Oviparous vs. Viviparous Animals - What's the Difference?

The viviparous lizard (Zootoca vivipara) is unique, in the sense that, some populations of this species are viviparous in nature, while others are oviparous.

Of the five modes of reproduction in animals, which are identified on the basis of the relation between zygote and parents, the two most common are oviparity and viviparity. While oviparous animals reproduce by means of laying eggs, viviparous animals resort to live birth.

In addition to these two, there is yet another mode of reproduction which is referred to as ovoviviparity, wherein, the young one is kept in an egg within the mother's body until right before hatching. At times, ovoviviparity is considered a less-developed form of viviparity.

Oviparity is relatively more common among animals than viviparity. Most oviparous animals resort to external fertilization, wherein male and female gametes are released in the environment where they come in contact with each other and eventually lead to the formation of the zygote.

In contrast, internal fertilization is seen in all three groups. In this case, male gametes are transferred to the female's body during the process of copulation, where the fertilization takes place.

Only five extant mammals are known to be oviparous in nature, namely the platypus (Ornithorhynchus anatinus), western long-beaked echidna (Zaglossus bruijni), Sir David's long-beaked echidna (Zaglossus attenboroughi), eastern long-beaked echidna (Zaglossus bartoni), and the short-beaked echidna (Tachyglossus aculeatus). These species are clubbed together as monotremes.

» Oviparous animals lay eggs.

» When it comes to oviparity, the development of zygote―the earliest developmental stage of the embryo―takes place outside the female's body.

» In oviparity, the chances of survival are less, despite the fact that the female makes every attempt to find a safe environment to lay eggs, and the eggs are covered with a hard shell to protect the developing embryo.

» All birds, most reptiles, and even some mammals are oviparous in nature.

» Oviparity is restricted to animals.

» Viviparous animals give live birth.

» In the case of viviparity, the development of zygote takes place inside the female's body.

» In viviparity, the chances of survival are relatively better―at least until birth―as the mother's body creates a shield for the developing embryo, and protects it from both, predation and harsh environment.

» Almost all mammals―except the five egg-laying species―and some reptiles and fish are viviparous in nature.

» Viviparity is seen in both, plants and animals.

While species like the bull shark (Carcharhinus leucas), lemon shark (Negaprion brevirostris), mako shark (Isurus oxyrinchus), etc., are oviparous in nature, species like oceanic whitetip shark (Carcharhinus longimanus), zebra shark (Stegostoma fasciatum), and swellshark (Cephaloscyllium ventriosum) are viviparous.

Oviparous sharks deposit their eggs in the ocean. These eggs eventually hatch to produce young ones―that's if they survive predators. Viviparous sharks, on the other hand, give birth to live young.

Like mentioned earlier, viviparity is seen in animals as well as plants. In viviparous plants, the germination of seeds occurs inside the tree. These seeds eventually detach from the mother plant and fall to the ground, where they go on to develop into adult trees.