Metamorphosis is a process by which animals undergo extreme, rapid physical changes some time after birth. The result of metamorphosis may be change to the organism’s entire body plan, such as a change in the animal’s number of legs, its means of eating, or its means of breathing.
In species that use metamorphosis, metamorphosis is also typically required for sexual maturity. Pre-metamorphic members of these species are typically unable to mate or reproduce.
Commonly known examples of metamorphosis include the process undergone by most insects, and the transformation of tadpoles into frogs. The diagram below shows the stages of this change, wherein the small fish-like tadpoles transform into what seems a completely different animal:
Animals that you may not know undergo metamorphosis include fish, mollusks, and many other types of sea creatures which are related to insects, mollusks, or fish. Lobsters, for example, which are closely related to insects, do undergo metamorphosis as part of their life cycle.
Metamorphosis is a remarkable process. The speed and extent of cell growth and differentiation is astonishing. In most species, such rapid growth and such sweeping changes to cell type only happen during embryonic development. Indeed, some scientists believe that the process of metamorphosis involves a sort of re-activating of genes that allow animal cells to change from one cell type to another.
The changes leading to metamorphosis are triggered by hormones, which the animal’s body releases as the right conditions for metamorphosis approach. In some animals a hormone cascade follows, with the trigger hormone causing the release of several other hormones that act on different parts of the animal’s body.