Question

According to Allen’s rule, mammals in cold regions have ………. to conserve body heat.
A.Smaller extremities (legs, tails, and ears)
B.Longer extremities
C.Larger body mass
D.Smaller body mass

Answer 1

Hint: Allen’s rule states that animals of colder areas have different size of extremities as compared to animals of warmer areas. This is one of the adaptations in the colder region animals to survive in a cold climate.

Complete step by step answer: This rule states that animals of colder areas have shorter extremities as compared to animals of warmer areas. Animals that do not show migration develop cold hardiness. Example- Sessile animals, Barnacles, Molluscs, several insects, spiders, and some fishes of the Antarctic region.
There are two types of animals:
Freeze tolerant animals-They have ice-nucleating proteins, which include ice formation in extracellular spaces at subzero temperature. Small water from a cell is withdrawn so solute concentration increases inside the cell to protect from freezing.
Freeze avoiding animals- Their body fluids contain antifreeze solutes. Example glycerol and antifreeze proteins. Solutes lower the freezing point below zero degrees Celsius. So, ice formation is prevented and animals remain active. Example- Icefish.
Mammals from colder climates generally have shorter ear and limbs to minimize heat loss, this is called Allen's Rule.
In the polar seas, aquatic mammals like seals have a thick layer of fat below their skin that acts as an insulator and reduces the loss of body heat.
So, the correct answer is option A. Smaller extremities (legs, tails, and ears).

Note:Various other rule given for adaptation are as follows:
Rensch’s rule: Birds of colder areas have narrow and acuminate wings while those of warmer areas have broader wings.
Jordan’s rule: Fish size as well as the number of vertebrae increase in colder areas as compared to warmer areas.
Bergmann’s rule: Warm-blooded animals have a larger size in cold climate areas than in hotter areas.
Gloger’s rule: Animals of warm and humid climates have darker pigments as compared to animals of cool and dry climate.