The merging of an egg and sperm cell inside the female body during sexual reproduction is known as internal fertilisation. External fertilisation offers the male more control over reproduction, whereas internal fertilisation gives the female more power. There must be a way for the male to deliver sperm into the female’s reproductive system for internal fertilisation to occur.
Copulation is the introduction of an intromittent organ into the vagina or cloaca in mammals, reptiles, and certain other groups of animals. The cloacal kiss is utilised in most birds, in which the two animals squeeze their cloacas together while exchanging sperm. Internal fertilisation is accomplished by passing a spermatophore, or a bundle of sperm, from the male to the female in salamanders, spiders, some insects, and some molluscs. In oviparous organisms, the embryos are laid as eggs, but in viviparous organisms, the embryos continue to develop inside the mother’s reproductive tract and are born later as they live young.
Evolution of internal fertilisation
Internal fertilisation has developed multiple times in animals. All of the features associated with internal fertilisation, according to David B.Dusenbery, were most likely the outcome of oogamy.
Sexual selection is hypothesised to have led to the development of internal fertilisation selection through sperm competition.
External fertilisation in amphibians gave rise to internal fertilisation.
Methods of internal fertilisation
Internal fertilisation in animals refers to fertilisation that takes place inside the female body and is accomplished in a variety of ways:
- Copulation is the insertion of the penis or other intromittent organ into the vagina (in most mammals) or the cloaca (in monotremes, most reptiles, certain birds, the amphibian tailed frog, and some fish), as well as in some non-vertebrate species, such as the extinct dinosaurs.
- Cloacal kiss, in which the two animals contact their cloacae together to transfer male sperm to female cloacae. Most birds, including the tuatara, use it because they lack an intromittent organ.
- A spermatophore is a sperm-containing cap put in the female’s cloaca by the male. Normally, sperm is kept in spermathecae on the cloaca’s roof until it is required for oviposition. Some salamander and newt species, as well as the Arachnida, insects, and molluscs, utilise it.
- Sperm cells are released into the water by sponges to fertilise.
Expulsion
The growing egg or offspring must be discharged at some point. There are a few different ways to reproduce. The following are the conventional classifications:
- Most invertebrates and reptiles, monotremes, dinosaurs, and all birds that lay eggs that continue to develop after being laid and hatch later have oviparity.
- Viviparity is seen in practically all mammals that bear young (such as whales, kangaroos, and humans). The female reproductive system spends more time with the growing young than the male reproductive system. The young are then freed to survive on their own, with variable degrees of assistance from the species’ parent(s).
- The garter snake, most vipers, and the Madagascar hissing cockroach all have ovoviviparous eggs (with shells) that hatch as they are laid, giving the appearance of live birth.
Advantages from Internal Fertilisation
Internal fertilisation enables the following:
- Female mate choice allows a female to choose her partner both before and after mating. External fertilisation does not allow the female to do this since she may have limited control over who fertilises her eggs and when they are fertilised.
- Deciding reproduction conditions, such as location and timing. [20] A female can only choose when she releases her eggs in external fertilisation, not when they are fertilised. In some ways, this is comparable to a mysterious female choice.
- On dry land, egg protection. Internally fertilising animals grow their eggs and progeny inside themselves, whereas oviparous species have a jelly-like ovum or a hard shell enclosing their egg. On land, this protects from predators as well as dehydration. When there is a regulated temperature and a protected space within the mother, there is a better probability of survival.
Disadvantages to Internal Fertilisation
- The mother’s health can and will be jeopardised throughout pregnancy. Extra energy demands are the source of the higher dangers associated with pregnancy.
- In most situations, internal fertilisation is followed by sexual reproduction. There are several hazards associated with sexual reproduction. The dangers of sexual reproduction are associated with intercourse, which is uncommon and only works properly when fertility is at its height. Externally fertilising animals can discharge egg and sperm into the water and reproduce without the requirement of a specific partner.
- Internal fertilisation yields fewer children when compared to external fertilisation. This is owing to the mother’s incapacity to hold and grow as many children as eggs, as well as her inability to create and gather enough resources to support a larger number of children.
Conclusion
Fertilisation, the process of combining a sperm and an egg, is the first step in sexual reproduction. This can happen both outside and inside the female body. Both systems have benefits and drawbacks. Once fertilised, the eggs might develop either inside or outside the mother. When an egg grows outside of the body, it is normally protected by a protective coating. Animal anatomy has evolved a variety of methods for fertilising, holding, and releasing the egg. The technique of fertilisation differs from animal to animal. Some species release the egg and sperm into the environment, while others keep the egg and sperm in the female body, then expel the developing embryo coated in a shell, while still others keep the developing offspring throughout the gestation period.