When you think about the structure and form of a tadpole, a plant-eating, streamlined creature designed for aquatic life, and that of a meat-eating terrestrial frog which is adapted for jumping on land, and know that they are one and the same organism, one can’t help but be impressed. The visible changes in this transformation are dramatic enough – legs emerging, head shape changing, tail being absorbed – but the internal changes a tadpole undergoes are just as dramatic. Research has shown that everything from a tadpole’s respiratory (gills replaced by lungs), urogenital and sensory systems to its digestive system (intestines becomes much shorter due to change in diet) is undergoing significant changes.
The length of time these changes take varies according to the species of amphibian. Most Green Frogs (Rana clamitans, pictured) undergo metamorphosis within the same breeding season or they overwinter as tadpoles and mature the following summer. (There are records of Green Frog metamorphosis taking up to 22 months). Biologists in Michigan found that eggs deposited before roughly June 25 were capable of developing in one season, whereas eggs deposited after roughly July 10 remained as tadpoles until the following year.
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