Adaptation

Environmental dynamicity, voluntary or compelled shifting of place and human activities may put organisms in a new niche or in environmental stresses or pressures. In such circumstances, the organisms must develop modifications for natural selection to act upon and to direct them to evolve characteristics suitable to the new situation. Thus, A biological adaptation is any structural (morphological or anatomical), physiological or behavioral characteristcs of an organism that has evolved over a period of time by the process of natural selection and that make it better suited in its environment and consequently garantee its reproductive success.Organisms that are adapted to their environment are able to:

• secure food, water and nutrients
• obtain air, warmth and spaces
• cope with physical conditions such as temperature, light and heat
• defend themselves from their natural enemies
• reproduce and rear offsprings
• respond to changes around them

The term adaptation is also sometimes used as a synonym for natural selection, but most biologists discourage this usage. Adaptation occurs in response to the change in the environment, relationship to other organisms or change in life style. Due to individual phenotypic plasticity, individuals will be more or less successful. Organisms that are not suitably adapted to their environment will either have to move out of the habitat or die out. The term die out in the context of adaptation means that the death rate over the entire population of species exceeds the birth rate for a long enough period for the species to disappear.

There is a great difference between adaptation and acclimation or acclimatization. Adaptation occurs over many generations; it is generally a slow process caused by natural selection. Acclimation generally occurs within a single lifetime and copes with issues that are less threatening. For example, if a human was to move to a higher altitude, respiration and physical exertion would become a problem, but after spending time in high altitude conditions one may acclimate to the pressure and function and no longer notice the change.

Types of Adaptation

Adaptation can be structural, physiological or behavioural. Structural adaptations are special body parts of an organism that help it to survive in its natural habitat (e.g., skin color, shape, body covering). Physiological adaptations are systems present in an organism that allow it to perform certain biochemical reactions (e.g., making venom, secreting slime, being able to keep a constant body temperature). Behavioral adaptations are special ways a particular organism behaves to survive in its natural habitat (e.g., becoming active at night, taking certain posture).

Based on the habitats for which organisms develop it, adaptation can be categorized into 3 fundamental types, namely aquatic, terrestrial and volant, each of which can be further divided into many subtypes.

Aquatic Adaptation

Aquatic Adaptation occurs in those plants and animals which live in water habitats, viz, fresh water, brackish water and sea water. Fresh water organisms develop features to prevent the entry of excess water or processes to drain exceess water regularly. In the contrary, marine organisms face scarecity of water due to hypertonic sea water. So they have mechanisms to retain water and throw excess salts that enter in water intake. The aquatic plants may be rooted plants (e.g., reeds), submersed plants (e.g., Hydrilla), planktons or floating plants (e.g., water hycinth). Similarly, aquatic animals may be benthic occuring at the bottom of water body or pelagic occuring in the water body itself. The animals may live partially or permanently in water. Thus they may be non-specialized to very highly specialized water dwellers. Primarily aquatic animals (e.g., fishes) show not a single terrestrial features, whereas the secondarily aquatic animals possess terrestrial respiration through lungs, and must visit land for laying eggs (e.g., turtle, whale). Partially water dwelling animals demonstrate amphibious adaptation with double features both for land and water (e.g., frogs, salamander) or mostly terrestrial features and only some basic aquatic adaptation (e.g., duck). The characteristic aquatic adaptations are:

• Body contour is spindle shaped and stream-lined. For this, head is elongated into rostrum or similar structure, neck is short, external ear (pinnae) are reduced and tail is laterally or dorso-ventrally compressed.
• Usually marine animals are excessively large (e.g., whale), because of the buoyancy of the salt water.
• Organs of locomotion and balancing vary greatly among the aquatic animals; fishes use paired and unpaired fins, whale and turtle have their limbs modified into paddles, in some others, hands and/or feet are webbed.
• Skin of most aquatic forms is rich in mucous glands to make it slippery. Fishes are equipped with dermal scales too. Aquatic mammals lack hair and skin glands (oil and sweat glands). In compensation, they have fatty layer below the skin known as bubbler. Besides insulating the body, it also help in floatation.
• Primary aquatic animals are capable of utilizing dissolved Oxygen of water for respiration through general body surface, internal or external gills, etc. However, secondary aquatic forms respire atmospheric air through lungs; nostrils are located at the apex of the head.
• In case of fishes, the hollow outgrowth of alimentary canal called air bladder functions as organ of floatation and accessary respiratory organ as it is filled with air. In whale and others, extraordinarily massive lungs and closable nostrils serve for the purpose.
• Fishes have lateral line systems extending the whole length of the body. It contains neuromast organs which act as rheoreceptors (pressure receptors).

Terrestrial Adaptation

Terrestrial adaptation is shown by the plants and animals occuring in the land habitats. As there are varied types of land habitats, the adaptations shown by organisms are also of diverse kinds.

Fossorial Adaptation

This adaptation occurs in the animals leading subterranean mode of life. They are equipped with digging organs and they dig for food, protection or for shelter. Zoologically, they are primitive, defenseless and unambitious animals. The adaptational features are:

• The body contour is cylindrical, spindle-shaped or fusiform (e.g., earhworms, moles, badgers) so as to reduce resistance in subterranean passage.
• The head is small and tapers anteriorly to form a burrowing snout.
• Neck and pinnae are reduced to avoid obstruction in quick movement through the holes. In some, tail is also shortened.
• The eyes remain small and non-functional.
• Limbs are short and strong. Hands are broad and stout with long claws and some extra structures for digging. In Gryllotalpa (mole-cricket), fore-legs are modified into digging organs.

Cursorial Adaptation

This is running adaptation and is required by the organisms leading life in grassland, as without the hiding places, fast running is the only means of protection from the enemies there. Horses, Zebras, Deers, etc. show this adaptation with following modifications:

• The neck is reduced and the body is steam-lined, this will reduce the air resistance while running.
• The bones of palms (carpals, metacarpals) and soles (tarsus, metatarsus) become compact and are often fused to form canon bone.
• The fore arm bone ulna and shank bone fibula are reduced.
• Distal segments of both limbs i.e., radius, tibia and canon bones are elongated to increase the length of the stride.
• Movement of the limbs is restricted to a fore and aft plane.

Arboreal Adaptation

This is also known as scansorial adaptation and is found in animals which are climbers on rocks, walls or trees. The features enabling them to be best suited in the habitat are:

• The chest, girdles, ribs and limbs are strong and stout.
• Feet and hands become prehensile with opposable digits (e.g., primates, marsupials). Sometimes, the digits are grouped as 3 digits and 2 digits for syndactyly (e.g., Chameleon). For facilitating the clinging, some have elongated claws (e.g., squirrels), while others bear rounded adhesive pads at the tip of the digits (e.g., tree frog Hyla). In wall lizard (Hemidactylus), there are double raw of lamellae in the ventral side of digits for creating vacuum to cling. This enables the animals to move even on the smooth vertical surfaces.
• Often the tail becomes prehensile too (e.g., Chameleon, monkeys).

Desert Adaptation

Desert adaptation is for the mode of life in extreme terrestrial habitat. Desert plants (xerophytes) and animals (xerocoles) show adaptations for three challenges: getting moisture, conserving moisture and defending oneself from biotic and abiotic factors. Many of these adaptations are just physiological and behavioral:

• Different plants and animals adopt different mechanisms to procure enough water. The sand lizard (Molcoh) and horned toad (Phrynosoma) have hygroscopic skin to absorb moisture like the blotting paper even from unsaturated air.

Volant Adaptation

True Flight

Jean-Baptiste Lamarck

It is possible for an adaptation to be poorly selected, the advantage it confers over generations decreasing, up to and including the adaptation becoming a hindrance to the species' long-term survival. This is known as maladaptation and can apply to both humans and animals in such fields as biology, psychology (where it applies to behaviors and other learned survival mechanisms) and other fields.

The theory of adaptation was first put forth by Jean-Baptiste Lamarck. His theories are also referred to as the inheritance of acquired traits.

Lamarck's theory was for a time held as an alternative scientific explanation for evolutionary change observed by Darwin in the The Origin of Species. The classic giraffe analogy offers the best delineation between the two.

• According to Darwin, more long-necked giraffes reproduce than short-necked giraffes and as such giraffes today have long necks.

• According to Lamarck, it was giraffes stretching their necks in response to higher leaves that resulted in giraffes having long necks. (This trait being passed on to the next generation)

Although neither theory in its conception could provide a complete description of the mechanism of transmission of trait variation (i.e., particulate inheritance), many recognized Darwin's theory immediately upon publication as a more complete and empirically supported theory. Modern genetics have since established the fundamental implausibility of Lamarckian inheritance, due to the one-way nature of transcription. However, see epigenetics and Baldwinian evolution for analogous processes in modern evolutionary theory.

External links

• Science aid: Adaptation Explanation of adaptation with cactus and polar bear examples, aimed at high school level

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