7 differences between EXTERNAL and INTERNAL fertilization

Fertilization is the process by which the transport and fusion of two sex cells (gametes) to give rise to a new individual. Fertilization is not the same in all animals, and two types can be differentiated: external and internal fertilization.

The type of fertilization will depend on whether the fusion of the gametes occurs within one of the parents (internal fertilization) or outside it, in the external environment (external fertilization). In this lesson from a TEACHER we will see the external and internal fertilization: differences and examples of animals that have this type of reproduction.

The fertilization is the process by which transportation is carried out and fusion of the egg and sperm. This specific process of fusion of the ovum and sperm is called syngamy.

Often times, the terms fertilization and syngamy are confused and used interchangeably but are not synonymous. The syngamy refers to a very specific moment of fertilization, the fusion of both gametes, while fertilization comprises a much broader process: since the gametes are expelled from their sexual organ, already mature, until the first divisions begin to occur cell phones.

Throughout the history of evolution, animals with sexual reproduction They have mainly developed two different mechanisms for the female gamete and the male gamete to meet in one place and can fuse.

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Organisms with sexual reproduction can have two main types of fertilization: external fertilization and internal fertilization. The main difference between the two types of breeding is where they take place.

• The internal fertilization is one in which the union of the gametes, ovum and sperm, takes place inside the female's body. Fertilization can occur at different heights of the female genital tract and, in certain groups, specialized structures such as the sewer. Most birds and some amphibians and reptiles, monotreme mammals and marsupials (among others) have sewers.
• The external fertilization is the one in which the fusion of male and female gametes, sperm and ovum, takes place in the external environment. Normally, although not always, the external environment is usually some body of water, be it the sea or a small pool.

Although the main difference between internal and external fertilization is where it occurs, there are other differences that either are a consequence of it, or are adaptations that animals have developed to ensure greater survival of their eggs.

Some differences between external and internal fertilization They are:

• Gamete released: while in external fertilization both gametes have to leave the animal's body, in internal fertilization the only gamete that leaves the parent is the sperm. The female gamete in internal fertilization does not leave the genital tract of the animal at any time.
• Male gamete release site: In external fertilization, the male gamete is released to the outside while in internal fertilization the male releases his gamete directly into the genital tract of the female.
• Number of gametes released: in external fertilization a greater number of gametes are released than in internal fertilization. This is because the female "takes care" of the gametes found in her body, while the released gametes can be prey to predators, so the greater the number, the more likely that some will survive their attacks.
• Type of embryonic development: external fertilization only occurs in oviparous animals, which develop inside an egg that protects them from the outside environment. On the other hand, in animals with internal fertilization, the type of embryonic development can be more varied: they can be oviparous, viviparous or ovoviviparous.
• Environment in which they live: Animals that have external fertilization usually lay their eggs in humid places or, directly, in the aquatic environment, so they have a great dependence on water. In contrast, internally fertilized animals have been able to live in a greater variety of environments.
• Fertility and survival rate: While externally fertilized animals have a higher fertility rate (they lay more eggs) but a lower rate survival, internally fertilized animals have a lower reproduction rate but their survival rate is higher. This is due, in part, to the greater amount of time and energy that internally fertilized animals often invest in their young.

Internal fertilization occurs in most land animals Like the mammals, birds, reptiles or insects. Some examples are:

• European eel or common eel (Anguilla anguilla)
• Orca (Orcinus orca)
• Great white shark (Carcharodon carcharias)
• Blue shark or blue shark (Prionace glauca)
• Dugong or dugong (Dugong dugon)
• European bee (Apis mellifera)
• Fruit fly (Ceratitis capitata)
• Common scorpion, yellow or scorpion (Buthus occitanus)
• Rooster and hen (Gallus gallus domesticus)
• Long-tailed chinchillaChinchilla lanigera)
• Dog (Canis lupus familiaris)
• Sea otter (Enhydra lutris)

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