External fertilization: when animals mate without penetration

What is the difference between internal and external fertilization?

In the case of internal fertilization, fertilization takes place inside the female’s reproductive system. The two sexual partners meet and there is therefore a coupling: the male reproductive cell (spermatozoid) then meets the female reproductive cell (oocyte).

In humans, it is the penetration of the man’s penis into the woman’s vagina, followed by ejaculation, which results in this fusion of gametes and the creation of an egg cell. But coupling by penetration may well be the general case in mammals, birds and reptiles, but internal fertilization can also do without penetration! This is particularly the case with the newt. The small male amphibian deposits in front of the female what is called a spermatophore, ie a gelatinous capsule containing spermatozoa, which the female recovers with her cloaca open. Fertilization then takes place inside his body.

In the case of external fertilization, there is no penetration and the encounter between male and female gametes takes place outside the female’s body.

⋙ The harlequin toad clings to the female for 5 months for the chance to mate

External fertilization: how does it work?

The principle of external fertilization is that it takes place outside the female’s body. There is no mating or penetration, but there is also no meeting between the gametes in the female’s reproductive system. This reproduction most often takes place in an aquatic environment where both fertilization and the development of the embryo will take place.

It is also important to remember that external fertilization produces more new individuals than internal fertilization.

External fertilization: which animals are affected?

Among the animals that practice external fertilization, we can mention the sea urchin, jellyfish, trout, salmon, batrachians, corals, etc. The case of the sea urchin is particularly emblematic of this type of reproduction: the female releases her gametes into the water at the same time as the male.

These releases are synchronized to promote encounter and therefore fertilization, but male and female sea urchins do not approach each other. Unlike salmon which release their eggs and sperm close to each other.

External fertilization: the special case of frogs

Nature is full of surprises… Evidenced by the atypical mode of reproduction of frogs: a coupling… but an external fertilization! During courtship, the female (which does not have a vagina) lays her eggs in the water while the male (which does not have a penis) clings to her and hugs her with his paws. This coupling is called an amplexus. The male will then fertilize the eggs with a white liquid, milt. He only releases her when he has fertilized the eggs.

Read also:

Parthenogenesis: those animals capable of reproducing without mating

Parthenogenesis: those animals capable of reproducing without mating

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