Metamorphosis Definition

Metamorphosis is the biological process that consists of the change of shape and structure of an organism during its development. It is a common phenomenon in the animal kingdom, especially among invertebrates and some vertebrates such as amphibians.

All organisms go through a growth stage during which their body size increases and they gradually acquire the characteristics of an adult of their species. An example of a growth process is the passage from childhood to adulthood: the child slowly acquires adult characteristics (development of the genitals, growth of body hair, changes in the voice).

The growth-related changes imply morphological changeswhich are defined as changes in the shape of the organism (such as changes related to increased body mass and size, organ growth) and physiological changes, which are changes in the physiology of the organism, which allow the adult organism to have functions that the young organism does not have; These types of changes are closely related to sexual maturity and reproductive capacity.

Growth is a natural process, common to all living beings, which involves bodily changes; but almost always, the pre-adult stage resembles an adult. In this sense, the changes in growth are slight.

There are other organisms that are born with a very different shape from the adult (for example: a butterfly is born as a caterpillar), and during its growth they undergo a process that implies drastic changes in their morphology, physiology and way of life.

Some well-known cases of metamorphosis are that of insects and amphibians: a caterpillar turns into a butterfly or a tadpole turns into a frog. In these cases, the pre-adult or juvenile form has a different way of life from the adult, and metamorphosis implies a series of morphological, physiological and behavioral transformations that allow the organism to adapt to different environments and living conditions.

Metamorphosis in insects and examples

Insects are the most diverse and abundant group of animals on the planet and are one of the most common types of living arthropods.

There are two types of metamorphosis: complete metamorphosis or holometabolous metamorphosis and incomplete metamorphosis or hemimetabolous.

In complete metamorphosis the organism goes through four distinct stages, or stages: egg, larva, pupa and adult or imago. The larva and the adult have very different shapes and habits, and the pupa is a resting phase where changes occur.

This type of metamorphosis is observed in Lepidoptera (butterflies and moths).

Butterflies usually have a short life, weeks or months. The female adults lay their eggs on the leaves of the plants, which is the exclusive food of their larvae: the caterpillars. Caterpillars grow rapidly and moult several times. They then transform into chrysalis, which is the pupal stage. The chrysalis is a silk structure that hangs from the leaves or branches. The pupa remains inside its chrysalis until metamorphosis is complete. Finally, the adult butterfly or imago emerges from the chrysalis.

There is also complete metamorphosis in beetles (Coleoptera) and in flies and mosquitoes (Diptera) and in bees, wasps and ants (Hymenoptera).

Honeybees are social insects that live in colonies consisting of a queen, thousands of workers, and a few drones. Their life cycle lasts between four and six weeks. The queen lays her eggs in the cells of the comb, where the larvae develop. During this period, the larvae are fed by the workers with honey and pollen for a few days, then the workers cover the cell with wax. Within the sealed cells metamorphosis occurs. Adults emerge by breaking the wax with their mandibles.

In beetles and flies, the larvae are worm-shaped with legs, and sometimes live underground. Fly larvae feed on decomposing organic matter and some are parasitic: the fly lays its eggs in wounds on animals or even humans, and the larvae feed on the host’s meat. Mosquito larvae are aquatic.

The incomplete metamorphosis It is characterized by having three phases: egg, nymph and adult. The nymphs resemble the adults, but are smaller and do not have wings or mature sexual organs.

Some examples of insects with incomplete metamorphosis are grasshoppers, stink bugs, and dragonflies.

The nymphs of hemimetabolous insects are very similar to the adult, but some, like dragonfly nymphs, are aquatic and are known as naiads.

Metamorphosis in amphibians and example

In vertebrates, the only group that has a metamorphosis in its life cycle are amphibians.

They go from being aquatic larvae to terrestrial or semi-aquatic adults. There is no pupal stage as in insects, and the transition from the larval form to the adult form occurs gradually.

The larval stage is called tadpole and is characterized by having an elongated body with a tail, a small mouth, external or internal gills to breathe underwater, and a herbivorous or detritivorous diet. Tadpoles hatch from eggs that adults lay in the water.

Metamorphosis can last anywhere from a few weeks to several years, depending on the species and environmental conditions.

During metamorphosis, the tail disappears and all 4 limbs grow, which allow them to jump or walk during their lives as adults on earth.

Lungs develop, which facilitate air breathing, and they lose their gills. This change implies that the adult will no longer be able to breathe underwater. Many amphibians spend much of their adult lives submerged, but since they do not have gills, they must come to the surface to breathe.

The mouth increases in size and in the tadpoles of toads and frogs, the retractable tongue appears, which helps them capture prey. The diet in most adult amphibians is carnivorous or insectivorous. The intestine also undergoes changes to adapt to such a diet.

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