· In the words of Huxley, 'adaptation is omnipresent'.
· It is mainly of three types: aquatic, terrestrial and amphibious.
TYPES OF ADAPTATION
1. AQUATIC ADAPTATION· Animals living in water are called aquatic animals and their adaptation to the watery medium is called aquatic adaptation.
· Aquatic animals are of two types: Primary and Secondary.
a. Primary Aquatic Adaptation
· Primary aquatic animals are evolved from aquatic ancestors and have never lived on land such as fishes, sponges, coelenterates, molluscs, echinoderms etc.
· They are primitive gill-breathing vertebrates.
· Body is streamlined to minimize water resistance during swimming.
· Presence of median fins (dorsal, ventral and caudal- unpaired) - dorsal and ventral fins help in balancing, caudal- to change the direction and paired fins (pectoral and pelvic) - control up and down movement and turning.
· Gills are the most remarkable aquatic breathing organs utilizing dissolved Oxygen of water.
· Swim bladder or air bladder: an elongated, thin-walled sac filled with air, balancing, maintains buoyancy.
· To go up- bladder is filled with gas, weight is reduced and fish rises up.
· Body is streamlined to minimize water resistance during swimming.
· Presence of median fins (dorsal, ventral and caudal- unpaired) - dorsal and ventral fins help in balancing, caudal- to change the direction and paired fins (pectoral and pelvic) - control up and down movement and turning.
· Gills are the most remarkable aquatic breathing organs utilizing dissolved Oxygen of water.
· Swim bladder or air bladder: an elongated, thin-walled sac filled with air, balancing, maintains buoyancy.
· To go up- bladder is filled with gas, weight is reduced and fish rises up.
· To descend down- deflates the bladder, weight is increased and fish sinks down.
· Scales protect the body from external injury and entry of water.
· Lateral line sense organs detect pressure and temperature changes.
· Nictitating membrane protects eyes from dirt and debris present in the water.
· Osmoregulation: The freshwater fishes have salt absorbing cells (special chloride cells) and marine fishes have salt secreting cells to maintain the isotonic condition of salt and water in the body.
· Scales protect the body from external injury and entry of water.
· Lateral line sense organs detect pressure and temperature changes.
· Nictitating membrane protects eyes from dirt and debris present in the water.
· Osmoregulation: The freshwater fishes have salt absorbing cells (special chloride cells) and marine fishes have salt secreting cells to maintain the isotonic condition of salt and water in the body.
b. Secondary Aquatic Adaptation
· Secondary aquatic animals are evolved from terrestrial ancestors, now in water for food and safety Example: Whales, turtles, crocodiles, polar bears, dolphins, penguins etc.
· They are lung-breathing amphibious vertebrates.
· Body is compact and streamlined, the neck is short.
· Limbs are modified into paddles or flippers, feet are webbed.
· Lungs are large and highly elastic that can store large volumes of Oxygen during long diving.
· Nostrils are often with muscular flaps to close them when diving.
· Swim bladders and External ear absent or rudimentary.
· Skin is naked and is without scales, hairs, glands.
· Body is compact and streamlined, the neck is short.
· Limbs are modified into paddles or flippers, feet are webbed.
· Lungs are large and highly elastic that can store large volumes of Oxygen during long diving.
· Nostrils are often with muscular flaps to close them when diving.
· Swim bladders and External ear absent or rudimentary.
· Skin is naked and is without scales, hairs, glands.
· Whale has thick blubber for retention of body heat. It has also a hydrostatic advantage (e.g., it helps in floatation or to keep positions in the water and act in combination with the buoyancy of the aquatic medium).
· Eyes small, protected by fatty secretion, placed high on the face.
· Example:
· Eyes small, protected by fatty secretion, placed high on the face.
· Example:
i. Reptilia- Turtles, Crocodiles and Alligators
ii. Aves- Ducks, Geese etc
iii. Mammalia- Hippopotamus
ii. Aves- Ducks, Geese etc
iii. Mammalia- Hippopotamus
DIFFERENCES BETWEEN PRIMARY AQUATIC ADAPTATION AND SECONDARY AQUATIC ADAPTATION
| Primary Aquatic Adaptation | Secondary Aquatic Adaptation |
|---|---|
| The body is streamlined. | Neck is absent |
| Locomotion occurs by fins, pectoral and pelvic fins (paired), dorsal, anal and caudal (unpaired). | Limbs are modified into flippers, paddles, webbed feet. |
| Gills are used for respiration. | Lungs are large and elastic so can hold more air. Nostrils are provided with muscular flaps. |
| Skin is covered with scales. Mucus makes it moist | Skin is without scales and glands but very thick. |
| Air bladder for buoyancy. | Air bladder is absent. They go to water make the extra effort and live on the surface. |
| Nictitating membrane is well-developed. | Nictitating membrane is not well-developed. |
| Lateral line sense organ is present. | Lateral line sense organ is absent and this phenomenon is supported by any other sense organ. |
2. TERRESTRIAL ADAPTATION
· Adaptation shown by animals on land is called terrestrial adaptation.
· It consists of volant, arboreal, fossorial and cursorial adaptation.
· Adaptation shown by animals on land is called terrestrial adaptation.
· It consists of volant, arboreal, fossorial and cursorial adaptation.
a) Volant (Aerial) Adaptation
· The adaptation shown by animals for flying is called flying or volant or aerial adaptations.
· Flight in animals is of two types: Active and Passive (Gliding)
i. Active flight
· It involves a long and sustained flight.
· Example: birds, bats, insects etc.
· Streamlined body and lack of any extra protuberances to minimize resistance while flying.
· Forelimbs are modified into wings and are provided with feathers.
· Streamlined body and lack of any extra protuberances to minimize resistance while flying.
· Forelimbs are modified into wings and are provided with feathers.
· The surface area of wings is increased by the development of elongated flight feathers.
· Feathers also insulate the body and prevent loss of heat that enables a bird to overcome intense cold at high altitudes and also maintain a high temperature which is essential for a high metabolic rate during flight.
· In bat, lateral extensions of the skin from forelimbs, hindlimbs and tail are joined to form patagium. In insects, wings are the thin membranous fold of the exoskeleton.
· Strong flight muscles are developed to control the movement of wings.
· Bones are filled with air (pneumatic), reducing relative body weight.
· Bones are filled with air (pneumatic), reducing relative body weight.
· The sternum is well-developed and bears a median keel for attachment of flight muscle.
· Perching mechanism (when a bird lands on a perch, the bending leg exerts a pull on flexor muscles which makes the toes automatically flex and grip the perch).
· Perching mechanism (when a bird lands on a perch, the bending leg exerts a pull on flexor muscles which makes the toes automatically flex and grip the perch).
· The perching is so efficient that birds can sleep while sitting on trees without any danger of falling. Specialized cushion pads are present on the underside of toes for grasping the twigs.
· Presence of single left ovary and oviduct in females, absence of teeth and urinary bladder, poorly developed rectum so the faeces passed out immediately, additional air-sacs connected to lungs that supply oxygen for rapid oxidation during flight and provide buoyancy, rapid digestion and minimum indigestible waste, effective digestive system., jaws modified into beak for picking, nest building etc., feathers (closely fitted and backwardly directed), absence of Gallbladder, cloacal aperture, strong chest muscles, keen eyesight, crop (to store food), gizzard (crushing and churning the food and reduce resistance while flying), oviparous, Urinary bladder is present in Rhea americana- South American Ostrich, the tail of a bird serves as a rudder in steering and balancing organ in perching.
· High haemoglobin in RBC.
· Presence of single left ovary and oviduct in females, absence of teeth and urinary bladder, poorly developed rectum so the faeces passed out immediately, additional air-sacs connected to lungs that supply oxygen for rapid oxidation during flight and provide buoyancy, rapid digestion and minimum indigestible waste, effective digestive system., jaws modified into beak for picking, nest building etc., feathers (closely fitted and backwardly directed), absence of Gallbladder, cloacal aperture, strong chest muscles, keen eyesight, crop (to store food), gizzard (crushing and churning the food and reduce resistance while flying), oviparous, Urinary bladder is present in Rhea americana- South American Ostrich, the tail of a bird serves as a rudder in steering and balancing organ in perching.
· High haemoglobin in RBC.
ii. Passive flight
· Passive flight or gliding includes short-distance flight.
· In this case, animals simply take an initial leap from a high point and are forced by gravity and glide to a lower level.
· It is shown by flying fish (Exocoetus), flying frog (Rhacophorus), flying reptile (Draco), flying snake (Chrysopalea), flying squirrel (Sciuropterus), flying lemur (Galeopithecus Volans), Ostrich etc.
· 5-6 elongated ribs support the patagium in Draco.
· Tree snake (Chrysopalea) glides by spreading its ribs and flattens its body before gliding or leaping in its prey.
· Flying frog (Rhacophorus) has very long webbed toes that help in prolong leaps and the digits terminate in adhesive pads which help in sticking to smooth surfaces.
· In Flying fish (Exocoetus), the pectoral fins are enlarged and help to glide over a considerable distance. The hyperbatic tail produces force to leave the water during gliding in the air.
· 5-6 elongated ribs support the patagium in Draco.
· Tree snake (Chrysopalea) glides by spreading its ribs and flattens its body before gliding or leaping in its prey.
· Flying frog (Rhacophorus) has very long webbed toes that help in prolong leaps and the digits terminate in adhesive pads which help in sticking to smooth surfaces.
· In Flying fish (Exocoetus), the pectoral fins are enlarged and help to glide over a considerable distance. The hyperbatic tail produces force to leave the water during gliding in the air.
DIFFERENCES BETWEEN ACTIVE AND PASSIVE FLIGHT
| Active flight | Passive flight |
|---|---|
| Forelimbs are modified into wings provided with feathers. | Wings are made up of patagia that do not flap (i.e. do not move up and down by the muscular action) |
| Strong flight muscles to support the wings. Bones are pneumatic. |
Pectoral fins are elongated in Exocoetus and feet are webbed in flying frog |
| In true flights, the power is implied and the movement in the air is sustained. | It involves no propulsion other than the initial force of jumping. |
b) Arboreal or Scansorial Adaptation
· These animals can easily walk on walls, rocks and trees.
· Example: Pisces – Anabas (Climbing perch)
· Amphibian– Hyla – Tree frog
· Reptiles- Lizards (Hemidactylus, Chameleon)
· Mammalian- Cats, Monkeys
· They have a smaller and slender body that offers less resistance.
· Girdle bones are well-developed to support the body weight.
· Feet may be prehensile or non-prehensile type. In prehensile type, digits are opposite. Example: Chameleons, Parrots, Woodpeckers etc.
· In non- prehensile type, claws are sharpened and hooked. Example: Cats.
· Adhesive lamellae- create a partial vacuum to cling on the wall. Example: Hemidactylus.
· Adhesive pads present on soles of feet. Example: Hyla.
· Function of scales- loss of water and protection from mechanical injury.
· Tongue is long, sticky and protrusible to catch the prey.
· Autotomy and regeneration- tail is automatically cut off and generated again.
· Claws help in holding the rough surface.
· Tail is long and prehensile for grasping the branches of the tree (used as fifth hand in Chameleon, Spider monkey) or non-prehensile (tail with scales and spines which prevent from slipping).
· Some arboreal animals can change their body colour with respect to their surroundings. Example: Chameleon, Calotes etc.
· Neck presence enhances the mobility of the head, locate the enemy easily.
· These animals can easily walk on walls, rocks and trees.
· Example: Pisces – Anabas (Climbing perch)
· Amphibian– Hyla – Tree frog
· Reptiles- Lizards (Hemidactylus, Chameleon)
· Mammalian- Cats, Monkeys
· They have a smaller and slender body that offers less resistance.
· Girdle bones are well-developed to support the body weight.
· Feet may be prehensile or non-prehensile type. In prehensile type, digits are opposite. Example: Chameleons, Parrots, Woodpeckers etc.
· In non- prehensile type, claws are sharpened and hooked. Example: Cats.
· Adhesive lamellae- create a partial vacuum to cling on the wall. Example: Hemidactylus.
· Adhesive pads present on soles of feet. Example: Hyla.
· Function of scales- loss of water and protection from mechanical injury.
· Tongue is long, sticky and protrusible to catch the prey.
· Autotomy and regeneration- tail is automatically cut off and generated again.
· Claws help in holding the rough surface.
· Tail is long and prehensile for grasping the branches of the tree (used as fifth hand in Chameleon, Spider monkey) or non-prehensile (tail with scales and spines which prevent from slipping).
· Some arboreal animals can change their body colour with respect to their surroundings. Example: Chameleon, Calotes etc.
· Neck presence enhances the mobility of the head, locate the enemy easily.
c) Fossorial or Burrowing or Digging Adaptation
· These animals adapted to live beneath the surface of the ground. Example: Moles
· Body small, compact, rigid or spindle-shaped which offers the least resistance in burrowing.
· Head is conical and produced into a snout and helps in digging. Example: Pig
· Tail is either reduced or vestigial, serves as a tactile organ.
· Eyes and ears are reduced, in some totally absent. In moles and mole cricket (insect), forelimbs are specially modified for digging.
· Forelimbs shortened with broad palm and strong claws for digging.
· Undergo hibernation.
d) Cursorial or Fast Running Adaptation
· Example: Reptiles- Lizard, Snake
· Aves- Emu, Ostrich
· Mammals- Cheetahs, Racehorse, Leopards, Tigers, Lions, Kangaroos, Hares, Rabbits, Dogs etc
· Body is streamlined with head and neck extended and ears are thrown back for swift passage through the air with minimum resistance.
· In Racehorse, head and neck extended, ears thrown backwards, muscles of the body are working like a machine.
· Limbs are slender and long. Femur and humerus are relatively shorter and tibia-fibula and radio-ulna are elongated.
· Foot- Plantigrade- entire palm or sole rests on the ground. Example: Bear, raccoons, baboons, man
· Digitigrade- walk on digits. Example: Birds, Dinosaurs
· Unguligrade- walks on modified nails or hoofs. Example: Horse and ungulates
· Double-hoofed- Deer, Cow, Camel
· Single-hoofed- Horse, Zebra, Rhino
· Mental alertness.
· Adapted for walking- Ambulatory
· Adapted for jumping- Saltatory
· Adapted for running- Cursorial
· Limbs are slender and long. Femur and humerus are relatively shorter and tibia-fibula and radio-ulna are elongated.
· Foot- Plantigrade- entire palm or sole rests on the ground. Example: Bear, raccoons, baboons, man
· Digitigrade- walk on digits. Example: Birds, Dinosaurs
· Unguligrade- walks on modified nails or hoofs. Example: Horse and ungulates
· Double-hoofed- Deer, Cow, Camel
· Single-hoofed- Horse, Zebra, Rhino
· Mental alertness.
· Adapted for walking- Ambulatory
· Adapted for jumping- Saltatory
· Adapted for running- Cursorial
3. AMPHIBIOUS ADAPTATION
· Animals that live both in water as well as on land are called amphibians and the adaptation is shown by them is called amphibious adaptation i.e. both terrestrial and aquatic adaptations.
· They show the following characteristics:
a) Aquatic adaptations
· The features possessed by amphibians to live on land are as follows:
· Body is compact, elongated or spindle-shaped or streamlined and the head is triangular.
· Cutaneous respiration inside water due to smooth skin.
· No neck so can swim easily in water.
· Gill respiration in the larval stage, cutaneous in water and pulmonary on land.
· Presence of a transparent nictitating membrane protects them from the dirt and mud in the water.
· External nostrils are placed at the tip of the snout- for easy breath with the help of lungs keeping its snout out of water.
· Possess long, muscular, webbed hind limbs for swimming.
· The features possessed by amphibians to live on land are as follows:
· Body is compact, elongated or spindle-shaped or streamlined and the head is triangular.
· Cutaneous respiration inside water due to smooth skin.
· No neck so can swim easily in water.
· Gill respiration in the larval stage, cutaneous in water and pulmonary on land.
· Presence of a transparent nictitating membrane protects them from the dirt and mud in the water.
· External nostrils are placed at the tip of the snout- for easy breath with the help of lungs keeping its snout out of water.
· Possess long, muscular, webbed hind limbs for swimming.
b) Terrestrial adaptations
· The features possessed by amphibians to live in water are as follows:
· Body is spindle-shaped.
· The bulging eyes compensate for the absence of the neck and help the frog to look nearly in all directions without turning the head.
· The nictitating membrane helps to keep eyes moist on land.
· Respiration occurs in the lung.
· Tongue is long, protrusible and sticky which helps to catch the prey.
· Forelimbs are smaller for balancing. Webbed hind limbs for leaping.
· Mucous glands make the skin moist and slippery to escape from the enemy easily. The absence of a tail helps to jump easily.
· Respiration occurs in the lung.
· Tongue is long, protrusible and sticky which helps to catch the prey.
· Forelimbs are smaller for balancing. Webbed hind limbs for leaping.
· Mucous glands make the skin moist and slippery to escape from the enemy easily. The absence of a tail helps to jump easily.
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