Animal Adaptation

The process of adjustment of organisms with their surroundings is called adaptation.

Every organism lives in an environment. To suit in that environment, organism develops certain structural, physiological, behavioral features which enable them to survive and reproduce successfully. The fitness or acclimatization or adjustment of animals with their habitat is called adaptation.

Types of Adaptation

Adaptations are of different types like:

1.           Aquatic adaptation                2.     Amphibious adaptation

3.     Arboreal adaptation              4.     Aerial adaptation etc.

A.     Aquatic adaptation

Aquatic animals live in water and are of two types i) Primary aquatic Animals and ii) Secondary aquatic Animals.

i.      Primary aquatic adaptational Characters

These adaptations are found in the primary aquatic animals, such as fishes. Important primary aquatic adaptations are as follows:

1. Streamlined body- Body is spindle shaped and suited for active locomotion in water. It offers little or no resistance in swimming.
2. Presence of fins- Locomotion takes place by paired and unpaired fins. The paired fins (pectoral and pelvic) and unpaired fins (dorsal, anal and caudal) act as paddles to propel the body and to control the direction of movement.
3. Respiration by gills- The respiratory organs are gills, which are well suited for gaseous exchange in water.
4. Scales- Body is covered with scales. These protect the body from external injury and water current.
5. Cold-blooded nature- Primary aquatic animals are cold blooded or poikilothermic. It means that body temperature is not fixed but is variable according to the environment. It enables the animals to survive in any temperature.
6. Swim or air bladder - The swim or air bladder is found in many fishes. In some it may serve as hydrostatic organ, help in floating. In others, it functions in breathing.
7. Lateral line system- Lateral line is a receptor organ which enables the fish to detect the changes caused by mechanical disturbances in the surrounding water.
8. Osmoregulation- It is a process of maintaining salt and water balance in animals. In primary aquatic animals, osmoregulation is greatly maintained.
9. Presence of nictitating membrane- Eyes have a third eyelids or nictitating membrane which protect the eyes from dirty water and ensure vision in water.

ii)     Secondary aquatic adaptation

These are found in the secondary aquatic animals such as aquatic amphibians, aquatic reptiles, and aquatic mammals. These live most of time in water but may come on land for a while. The adaptational features of secondary aquatic animals are:

1. Fish like shape- Many secondary aquatic animals have a fish like shape of the body. It is suited for active locomotion in water. It offers little or no resistance in swimming.
2. Locomotory organs- They have fins and other locomotory organs for movement in water. In marine turtles and seacows, fore limbs are modified into paddles. In aquatic amphibians, tortoises and crocodiles the limbs have webbed digits.
3. Respiration - All the secondary aquatic animals are lung breathers. In aquatic mammals, muscular flaps are present at the tip of snout which close the nostrils during swimming. Lungs are large and highly elastic, thereby storing much air which is used during prolonged period of diving. They also have strong breathing capacity.
4. Shortening of neck - A shortened neck helps the animal to swim in the water easily. In many of them, the neck is almost absent and the head is joined directly to the trunk. In whales, the cervical vertebrae are fused.
5. Lightness of bones - In aquatic forms the bones are generally light and spongy.
6. Modification of skull - The cranium is shortened and produced into a pointed snout or rostrum which cuts the water efficiently and makes an easy passage for the swimming in the water.
7. Absence of hair and skin glands - The skin lacks hairs besides few bristles near the mouth. Similarly, skin glands are also absent as they are not essential for aquatic mode of life. A thick layer of fat (blubber) is present beneath the smooth skin which prevents the loss of heat in cetaceans (whales). In some aquatic forms, the smooth moist skin is also used as an accessory respiratory organ.
8. Lateral line system- Some secondary aquatic animals like amphibians have lateral line receptors and others like whales can echo-locate objects.

B.     Amphibious Adaptations

The amphibians are the first group among chordates that live outside water. The amphibians show both terrestrial and aquatic adaptations.

i.      Adaptations for living in water

1.  Body shape: The body is compact boat shaped or streamlined, which offers least resistance during swimming and diving.

2.  Hind limbs: The hind limbs are long muscular, powerful and webbed and work like oar while swimming.

3.  Respiration: Amphibians show cutaneous respiration in water. They show gill respiration in larval stage. External gills are present in Necturus.

4.  Nictitating membrane: The transparent nictitating membrane protects the eyes from the dirt in water and also helps in viewing inside water.  

5.  Lateral line systems: Lateral line receptors are found in amphibians, which can detect pressure changes in surrounding water.

ii.     Adaptation for living on land:

1.   Limbs: They have two pairs of limbs for walking and leaping.

2.   Eye lids: Eyes are provided with eye-lids, which are movable.

3.   Skeleton: It is large and bony.

4.   Respiration: It takes place by lungs and moist skin.

5.   Protrusible tongue: The long protrusable and sticky tongue helps in catching the prey.

6.   Hyla has tree living habit and thus exhibit many adaptations for arboreal life.

7.   The tree frog, Rhacophorus shows volant (flying) adaptation. It uses its large webbed feet in making long sailing leaps among the trees.

C.     Arboreal adaptation

        It is also known as scansorial adaptation. The animals are adapted for 

        climbing. Various types of climbing adaptation are-

i.     Wall and rock climbers- These animals can climb on the wall a nd rocks. Examples- wall lizards, flying squirrels, etc.

ii.   Arboreal forms - These are adapted for living on trees.  Examples are Calotes, Chameleon, etc.

The adaptational features of scansorial animals are as follows –

1.    Stout body - Body and head is stout and laterally compressed.

2.    Dry skin - The skin is dry and covered by epidermal scales. Scales protect the body and prevent loss of water from skin.

3.    Limbs - Limbs are strong to bear weight of the body. The digits have sharp claws so as to enable the animal to walk on trees and other vertical surfaces.

4.    Presence of neck- The presence of neck between the head and trunk provides mobility to the head and, therefore, enhances the efficiency of eyes in locating its enemies or its preys.

5.    Strong girdle bones - Pectoral girdle is strong specially to support weight of the body. The shoulder and pelvic girdles are especially strong.

6.    Feet– Arboreal forms have prehensile or non-prehensile feet. The soles of tips of digits may have adhesive pads. Some have lamellae on the ventral side of digits which create vacuum, as in wall lizards.

7.    Tail – Tail is very long and used to balance the body during locomotion. In Chameleon, tails is long and prehensile to hold the branch of trees.

8.    Changing colour – It can also change body colour with respect to the surrounding. Animal changes their colour in order to hide from the enemies. This phenomenon is called mimicry.

D.     Aerial adaptation

        It is also known as Volant or flight adaptation. The animals are adapted             for flight and are of two types

i.      True or active flight     

ii.      Passive Flight or Gliding

i.      Adaptational features for true flight

In this type, animals are able to fly for a long distance. Most of the birds are true fliers. The adaptational character for the true flight are:

1.   Streamlined body - Body is spindle shaped or streamlined which provides least resistance to air during flight.

2.   Fore limbs modified into wings - The fore limbs are modified into wings as in the birds. In bat the wings are made up of fold of skin known as patagium.

3.   Presence of feathers - Body is covered with feathers which act as blanket to insulate the body. It also makes the body light.

4.   Pneumatic bones - Bones are pneumatic (i.e., hollow bones having air cavities). They provide lightness to the body.

5.   Presence of air sacs - Air sacs are present in the lungs. These make respiration efficient and lighten the body. These are also useful in compensating oxygen during flight at high altitude.

6.   Developed flight muscles - In birds the flight muscles are strongly developed. The flight muscles are pectoralis major, pectoralis minor and coracobranchialis. The pectoralis major and coracobranchialis are responsible for downward movement of wings while pectoralis minor is responsible for upward movement of wings.   

7.   Short tail - The short tail of a bird bears a series of tail feathers arranged in a fan-like maneer. It serves as a rudder in steering and as a counter balance in perching.

8.   Reduction in the body weight– There is reduction in the body weight by following ways which assist in flight (1) complete loss of teeth, (ii) lack of urinary bladder, (iii) extensively fused vertebrae.

ii)     Adaptational feature for passive flight (gliding)

In this type, animals are not able to fly for long distance for a long time. They just fly covering a short distance or from one branch to the others. This type of flight is preformed by a number of arboreal animals like the flying fish (Exocoetus), flying dragon (Draco), flying (Rhacophorus), and by some mammals. The adaptational features are as follows:

1.   Development of patagia – Patagium is a wing like structure made up of a fold of skin situated between the fore and hind limbs. In flying dragon (Draco), it extends on either side of the trunk and is supported by 5 to 7 pairs of long ribs. It helps in propelling the body forward.

2.   Enlargement of pectoral fins – In flying fish, pectoral fins are very large and highly developed. They are used as parachutes, helping the fish to make great leaps out of water.

3.   Webbed feet - In some animals like flying frog (Rhacophorus), the feet are webbed, helping the animal to make long leaps. The digits terminate in adhesive pads which help in sticking to the smooth surfaces.