Introduction to Animal Adaptation

Any changes in organisms which make it slowly or rapidly better to its environment are called animal adaptation. It can also be defined as, "The structural, physiological and behavioural features that organisms develop which enable them to survive and reproduce successfully in the environment." Simply it gives the process of adjustment of organisms to their surrounding habitat.

Types of animal adaptation

• Aquatic adaptation
• Amphibious adaptation
• Terrestrial adaptation
• Cursorial adaptation
• Fossorial adaptation

Aquatic adaptation

These are the modification found in those animals which can survive in water.

Primary aquatic adaptation

The animals which are the primarily the inhabitant of water never lived on the land and gills breather show primary aquatic adaptation. Eg; Fishes.

Adaptational features in primary aquatic animals

• Streamlined body- to avoid water resistance during swimming.
• Fins- acts as paddles to slow and balance the body while changing direction.
• Scales- to protect the body from external injury.
• Gills- may or may not be covered by the operculum and better suited for gaseous exchange.
• Swim bladder- acts as an hydrostatic organ to float on the water surface and also serves as an accessory respiratory organ.
• Skin with mucus gland- slippery skin helps to escape away from the predator and also save from fungal infection.
• Lateral line system- acts as the receptor to detect physical and chemical changes in water.
• Nictitating membrane- to protect the eye from the dirt present in water.
• Osmoregulation- to control salt and water content in the body.

Secondary aquatic adaptation

The animal which lived on the land due to certain circumstances such as the scarcity of food, unfavourable climate, the risk of predators etc. compelled to live in water and lung breathers is a secondary aquatic adaptation. Eg; Turtle, crocodile, whale etc.

Adaptational features of secondary aquatic adaptation

• Streamlined body- to avoid water resistance during swimming.
• Large and spongy skeleton- to float on water surface.
• Modification in limbs- limbs are modified according to the habitat. Eg; Turtle has paddle-like limbs to swim.
• Short neck- to balance the body during swimming and changing direction.
• Respiration- they respire through lungs, nostrils are closed by muscular flaps during swimming which prevents entry of water through the nostril.
• Spontaneous snout- cranium is elongated at the anterior end forming snout which provides easy passage for swimming.
• Sensory receptor- some animals have a mid-dorsal line to detect the changes in surrounding whereas whale can echolocate the objects.
• The absence of hair and skin gland- In place of hair and skin gland fats deposited under the subcutaneous layer acts as thermo insulators.

Amphibious adaptation

The animals which can survive both on the land as well as in water show amphibious adaptation. Eg; frog, toad etc.

Adaptational features of amphibious adaptation

• Streamlined body
• Webfeet
• Respiration
• Position of a nostril.
• Nictitating membrane
• Inbulging of eye
• Mid-dorsal line

Adaptational features to live on land

• Longer hindlimbs
• Short and strong forelimb
• Pulmonary respiration
• Eyelids
• bony skeleton
• Protrusible tongue
• Camouflage

Terrestrial adaptation

Aerial or Volant

Volant animals are well adapted for the aerial mode of life or for flight. There are two types of flight. They are;

Active or true flight

In this flight, the animal can fly for a long time covering a long distance. Eg; bird, insect, bat etc.

Adaptational feature

• Streamlined body- To avoid air resistance during flying.
• Forelimbs are modified into wings for flying.
• Feathers act as thermo insulator and also make the body lighter.
• Pneumatic or hollow bones - To make body light.
• Air sacs in lungs- Organs of buoyancy which help to fly and also serve as accessory respiratory organs.
• Flight muscles- There are well-developed flight muscles attached to keel-shaped sternum which support the body during flying.
• Acute and sharp vision- Well developed and enlarged optic lobes are found to provide sharp vision.
• Perching mechanism- Capability of gripping the branches of trees which prevent from falling down while resting on the branches of the tree.
• Short tail- To change the direction while flying.
• Reduction in body weight- Absence of teeth, urinary bladder, rectum, one ovary in female help to reduce body weight which provides lightness during flying.
• Jaws are modified into beak for picking the grains and food particles.
• Monocondylic skull- They can rotate their head around 360° used for feeding, nesting, offence and defence.

Passive flight or gliding

In this type, animals cannot fly for a long time so, they cover a short distance. Eg; flying fish(Exocoetus), flying lizard(Draco), flying frog(Rhacophorus) etc.

Adaptational feature

• Enlarged pectoral fin-In exocoetus, the pectoral fins enlarged which act as a parachute to glide over the water and tail exerts the force to leave water surface.
• Patagium-In flying lizard,infolding of skin is present in between forelimbs and hind limbs which help to fly.
• Enlarged webbed feet-In flying frog webbed feet are enlarged which help to fly from one rock to another.

Arboreal or Scansorial adaptation

Wall or rock climbers

Wall lizard has adhesive lamina, adhesive pads, tails, claws which help to climb on the vertical wall. Kangaroo has a balancing tail to jump from one rock to another.

Terrestrial-arboreal forms

Some animals make their nest on the trees but regularly visit on the ground for searching food. Eg; squirrel, slot bear etc.

Arboreal forms

They are tree dwellers, may be branched, runners, suspended beneath the branch or climbers. Eg; Calotes, Chameleon, monkey etc.

Adaptational features in arboreal form

• Strong chest bond: They have strong chest bond, sub-circular thorax, ribs with great curvature for the arboreal mode of life.
• Strong girdle bones- To support the body weight during climbing and hanging.
• Prehensile tail- To hang on the branches of trees.
• Laterally compressed body- To avoid air resistance during climbing.
• Protrusible tongue- To capture the prey.
• Eyelids- To protect the eyes.
• Claws- To climb on a rough surface of trees.
• Camouflage- Capability of changing skin colour according to surrounding to be unnotified from predators.

Cursorial adaptation

Cursorial animals are those animals which live in open places and are adapted to run on the hard ground. They are also known as the fast runners e.g. lion, deer, horse etc. Adaptational characters of them are as follows:

1. The body is streamlined which helps them for swift movement.
2. The limbs are long and strong.
3. Locomotion is digitigrade.

Fossorial adaptation

Animals which dig into burrows for shelter and food are called fossorial animals. They have adaptations for burrowing.

Adaptational features

• Spindle-shaped body to offer little resistance during going in and out of burrows.
• Small tapering head with snout for burrowing
• Eyesight is reduced as they are of no use in the dark
• External ears tend to disappear as they might be an obstruction in burrowing.
• Short and stout limbs are provided with strong claws for digging.
• They hibernate during winter or unfavourable conditions.