a low at dawn, then rises till sunset and dips during the night.[50] A nervous camel may vomit if carelessly handled, and need not indicate any disorder. A rutting male may also develop nausea.[14]

The dromedary is prone to trypanosomiasis, transmitted by the tsetse fly. The main symptoms are recurring fever, anaemia and weakness; the disease is typically fatal for the camel.[51] Brucellosis is another prominent malady. In an observational study, the seroprevalence of this disease was generally low (2 to 5%) in nomadic or moderately free dromedaries, while it was high (8 to 15%) in denser populations. Brucellosis is caused by different biotypes of Brucella abortus and B. melitensis.[52] Other internal parasites include Fasciola gigantica (trematode), two types of cestode (tapeworm), and various nematodes (roundworms). Among external parasites, Sarcoptes species cause sarcoptic mange.[17] In a 2000 study in Jordan, 83% of the 32 camels tested positive for sarcoptic mange.[53] In another study, dromedaries were found to have natural antibodies against the rinderpest virus and the ovine rinderpest virus.[54]

In 2013, a seroepidemiological study (a study investigating the patterns, causes and effects of a disease on a specific population on the basis of serologic tests) in Egypt was the first to show that the dromedary might be a host for the Middle East respiratory syndrome coronavirus (MERS-CoV).[55] A 2013–14 study of dromedaries in Saudi Arabia concluded that the unusual genetic stability of MERS-CoV coupled with its high seroprevalence in the dromedary makes this camel a highly probable host for the virus. The full genome sequence of MERS-CoV from dromedaries in this study showed a 99.9% match to the genomes of human clade B MERS-CoV.[56] Another study in Saudi Arabia revealed the presence of MERS-CoV in 90% of the evaluated dromedary camels, and even suggested that camels could be the animal source of MERS-CoV.[57]

Fleas and ticks are common causes of physical irritation. In a study in Egypt, a species of Hyalomma was predominant in dromedaries, comprising 95.6% of the adult ticks isolated from the camels. In Israel, the number of ticks per camel ranged from 20 to 105. Nine camels in the date palm plantations in Arava Valley were injected with ivermectin, but could not be effective against Hyalomma tick infestations.[58] Larvae of Cephalopsis titillator, the camel nasal fly, can cause brain compression and nervous disorders, which might prove fatal. Illnesses that can affect dromedary productivity are pyogenic diseases and wound infections due to Corynebacterium and Streptococcus, pulmonary disorders caused by Pasteurella (like hemorrhagic septicemia) and Rickettsia species, camelpox, anthrax, and cutaneous necrosis due to Streptothrix and deficiency of salt in the diet.[17]

Ecology

Herd of dromedaries in Israel

The dromedary is diurnal (active mainly during the daytime); free-ranging herds feed and roam throughout the day, though they rest during the hot noon hours. The night is mainly spent in resting. Dromedaries form cohesive groups of about 20 individuals, led by a dominant male and consisting of several females. Females may also lead in turns.[17] Some males either form bachelor groups or roam alone.[59] Herds may congregate to form associations of over hundreds of camels during migrations at the time of natural calamities. The males of the herd prevent the female members from interacting with other bachelor males by standing or walking between them and might drive them away. Short-term home ranges of the feral camels in Australia are 50–150 km2 (19–58 sq mi) in area; annual home ranges could spread over several thousand square kilometres.[17]

Some special behavioural features of the camel include snapping at other camels without biting them and showing displeasure by stamping their feet. They are generally non-aggressive, with the exception of rutting males. Camels apparently remember their homes; females in particular remember the place they first gave birth or suckled their offspring.[17] Males turn aggressive in the mating season, and might even wrestle. A 1980 study showed that androgen levels in males influences their behaviour. Between January and April, when these levels are high due to the rut, they become difficult to manage, blow out the palate from the mouth, vocalise, and throw urine over their back.[60] Camels scratch parts of their bodies with their front or hind legs or with their lower incisors. They may also rub against tree bark and roll in the sand.[17]

Free-ranging dromedaries face the large predators typical of their regional distribution, which includes wolves, lions and tigers.[29]

Diet

Dromedaries are primarily browsers.

The diet of the dromedary mostly consists of foliage, dry grasses, and available desert vegetation (mostly thorny plants) growing in the camel's natural habitat.[61] A study gave the following composition of the typical diet of the dromedary: dwarf shrubs (47.5%), trees (29.9%), grasses (11.2%), other herbs (0.2%) and vines (11%).[62] The dromedary is primarily a browser, with forbs and shrubs comprising 70% of their diet in summer and 90% in winter. The dromedary may also graze on, or suck in, tall young succulent grasses.[63]

In the Sahara, 332 plant species have been recorded for the dromedary. These include Aristida pungens, Acacia tortilis, Panicum turgidum, Launaea arborescens and Balanites aegyptiaca.[29] The dromedary will feed on Acacia, Atriplex, and Salsola plants whenever available.[63] The feral dromedaries in Australia prefer Trichodesma zeylanicum and Euphorbia tannensis. In India dromedaries are fed with forage plants such as Vigna aconitifolia, V. mungo, Cyamopsis tetragonolaba, Melilotus parviflora, Eruca sativa, Trifolium species and Brassica campestris.[63] The dromedaries keep their mouths open while chewing thorny food. They use their lips to grasp the food, then chew each bite 40–50 times. Features like long eyelashes, eyebrows, lockable nostrils, caudal opening of the prepuce and a relatively small vulva help the camel avoid injuries, especially while feeding.[61] They graze for 8–12 hours per day and ruminate for an equal amount of time.[17]

Adaptations

Footprint in dry sand

The dromedary is specially adapted to their desert habitat; these adaptations are aimed to conserve water and regulate body temperature. The bushy eyebrows and the double row of eyelashes prevent sand and dust from entering the eyes during strong winds characteristic of deserts, and shield the eyes from the sun's glare.[64] The dromedary is able to close its nostrils voluntarily; this assists in water conservation.[65] The dromedary can conserve water by reducing perspiration, which it achieves by fluctuating the body temperature throughout the day from 31 to 41.7 °C (87.8 to 107.1 °F). The kidneys are specialised to minimise the loss of water through excretion. Groups of camels also avoid excess heat from the environment by pressing against each other. The dromedary can tolerate greater than 30% water loss, which is generally not possible for other mammals. In temperatures ranging from 30 to 40 °C (86 to 104 °F), it needs water every 10 to 15 days; only in the hottest temperatures does the dromedary take water every four to seven days. This camel has a fast rate of rehydration and can drink at the speed of 10–20 L (2.2–4.4 imp gal) per minute.[17] The dromedary has a rete mirabile, a complex of arteries and veins lying very close to each other which use countercurrent blood flow to cool blood flowing to the brain–this is effective in controlling the temperature of the brain.[66]

The hump stores up to 80 lb (36 kg) of fat, which the camel can break down into water and energy to meet its needs when resources are scarce; the hump also helps dissipate body heat.[67] If the hump is small, the animal can show signs of starvation. In a 2005 study, the mean volume of adipose tissues (in the external part of the hump that have cells to store lipids) is related to the dromedary's unique mechanism of food and water storage.[68] In case of starvation, they can even eat fish and bones, and drink brackish and salty water.[5] The hair is longer on the throat, hump and shoulders. Though the padded hooves effectively support the camel's weight on the ground,[65] they are not suitable for walking on slippery and muddy surfaces.[17]

Reproduction

Mating
Calf suckling

Since camels have a slow growth rate,[69] they reach sexual maturity only in advanced years.[14] This age varies geographically and also depends on the individual, as does the reproductive period of their life.[14] Females reach sexual maturity typically around three years of age and mate around age four or five. Males begin to mate at around three years of age, too, but still are not sexually mature until six years of age. Mating occurs once a year, and peaks in the rainy season. The mating season lasts three to five months, but may even last a year for older animals.[14]

During the reproductive season, males splash their urine on their tails and nearer regions. Males extrude their soft palate to attract females – a trait unique to the dromedary.[70] Copious saliva turns to foam as the male gurgles, covering the mouth. Males threaten each other for dominance over the female by trying to stand taller than the other, making low noises and a series of head movements including lowering, lifting, and bending their necks backwards. A male tries to defeat other males by biting at his legs and taking the opponent's head in between his jaws.[39] Copulation begins with a necking exercise. The male smells the female's genitalia, and often bites her in that region or around her hump.[71] The male makes the female sit, and then grasps her with his forelegs. The camelmen often aid the male to enter his penis into the female's vulva.[72] It is disputed whether the male dromedary can penetrate the female on his own or not.[14] Copulation time ranges from 7 to 35 minutes, averaging 11 to 15 minutes. Normally, three to four ejaculations occur.[14] The semen of a Bikaneri dromedary was found to be white and viscous, with a pH of around 7.8.[71]

A single calf is born after a gestational period of 15 months. Calves move freely by the end of their first day. Nursing and maternal care continue for one to two years. In a study to find whether young could exist on milk substitutes, two male young camels, one month old, were separated from their mothers and were fed on milk substitutes prepared commercially for lambs. For the initial 30 days, the changes in their weights were marked. Each gained 0.400 kg (0.88 lb) and 1 kg (2.2 lb), respectively, per day. Finally, they were found to have grown properly and weighed normal weights of 135 kg (298 lb) and 145 kg (320 lb).[73] Lactational yield can vary with species, breed, individual, region, diet, management conditions and lactating stage.[74] Maximum milk is produced during the early period of lactation.[14] The length of the lactation period can vary from nine to eighteen months.[75]

Dromedaries are induced ovulators.[76] Oestrus might be cued by nutritional status of the camel and the daylength.[77] If mating does not occur, the follicle, which grows during estrus, usually regresses within a few days.[78] In one study, 35 complete estrous cycles were observed in five nonpregnant females over a period of 15 months. The cycles were about 28 days long, in which follicles matured in six days, maintained their size for 13 days, and returned to their original size in eight days.[79] In another study, ovulation could be best induced when the follicle reaches a size of 0.9–1.9 cm (0.35–0.75 in).[80] In another study, pregnancy in females could be recognized as early as 40 to 45 days of gestation by the swelling of the left uterine horn, where 99.52% of pregnancies were located.[81]

Distribution

Domesticated dromedary camels at the Great Pyramid of Giza, Giza, Egypt

The dromedary has not occurred naturally in the wild for nearly 2000 years. In the wild, the dromedary inhabited arid regions, notably the Sahara Desert in Africa. The original range of the camel’s wild ancestors was probably southern Asia and the Arabian peninsula. Its range stretched across the dry hot regions of northern Africa, Ethiopia, the Near East, and western to central Asia.[82] The dromedary typically thrives in areas with a long dry season and a short wet season.[83] They are sensitive to cold and humidity,[35] though certain breeds can thrive under humid conditions.[83]

In the present day, the domesticated dromedary is generally found in the semi-arid to arid regions of the Old World.[83] In Africa, which holds more than 80% of the world's total dromedary population, the dromedary occurs in almost every desert zone in the northern part of the continent. The Sahel marks the southern extreme of its range, which is nearly 2–3°S latitude, where the annual rainfall may be 550 mm (22 in). The Horn of Africa holds nearly 35% of the world's total dromedary population,[83] the maximum occurring in Somalia, followed by Sudan and Ethiopia (as of the early 2000s).[84] According to the Yearbook of the Food and Agriculture Organisation (FAO) for 1984, eastern Africa had about 10 million dromedaries, the largest dromedary population of Africa. Western Africa followed with 2.14 million dromedaries, while northern Africa had a population of nearly 0.76 million.[85] Populations in Africa increased by 16% from 1994 to 2005.[84][86]

A pair of camels in Israel

The dromedary is also found in feral populations in northern Australia, where it was introduced in 1840.[87] The total dromedary population in Australia is 0.5 million as of 2005. Nearly 99% of the populations are feral, and increasing at an annual growth rate of 10%.[84] The majority of the Australian feral camels are dromedaries, with only a few Bactrian camels. Most of these dromedaries occur in Western Australia, while smaller populations occur in the Northern Territory, Western Queensland and northern South Australia.[84]

In Asia, nearly 70% of the total population occurs in India and Pakistan. The combined population of the dromedary and the Bactrian camel has seen a fall of around 21% between 1994 and 2004.[88] The dromedary is sympatric with the Bactrian camel in Afghanistan, Pakistan, central and southwestern Asia.[89] India shelters a dromedary population of less than one million, with the maximum numbers (0.67 million) in the state of Rajasthan.[84] Populations in Pakistan have fallen from 1.1 million in 1994 to 0.8 million in 2005 – a 29% decline.[88] According to the FAO, the dromedary population in the Persian Gulf was nearly 0.67 million in 2003, distributed over six countries. In the Persian Gulf region the dromedary is locally classified into breeds based on coat colour, such as Al-Majahem, Al-Hamrah, Al-Safrah, Al-Zarkah and Al-Shakha. The UAE has three prominent breeds: Racing camel, Al-Arabiat and Al-Kazmiat.[90]

Domestication

Woodcut illustration from the book The History of Four-Footed Beasts and Serpents by Edward Topsell

The dromedary was first domesticated probably in Somalia or the Arabian Peninsula about 4000 years ago.[91] In the ninth or tenth century BC, the dromedary became popular in the Near East. The Persian invasion of Egypt under Cambyses in 525 BC introduced domesticated camels to the area. The Persian camels, however, were not particularly suited to trading or travel over the Sahara; journeys across the desert were made on chariots pulled by horses.[92][93] The dromedary was introduced into northern Africa (Egypt) from southwestern Asia (Arabia and Persia).[51][94] The popularity of dromedaries got the next major boost after the Islamic conquest of North Africa. While the invasion was accomplished largely on horseback, the new links to the Middle East allowed camels to be imported en masse. These camels were well-suited to long desert journeys and could carry a great deal of cargo, allowing substantial trade over the Sahara for the first time.[95][96] In Libya, they were used for transportation within the country, and their milk and meat constituted the local diet.[97]

Individuals were also shipped from southwestern Asia to Spain, Italy, Turkey, France, Canary Islands, the Americas and Australia.[14] Dromedaries were introduced into Spain in 1020 AD and to Sicily in 1059 AD.[98] Dromedaries had also been exported to the Canary Islands in 1405 AD, during the times of European colonisation of the area, and still exist, particularly in Lanzarote and to the south of Fuerteventura.[98] Attempts had been made to introduce dromedaries into the Caribbean, Colombia, Peru, Bolivia, and Brazil between the 17th and the 19th centuries; some were imported to the western United States in the 1850s and some to Namibia in the early 1900s, but presently they exist in small numbers or are absent in these areas.[28]

In 1840, about six camels were shipped from Tenerife to Adelaide, but only one survived through the trip, reaching the destination on October 12 that year. The animal, a male, was called Harry and was owned by the explorer John Ainsworth Horrocks. Although Harry had proved to be bad-tempered, he was included in an expedition in the following year because he could carry heavy loads. The next major group of camels were imported in 1860 and between 1860 and 1907 some 10 to 12 thousand were imported. These were used mainly for riding and transportation.[99][100]

Relationship with humans

The strength and docility of the dromedary make it a popular domesticated animal.[14] As summarised by Bulliet, the camel can be used for a wide variety of purposes: milking, riding, transport, feeding (on their meat), ploughing, trading and clothing (using their wool and leather).[26] The main attraction these animals have for nomadic groups in deserts is the wide variety of resources they provide them with, which is crucial for their survival. For instance, the camel is the backbone for several Bedouin pastoralist tribes of northern Arabia, such as the Ruwallah, the Shammar and the Mutayr.[101]

Riding camels

Main article: Camel racing
Dromedaries at Bait al-Faqih market, Yemen
A camel in the Judean Desert decorated for a tourist camel ride

Although the role of the camel is diminishing in many areas across its range with the advent of technology and modern means of transport, it is still an efficient mode of communication in remote and less developed areas. Used in warfare since the 2nd century BC,[102] the camel still remains popular in sports such as camel racing, particularly in the Arab world.[14] The riding camels of Arabia, Egypt and the Sahara are locally known as the Dilool, the Hageen and the Mehara respectively; several local breeds are included within these groups.[28]

Ideally, the riding camel should be strong, slender and long-legged with thin and supple skin. The special adaptations of the dromedary's feet allow it to walk with ease even on sandy and rough terrain, and even on cold surfaces.[103] The camels of the Bejas (of Sudan)[94] and the Anafi camel (bred in Sudan) are two common breeds used as riding camels.[14]

Leese identified and explained four types of speeds or gaits of the dromedary: walk, jog, fast run and canter. The first is the typical speed of walking, around 4 km/h (2.5 mph). Jog is the most common speed, nearly 8–12 km/h (5.0–7.5 mph) on level ground. He estimated a speed of 14–19 km/h (8.7–11.8 mph) during a fast run, by observing northern African and Arabian dromedaries. He did not give any particular speed range to describe the "canter", but implied that it was a sort of galloping which if induced could exhaust both the camel and the rider. Canter could be used only for short periods of time, for example in races.[104]

The ideal age to start training dromedaries for riding is three years,[39] although they may be stubborn and unruly.[105] Firstly, the head of the camel is controlled, followed by training it on how to respond to commands on sitting and standing, and to allow mounting.[28] At this stage camels will often try to run away when one tries to mount on it.[14] The next stage involves training in responding to reins. The animal must be given loads gradually and not forced to carry heavy loads before the age of six.[28] Riding camels should not be struck on their necks, rather they should be struck in the area of their body just behind the right leg of the rider.[39] Leese described two types of saddles generally used in camel riding: the Arabian markloofa (used by single riders) and the Indian pakra when two riders mount the same camel.[28]

Baggage and draught camels

The baggage camel should be robust and heavy. Studies have recommended that an ideal baggage camel should have either a small or a large head with a narrow aquiline nose, prominent eyes and large lips. In addition to this, the neck should be medium to long so that the head is held high, the chest should be deep, and the hump should be well-developed with sufficient space behind it to accommodate the saddle. The hindlegs should be heavy, muscular and sturdy.[106] The dromedary can be trained to carry baggage from the age of five years, but must not be given heavy loads before the age of six years.[107] The hawia is a typical baggage saddle from Sudan.[106] The methods of training the baggage camels are similar to those for riding camels.[14]

Draught camel are utilised for several purposes such as ploughing, processing in oil mills and pulling carts. There is no clear description for the ideal draught camel, though the strength of the animal, its capability to survive without water and the flatness of its feet could be used as yardsticks.[14] It may be used for ploughing in pairs or in groups with buffaloes or bullocks.[28] The draught camel can plough at a speed of 2.5 km/h (1.6 mph), and should not be used for more than six hours a day (four hours in the morning and two in the afternoon).[105] The camel is not easily exhausted (unless diseased or undernourished), and has remarkable endurance and hardiness.[23]

Dairy products

Main article: Camel milk
Dromedary being milked in Niger

Camel milk is a staple food of nomadic tribes living in deserts. According to a study, it consists of 11.7% total solids, 3% protein, 3.6% fat, 0.8% ash, 4.4% lactose, and 0.13% acidity (pH 6.5). The quantities of sodium, potassium, zinc, iron, copper, manganese, niacin and vitamin C were relatively higher than the amounts in cow milk. However, the levels of thiamin, riboflavin, folacin, vitamin B12, pantothenic acid, vitamin A, lysine, and tryptophan were lower than those in cow milk. The molar percentages of the fatty acids in milk fat were 26.7% for palmitic acid, 25.5% oleic acid, 11.4% myristic acid, and 11% palmitoleic acid.[108] While camel milk has higher thermal stability compared to cow's milk,[109] it does not compare favourably with sheep milk.[14]

Daily yield generally varies from 3.5 to 35 kg (7.7 to 77.2 lb) and from 1.3% to 7.8% of the body weight.[110] Amount of milk yield in dromedaries varies geographically, and depends upon their diet and living conditions.[14] At the peak of lactation, a healthy female would typically provide 9 kg (20 lb) milk per day.[23] Leese estimated that a lactating female would yield 4 to 9 L (0.88 to 1.98 imp gal) besides the amount ingested by the calf.[28] The Pakistani dromedary, considered a better milker and bigger, can yield 9.1–14.1 kg (20–31 lb) when well fed.[111] Dromedaries in Somalia may be milked two to four times a day,[75] while those in Afar (Ethiopia) may be milked as many as six or seven times a day.[112]

The acidity of dromedary milk stored at 30 °C (86 °F) increases at a slower rate than that of cow milk.[17] Though the preparation of butter from dromedary milk is a difficult task, it has been carried out successfully in 1959 in the erstwhile USSR. In this attempt the cream of the dromedary milk, containing 4.2% fat, had yielded 25.8% butter.[113] In 2001, dromedary milk was studied to find if it could form curd. Milk coagulation did not show actual curd formation, and had a pH of 4.4. It was much different from the curd produced from cow milk, and had a fragile heterogeneous composition probably composed of casein flakes.[114] Nevertheless, cheese (even hard cheese) and other dairy products can be made out of the camel's milk. A study found that bovine calf rennet could be exploited to coagulate dromedary milk.[115] A special factory has been set up in Nouakchott to pasteurise and make cheese out of camel's milk.[116] Mystical beliefs surround the use of camel milk in some places; for example, it may be used as an aphrodisiac in Ethiopia.[117]

Meat

Main article: Camel meat
Meat of dromedary served as food

The meat of a five-year-old dromedary has a typical composition of 76% water, 22% protein, 1% fat, and 1% ash.[77] The carcass, weighing 141–310 kg (311–683 lb) for a five-year-old dromedary,[77] is composed of nearly 57% muscle, 26% bone, and 17% fat.[118] Seven to eight-year-old camels can produce a carcass of weight of 125–400 kg (276–882 lb). The meat is a raspberry red to a dark brown or maroon, while the fat is white in colour. It tastes like beef and has the same texture.[118] A study of the meat of Iranian dromedaries revealed its high glycogen content, due to which it was sweet like horse meat. The carcass of well fed camels was found to be covered with a thin layer of good quality fat.[119] In a study of the fatty acid composition of raw meat taken from the hind legs of seven young males (one to three years old), 51.5% of the fatty acids were saturated, 29.9% monounsaturated, and 18.6% polyunsaturated. The major fatty acids in the meat were palmitic acid (26.0%), oleic acid (18.9%), and linoleic acid (12.1%). In the hump, palmitic acid was dominant (34.4%), followed by oleic acid (28.2%), myristic acid (10.3%), and stearic acid (10%).[120]

Camel slaughter in Mauritania

Dromedary slaughter is tougher than the slaughter of other domestic livestock such as cattle, due to the large size of the animal and the significant amount of manual work involved. Both males and females are slaughtered, but the males are slaughtered in larger numbers.[121] Though less affected by mishandling than other livestock, the pre-slaughter handling of the dromedary plays a crucial role in determining the quality of meat obtained – for instance, mishandling can often disfigure the hump.[122] The animal is then stunned, seated in a crouching position (with the head in a caudal position) and slaughtered.[121] The dressing percentage (the percentage of the mass of the animal that finally forms the carcass) is 55–70%,[77] more than the 45–50% in the case of cattle.[14] Camel meat, however, is rarely consumed by camel herders in Africa, who use it only during severe food scarcity, or for rituals.[14] Camel meat is processed into food items such as burgers, patties, sausages, and shawarma.[118] Dromedaries can be slaughtered between four and ten years of age. As the age of the animal increases, the meat grows tougher and deteriorates in taste as well as quality.[14]

A 2005 report, issued jointly by the Ministry of Health (Saudi Arabia) and the United States Centers for Disease Control and Prevention, details five cases of bubonic plague in humans, resulting from the ingestion of raw camel liver. Four of the five patients had severe pharyngitis and submandibular lymphadenitis. Yersinia pestis was isolated from the camel's bone marrow, as well as from the jird (Meriones libycus) and also from fleas (Xenopsylla cheopis) captured at the camel's corral.[123]

Camel hair, wool and hides

Camels generally do not develop long coats in hot climates. Camel hair is characterised by its lightness, low thermal conductivity and durability. Hence camel hair is quite suitable for manufacturing warm clothes and blankets, and even tents and rugs.[14] Hair of highest quality is typically obtained from juvenile camels or those in the wild.[39] In India, camels are clipped usually in spring and around 1–1.5 kg (2.2–3.3 lb) hair is produced per clipping. However, in colder regions one clipping can yield as much as 5.4 kg (12 lb).[39][105]

A dromedary can produce 1 kg (2.2 lb) wool per year, whereas a Bactrian camel has a much higher annual yield of nearly 5–12 kg (11–26 lb).[49] Young dromedaries, under the age of two years, have a fine undercoat that tends to fall off, and should be cropped by hand.[112] Not much information has been collected about camel hides, though it is known that they are usually of inferior quality and less preferred for manufacturing leather.[14]

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