There are only three species of camels, the Dromedary camels, Bactrian camels, and wild Bactrian camels. Humans have kept camels for thousands of years because of their extraordinary ability to withstand hunger and thirst for long in the most inhospitable environments. Their ability to flourish in harsh ecological conditions has made them the most favorite domestic animal among the desert dwellers. Their adaptive traits have enabled camels to survive in a prolonged water-deprived environment, high ambient temperatures, particularly in areas where water is scarce, and to survive in poor quality or scarce food resources. They are physiologically and anatomically armed with homeostatic traits which have allowed them to reproduce, survive, and support human life in hostile environments. As a result, camels are highly valued as a source of milk and meat in arid and semi-arid regions where other domestic animals may not survive.
They can survive for days without water
During the cold season or winter or in mild climates where green forage is available, camels can go for several months without a drink and they can even refuse to drink when offered water. In hot conditions, camels may go for 8-10 days without drinking and may lose up to 30% of their body weight as a result of dehydration. In temperatures varying between 86 degrees Fahrenheit and 95 degrees Fahrenheit these animals may go for up to 10 to 15 days without drinking. However, when temperatures go beyond 104 degrees Fahrenheit, they might need water after a short period.
Unique digestive and urinary systems
The urinary and digestive tracts of camels are well suited to conserve water. For instance, cattle may lose up to 5 gallons to 10.5 gallons of fluids every day through feces, while camels lose only 0.3 gallons. This is the leading method used by camels to resist the deprivation of water in the desert. Most fluids are absorbed towards the end of their exceptionally long intestines. The rumen plays a significant role in maintaining water balance. The foregut of a camel or a hydrated rumen of an ungulate animal would contain large amounts of water which could be about 20% of the animal’s body weight, and it acts as a reservoir for a short time deprivation of water. The kidneys play an important role in removing excess water, unwanted nitrogenous metabolites, and maintaining a relative osmotic concentration of blood. The kidneys of a camel have a long loop of Henle, which increases the osmolality of urine. When the camel is dehydrated, the kidneys reduce the loss of water by decreasing the rate of filtration while at the same time increasing the reabsorption of water. The loop of Henle in camels is about 4 to 6 times longer compared to cattle.
Tolerance against water loss and water intake
Camels can survive after losing water equivalent to more than 30% or even 40% of their body weight, while other mammals would die instantly after losing half of this amount. After water deprivation, all animals need to rehydrate to survive. A camel could drink water equivalent to 1/3 of its body weight, and this could be about 29 gallons, which they can consume within 10 minutes. If other animals consume this amount of water, they could easily die. The camels can store large volumes of water in their gut for up to 24 hours to avoid diluting the blood.
Unique blood cells
The viscosity of blood in a camel can remain relatively the same even when it is severely dehydrated. This is one of the most critical evolutionary adaptive traits among the camels during excessive dehydration and high heat load. The composition of the blood remains almost constant, and the functions of the hemoglobin remain normal as well. The red blood cells or the erythrocytes of a camel have an oval shape, and it is non-nucleated, which makes them withstand huge variation in osmotic pressure without rupturing. These cells can swell and increase in size to twice the original volume after rehydration. The oval-shaped erythrocytes can flow much faster with ease compared to the round-shaped cells of other mammals.
Rete mirabile or Carotid rete
A camel is always armed with different arsenals to ensure its survival in a harsh environment like a desert. Some of these unique adaptations include an artery that branches into a series of blood vessels found at the posterior region of the brain (rete mirabile or carotid rete), which come into contact with a network of small venules transporting blood back from the nasal passages. In this region, the blood from the artery exchange heat with the blood in the veins, which have been cooled in the nasal passages by respiratory evaporation. Through this mechanism, the blood reaching the brain of a camel is 39.16 degrees Fahrenheit cooler compared to the body temperature. This process of selective brain cooling allows the camel to maintain temperatures below the critical thermal values when the temperature in the body is excessively high.
Other Anatomical adaptations
Camels have thick coats that insulate them from excessive heat radiated from the sun, and during summer, their coats reflect light and help them avoid sunburn. The thickness of the coat varies as they grow and shed them according to the season and the prevailing conditions. The sweat also evaporates directly from the skin and not on the tip of the hairs like other animals. As a result, the latent heat of vaporization is taken from the skin, which is a more effective way of cooling besides saving more energy. Camels have nostrils that can close, and this protects them from sand blown by the desert wind. The nostrils are also slit-like, and when they exhale, water vapor is trapped, and they are reabsorbed into the body again. Long eyelashes protect the eyes from blowing sand and sun rays. In their eyes, they have a third eyelid, which is clear and protects the eyes from the sand as well. They also have broad and large footpads that help the camel to walk with ease through the desert sand. The large leathery footpads help in dispersing the bodyweight on a relatively large surface area, and their feet will not sink in the loose sandy soils.