Explore the biology behind a frog’s ability to jump

Topic Explore the biology behind a frog's ability to jump.

Frogs, as we know, are carnivorous, tailless amphibians.if we do not consider their larval stage, i.e. adult frogs are tailless, they have long hind legs, elongated ankle bones, webbed toes, their toes lack claws, they have large eyes and smooth or warty skin. They have a short vertebral column with about ten free vertebrae and fused tail bones. Their skins are highly permeable to oxygen which gives them the advantage of surviving in places with little air. For this purpose the skin of frogs are moist, which also paves the way for any toxic material to dissolve in the water film and pass on to its blood stream, and may prove lethal. This might be a reason for the decline of frog population across the globe. All the frogs belong to the order Anura of clade Salientia of class Amphibia, as classified in the six kingdom classification. Frogs comprise of about 4,800 species which accounts for 85% of amphibian species. They are the most populous group amongst the amphibians, their prevalence is thought to be because of their unique jumping power.

The word frog probably roots from proto-Indo-European (old English) word which means "to jump". A frog's jump is very unique in the sense that the jump is far more powerful than what it normally should be, with equivalent muscles power. Frogs jump as an escape mechanism or to catch a tough prey. They are considered to be the best jumpers amongst the vertebrates, relative to their size. For example, Litorianasuta (the striped rocket frog) jumps about fifty times of its body length. Different frog species have different jumping abilities. The Indian skipper frog (Euphlyctiscyanophlyctis) can jump from a surface floating on water and owing to its broad feet it can also run across the surface of the water for several metres (yards). While northern cricket frog (Acriscrepitans), which is small in size, can skitter, i.e., performs a series of short rapid jumps over the surface of a pond.

Frogs vary in size with the smallest yet discovered being Paedophryneamauensis of Papua, New Guinea, which measures around 7.7 mm or 0.3 inch and the largest yet recorded being the goliath frog (Conraua goliath) of Cameroon, measuring about 300 mm or 12 inches or 1 ft.

In a jump force has to be generated to throw the whole body of the organism against gravity. Studies have shown that the force a muscle can generate depends upon the length of the muscle in relaxed state. Using this force-length relationship an optimum muscle contraction length can be defined where the force generated is maximum for a particular type of muscle. The intensity of jump is governed by the muscle work done, which in turn will be the product of muscle force generated and the distance covered by the muscles to generate the force.
Although the features of a Frog's body that add to its jumping ability are its long hind limbs, small body weight and a stout vertebral column. The hind limb comprises of a single strong bone in place of the tibia, fibula and tarsals. To add power to the take-offthe meta-tarsals are elongated, which helps it to push harder against the ground. To further power the leaps the illium is elongated and forms a mobile joint with the sacrum. But Frogs have the ability to jump beyond its muscular ability, i.e., it has been found that if only the muscles of the frog's legs were responsible for its jumping mechanism then the jump would have not been so intense, it would be a small fraction of the present jump.Although the muscles for jumping constitute about 17% of the frog's body weight. Apart from the enlarged musculature, the tendons in the hind limbs of frogs play a vital role in imparting the force to the jump.

As the frog gears up for the jump, the calf muscles(planaris) shortens or contracts, and the tendons associated with it stretches. After about 10-1 seconds the muscular contraction stops at a length 30% of the initialnormal length (at relaxed condition). Now the muscle expands and the stretched tendons recoil like a mighty spring which propels the frog forward by the forceful movement of the ankle joint. The tendons act like springs to further increase the force imparted by the muscles. A similar mechanism of jumping has been recorded in locusts and grass hopers.

Energy has to be absorbed during the landing phase of the jump.Frogs use forelimbs and their bodies for landing purpose. In the fore limbs the radius and ulna are fused into a single bone.

As biology is a field full of exceptions, it would be incomplete if we miss out on the exceptions to the long jumpers. Frogs belonging to the families Bufonidae, Rhinophrynidae, and Microhylidae have relatively shorterhind legs and so it prefers walking rather than jumping. When they need tomake quick movements, they speed up the movement of their limbs which might turn out to be an ungainly hopping gait. The Great Plains narrow-mouthed toad (Gastrophryneolivacea) has a locomotionthat is characterized by a combination of running and short jumps that are usually only an inch or two in length. Fowler's toad (Bufofowleri) was placed on a treadmill in an experiment to study the jumping at varying speeds of the treadmill. Hence by measuring the toad's oxygen uptake it was found that jumping was an inefficient use of resources during sustained locomotion but on other hand it seemedto be a useful strategy when short bursts of high-intensity activity was required, as in an emergency situation.

Short and slim hind limbs are characteristic of the red-legged running frog (Kassinamaculata) which enables it to run faster rather than jump. It can also climb trees and shrubs, and prefers to do so at night probably to catch insects for food.

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