- What are viviparous animals?
- Examples of viviparous animals
- How is the viviparous gestation?
- How do they reproduce?
- Oviparous animals
- Ovoviviparous animals
We explain what viviparous animals are, how is their reproduction and gestation. Also, differences with oviparous and ovoviviparous animals.
What are viviparous animals?
Viviparous animals are those that reproduce through internal fertilization and their embryos develop in specialized organs within the mother's womb. The embryos leave the maternal body at the end of the gestation, through a birth canal. In this they differ from oviparous and ovoviviparous animals.
The embryos of viviparous animals are connected to the mother's body from which they receive nutrition and defense. Birth occurs when the embryos have already matured and the beginning of their individual existence corresponds.
That they can have an existence outside the maternal body means that they are able to subsist as an independent organism, which can feed, extract, breathe, etc. However, in much of the species they continue to require care. In the case of mammals they even require breastfeeding until later.
It is assumed that the emergence of viviparity in animals occurred with the appearance of the first mammals, since the reptiles They are oviparous. There are several hypothesis to explain saying evolutionary change, but they agree on the advantages over factors of risk as the predation, the cold climate or the physical risk involved in keeping the embryo inside the warm maternal body.
It is estimated that it was also the evolutionary step that would allow reptiles to adapt to climates cold in which the laying of eggs was too thermally risky.
Examples of viviparous animals
All mammals are perfect examples of viviparous animals, regardless of their gestation period. From cats, dogs, rats, pigs and rabbits, to lions, giraffes, elephants, apes and even the human being.
Marine mammals are not exempt: killer whales, dolphins, whales, seals, narwhals or sperm whales, as well as some specific types of amphibians like salamanders and newts.
How is the viviparous gestation?
Gestation is the time that the fertilized embryo lasts inside the mother's womb, until its maturation and expulsion through the birth canal. During this period, the maternal body nourishes the embryo through an umbilical cord or equivalent, sharing blood, fluids and nutrients, which implies important changes in the metabolism and the conduct of the mother.
The length of this gestation period can vary according to the species, but usually ends when the embryo is sufficiently developed to be born. In the case of humans, this gestation is around 9 months, while in lions it does not exceed 110 days, and in the case of mice, only about 20.
How do they reproduce?
The reproduction of viviparous animals is generally and mostly sexual, that is, through intercourse between males and females, during which internal fertilization of the female occurs. For this, the male penetrates it with his penis and deposits his seminal fluid inside, in which the sperm go.
When the sperm enter the egg, that is, they fertilize it, the embryo is produced. The latter grows inside the mother's womb, wrapped in a placenta, for a certain period of time and is finally expelled through the birth canal, to begin its existence as an independent organism.
Oviparous animals
Oviparous animals, unlike viviparous ones, are those that lay eggs, as do lizards, birds or fish, among many others. This form of reproduction it is much older than viviparism.
In some cases, fertilization is internal, that is, the already fertilized eggs are deposited by the female and hatch on their own later, when the embryos are mature. In other cases, fertilization is external: the female lays her unfertilized eggs and then the male sprays them with his sexual fluids, fertilizing them outside the maternal body.
In both cases, the fertilized eggs allow the embryo to grow in a protected environment isolated from the outside by means of an impermeable shell, inside which are all the materials necessary for its development.
The relationship between parents and their fertilized eggs can be very diverse. Some species jealously guard them or even transport them from one place to another. The mother can watch over her eggs, hatch them (warm them with her body, like birds) or bury them in a safe place, waiting for the eggs to hatch.
In other species the female leaves them to their own devices, depositing large amounts to ensure that at least some percentage of them survive.
Ovoviviparous animals
Ovoviviparous animals are a kind of intermediate category between oviparous and viviparous. In their case, the eggs are produced within the mother through internal fertilization through intercourse, but these remain within the mother's body until the embryos are sufficiently developed.
Laying is carried out when the eggs are close to hatching, or directly at hatching, giving the wrong impression that the young have been calved.
Unlike viviparous animals, these animals are not connected with their young through the placenta, so the development of embryos does not depend on the food resources of their body, but on the content of each egg. At most the maternal body allows the exchange of gases, as in the case of sharks and stripes.
This is a common breeding method for many species of fish, sharks, rays, some reptiles (such as chameleons), and certain Invertebrate animals.