EVOLUTION AND SYSTEMATIC POSITION OF THE GENUS CAMELUS
Evolution and domestication of the genus Camelus. Camel breeding has been developing since ancient time and, in the opinion of the authoritative scientists, it has a perspective to keep its importance in the traditional breeding regions of Kazakhstan and also to advance to the rank of the main branch of livestock breeding in ecologically unfavorable regions, such as Aral and Caspian ones. Proceeding from this, it is necessary to know the evolution of the genus Camelus representatives.
According to the Soviet scientist S.N.Bogolyubsky, 1934, the most ancient geological remains of animals, taking after the camel, were found in the Eocene layer in North America. Their age is about 40-50 million years. It should be noted here that the predecessor of a modern camel was of a hare size and had four dactyls, with the first and the second ones being under-developed. That fossil was called Protolopus. In the course of his body size growth and dactyl-walking strengthening, it evolved into Poebrotherium. The Poebrotherium was of a modern sheep size, with something like small hoofs appearing at the end of his 3rd and 4th dactyls [1].
The third fossil to be mentioned is Procamelus, being of a modern lama size, with the side dactyls of its extremities reduced completely and only one pair of incisors preserved on his upper jaw.
From Procamelus there come two branches: modern lamas and camels. At the end of the Tertiary Era, about two million years ago, camels were migrating to Eurasia till the Ice Age. Lamas migrated to South America across the Central America, which was at the stage of formation and represented a narrow strip of land. By the end of the Ice Age camels and the whole genus Camelus had become extinct in their initial place of inhabitance [2]. But, according to V.I.Svistun, 1971 [3], camels were widely spread in the South-European part of the USSR till the Ice Age. This opinion was given due to the discovery of camel remains (Golopoda Camelidae) in the Pontic deposits. B.S.Kozhamkulov and V.G.Kogenov, report the discovery of remains, looking like camels, in the mountains of Tien Shan [4]. The age of remains was determined to be 4 million years. The fossil was called Paracamelus. It was of a modern elephant size and lived at the height of 2200 meters above the sea level. So the question of evolution in the family Camelidae remains open.
In the common opinion of leading scientists, such as P.V.Kugenev [5], M.E.Fowler [6], and W.Beebe [7], having paid special attention to the problem of phylogenesis in their papers, the evolution of camels was going by way of adaptation to arid plains and, in relation to that, they continued to change in the direction of their body size growth [8]. From Eurasia the wild ancestors of camels went to Africa [1,2,5]. Evolution in arid plains was going in a way that camels began to adapt themselves to the hot climate of deserts and semi deserts. Under those conditions camels became irreplaceable animals for nomads. The camel is not only “the miracle of the desert”, but also “the ship of the desert” [9-12].
The evolution of another branch, lamas, was going by way of their adaptation to the life in mountainous regions [2, 12].
Camels are represented by two species: one-humped (Camelus dromedarius), dromedaries and two-humped (Camelus bactrianus), Bactrians. In the 1st millenium B.C. two-humped camels were named Bactrian’s after the area of Bactria - the state, which existed at that time. According to P.V.Kugenev “Bactria was represented by the northern regions of Afghanistan, and at that time it was one of the most ancient agricultural centres in Central Asia, where a lot of tamed camels were kept, the camels being probably two-humped” [5]. In the opinion of I.I.Lakoza, one-humped camels were tamed on the Arabian Peninsula 5000 years before our era [2]. But many scientists, such as M.E.Fowler [6], W.Beebe [7] and others, assume that the one-humped camel, called by the Greek “dromaies”, i.e. ‘fast running’, had been raised in Africa, namely: in the north-eastern part of that continent.
In the review, given by N.I.Burchak-Abramovich [9], H.Gauthier-Pilters [10], N.M.Yermolayeva [11], V.G.Shagayeva [12], there is no common opinion on the domestication centers of pad-footed animals (Tylopoda), in particular, of the genus Camelus.
According to the Chinese chronicles, in West China the two-humped camel was already well-known in the first millennium before our era. It is quite probable, that in those ancient times the biological range of the wild two-humped camel was much wider, than now. In relation to that, there could be also other places of domestication, situated to the West from Mongolia. The Romans called the two-humped camel the Bactrian, according to the name of Bactria, the country in Central Asia. But to that country the camel could also come later, having been already domesticated and brought from the East. Thus, taming of the two-humped camel took place at least one thousand years before our era (3000 years before our days) in the regions of Central Asia and, perhaps, in Kazakhstan and Eastern Siberia. Taming, with the subsequent domestication, of the two-humped camel is connected directly with the development of Mongolian and Turkic cultures.
The one-humped camel was probably domesticated for the first time in the central or south Arabia about 4000 years B.C. The most ancient mention of the domestic dromedary was made in the Bible. It is mentioned in it, that Abraham sent his servant with ten camels from Palestine to Mesopotamia to find a bride for his son Isaac. This happened about 1800 years B.C. Those camels were carried to India and North Africa for riding and carriage of cargoes.
Thus, modern camels originate from two wild ancestors: one-humped and two-humped wild camels. The evolution of wild ancestors took place in the restricted area of deserts and semi deserts, which is now the biological range of our domestic camel. After domestication the camel was left by the man in the same area of arid steppes, deserts and semi deserts, where the camel’s wild ancestors lived, i.e. the living conditions of camels were not changed by the man to such a great extent as those of other farm animals. Though the camel was tamed a very long time ago, it changed less than other animals and preserved a set of traits of its wild ancestor: some exterior and constitution features, colour, season character of reproduction and other biological characteristics.
The camel is well-adapted to the severe continental climate with its sharp temperature fluctuations, it reconciles itself both to heat and frost, but it is very sensitive to elevated humidity.
In Europe, beside Russia, camels are bred in Spain and Norway. They began to develop such a non-traditional branch of livestock breeding as camel breeding in Norway not long ago, since the 1960-s, when the Kazakh breed Bactrians in the amount of 25 heads were bought by that country from Kazakhstan.
In 1860 24 camels were carried from India to Australia. There, in the zone of salt-marsh deserts and dry steppes camels have acclimatized themselves quite well and the total number of these animals is increasing there with each year.
Due to great attention of the world community to the problem of preserving the most valuable genofund of two-humped and one-humped camel breeds in the countries of Central Asia, Kazakhstan and Mongolia, the hope has arisen that camel breeding will be not only preserved, but also developed.
Wild camels. The most ancient data about wild camels are in the Chinese annals. But relatively detailed descriptions of their life and constitution refer only to the end of the 19th century. The Chinese assumed, that camels’ Motherland was the most wild locality – the Shamo (“the sandy sea”) or the Gobi (“the desert”). Already in the middle of the 19th century Si-Yu-Ven-Kiang-Lo, the scientist and writer (mentioned by I.I.Lakoza, 1953 [2]), stated, that beside wild donkeys and horses there were also wild camels. Despite numerous evidences, the European scientists doubted that there existed any wild camels, until N.M.Przhevalsky managed to see and describe them, to deliver their pictures, pelts and skeletons.
After N.M.Przhevalsky, who delivered his collection to the Zoological Museum of the Russian Academy of Sciences, the wild two-humped camels were described by the Swedish scientist and traveler Sven Gedin. Beside biological observations, made by Przhevalsky and Sven Gedin, there is Lekhe’s anatomical research. According to Lekhe, the difference in the appearance of the wild two-humped camel and the domestic one is expressed in the following traits: the wild camel’s humps are smaller; its longer hair is developed on the tops of its humps, the neck, the chick, the external side of its hips, the proximal parts of its forearm and the tip of its tail; its face is shorter; its ears are shorter; on the knees of its fore-feet there are no pads found.
There is also some difference in the skull: a stronger ridge on the back of its head, a larger width behind the eye-holes, a larger length of the face axis, etc. But all these features are not sharp.
Systematic position of the genus Camelus. According to the zoological classification, given by A.B.Baimukanov [13], camels belong to the artiodactyl order (Artiodactyla), the ruminant or hole-toothed sub-order (Ruminantia), the pad-footed super-family (Tylopoda) and the camel family (Camelidae). This zoological classification generally coincides with the systematic classification suggested by I.I.Lakoza [2].
According to P.V.Kugenev [5], the camel family (Camelidae) is included into the pad-footed (Tylopoda) ruminant sub-order, the artiodactyl order, i.e. the pad-footed are distinguished into an independent group, in a parallel way to the ruminants. This systematics was shown in the book “Breeding of farm animals” [14]. The family Camelidae, in its turn, is presented by two genera: lamas and camels. The first ones are subdivided into two species: guanacos and vicunas, the second ones are presented by dromedaries and Bactrians. This scheme, in our opinion, certainly, does not reflect the zoological classification of the family Camelidae. Firstly, camels and lamas are the same ruminants as the representatives of the hollow horned families - giraffes and deer, i.e. the family Camelidae is referred to the ruminant sub-order. Lamas and camels are pad-footed. This is their characteristic feature. So it would be more accurate to refer camels to the pad-footed sub-family, as it is shown in the paper of A.B.Baimukanov [13].
According to another classification, given in the 2nd edition of the book “World List of Domestic Animals’ Species”, published in Rome with assistance of FAO/UNEP [15], the camel family is referred to the ruminant suborder (Ruminantia), the artiodactyl order (Artiodactila). The family Camelidae is represented by two genera: the New-World camelids and the Old-World camelids. The Old-World camelids include two species: dromedaries and Bactrians, while the New-World camelids are llamas, guanacos, alpacas and vicunas.
According to the classification of an American scientist M.E.Fowler [6], the corn-footed are presented by two genera: the South-American camelids (SACs) or Old- World camelids and the New-World camelids. Further, the South-American camelids are represented by two species: llamas and vicunas, the author giving here for the first time the substantiation, discussionable enough, about the necessity to refer llamas and vicunas to independent species, as it is fixed after dromedaries and Bactrians, the Old –World animals. Representatives of the llama species are the guanaco, alpaca and llama sub-species. Another branch, vicunas, is represented by the vicuna itself, the Peruan vicuna and Argentine vicuna sub-species. Thus, the present classification of camels, to this or that extent, coincides with the generally accepted zoological classification of the family Camelidae [13, 15].
Proceeding from the abovesaid, it can be concluded that the main dispute in systematics is about referring camels to artiodactyls: whether to distinguish camels into a special corn-footed sub-order or to confine ourselves by the rank of a super-family; whether it is expedient to divide the Camelidae family representatives into two genera: the Old-World camelids and the New-World camelids or to remain a supporter of A.Baimukanov [13] and I.I.Lakoza [12], according to whom the camel family includes two genera: camels (Camelus) and lamas (Lama).
According to camel breeding papers dated 1894 (A.G.Leonard [16]), the discussion or scientific dispute about the systematic position of the genus Camelus representatives always took place and , as a rule, one systematics used to be replaced by another.
Before the classification, suggested by K.Linney in 1766, camels were subdivided into three groups: Turkestan two-humped Bactrian camels, Arabian one-humped camels and fast-running one-humped camels, called by the Romans “Camelus droma” -dromedaries.
Within the camel genus K.Linney distinguished two independent species of one-humped and two-humped camels, having taken the number of fat humps as a trait of their specific difference. This classification was accepted without any objections by the majority of naturalists.
In 1815 Porte (cited by R.G.Leonard [16]), who worked with camels in Italy, raised again the question about incompleteness of the classification that existed and suggested to distinguish the group of fast-running dromedaries into a separate species. Later K.Linney’s classification was criticized in another plane, with disputing the substantiality of distinguishing the species of dromedaries and Bactrians. In this discussion the majority of naturalists considered the main criterion of specifying the species or variety to be the fertility or barrenness of hybrids.
According to F.X.Lesbre [17], the difference between dromedaries and Bactrians is even greater than between horses and donkeys, and the hybrids of dromedaries and Bactrians are barren. O.Buffon [18], saw the difference between these animals in the number of humps and considered their hybrids to be very fertile. The French researcher C.Cauvet [19], affirmed that the hybrids of dromedaries and Bactrians were barren like mules due to the difference in skeleton development and the origin from independent wild ancestors.
One of the main reasons of the protracted discussion in the beginning of the 20th century was that the science abroad had no reliable facts. In the opinion of I.I.Lakoza [20], the above listed authors [16-19], “had an opportunity to receive the actual material only on one type of camels - dromedaries”. It is quite understandable due to the fact, that dromedaries are raised in the western part of the Asian continent and in African countries, while Bactrians are raised in the eastern part of the Asian continent [20,21]. The range borders of both types camels pass through camel breeding regions of Kazakhstan. Otherwise saying, in Kazakhstan there are both dromedaries and Bactrians, and also a large number of their hybrids. So the best opportunities to study the main aspects of biological and agricultural sciences in the branch of camel breeding, so poorly studied or not studied at all, are in the Republic of Kazakhstan.
Proceeding from the analysis of Soviet and foreign papers of the first half of the 20th century, it should be noted here, that the factual data on camel hybrids are given in detail in Soviet zootechnical papers. For example , V.N.Kolpakov [21] and S.N.Bogolyubsky [21], give in their papers scientifically grounded data, with taking into account the development of science of that time, about camel species and their hybrids, and give the facts, well-known to all camel breeding practicians, of unlimited fertility of these hybrids. Proceeding from hystological studies, G.M.Pkhakadze [22], proved that the hybrids of dromedaries and Bactrians had quite normal spermatogenesis and ovogenesis. Thus, the problem of specific separation of dromedaries and Bactrians, if to proceed from the traditional biological concept of species, suggested by E.Meyer [23], seems to be solved negatively due to the indisputable fact of unlimited fertility of camel hybrids. From the point of view of zoo technical science, the specific separation is proved due to the spread of one-humped and two-humped camels under different natural climatic conditions. The biological range of dromedaries includes hot deserts of subtropical and tropical zones, while that of Bactrians includes deserts and steppes of Kazakhstan, Mongolia, Siberia and China, places with long and severe winters. Thus, dromedaries and Bactrians are isolated not in a reproductive way, but by the biological range [23-24]. In the opinion of the Soviet scientists [25-43], FAO/UNEP [15] and others, the peculiarity of camels’ biological range is not occasional, and it cannot be explained only by economic reasons of expedient breeding of certain species (dromedaries or Bactrians of certain breeds) and interbreed hybrids in certain natural climatic zones. In our opinion, the reason here is of more deep biological nature, which, according to the above-mentioned authors, influenced somehow the phenotype and productivity.
In the opinion of V.Lundholm [44] and P.V.Kugenev [5], the productivity specialization (meat-fleece, milk, meat-milk) in camels took a long time in the process of domestication.
Specific peculiarities of domestication as an evolution phenomenon are in the scales and rates of morphophysiological transformation of domestic animals, the mechanism of which is still not revealed.
According to I.I.Lakoza [2], accumulation of fat in camels’ humps is the result of domestication, and their wild ancestors had no humps. That is, appearance of humps did not bear any adaptive character. According to A.G.Bannikov [45], wild camels have compact accumulation of fat in their humps, which plays a great role in the area of their inhabitance (lack of water supply, poor vegetation), they are of smaller size than their domesticated relatives. That is, in the process of domestication the wild camel had changed into two-humped and one-humped camels. These two species have remarkable changes in their body composition: the body size and body proportions.
In the process of camels’ domestication there happened no substantial changes in their physiological functions, i.e. the season rhythm of their offspring reproduction was preserved. To our mind, this trait of camels is strictly stabilized and does not depend on their species, breed or biological range. That is there is no hereditary variety in relation to reproduction: almost all of them mate once per two years, within the terms strictly determined.
The diversity in camels’ productivity (meat, fleece, milk) is the result of purposeful selection. Their high productivity is achieved due to regular artificial selection, carried out by mankind for many thousand years.
Under modern conditions of camel breeding, when different farms (breeding and commercial farms for milk production and fattening) are created, it is impossible to avoid inbreeding . When restricting free crossing and inbreeding, applied in camel breeding, there appear homozygous recessive mutations, hidden , as a rule, in natural populations. For example, the white colour of camels shows itself only in the homozygous state and occurs seldom. But due to rigid selection and use of temperate inbreeding, it became possible to raise the line of white Kalmyk Bactrians [46] and Turkmen dromedaries [47]. That is the process of mutations does not stop under the conditions of domestication either. Revealing the reserves of hereditary mutability is always accompanied by the rise of total reactivity of the organism to negative factors and, hence, by the rise of mutability.
Domestication and selection increase the rate of forming phenomena in the result of breaking the regulating systems of development and arising of new forms of interaction between the genes. All this results in the phenotypic display of mutations, having not been displayed before, in the new genotypic environment, i.e. this results in revealing the population’s genetic reserves. Knowing the bases of camels’ evolution and ecology, to our mind, it is possible to carry out efficiently the selection-genetic and the selection-pedigree work to increase the productivity and reproduction ability, with taking into account the latest achievements in biological and agricultural sciences. It is confirmed by the research work, carried out by F.C.Bodenheimer [48, 49], T.W.Box [50], R.Capot-Rey [51], F.M.Elamin [52], J.O.Evans, J.G.Powus [53], C.R.Field [54]. and other scientists.
According to P.V.Kugenev [5], the attempts to cross lamas and camels appeared to be vain, showing a great evolutionary isolation of South-American camelids and camels. Proceeding from this, it is quite possible to agree with the zoological classification, according to which lamas and camels are referred to independent genera Lama and Camelus. But the classification, suggested by M.E.Fowler [6], /, supported by many scientists from Europe and America, is not perfect, since it doesn’t take into account the karyotypic characteristics of the genus Camelus representatives.
The cytogenetic research work, carried out by D.A.Baimukanov et al. [55-56] on Camelus bactrianus, Camelus dromedarius and their hybrids, showed similar diploid number of chromosomes in the animal groups under study, equal to 74. According to T.D.Bunch et al. [57], two-humped and one-humped camels, guanacos and llamas have similar diploid number of chromosomes (74) and close morphology. This shows the rigid karyotypic stability in the family Camelidae. It should be noted here, that, according to T.D.Bunch et al. [57], the karyotype of camels and llamas is represented by 3 pairs of autosomes of a methacentric form, 33 pairs of autosomes of an acrocentric form and sexual X and Y gonosomes. D.A.Baimukanov et al. [55-56], report that the karyotype of camels is represented by 6 pairs of autosomes of a methacentric form, 30 pairs of autosomes of an acrocentric form and sexual X and Y gonosomes of a methacentric form. Perhaps, such a difference in the morphology of chromosomes is related to interbreed differences. But, taking into account the high karyotypic stability in these species, such assumption seems to be improbable.
The phenotypic variety of existing camel breeds is not related, apparently, to the chromosome number karyotype mutability, but is determined by certain changes on the molecular level. Thus, it should be noted here, that in spite of the presence of such a clearly expressed phenotypic distinction, like the number of fat accumulations on the back in the form of humps, the karyotypes of two-humped and one-humped camels appeared to be identical. In other animal species, having fat accumulations, in particular, in fat-rumped sheep, there was found the same feature [57], i.e. absence of karyotypic distinctions in presence or absence of fat accumulations near the tail.
Academician M.F.Ivanov [58] pointed out, that fat-rumped sheep appeared at the time, when the process of sheep domestication was already over, since in wild populations there are neither long-tailed, nor fat-tailed or fat-rumped sheep. Long-tailing, as the author states, appeared in the result of mutations. Later, under the conditions of arid steppe and semidesert pastures with their poor fodder resources, in one part of lean-tailed sheep there appeared an ability to stock up fat in the field of their tail with a proper change of its form. Apparently, this explanation is also applicable to the arising of humps in camels, i.e. this feature arose in the result of genetic mutations. All the subsequent natural selection during many centuries resulted in creation of two-humped and one-humped camels in different biological ranges.
It can be noted here, that the results of investigations performed, stating the absence of interbreed distinctions in the diploid number of chromosomes and general morphology of chromosomes in the karyotype, correspond to the data, reported by I.K.Sharipov [59], on cytogenetics of sheep. Wide karyological investigations of the sheep of different breeds, with hundreds of animals used, did not permit the author to state the presence of any interbreed distinctions by the number or morphology of chromosomes, including those by the pattern of Gymza-strips.
All the breeds have the same diploid number of chromosomes, equal to 54, though in the wild relatives of sheep, i.e. the snow ram, the mouflon, the archar and urial, a wide chromosome polymorphism was found, from 2n=52 in the snow ram to 2n=58 in the urial. Only the mouflon, which is considered the direct ancestor of sheep, has a 54-chromosome karyotype. Similarly to this, among the pad-footed the 74-chromosome karyotype is found in llamas and guanacos, which can be considered the wild ancestors of camels on the basis of karyotypic data.
Taking into consideration all stated above and also the result of our own investigations, we assume it to be necessary to specify the systematic position of camels according to the biological conception of species’ formation [23]. According to the zoological classification, suggested by us, and, proceeding from the facts of free crossing of one-humped and two-humped camels and similarity in the number and morphology of chromosomes, Camelus dromedarius and Camelus bactrianus are referred to sub-species. As for lamas, we have decided to agree with the generally accepted classification, suggested by FAO/UNEP [15]. For a more precise characteristics of the evolutionary isolation of lamas and camels, we have decided to consider it expedient to accept lamas as representatives of the genus of not humped camels, and Bactrians and dromedaries as those of the genus of humped camels.
According to FAO/UNEP [15], guanacos and vicunas are wild animals, while llamas and alpacas are domestic ones. We consider it to be premature to refer vicunas to an independent species, though there is the fact of impossibility to cross vicunas with llamas, alpacas and guanacos. But llamas, alpacas and guanacos can be crossed with each other [15]. Thus, camels are represented by two sub-species: Bactrians (Camelus bactrianus) and dromedaries (Camelus dromedarius), are referred to the chord type, mammal (Mammilla) class, artiodactyl (Artiodactila) order, ruminant (Ruminantia) sub-order, pad-footed (Typoloda) super-family and camel (Camelidae) family.
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Источник для подробного ознакомления:
1. Baimukanov D.A., Baimukanov A.B. Evolution and genetics of Camels. –Almaty, 2014. -55 p., tabl.19, fig.22 (in English).
2. Баймуканов А., Баймуканов Д.А., Амерханов Х.А., Юлдашбаев Ю.А., Гаряев Е.Б., Гаряева Х.Б. Селекция верблюдов: теория и практика // Монография (ISBN 978-5-9675-1836-2). – Москва: РГАУ-МСХА имени К.А. Тимирязева.2021. -333 с. https://www.elibrary.ru/item.asp?id=46806628
3. Баймуканов Д.А., Юлдашбаев Ю.А., Баймуканов А., Монгуш С.Д. Продуктивное и племенное верблюдоводство / Учебник. Кызыл, 2020. 220 с. https://elibrary.ru/item.asp?id=48225900
4. Продуктивное и племенное верблюдоводство: учебник для вузов (ISBN 978-5-507-46122-6) / А. Баймуканов, В. И. Трухачев, Д. А. Баймуканов, Ю.А. Юлдашбаев, Х. Б. Гаряева. — Санкт-Петербург: Лань, 2023. — 308 c.: вклейка (16 с.). — Текст: непосредственный. https://www.elibrary.ru/item.asp?id=46806628 https://www.labirint.ru/books/960308/
Статью подготовили:
Дастанбек Асылбекович Баймуканов
Член-корреспондент Национальной академии наук Республики Казахстан при Президенте Республики Казахстан, Главный научный сотрудник отдела животноводства, ветеринарии, анализа кормов и молока Товарищество с ограниченной ответственностью «Научно-производственный центр животноводства и ветеринарии», 010000 (Z10P6B8), Республика Казахстан. г. Астана, ул. Кенесары, 40, офис 1505
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