The different modes of reproduction in animals are classified based on how they give birth to their young, this includes viviparous, oviparous and ovoviviparous . Apart from this, animals also have different types of reproduction, be it sexual or asexual . In this article we are going to explain how animals reproduce and the different existing types. We will also include examples to give you a better understanding. Read on to learn more
Types of reproduction in animals
In the animal kingdom, animals can reproduce in two different ways:
- Asexual reproduction: In asexual reproduction, the young originate from a single parent, which can occur in different ways. Hermaphroditic species are included in this group.
- Sexual reproduction: the other form of reproduction is sexual, which occurs through the copulation of the genetic material of two individuals. In sexual reproduction, fertilization can occur externally or internally. In the first case, we have as an example fish, amphibians and many invertebrates. The second case is typical of most reptiles, birds and mammals. On the other hand, the development of the zygote can also occur inside or outside the female, although the nutrition of the embryo can be dependent or independent of the mother.
What are oviparous animals
The adjective “Ovi” means an egg , while “Parous” means birth . Therefore, an offspring that hatches from an egg is the main characteristic of oviparous animals. There are many species that are called oviparous in our animal kingdom. In general, to protect the embryo that has developed inside the egg, it has a hard shell. When the maternal gene enters the ovum or egg, it begins to form a shell around it. The process of reproduction and formation of an egg occurs after the mating of an adult male and female animal. In other words, it is sexual reproduction . As the egg develops outside the mother’s body, it is the result of external fertilization.
External fertilization is when the egg is expelled from the body by the mother and then the sperm travels to it , uniting with an egg in an open environment rather than being specialized inside. External fertilization in which sperm and eggs are ejaculated works mainly for aquatic species in the marine environment. Some mimic internal fertilization. Therefore, those who perform external fertilization lay multiple eggs, while those with internal fertilization, especially non-aquatic species, lay one egg at a time. All invertebrates are naturally oviparous . They lay eggs and allow embryonic development to occur inside the egg.
What are Viviparous Animals
Viviparous animals are those that develop their young embryos within the body . After the female mates with a male of the same species, a new being is created. During the gestation process (development of the embryo), the embryo will inherit characteristics from both parents. The vast majority of viviparous animals are quadrupeds (they have four legs) for running, walking and running. Humans are bipedal, but few other mammals are bipedal in their mode of movement.
Viviparous animals differ from egg-laying animals, such as birds and most reptiles. The latter obtain all the food as they develop from the yolk and the white or protein-rich albumin of the egg itself, not from direct contact with the mother , as is the case with viviparous young.
The offspring of viviparous and oviparous animals develop from fertilized eggs, but the eggs of viviparous animals lack a hard outer shell or shell like a chicken egg. Viviparous hatchlings grow into the adult female until they are able to survive on their own outside of her body . In many cases, the developing fetuses of viviparous animals are connected to a placenta in the mother’s body. This is a special membranous organ with an abundant blood supply that lines the uterus in pregnant mammals. Provides nutrition to the fetus through a supply line called the umbilical cord. The time between fertilization and the birth of viviparous animals is called the gestation period .
What are ovoviviparous animals
Ovoviviparous is a zoological term that refers to animals that produce eggs but retain them within the female’s body until hatching occurs, thus “live” young are born . The egg-hatching strategy of ovoviviparity occurs in a fairly wide diversity of animals, including certain insects, fish, lizards, and snakes. However, ovoviviparity is much less common than external development of fertilized eggs (i.e. oviparity).
Ovoviviparous insects do not provide oxygen or food to their developing eggs; they simply provide a safe brood chamber for development. However, ovoviviparous species of fish, lizards, and snakes appear to provide some nutrition and oxygen to their progeny.developing within the oviduct (although most of the nutrition is provided by the yolk of the eggs). Furthermore, in these species, the eggshell has a very reduced thickness and is essentially reduced to a membrane. Because some nutrition is provided to the developing egg and larva and the eggshell is essentially absent, cases of ovoviviparity in fish, lizards, and snakes are considered by some zoologists to represent true live birth or viviparity.
There are many cases of ovoviviparity, but here we will only look at a few cases of vertebrates. The guppy (Lebistes reticulatus) is a small freshwater fish that is native to the West Indies and northern South America, and is commonly kept as a pet in aquariums. This is fertilized internally and the eggs are retained in the female’s oviduct where they hatch and develop, so that live young are born.
Similarly, the grass snake (Thamnophis sirtalis) is a common and widespread species in North America. This species achieves internal fertilization by copulation, incubates the eggs within the female’s oviduct, and gives birth to live young in late summer. At birth, young snakes are encased in an amniotic sac from which they quickly escape and then scurry away to lead an independent life.
An extremely unusual case that may represent a borderline case of ovoviviparity involves a very rare (and possibly extinct) species of Australian frog. The gastric-hatching frog (Rheobatrachus silus) is believed to fertilize its eggs externally (fertilization has never been observed by scientists), but the female then swallows the eggs and retains them in her stomach. There, the eggs hatch and develop over a period of approximately 37 days, to “hatch” as small frogs through the female’s mouth, almost identical in morphology to the adult, except in size.
In this case, the fertilized eggs develop, hatch, go through their larval stage (ie, the tadpole stage) and metamorphose into a frog, which is “born” through the mouth. While incubating eggs, the female does not eat and suppresses the production of stomach acids and digestive enzymes so as not to digest her progeny. The extraordinary case of the gastric brooding frog may represent the only known case of an externally fertilized ovoviviparous species (unless the definition of ovoviviparity is restricted to cases where the eggs hatch within the female’s reproductive tract).