Discuss the adaptations for temperature variation in animals.

Explanation

1. Some animals bring changes in their morphology.

Allen.s rule showing relationship between size of pinnae and temperature A. Arctic fox. B. Red fox. C. Desert fox or anatomy for thermoregulation as evident from following rules :-
(i) Bergaman.s rule. The birds and mammals (warmblooded animals) of cold regions are large sized than those of Warmer region e.g., polar bear is much larger in size than the black bear of temperate area, and Antarctic penguin is about one-metre long while the penguin of equatorial Galapagos islands is only half a metre long. It is so as a large sized body will have less surface area per unit of weight so loses less heat.
(ii) Allen.s rule. The tail, snout, pinnae of ears and legs of mammals are relatively shorter in colder part than in the warmer parts (Fig.). It was noticed in foxes and gazells. The pinnae of the desert fox (Megalotis) are largest sized while those of red fox (Vulpes) are small sized and those of arctic fox (Alopex) are smallest in size. This is so as small structures lose less heat. Similarly, legs, ears and pinnae of Gazella picticanda of Himalayas are shorter than those of G, benetli of plains.
(iii) Jorden.s rule. The fishes found in waters of low temperature tend to have more vertebrae than those of warmer waters e.g., 58 vertebrae in a cod hatching at `4-8^(@)`C and 54 vertebrae in a cod hatching at `10-11^(@)`C.
(iv) Gloger.s rule. The mammals, birds and insects of tropical region (warmer region) are more darker in colour and heavily pigmented than those of arctic region (cold region). But Hyla (tree frog) and Phrynosoma (Horned toad) are dark skinned in low temperatures.
(v) Rensch.s rule. The birds of colder regions tend to have relatively narrow wings than the birds found in warmer areas.
2. Polar bears and polar sea animals like seals have a thick layer of fat, called blubber, in their subcutaneous zone of skin. The blubber acts as an insulator and reduces the loss of body.s heat.
3. Small aquatic animals like Cladocera, Daphnia etc. show change in their body shape with seasonal temperature changes, called cyclomorphosis.