External fertilization: what is and animals

External fertilization is the process where Male sperm fertilizes or fertilizes a female ovule abroad. Thus, this occurs outside the female’s body, unlike how it happens in internal fertilization. The external fertilization process can also be called Freza or spawning. These eggs have a layer that protects from outside, but can be easily penetrated by sperm.

This type of fertilization depends largely on the environment. To facilitate the process, it must be carried out In the water and that there is a means of transport for sperm. The presence of water also prevents gametes from drying out. There are animals that do not move and depend on water currents so that gametes can be found.

Eggs can be placed in a nest, Between algae, on the substrate or on rocks. These sites are called frezaderos and are chosen by giving the Ideal environment for external fertilization in terms of oxygenation, refuge, temperature, depth and possibility of prospering. On the other hand, gametes can simply be discharged on water. The choice of site and strategy depends on the species and the organism.

We recommend you read more about what an aquatic ecosystem is to learn more about the environment in which external fertilization occurs.

External fertilization works with A male organism and a femaleboth of the same species. The process is as follows:

1. The female puts her ovules in waterin its outer environment.
2. The male Free the water sperm so that ovules can be fertilized. There is normally synchronization so that the release of gametes occurs at the same time, but it can happen that sperms are released sooner or later, but that is a clear disadvantage.
3. Once The sperm enters the ovules, fertilization occurs. The result of external fertilization is a new son of the two parents.

To better understand external fertilization, it is advisable to indicate some examples of species of animals with external fertilization, although we can already imagine that they are always animals that live or seasons in the water.

Corals (anthozoa class)

The corals are Aquatic animals without movement. With the information that we have given you so far, you will imagine what your fertilization is like. These organisms are composed of Polyps that can be male or female, in the same coral hermaphrodite. Each releases their corresponding gametes and with the help of the sea currents manage to meet. When fertilizing, they produce a call plot that will spend a few days off and then settle in the substrate to grow as a sessile coral. Here you can meet hermaphrodite animals.

In addition to having external fertilization, corals are important Sites for depowering of tropical fishbecause they are in shallow, warm and recesses so that the fry can develop quietly. For this reason, coral reefs have an incomparable wealth of biodiversity.

We encourage you to know these curious animals better reading this other post about what a coral reef is.

Frogs and toads (anura order)

Frogs have a courtship process, unlike most animals with external fertilization where gametes are more easily released. Once The female accepts the maleshe Put the eggs on the water While the male hugs her. This act is known as Amplexo hug. While the eggs leave the female, The male fertilizes them. This is a case in which there must be acceptance of the female so that fertilization can occur.

Here you can read about the life cycle of a frog.

Salmon (Psalm spp.)

In salmon the external fertilization process is particular because They swim against the spawning to spawn. They return From the ocean to the rivers Well, here are rocky surfaces on which it is safer that external fertilization can occur successfully. In this case, the female acceptance is not necessary, only sperm and ovules are released and these are fertilized by the nearest sperm.

To finish talking about external fertilization, we will comment on their advantages and disadvantages for these species, although, obviously, for these the advantages weigh more and, therefore, evolution has led them to this type of fertilization.

Advantages of external fertilization

• In order to increase the probability that both gametes join, males release an amount of sperm and females a similar amount of ovules. This strategy considers that some gametes can be lost for being released into open water.
• This type of fertilization prevents wear and physical load that implies internal fertilization.
• It allows a development of eggs and young as sure as possible taking into account the environment in which they live.
• It also avoids the need to go through courtship processes, except cases such as some amphibians.

Disadvantages of external fertilization

• There is a risk that gametes, both female and masculine, being ingested by other animals. Many aquatic animals are filter and can eat them, so that gametes can be lost.
• The gametes are exposed to strong sea currents, which can be counterproductive and affect fertilization.
• The production of multiple gametes is a high energy expenditure.
• Many ovules can be without fertilizing for being thrown out, which is an energy and gametes waste.
• There is no parental care, so children are vulnerable to external dangers.
• Not all young get to survive.

As you can see, in the advantages of fertilization and in disadvantages there are different points but also in common with respect to internal fertilization. Now that you have learned all this about what external fertilization is and you know some animals that have it, we recommend you read this other article about the reproduction function: what it consists of and why it is important.

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