ADAPTATION OF THE CAMEL TO DESERT ENVIRONMENT
Dept, of Vet. Hygiene and Management , Faculty of Veterinary Medicine, Cairo University
The camel attained its greatest importance to man in times of warfare and when warfare become mechanized, interest in the camel tapered off . Physiological research renewed the interest of camel first purely academically then the camel’s social ability to survive could be used for the benefit of man and therefore interest in the camel today in congresses dealing with the problem of food in drought areas .
Adaptation of animal to its environment in general is used often for the process of adjustment to the environmental changes . Adaptations of the camel to the desert environment encompass anatomical , behavioural and physiological changes . It is quite clear that , the camel does not have any special mechanism for survival but relies on mechanisms known to and utilized by another animals . All the desert species have fluctuating body temperature decline in metabolism and utilization of intestinal water. The camel, however is able to utilize these mechanisms more effectively when exposed to the direct rays of the sun and for extremely long periods without drinking water (Nielsen,1979).
Regarding the desert environment , there are several problems facing the desert animals, those are lack of food and water ( starvation ) , sandy or stony ground , thorny plants or trees , hot and windy climate and finally the presence of natural enemies .The camel is one of the most important desert animal and the following points discussing how the camel cope with the desert environment .
1- Anatomical adaptation
a- Head and neck
¨ The head of the camel is small in comparison to that of other domestic animals . It bears no horns and has small bluntly erected ears to hear the minimal sound vibration and hear for long distance in the desert . Also , the ear contains small hairs to filter and warm the air entered the ears in sandy environment .
¨ The eyes are large and prominent enable the camel to see in different directions and for long distances . The massive supraorbital fossa or processes give some protection with the long lashes against the sandy environment of the desert in windy day .
¨ Also , the nostrils of the camel are long slit- like appearance having wing , so the camel is the only animal who can close its nostril as protection against sand and winds .
¨ The upper lip is split and hairy , extensible and slightly prehensile , it is very sensitive . This modification help the camel to select its food
¨ ( selective feeding ) and avoid the thorny plants .
¨ The camel has a long arched neck helping him to manipulate the high tree plants and to explore the enemy from long distances .
b- Trunk and tail
¨ Most of the fatty tissues of camel is stored in the hump than being diffused throughout the body . The hump acts as food ( fat ) storage which will be converted to energy and water in case of starvation in the desert .
¨ Skin of camel is attached rather tightly to the underlying tissues and has short fine hairs ( weber) which help in thermoregulation .
¨ Prepuce of camel is normally directed posteriorally , it is possible that this elevated position keeps the organ from touching the hot sand when the camel squats on the ground and avoiding its contamination with sand .
¨ Placenta of she camel is simple diffuse smooth type as in mare with no cotyledons so the retention of placenta is rare.
The legs are relatively long and slender , an adaptation , perhaps to a long easy gait in sandy environment , and to adaptive cooling , and terminate in large disk -like feet .More than 65% of the camel’s total weight is supported by the front limbs . the chest is deep and narrow which allows the balance to be shifted easily , so that it is directly over the weight bearing foreleg during locomotion .
The foot of the camel is well designed to cops with the loose sandy soils of the desert . The bearing surface of the foot is like a large plate , this plate is able to maintain flat contact with the ground throughout the duration of the stride due to exception rotation at the first digital joint . The foot stays out on taking the weight of the camel and thus act as a firm base for levering the weight forward to the next stride . the camel foot is excellent for movements on sand . It is less suitable for traversing stony desert althought some hardening occurs in animals habituated to this kind of country .The presence of the peculiar horny pads on the elbows , stifle and chest prevent more injuries to camel from the stony desert .
2- Physiological adaptation
Physiological adaptation defined by biologists as the physiological processes involved in adjustments by the individual to climatic changes and changes in food quality …… etc.The requirements for survival in hot arid areas are very important . Temperature must be maintained and water must be conserved . The camel losses body heat by sweating more efficiently than other mammals .Adaptation of camel to desert environment are listed below
¨ In most mammals fat is spread over the body surface just under the skin . In the camel , the fat is concentrated in the hump which enables sweat to be evaporated easily over the rest of the body surface and this is adaptation to heat transmission .
¨ The skin is supple , covered with short fine hairs ( waber ) , which act as insulating medium and may be longer in cooler climates or during the cool seasons in hot areas ( thermoregulation )
¨ The poll glands which are situated towards the top of the back of the neck behind ears and cover an area of about 6x4 cm in both sexes . It is more active under condition of heat and fatigue than that at any other time except when the male is in rut , so it act as modified sweat gland to help in the evapration .
¨ Also , the coat of the camel is fairly sparse which allows sweat to evaporate at the surface of the skin. In mammals with very thick coats evaporation occurs at the ends of the hair a less efficient process .
¨ The body temperature can vary over a wide range under condition of dehydration . The large mass of the camel acts as a heat buffer .
¨ The camel can lose 25% of its body weight over a period of time without losing its appetite for food and can then make up this amount in just 10 minutes by drinking . While in other animals , water lost is drawn from the body tissues and the blood plasma .As a result the blood becomes viscous and the heart can no longer pump and explosive heat death then occurs . In camels, very little water is drawn from the blood, which remains fluid and can thus cotinue its function of heat transfer (Dorman,1984)
2- Energy balance
The camel is able to save considerable amounts of energy by allowing its body temperature to rise during the day , thus absorbing heat would be dissipated by some form of cooling . The variations in the camel’s temperature were formerly thought to be an indication of poor thermoregulation . It is now realised that the rises in temperature indicate a sophisticated control mechanism rather than poor regulation .
3- Water balance
Water is essential to life and the camel has often to survive on limited quantities for long periods of time . To do this , it has developed not only a very low rate of water use but mechanism for restricting water loss as soon as its intake is reduced
a- The hump is mainly comprised of fat and thus the metabolic water content is high , complete oxidation of fat in the hump results water ( 20 kg of fat , would release a total of just over 21 kg of water ) . Oxidation of an equivalent amount of starch yields less water .
b- The camel’s stomach contains a large amount of fluid secreted by the glandular sac areas which called “ water sacs “
c- Water is lost from the body by evaporative cooling , in the urine , and in the feces . The structure and function of the kidney are extreme importance in water conservation the long loops of Henle in the medulla have the function of urine concentration . Urea is reabsorbed from the intestine and transferred back to the stomach for reconservation to protein . The kidney controls water loss in two ways : either by the absolute concentration achieved or by reduction in flow of urine . Concentration of urine not only serves to conserve water but allow camels to drink water even more concentrated than sea water and to eat very salty plant that would otherwise be poisonous . A reduction in urine flow is also achieved by reducing th glomelular filtration rate from a norm of 55-65 ml/100kg body weight / minute to 15 ml / 100kg / min .
d- Fecal water loss is also small in camel . Final reabsorption of water occurs in the colon.
3- Milk and milk quality .
In the meaning of koran “ which explain what the prophet Mohammed preached “ it clearly states that , when men who lived in the desert turned to God for help in surviving in the inhospitable climate . God answered their pleas and gave them the she- camel to drink of their milk . It was the camel’s ability to convert the scent desert food sources into milk and meat for human consumption that was instrumental in the domestication of this animal. Only the camel can survive and continue producing milk in arid areas(Yagil,1985) . It is common practice for nomads crossing the desert to take milch camel with them because the long marches without water do not depress milk secretion . Young camels can derive their nutritional and water requirements entirely from milk in times of water restriction(Yagil,1985).When lactating camels were subjected to chronic dehydration ( 10 days of water restriction followed by1 h . water followed by another 10 days dehydration ) from spring to the end of summer ,milk secretion was not affected( Wilson,1984) . Full exploitation of the camel’s ability to survive and lactate in drought areas will only be possible when the reproductive performance is improved .
Camels milk contains an average of 70 kal/ 100g milk . It is calculated that 3 –4 kg of milk would cover the daily caloric requirements of an adult man as 1.8kg milk would covered a man’s daily protein requirements ,therefore camel milk is an ideal source of nutrition for man in the desert and is often the only source . Camel milk normally has a sweet sharp taste but some times it tastes salty. The taste is affected by the nutritional and environmental factors.The she-camel secretes a highly diluated milk with a low fat content whereas , the cow , ewe and goat all secretes concentrated milk when drinking water is scarce. Chronically dehydrated camels (drinking water for only 1 hr once a week ) secrete milk with over 90% water and with only 1% fat , this is superadaptation for a desert environment ( normal milk contains 84% water and 4.5% fat ). The physiological explanation of this phenomenon is as lactation is a water losing process for the mother, the hormone ADH and aldosterone are secreted in addition to milk secreting hormones ( prolactin and oxytocin ). ADH and oxytocin cause the release of ACTH aldestrone and prolactin , respectively . ADH , oxytocin and prolactin all have an antidiuretic effect while aldesterone , prolactin and ADH act on the intestines to absorb water and ADH cause the secretion of water into the milk as occurs in the sweat gland.
The extensive discussion about milk fat is appropriate as in times of water depletion it is the ability of camels to replace fat with water that will guarantee the survival of a species and the low –fat and high- water contents of camel’s milk decrease the calf-death rate in arid areas and it is appropriate for the need of children from milk ( normally severe dehydrated mammals give less water and more fat milk )(Yagil andEtzion,1980).
The increased lactose , with increased water , would explain the continuing lactation under adverse conditions . In general , camel milk is rich in chloride and vit.C ( varying from 5-7 % to 9.8 % ) . The vit C level is three times higher than those in cow milk . As lactation progresses so the vit C concentration in milk increased because fruit and vegetables are scarce in the arid zones , milk becomes an important source of vit C for the human diet in the desert .
III Behavioural adaptation
Under conditions of dehydration and intense heat the camel adopts behavioural mechanisms to conserve energy
1- The camel sits down in the early morning before the ground has warmed up . It tucks its legs underneath it’s body so that it absorbs little heat from the ground by conduction
2- The camel orientates itself towards the sun presenting the least possible body area for the absorption of radiant heat . Any heat absorbed from the ground or the sun would have to be dissipated later in the day
3- A group of animals may lie down together , thus presenting an even smaller target area for heat accummulation
4- The camel’s metabolic rate increases in the normal way as the temperature rises
· Ingestive behaviour
Camels are selective feeder not only with regard to plants but also in respect of the parts of the plants they eat .The natural selective feeding habits of the camel are considered the morpho physiological adaptation of the camel’s digestive tract
The digestive anatomy and physiology of the camel are peculiar in the adaptation to a wide rang of food types and in particular , coarse forage , without the necessity of a specialized cellulose fermenting rumen . The camel does , however posses adaptive mechanisms to compensate for long periods of poor quality food and water deprivation , for example , there is a slow decease in weight through fluid loss during exposure to high temperature (41c ) allowing adjustments of fluid spaces and a stable metabolism(Yousri,1976).
Camels are browsing animals, they feed on thorny plants of the desert. Anatomical adaptation as the mobile and prehensive split upper lip enable them to avoid the injuries of the desert plants , the camel jaw and dental pad enable it to seize and tear branches off trees if required , and with slow lateral movements of the jaw , the thorns of these plants are destructed . Also a small but mobile tongue with numerous hard , dentigerous papillae protruding from the lining of the cheeks and lateral aspect of the tongue assist in the mastication and ingestion of food . Although camels can resist thorns to some extent they are not completely immune to them and on very thorny species feeding is a slow business(Higgins,1986) .
The oesophagus has a large potential diameter with many mucus –secreting glands . The areopharyngeal and oesophageal anatomy assist in the movement of hard materials without causing irritation to mucosa .
The camel is a triple-purpose animal producing milk, meat and transport. It also provides hair and hide in some areas . Its comparative advantages over other domestic animals within the camel’s optimal environmental limits as follows :
1- Its water economy resulting from the ability to reduce water loss to a considerable degree
2- Its ability to support a very high degree of water loss amounting to as much as 30 % of its initial body weight .
3- Its massive capacity for making up water loss in a very short time when water becomes available ( can drink 180 litre / 24 hr .) .
4- The three previous factors enable the camel to go voluntary without water for up 10 days.
5- The camel doesn’t lose its appetite for food as it dehydrates, unlike other food producing domestic animals .
6- The ability of camel to fluctuate its body temperature coupled with anatomical and behavioural adaptation enable considerable saving in energy to be made .
7- The camel is primarly a browsing animal enabling it to make use of fodder often not relised by other domestic animals .
8- The huge plate-like feet themselves are less damaging to soil structure than the smaller cloved hooves of the other common domestic animals .
By utilizing all the knowledge concerning the physiology and behaviour of the camel, this animal which is so capable of surviving the extreme conditions in the desert can return to be a provider of food for man, as it was in Biblical times when man turned to God for help and was given the camel “ to drink of its milk “
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