The whole life cycle of a frog occurs in three stages:
- Tadpole (larva)
- Adult frog
The development of tadpole (juvenile state) into an adult frog is called metamorphosis. By this a of young larva of frog changes into an adult. To lay eggs, the female frog should mate in the breeding season to ensure the fertilization of eggs by sperm. The breeding season of frogs usually occurs during spring in temperate climate and rainy season in tropical climates. When the male frog is ready to mate, it calls upon its female mate by a loud croaking sound. Male frogs are often heard, making such sounds in rainy season, which creates a ‘chirp ‘ -sound. During mating, the male frog holds onto the back of female frog by clasping its front legs around her waist or neck. This kind of hold or embrace is called as ‘amplexus.’ The amplexus position ensures there is optimal fertilization of eggs with sperms as the female lays it.
Life Cycle of Frog
Egg is the first stage. The frog lay its eggs in calm waters around the vegetation. The intention to do so is to protect its eggs from predators. Each female frog lays many eggs that get aggregated into groups called ‘spawn.’
As the eggs get laid, the male sperm fertilizes it. In many species of frogs, it is seen that they do not care about the eggs and leave them to propagate themselves. However, in few species like marsupial frogs, Rana clamitans etc. parental care is seen in which they protect their eggs and nurture the development of their eggs. As the development of the eggs starts, the zygote present in the eggs splits into more and more cells and starts developing into a ‘tadpole’- the larva of frog. Within one or three weeks, the eggs are ready to hatch, and a tiny tadpole breaks free.
Tadpole constitutes the second stage of frog life cycle. The morphological characters of a tadpole comprise of
● Rudimentary gills
● A mouth
● And a long tail.
In the very first week of tadpole hatching, only small amount of movement is seen. During this time, the tadpoles to sustains by absorbing the remaining amount of yolk from the egg. After the full absorption of yolk by the tadpole, the larva becomes strong enough to swim in water on its own. The food of tadpole larva comprises of algae and another sort of vegetation, which makes them herbivores. They filter most of their food by tearing apart the small edible plants. As they grow gradually, the tadpoles begin to develop hind limbs. The body gets elongated, and diet becomes more efficient and healthy. Their food shifts to larger plant matter and even insects. Later in due course of development, the front limbs grow, the tail gets disappear, skin forms over the gills, and cartilage gets replaced by bones. The skull also changes and transforms into an adult-like rather than a larval type.
This is the third and final stage of life cycle. At approximately 12 weeks of age, the tadpole body gets fully grown-up by tail shrinking and gills absorption into the body, meaning that the tadpole has reached the adult form of its life cycle.
The adult form of frog is now ready to set out for its life’s journey into the land or water, and in time, repeat the life cycle to sustain their future existence in this world.
Metamorphosis occurs in most other amphibians in which they undergo some remarkable, characteristic changes throughout their life cycles. Hormones play a vital role in the transformation of eggs into adult. Mainly, prolactin and thyroxine control this process in frogs.