The Life Cycle of a Frog

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Overview

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The life cycle of a frog consists of three stages: egg, larva, and adult. As the frog grows it moves through these stages in a process known as metamorphosis. Frogs are not the only animals to undergo metamorphosis, most other amphibians also undergo remarkable changes throughout their life cycles, as do many species of invertebrates. During metamorphosis, two hormones (prolactin and thyroxine) control the transformation from egg to larva and adult.

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Breeding

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The breeding season for frogs usually occurs during the springtime in temperate climates and during the rainy season in tropical climates. When male frogs are ready to breed, they often use loud croaking calls to attract a partner. These calls are produced by filling a vocal sac with air and moving the air back and forth to create a chirp-like sound. When mating, the male frog holds onto the female's back, clasping his arms around her waste or neck. This embrace is referred to as amplexus and its purpose is to ensure the male is in the optimal position to fertilize the female's eggs as she lays them.

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Life Cycle Stage 1: Egg

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Many species lay their eggs in calm water amongst vegetation where the eggs can develop in relative safety. The female frog lays numerous eggs in masses that tend to clump together (these egg masses are referred to as spawn). As she deposits the eggs, the male releases sperm onto the egg masses and fertilizes the eggs.

In many species of frogs, the adults leave the eggs to develop without further care. But in a few species, parents remain with the eggs to look after them as they develop. As the fertilized eggs mature, the yolk in each egg splits into more and more cells and it begins to take on the form of a tadpole. Within one to three weeks, the egg is ready to hatch, and a tiny tadpole breaks free of the egg.

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Life Cycle Stage 2: Tadpole (Larva)

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A frog's larva is also called a tadpole. Tadpoles have rudimentary gills, a mouth, and a long tail. For the first week or two after the tadpole hatches, it moves very little. During this time, the tadpole absorbs the remaining yolk left over from the egg, which provides much needed nourishment. At this stage, tadpoles have rudimentary gills, a mouth and a tail. After absorbing the remaining yolk, the tadpole is strong enough to swim on its own.

Most tadpoles are feed on algae and other vegetation so they are considered herbivores. They filter material from the water as they swim or tear away bits of plant material. As the tadpole continues to grow, it begins to develop hind limbs. Its body elongates and its diet grows more robust, shifting to larger plant matter and even insects. Later in their development, front limbs grow and their tail shrinks. Skin forms over the gills.

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Life Cycle Stage 3: Adult

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At approximately 12 weeks of age, the tadpole's gills and tail have been fully absorbed into the body—the frog has reached the adult stage of its life cycle and is now ready to venture out onto dry land and in time repeat the life cycle.