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All animals, from birth, undergo morphological, anatomical and biochemical changes to reach the adult state. In many of them, these changes are restricted to size increase of the body and certain hormonal parameters that regulate growth. However, many other animals go through such significant changes that the adult individual does not even look like the juvenile, we talk about the metamorphosis of animals.
If you are interested in knowing what is metamorphosis, in this PeritoAnimal article we will explain the concept and give some examples.
insect metamorphosis
Insects are the metamorphic group par excellence, and also the most common to explain the animal metamorphosis. They are oviparous animals, which are born from eggs. Their growth requires the detachment of the skin or integument, as it prevents the insect from growing in size like other animals. The insects belong to the phylumhexapod, because they have three pairs of legs.
Within this group there are also animals that do not undergo metamorphosis, such as the diplures, considered ametaboles. They are mainly wingless insects (which do not have wings) and the post-embryonic development is notable for few changes, as it is usually only observed:
- Progressive development of Organs genitals;
- Increase in animal biomass or weight;
- Small variations in the relative proportions of its parts. Therefore, the juvenile forms are very similar to the adult, which can change several times.
In pterygote insects (which have wings) there are several types of metamorphoses, and it depends on the changes that occur if the result of the metamorphosis gives an individual more or less different from the original:
- hemimetabola metamorphosis: from the egg is born a nymph which has wing sketches. The development is similar to the adult, although sometimes it is not (for example, in the case of dragonflies). are insects without a pupal state, that is, a nymph is born from the egg, which, through consecutive molting, passes directly to adulthood. Some examples are Ephemeroptera, dragonflies, bed bugs, grasshoppers, termites, etc.
- holometabola metamorphosis: from the egg, a larva is born that is very different from the adult animal. The larva, when it reaches a certain point, becomes a pupa or chrysalis which, when hatching, will originate the adult individual. This is the metamorphosis that most insects undergo, such as butterflies, cockroaches, ants, bees, wasps, crickets, beetles, etc.
- hypermetabolic metamorphosis: insects with hypermetabolic metamorphosis have a very long larval development. Larvae are different from each other as they change, because they live in different habitats. Nymphs do not develop wings until they reach adulthood. It occurs in some coleoptera, such as tenebria, and is a special complication of larval development.
The biological reason for the insects' metamorphosis, in addition to the fact that they have to change their skin, is to separate the new offspring from their parents to avoid competition for the same resources. Typically, larvae live in different places than adults, such as the aquatic environment, and they also feed differently. When they are larvae, they are herbivorous animals, and when they become adults, they are predators, or vice versa.
Amphibian metamorphosis
Amphibians also undergo metamorphosis, in some cases more subtle than others. The main purpose of amphibian metamorphosis is eliminate the gills and make room for thelungs, with some exceptions, such as the Mexican axolotl (Ambystoma mexicanum), which in the adult state continues to have gills, something that is considered a evolutionary neoteny (conservation 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 in the case of salamanders and newts, or very different, as in frogs or toads. THE frog metamorphosis is a very common example to explain amphibian metamorphosis.
Salamanders, at birth, already have legs and a tail, like their parents, but they also have gills. After the metamorphosis, which can take several months depending on the species, the gills disappear and the lungs develop.
In anuran animals (tailless amphibians) as frogs and toads, the metamorphosis is much more complex. When the eggs hatch, the smalllarvae with gills and tail, no legs and mouth only partially developed. After a while, a layer of skin begins to grow on the gills and small teeth appear in the mouth.
Afterwards, the hind legs develop and give way to the members front, two lumps appear that will eventually develop as members. In this state, the tadpole will still have a tail, but will be able to breathe air. The tail will slowly decrease until it disappears completely, giving rise to the adult frog.
Types of metamorphosis: other animals
It's not just amphibians and insects that go through the complex process of metamorphosis. Many other animals belonging to different taxonomic groups also undergo metamorphosis, for example:
- Cnidarians or jellyfish;
- Crustaceans, such as lobsters, crabs or shrimps;
- Urochord, specifically sea squirts, after metamorphosis and establishment as an adult individual, become sessile or immobile animals and lose their brain;
- Echinoderms, like starfish, sea urchins or sea cucumbers.
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