Metamorphosis: Birth to Maturity Transformations

Metamorphosis: The Intricate Journey from Birth to Maturation in Nature

We all grow every moment; we grow mentally and physically. Also, there are a lot of changes that our body undergoes, like changes in skin color, hair color, growth in height, weight, etc.
So we transform from kids to adults.

The same phenomenon occurs in animals also, where a larva grows into an adult; this phenomenon is called Metamorphosis. In technical terms, Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.

Some insects, fish, amphibians, mollusks, crustaceans, cnidarians, echinoderms, and tunicates undergo Metamorphosis, which is often accompanied by a change of nutrition source or behavior.

Why is Metamorphosis required?

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.

You might have seen a butterfly cacoon hatching. This is a classic example of Metamorphosis; the hormones cause drastic changes to the functioning of cells and even behavioral changes, such as the caterpillar spinning its cocoon.

Examples of Metamorphosis

Many of us may have witnessed the process of Metamorphosis firsthand by raising caterpillars into butterflies in school. The idea of a worm-like caterpillar wrapping itself in a cocoon for weeks and then emerging as a beautiful butterfly is certainly strange. But the obvious changes in appearance, such as the growth of wings, don't do justice to just how strange this process is.

In the cocoon, caterpillars don't simply gain legs, wings, and an exoskeleton. They also grow new eyes, lose their leaf-eating mouth parts and replace them with nectar-sucking proboscises, and gain mature reproductive organs.

The Metamorphosis of a tadpole into a frog is a little less violent than that of a caterpillar into a butterfly, but the processes share some important common features.
Tadpoles do not dissolve their bodies into mush, but they do "digest" them in a less spectacular way. Using the process of apoptosis – or "programmed cell death" – the tadpoles "order" the cells they don't need anymore to shred their DNA and die. The dead cells are then cannibalized for energy and raw materials to make other cells.

The cells of their tails are broken down and used to make their developing legs; a similar process happens with the gills, which disappear as the tadpole begins to develop air-breathing lungs.

One interesting thing to note is that tadpole metamorphosis and insect metamorphosis likely developed separately; the common ancestor of insects and amphibians diverged long ago, and the ancestors of modern insects are not thought to have used Metamorphosis. When the same phenomenon evolves twice in radically different organisms, that's a sure sign that it is a useful adaptation!

References

1. Gilbert, S. F. (2010). Developmental Biology. Sinauer Associates.
2. Hadley, M. E. (1973). Endocrinology of Insects. Alan R. Liss.
3. Nijhout, H. F. (1994). Insect Hormones. Princeton University Press.
4. Emlen, D. J. (2012). The evolution of animal weapons. Annual Review of Ecology, Evolution, and Systematics, 39(1), 387-413.

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