In this article we will discuss about Protective Colouration and Mimicry.
Protective Colouration:
One of the morphological characters of the animal is the colouration. Animals living in tropics show a wide range of colours. Colouration helps the animal in different ways. But all colours are not biologically important.
Colour Production:
Colouration may be due to physical colours or chemical colours. Physical colour is due to the structure of surface which may refract or defract light rays e.g. Colouration in many beetles and butterflies.
Chemical colouration is due to the presence of colour pigments like melanin, carotenoid, flavine, pterine etc. These pigments may be external and give a colour to the organism. Pigments are usually found in special bodies called chromatophores. Amphibians and reptiles can change colouration due to concentration and dispersal of melanin granules, controlled by pituitary hormone melanocyte stimulating hormone (MSH).
Types of Colour:
From biological standpoint, there are two types of colours in animals. They are indifferent colours and valuable colours. Indifferent colours have no selection value. Examples of indifferent colours are coloured fin rays of deepsea fishes, black fur of melanic leopard and coat colour of domestic horses.
Albinism is total absence of colour in hair, feathers or skin and even in the iris of the eye. Melanism is the reverse of albinism. There is a profusion of black melanin giving totally black colour to the entire animal. Both albinos and melanos arise by mutations of the normally coloured individuals.
Valuable colours are physiologically important. They perform different functions.
Following are main types of valuable colours:
1. Sympathetic Colours
2. Alluring colours
3. Warning colours
4. Mimetic colours
5. Signal & Recognition marks
6. Confusing colours
7. Sexual colours
1. Sympathetic Colouration:
It is also known as cryptic or concealing colouration. In this animal harmonize with its surrounding, its colouration blends into the background and loses its conspicuousness in order to escape from its enemies. So this colouration is protective in function.
Examples of protective colouration:
(i) Arctic hare:
They are white in colour and it blends the white colour of ice in surrounding. It is difficult for enemies of hare to locate the prey.
(ii) Grasshoppers:
Several grasshoppers have brillantly coloured hind wings, but their forewings and remainder of the body are coloured to harmonize with the earth.
(iii) Caterpillars:
Caterpillar of hawk-moth Sphinx convolvuli when full grown is either green like its food plant or brown like the ground beneath showing double adaptation. The four young stages of the caterpillar are green and the last stage it becomes brown. This suggests that the brown is a relatively modem adaptation.
(iv) Toads:
Bufo typhonicus and B. superciliaris are brown or grey resembling to dead leaves found on the forest floor.
(v) Leaf fish:
The leaf fish Monocirrhus polycanthus inhabits the river is very similar to leaves floating in the water.
(vi) Birds & Mammals:
A number of animals show a change of colour from summer to winter, harmonizing with the brown of leafy soil or rock in summer, and with snow-coloured ground in winter. The stimulus to change colouration is due to increasing warmth or cold as the case may be.
2. Alluring Colours:
It is meant to allure the other animals. It is shown by certain carnivorous forms like black and white spider Orvythos which resembles the dropping of bird when at rest on a leaf.
3. Warning Colours:
Also known as revealing colours. They are conspicuous red and yellow found on the bodies of poisonous or unpalatable animals like coral snakes, tiger salamander, Gila monster, caterpillar, butterflies etc. These creatures are practically immune from attack if they are recognized in time. The advertisement of their dangerous nature is a very conspicuous one.
4. Mimetic Colours:
It is a colour resemblance between an animal and any other object animate or inanimate. It may be either such as to conceal or a warning colouration.
5. Signal Marks:
They are important among gregarious animals where mutual aid in time of danger is a characteristic. For example in Virginia deer, a member of quietly grazing herd, put up a tail like signal flag showing conspicuous white of underside.
This acts as a warning to others and in an instant, the herd is in full retreat Recognition Marks:
They are conspicuous marking on the individuals of the same species. Eg. Red and orange spots on the side of the fish Salvelinus frontinalis (brook trout).
6. Confusing Colours:
These colours are shown by moths and butterflies. During flight their colours are very conspicuous. A sudden settling of the insect, the brilliant colours instantly disappears and one loses sight of the insect completely. Its exposed colouring now harmonize with the support on which it rests.
7. Sexual Colouration:
Males of many species are brightly coloured than the female as in peacock.
Mimicry:
Mimicry is the superficial but close resemblance of one organism to another or to inanimate objects in form, colour, attitude and action. This helps the organism for concealment, protection or some other advantage. The term mimicry is derived from Latin mimicus means imitation or simulation. The organism which mimics is called as mimic and the organism imitated is the model.
Types of Mimicry:
Mimicry can broadly be classified into 3 types:
They are:
1. Protective mimicry
2. Aggressive mimicry, and
3. Conscious mimicry.
Protective Mimicry:
This includes imitation of organism to other organisms or surrounding in form of colour or behaviour. It is protective in function. This could be obtained either by concealment or by warning.
(i) Concealing Mimicry:
It is common type of protective mimicry. The organism conceal themselves by changing colouration fitting with the surrounding. In some cases they mimic the shape and colour of other organism or object.
Examples:
(a) The crab Cryptolithodes has smooth rounded form and white colour. It harmonize perfectly with white quartz pebbles of the beach.
(b) The caterpillars of Geometrid moth Selenia tetralunaria mimic the twigs and smaller branches of birch tree. The caterpillar escapes observation of predators by grasping the branch with its two hinder pairs of prolegs and throws its body outward at an angle.
(c) Many of walking-stick insects mimic twig by their slender body, attenuated limbs and sympathetic colouration.
(d) The most perfect example is the leaf insect Phyllium. It possesses flattened and expanded body and limbs. It is green in colour except for irregular small yellowish spots which resemble the fungus or rust growth upon a leaf.
(e) Indian dead-leaf butterfly, Kallima paralecta is the best example of protective mimicry. Its wings are strikingly coloured above with a reddish yellow or bluish white band. When the butterfly sits down, wings are folded with the upper surface together.
Only the under surface with dull brown colour and leaf like marking are visible which perfectly resembles a dry leaf. Moreover, wings are prolonged into the stem-like structure and other features resemble to leaf with an extreme perfection.
(f) Phyllopteryx eques is commonly called as Australian leaf seahorse. It has leaf-like cutaneous out growths over the body and very much resembles to sea weeds.
(ii) Warning Mimicry:
In this type, nonpoisonous and harmless organisms mimic the poisonous and harmful organism. Likewise the palatable forms resembles and advertise to be non-palatable.
(a) Many coral snakes belonging to the family Elapidae are beautifully coloured often with red and black bands edged with yellow. They possess a strong poison but harmless to man because of limited extent of the gape. Each of the several species of poisonous snake is mimicked by other species of harmless snakes belonging to different genera of family Colubridae.
(b) The nonpoisonous hog-nose snake, Heterodon, has flattened and triangular head. It frequently hiss and strike to show that it is very dangerous.
(c) The palatable Viceroy butterfly Basilarchia archippus which can be easily preyed upon, mimics the distasteful non-palatable Monarch butterfly Anosia plexippus.
(iii) Cryptic Structures:
Many organisms have cryptic structures to confuse and befool the predators.
(a) Black spots or eye spots present on the wings and body of Butterflies, caterpillars, peacock etc. The sudden display of these marking help to frighten the enemies. Black spots are also found on the body of fishes like Notopterus chitala and Burmese soft shelled turtle Trionyx hurum. Since the predators attack the prey towards eye or their vicinity, these marking misguide them.
(b) Dummy head:
Some organisms possess structures resembling to head in the posterior part of the body. These dummy head misleads the predators which normally attack towards the head. Examples are Lantern fly of Thailand, butterfly (Thecla) and Trinidad linus.
Aggressive Mimicry:
This is exhibited by certain carnivorous spiders, fishes and lizards. These animals remain unnoticed by matching with the surrounding. On the approach of prey, they pounce over and kill them.
The aggressive mimicry are of two types:
1. Concealing mimicry, and
2. Alluring mimicry.
(i) Concealing mimicry:
The animals develop cryptic colours and blend with surrounding. Spiders resemble in space and colour to the flowers on which they live. These predators are not easily distinguished from the flowers.
(ii) Alluring mimicry:
In this type the predator possesses some lure to attract its prey. The mislead prey become a victim. Certain spiders mimic the flowers of orchid and insects are attracted to collect honey. Deep sea Angler fish Lophinus has first ray of dorsal fin modified to illicium and it works as a bait.
Conscious Mimicry (Simulation of death):
Certain animals exhibit conscious imitation and on approach of danger behave as they are dead bodies. American opossum Didelphis virginiana becomes unconscious and simulates as dead. Many hard bodied beetles fall down like pebbles, when they are about to be seized by the enemy. For the enemy it is difficult to locate them among leaves and grass beneath.