The camel, a desert champion
The camel has been termed an excellent desert animal that can withstand high temperatures as well as weeks without food or water (Schmidt-Nielsen, 1962), which has led to variant exploitations by man in Asia and Africa not only as a transporter of everyday supplies but also as a source of meat, milk, hides and wool (Bornstein, 1990). Its habitat is mainly arid and semi-arid deserts whereby they are either hot and dry or cold and dry leading to a need of regulatory mechanisms by the camel so as to survive in such environments. Its ability to survive and perform in such harsh conditions with very little supplies has led to most researchers questioning the anatomy and physiology of this animal, trying to find the reason it has been able to gain the reputation as a beast of burden traditionally.
Classified under the order Artiodactyla, suborder Tylopoda, the camels are ruminating animals although not put in the same boat as the ruminants due to differences in foot anatomy, stomach structure as well as absence of horns (Yam & Khomeiri, 2015). They fall into the family Camelidae that has three genera which are: the old world camels, Camelus, which has two species, the C. dromedaries and the C. bactrianus (Teka, 1991); the new world camels, Lama, which has the species L. glama, L. guanicoe, L. pacos and lastly the Vicugna which has one species, the V. vicugna (Yam & Khomeiri, 2015). All the three genera occupy different habitats and thus any physiological adaptations that they have correlate to their environment, thus they exhibit different physiological and anatomical patterns.
Fig1: The Camelus dromedaries (left) and the Camelus bactrianus (right) showing different morphology in relation to their different habitats.
Fig 2: The new world camel species; L. glama (Ilama), L. guanicoe (Guanoco), L. pacos (alpaca) and V. vicugna (vicuna).
The most common species are the C. dromedaries (Dromedary) also called the Arabian camel which is one-humped and found occupying Northern Africa, the Near east and West Central Asia whereby conditions are arid or semi-arid (Teka, 1991). The C. bactrianus (Bactrian) that resides in the low temperature zone areas of southern Russia, Mongolia, east-central Asia as well as China. Such environmental conditions prompts the camel to conserve water and they do so by reducing their faecal, urinary and evaporative losses of water. The process is regulated by the kidney which decreases the filtration rate by increasing tabular reabsorption of water (Teka, 1991), hence less amount of water is lost to the external environment. It also has a very large alimentary canal that allows the constant reabsorption of water and thus reducing the water loss (Bornstein, 1990). The Dromedary tends to excrete concentrated urine in a bid to conserve water as regulated by the kidney which allows the animal to go for a maximum of two weeks without water and when the water is availed to them they are able to drink more than 25 to 33% of their weight (Teka, 1991).
The water conservation has also been attributed to the camel’s hump which consists of a large content of adipose tissue. As the camel is running on a short supply of food, soon the fats deposits are going to be used up providing energy and such metabolism yields oxidation water whereby 1gram yields about 1.1 grams of water (Schmidt-Nielsen, 1962). Contrary to popular belief it has been argued that the substantial water gain was negligible in comparison to the water lost as the oxidation water was going to be channelled to respiration by evaporation of the water from the lungs in the form of dry air (Schmidt-Nielsen, 1962). This leaves the hump as a fat storage organ rather than a water storage organ which allows adaptation to a limited supply of food.
Size of the camel also plays a pivotal role in the adaptations of the camel to its environment. These are large organisms with an adult Dromedary standing over 2meters and reaching a weight of 400kg-700kg giving the animal a large skin surface in relation to the body mass (Bornstein, 1990). The body heats up less quickly than off small organisms thus maintaining body temperature in the hot area.
Camels have the ability to store heat in their body attained from a 35-40oC hot environment during the day time increasing their body temperature to about 41oC during the daytime and useful during the night where temperatures may drop drastically. The heat may be lost through conduction, convention and radiation without a substantial amount of water lost (Yam & Khomeiri, 2015). This is a very imperative adaptation by the Bactrian as it resides in a cold climate and the addition of two humps are an added advantage to fat conservation for regulating the body temperature in a cold environment. The presence of fur on the camel also assists in the insulation of the animal at low temperatures giving it an added advantage at survival in the cold and arid areas (Schmidt-Nielsen, 1962).
For thermo-regulation maintenance the camel pants and sweats. Recent studies have shown the camel has some sweat glands although these were not the classical ‘apocrine type’ normally noted in organisms (Tana & Abdalla, 1980). Sweat glands were present in the Dromedary in all skin areas with the exception of the lips, external nares and the perianal region with the Bactrian having less number of the sweat glands per millimetre of skin area although present (Yam & Khomeiri, 2015). Hence despite its environmental conditions, thermo-regulation is an essential to its survival.
A hot environment means a general high metabolic rate, although this is not the case in camels, dehydration in turn leads to a lower metabolic rate due to the inhibition of thyroxin during periods of distress, that is, dehydration. This prompts a decrease in pulmonary water loss and in turn reduced metabolism (Yagil et al., 1978).
Camels are able to feed on a wider variety of plants somewhat considered unsuitable for most herbivores which is another adaptation that allows them to thrive in harsh environments. The species of preference in the diet differ in different areas although common examples include species of Acacia, Indigofera, Salsola and Balanites Aegyptiaca (Teka, 1991). These are usually thorny and hard, and a camel has the ability to feed even under severe dehydration which makes them the preferred domesticated species in these parts of the world.
Other physiological adaptations include wide even-toed feet that allow locomotion ease in sandy deserts, long eye lashes as well as slit nostrils that allow the protection from dust particles in the eye and nose. Some behavioural adaptations for water conservation are: seeking shade; orientation lengthwise to the sun; sitting with legs folded under body; exposing minimal surface as well as sitting on one spot to avoid contact with hot surface (Schmidt-Nielsen, 1962).
Fig 3:Camelus batrianus juveniles regulating temperature by folding legs under body.
Over the years camels have adapted to the existing environment due to morphological, behavioural, physiological as well as anatomical adaptations to the environment, although this is slowly being put to waste by climatic changes (Faye, 2014). This has given rise to dire effects which include diseases as well as a depletion in feeding resources, posing as a threat to the species as a whole thus the need to conserve the environment.
REFERENCES
Bornstein, S. (1990). The ship of the desert. The dromedary camel (Camelus dromedarius) a domesticated animal species well adapted to extreme conditions of aridness and heat. Rangifer: special Issue, 3, 231-236.
Faye, B. (2014). The Camel today: assets and potentials. Anthropozoologica, 49(2), 167-176.
Schmidt-Nielsen, K. (1962). Comparative physiology of desert mammals. Agricultural Experiment Station, 21, 9-21.
Tana, A. A. M., & Abdalla, A. B. (1980). Light and electron microscopy of the sweat glands of the dromedary camel. Acta. Vet.BRNO, 49, 31-35.
Teka, T. (1991).The Dromedary in East African Countries. Commission on Nomadic peoples, 29, 3-9.
Yagil, R., Etzion, Z., & Ganani, J. (1978). Camel thyroid metabolism: effect of season and dehydration. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, 45, 540-544.
Yam, B. Z. A., & Khomeiri, M. (2015). Introduction to Camel origin, history, raising, characteristics, and wool, hair and skin: A Review. Research Journal of Agriculture and Environmental Management, 4(11), 496-508.
