Character of Animals:
The colder it gets outside the body, the more food he needs. Man insulates his body with heavy clothing and takes shelter. Some animals are insulated with fur, fat or feather, and also take shelter. Some hibernate in winter, and others migrate to avoid it. Most striking of all the main adaptations are internal physiological processes which help to conserve, tolerate and dissipate heat.
The warm-blooded animals of the same or related species tend to be larger in cold regions and become smaller towards the equator was accepted for a long time. The principle, called Bergmann’s rule – the larger an object, the more slowly it tends to lose heat. In
Primary heat – preserving mechanism is not size or shape, but insulation. It takes two forms: a layer of fat, or of tissue heavily impregnated with oil, just under the skin; and a layer of fur or feathers just over the skin. Thus insulated.
A bird ruffles its feathers, a dog or wolf or fox can fluff out its fur to trap air and gain temporary warmth. Animal can reduce heat-loss by modifying its shape, curling up in a ball to rest or sleep with nose and ears, paws and tail all tucked in. During the relatively hot weather, the carbohydrates in their food are converted into fat, for winter insulation and nourishment.
Some animals to maintain two internal temperatures, a tropical one for the body in general and a radically lower one for the extremities e.g., arctic birds prevent their legs and feet from freezing by increasing the blood circulation to the legs while still keeping them much colder than the body.
Curious, flightless sea bird, the penguin, lives only in the southern oceans. Penguins make wonderful use of their truncated wings to dive and swim through the water at up to 50 km an hour.
Penguins are well represented in the Antarctic avifauna. The living Penguins belong to the order Sphenisciformes with its single family Spheniscidae. The family is almost entirely restricted to the southern hemisphere.
The common penguins are Emperor (Aptenodytes forsteri), King (A. patagonica), Adelie (Pygoscelis adeliae), Chinstrap (Pygoscelis antarctica), Northern Gentoo (P. papua papua), Southern Gentoo (P. papua ellsworthii), Macaroni (Eudyptes chrysolophus) and Rockhopper (E. crestatus). The largest POLAR penguins – emperors live farthest south.
All species, though their head markings differ, have almost identical plumage the well known white shirl fronts, with backs and wings of rich black or midnight blue. The physical characteristics that distinguish penguins from other birds are briefly those that equip them for swimming and diving.
Short-necked and squat on land, they become elongate and fusiform in the water, swimming like tiny torpedoes with flipper-wings outstretched and vibrating.
The legs, set well back on the body so that the birds walk upright, become steering organs at sea; the partly-webbed feet combine with triangular tail to form .i flexible rudder. Huge wing muscles, covering a sternum that extends well down the body, provide both the motive power for swimming and the barrel like shape; sleek feathers and subcutaneous fat combine to give both the streamlined form and the efficient insulation that helps them to maintain a high body temperature in cold water.
This complex of characters enables penguins to swim efficiently, to spend long periods at sea without chilling or becoming waterlogged, and yet to remain mobile and efficient on land.
At sea they swim with the effortless ease of dolphins. Moving at speed they ‘porpoise’ in and out of the water, a method of swimming that allows them to snatch breath without loss of speed, and reduces friction by coating their plumage in a skin of air bubbles.
The dual Insulation of feathers and fat is remarkably efficient, allowing incubating or otherwise inactive birds to retain their full body temperature in conditions of extreme cold and strong winds.
King of the Ice-Polar Bear:
The polar bear is the undisputed ruler of a vast and desolate arctic domain. Born as likely as not in a snow cave out on the ice pack, a polar bear may never see land but spend its entire life travelling across the pack-ice in search of food. The polar bear has dense and oily fur. It grows to an immense 1600 pounds.
The must ox was the lord of the cold arid zone. Heavy coat protects it from winter cold and from summer hordes o’ blood-sucking insects. Its heavy hoofs can easily break the ice-crusts covering its favourite willow twigs.
When danger threatens, the bulls form a line in front of the cows and young i.e. they protect their young from wolves by forming a defensive circle around them. Their massive horns are a match for wolves and even Eskimos with primitive weapons.
The musk ox bears a prime commercial asset:
Under its long, coarse outer hair is a thick undercoat of wool that surpasses cashmere in soft lightness and strength.
Animal Characteristics in Cold Arid Zone:
1. Fishes of cold arid zone have more vertebrate than their relatives from warmer seas.
2. Legs and ears tend to short and rounded.
3. A heat exchange system. The feet of penguins, gulls and other birds function at very low temperatures. A heat exchange system of entwined veins and arteries cools the blood flowing to the extremities so that warmth is not wasted. The system can serve two purposes – circulation is restricted and heat retained when the surroundings are cold yet blood can be Hushed to the extremities if the animal needs to lose heat.
4. Many arctic mammals and birds have evolved relatively large feet which act as snow-shoes.
5. Marine mammals of cold deserts, the walruses and seals, spend a considerable part of their lives on shore.
6. Birds are the most conspicuous animals of the cold arid zone in summer.
7. Animals must be able to survive the change from cold and darkness o! winter to the warmth and light of summer and vice versa.
8. Animals store food before the winter begins and hiding it in a cache underneath rocks.
9. Breeding – most species produce their young at the beginning of the summer when the weather is warmer and food is plentiful.
10. Migration – The birds migrate to warmer climate on approach of winter.
11. Colouration – The white colouration of mammals and birds has been ascribed to the effects of cold.
Seasonal colour change is an hereditary factor under genetic control, e.g. in the north of Scotland the stoat, weasel and mountain hare become white in winter.
12. Hiding – Lemmings hide in their burrow under snow.
13. Hibernation – It does not take place probably because the short, cold summer does not allow sufficient accumulation of food reserves. But a few invertebrates survive cold in larval of pupal stages.
Animal Adaptation of Cold Arid Zone:
Survival under the harsh conditions of the polar regions is not simple. The organisms must tolerate both extreme low winter temperatures, as well as short cold summers and their adaptations must involve several kinds of ecological and physiological mechanisms.
Low temperature tolerance, increased metabolic rates, life cycle strategies, anaerobiosis, choice of microhabitats and morphological adaptations are among the factors involved. In adapting to polar desert Nacella (benthic invertebrate) alone has adopted to withstand short periods below -2°C. It adopts one of two strategies.
1. Resistance adaptations:
The mucous cocoon of Nacella increases the animals tolerance of lower temperatures.
2. Capacity adaptations or metabolic cold adaptation:
It is the development of low temperature enzyme systems which allow the animal to function at a relatively high metabolic rate. Growth is generally slow, reflecting the overall low level of food availability throughout the year, and in many species, is accompanied by longevity e.g. Nacella can survive at least 100 years.
Change sources of food – since food is generally scarce, particularly on the continental shelf, there is a widespread predilection for obligatory and facultative necrophagy among a number of taxa. Low temperature allows the animals to function at low basal metabolic rates, thus reducing their food requirements.
Brooding or vivipary is found in 80% of Antarctic sponges. Many Antarctic invertebrates have a number of characteristics in common, principally slow growth, deferred maturity, longevity, large size and reduced reproductive effort.
Periods of sparse food availability are an inevitable hardship of living at high latitudes where the summer periods of phytoplankton production are short. Cold is in many respects advantageous, because it permits lower basal metabolic rates, thus reducing overall energy requirements. Cold-hardiness
On the basis of cold-hardiness the insects are of following types:
1. Freezing tolerant – Insects are able to survive the actual formation of ice in their tissues.
2. Freezing susceptible – Terrestrial arthropods are killed by ice formation.
Insects depend on super-cooling to survive temperatures below the freezing point of their body fluids. Super-cooling to -40°C and -50°C has been recorded in insect eggs. The factor of great importance for super-cooling is the presence of cryoprotectant substances like glycerol or other polyhydric alcohols and sugars.
The effect of glycerol on super-cooling is purely physical. Because of the hydrophilic properties of this substance the amount of free water is reduced, and the chances of ice nucleation are decreased. Cryoprotectant substances are also important for cold hardiness.
Some invertebrates have the ability to undergo instantaneous and seasonal metabolic compensation for temperature changes. The increased metabolic rate following cold acclimation, i.e. a period of exposure to low temperatures, increases the activity and performance of the animals compared to warm acclimated specimens.
In some marine invertebrates compensation is complete within the temperature range of their environment, making it possible for them to maintain the same level of activity under all conditions.
Increased metabolic rates may be required to maintain development, reproduction and other activities under extreme temperature conditions, and terrestrial arthropods of the Antarctic may live in a state of permanent cold acclimation. Compared to temperate species, the metabolic rate of the Antarctic mite Alaskozetes antarcticus in the range of 0°C to 10°C, is twice as high.
Extending the life cycle is an important adaptation in many species. Extended life cycles are often connected with the ability to postpone part of the development when conditions in one year are unfavorable. As a result, many species over-winter in more than one stage.
Anaerobiosis (Life without Oxygen):
During the early part of the winter, because of repeated freezing and thawing, the surface of the ground is frequently covered by a layer of ice and check the respiration of plants and other organisms. Some insects from temperate mountainous areas are able to survive several months in an atmosphere of pure nitrogen at 0°C e.g. Alaskozetes antarcticus was the most tolerant- and more than 80% survived twenty-eight days of anaerobiosis at 0°C.
Polar fishes in comparison with temperate species show a tendency to decrease the haemoglobin content and the number of red blood cells (erythrocytes). The blood of Channichthytids is translucent with a yellowish tint and the gill filaments appear to be creamy white. This has led to their common names ‘ice-fish’ or ‘white blooded fish’.
Some species are able to survive -5°C temperature in a super-cooled state, if they do not come into contact with ice. In order to survive in ice- laden coastal waters polar fish have evolved macromolecules of glycoproteins in their coelomic and intercellular fluid throughout the year. The macro molecules have unique anti freezing properties.
The mechanism by which the glycoproteins lower the freezing point of water as well as preventing ice from forming in the body fluids is not yet fully understood. Kidney Structure in most marine teloeosts glomerular kidneys are present which are able to filter out molecules up to about 40,000 Daltons in size and excrete them into the urine.
Urine is formed by secretion. The non-glomerular kidneys may be considered as an evolutionary adaption to reduce glycoprotein loss to a minimum and thus save energy otherwise lost for the resorption of glycoproteins.
The elevation in metabolic rate due to cold is termed as cold adaptation. It is evolutionary adaptation to overcome the rate depressing effects or temperature. It is also meant that more energy was required for maintenance and less was therefore available for growth and activity e.g. slow growth rate in polar fish.
Temperature is a major factor governing the rate of metabolism as well as all other chemical reactions. The rate of reaction in biochemical systems normally slows down by a factor of 2-5 per 10°C, i.e. the difference in metabolic rate of tropical fish (30°C) can be expected to be nearly 20 fold that of Antarctic fish.
Krill’s although originally heavier than sea water, have evolved a number of specializations of the digestive, muscular, integumentary and skeleton system which made them neutrally buoyant.
The main buoyancy adaptations are:
1. Skeleton weakly calcified.
2. Scales incompletely mineralized.
3. High lipid content in white muscle e.g. in Dissostichus.