One of the great aspects of evolution has been the conquest of the terrestrial environment by animals. The passage from water to land was undoubtedly a unique event that changed the development of life on the planet. But this wonderful transition process left some animals with an intermediate body structure between water and land, which, although fully adapted to terrestrial environments, remain generally linked to water, mainly for reproduction.
The above refers to amphibians, whose name precisely comes from their double life, aquatic and terrestrial, the only vertebrates that are currently capable of metamorphosing. Amphibians belong to the group of tetrapods, they are anamniotes (without amniotic sac), although with certain exceptions and most breathe through gills in the larval phase, but in a pulmonary way after metamorphosis. In this article on our site, we want you to know how these animals reproduce, since it is one of the aspects that keeps them linked to the aqueous environment. Keep reading and learn about the reproduction of amphibians
Classification of amphibians
Currently, amphibians are grouped into the Lissamphibia, and this in turn branches or divides into three:
- Gymnophiona: they are commonly known as caecilians and are characterized by being legless. In addition, they are the ones with the fewest species.
- Caudata: these correspond to salamanders or newts.
- Anura: This corresponds to frogs and toads. However, it should be noted that these two terms have no taxonomic validity, but are used to distinguish smaller animals with smooth, moist skin from those with drier, rougher skin.
For more information, we encourage you to read this other article on Characteristics of amphibians.
Type of amphibian reproduction
All these animals have a type of sexual reproduction, however, they express a wide variety of reproductive strategies. On the other hand, although it is common to believe that all amphibians are oviparous, it is necessary to make a clarification in this regard.
Are amphibians oviparous?
Caecilians have internal fertilization, but can be oviparous or viviparousFor their part, salamanders can have internal or external fertilization, and in terms of the modality of embryonic development, they exhibit several ways depending on the species: some lay fertilized eggs that develop outside (oviparity), others keep the eggs inside from the body of the female, expelling them when the larvae have formed (ovoviviparity) and in other cases they keep the larvae internally until they undergo metamorphosis, expelling the fully formed individuals (viviparity).
As for anurans, they are generally oviparous and with external fertilization, but there are also some species with internal fertilization, and cases of viviparity have also been identified.
How is the reproduction process of amphibians?
We already know that amphibians express multiple reproductive forms, but let's learn more about how amphibians reproduce.
Caecilian reproduction
The male caecilians have a copulatory organ with which they fertilize the females. Some species lay their eggs in moist areas or near water and the females take care of their eggs. There are other cases in which the females are viviparous and keep the larvae in their oviduct all the time, from which they feed.
Reproduction of caudates
As for the caudates, a reduced number of species express external fertilization, while the majority present internal fertilization The male, after to carry out a courtship, it leaves the spermatophore generally on a leaf or branch so that it is later taken by the female. Then, the eggs will be fertilized inside the body of the future mother.
On the other hand, some species of salamanders lead a fully aquatic life and lay their eggs in this environment, laying them in masses or groups, and from these larvae will emerge with gills and a tail in the shape of a fin. But other salamanders lead a terrestrial adult life after completing the metamorphosis. The latter lay their eggs on the ground in the form of small clusters, generally under moist, soft soil or under moist logs.
Various species tend to keep their eggs for protection and, in these cases, the larval development occurs entirely inside the egg, so individuals with a similar shape to adults hatch from this. Cases have also been identified in which the female maintains the larvae during their complete development to the adult form, at which point she expels them.
Reproduction of anurans
Male anurans, as we have mentioned, generally fertilize the eggs outside, although a few species do so internal. These attract the females through the emission of their songs, and when she is ready, she will approach and the amplexus will occur, which is the positioning of the male on the female, so that as she releases the eggs, the male fertilize them.
The oviposition of these animals can occur in various ways: in some cases it is aquatic, which includes various ways of laying eggs, in others it occurs in foam nests on the water and can also be done arboreal or terrestrial. There are also some cases in which larval development occurs on the mother's skin.
Why is water necessary for amphibians to reproduce?
Unlike reptiles and birds, amphibians produce eggs without the shell or hard covering that surrounds the embryo of these animals. This, in addition to allowing gas exchange with the outside because it is porous, offers high protection against a dry environment or a certain level of high temperature.
Embryonic development of amphibians
Due to the above, the embryonic development of amphibians must occur in a aqueous medium or in humid environments so that the eggs are protected, mainly against moisture loss, which would be fatal for the embryo. But as we already know, there are amphibian species that do not put them in the water. In these cases, some strategies consist of doing it in humid places, underground or covered by vegetation. They can also produce large numbers of eggs encased in a gelatinous mass, providing the ideal conditions for development. Even species of anurans have been identified that carry water to the terrestrial place where the eggs develop.
These vertebrates are a clear example that life seeks the evolutionary mechanisms necessary to adapt and develop on Earth, which is clearly seen in its various ways of reproducing, which constitutes endless strategies for the perpetuation of the group.
Amphibian conservation status
Many species of amphibians are cataloged to some degree of danger of extinction, mainly due to their dependence on bodies of water and the susceptibility that may be due to the massive changes that are currently occurring in rivers, lakes and wetlands in general.
In this sense, forceful actions are necessary to stop the deterioration to which these ecosystems are subjected in order to conserve amphibians and the rest of the species that depend on these habitats.
