All animals, from birth, undergo morphological, anatomical and biochemical changes to reach adulthood. In many of them, these changes focus on the increase in size of the body and certain hormonal parameters that guide growth. However, many other animals carry out such significant changes that make the adult individual not resemble the juvenile at all, we speak of the metamorphosis in animals
We invite you to read this article on our site, where you will discover what metamorphosis is and how it occurs in different groups of animals.
Metamorphosis in insects
Insects are the metamorphic group par excellence and the most common to explain metamorphosis in animals. They are oviparous animals that hatch from eggs. Its growth requires the shedding of its skin or integument, since this prevents it from growing in size like other animals. Insects belong to the phylum of hexapods, because they have three pairs of legs.
Within this group there are animals that do not undergo metamorphosis such as the dipluros, considered ametabolosThey are primarily wingless insects (they do not have wings) and few changes can be seen in their post-embryonic development, since generally only:
- Progressive development of their genital organs.
- Increase in biomass or weight of the animal.
- Slight variations in the relative proportions of its parts. Therefore, the juvenile forms are very similar to the adult, which can moult several times.
In pterygotic insects (which have wings) there are several types of metamorphosis,depending on the changes that occur, if the result of the metamorphosis gives an individual more or less different from the original:
- Hemimetabolous metamorphosis: from the egg hatches a nymph that has wing outlines. The development is similar to the adult, although sometimes not (eg dragonflies). They are insects without the pupal stage, that is, a nymph is born from the egg which passes directly to the adult stage through consecutive molts. Some examples are mayflies, dragonflies, bedbugs, grasshoppers, termites, etc.
- Holometabolic metamorphosis: a larva is born from the egg, very different from the adult. The larva, at a certain point, transforms into pupa or chrysalis which, when it hatches, will give rise to the adult individual. This is the metamorphosis that most insects present, such as butterflies, cockroaches, ants, bees, wasps, crickets, beetles, etc.
- Hypermetabolic metamorphosis: Insects with hypermetabolic metamorphosis have a very long larval developmentLarvae are different from each other as they molt, because they live in different habitats. Nymphs do not have developed wings until they reach the adult stage. It occurs in some beetles such as tenebria and consists of a special complication of larval development.
The biological reason for metamorphosis, aside from having to shed, is to separate the new offspring from the parents to from competing for the same resources The usual thing is that the larvae live in places other than the adults, such as the aquatic environment and, also, that they feed differently, when they are larvae they are herbivorous animals and when they are adults they are predators or vice versa.
Metamorphosis in amphibians
Amphibian animals also undergo metamorphosis, in some cases more subtle than in others. The main reason for the metamorphosis of amphibians is to eliminate the gills and give rise to the lungs, with some exceptions, as is the case of the Mexican salamander (Ambystoma mexicanum) that in its adult state continues to present gills, considered a evolutionary neoteny (maintenance of juvenile structures in the adult state).
Amphibians are also oviparous animals. From the egg comes a small larva that can be very similar to the adult, as is the case with salamanders and newts, or very different, as in frogs or toads. In fact, the frog is a very common example to explain metamorphosis in amphibian animals.
Salamanders, at birth, already have legs and a tail like their parents, but they have gills. After metamorphosis, which can be delayed for several months depending on the species, the gills disappear and the lungs develop.
In anuran animals (amphibians without tails) such as frogs and toads, metamorphosis is much more complex. When the eggs hatch, they hatch small larvae with gills and a tail, no legs and a half-developed mouth. After a while, a layer of skin begins to grow over the gills and small teeth appear in the mouth.
Then the hind legs develop and, where the the front legswill appear, we find two bumps that will eventually develop into limbs. In this state, the tadpole will still have a tail, but it will be able to breathe air. The tail will slowly decrease until it disappears completely, giving rise to the adult frog
Metamorphosis in other animals
Not only amphibians and insects go through the complex process of metamorphosis. Many other animals belonging to other taxonomic groups also suffer from it, for example:
- Cnidarians or jellyfish
- Crustaceans, such as lobsters, crabs or shrimp.
- Urochordates, specifically, sea squirts, after metamorphosis and establishment as an adult individual, become sessile or immobile animals andthey lose their brains.
- Echinoderms such as starfish, sea urchins or holothurians.
