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Oviparous Definition
Oviparous term is used to describe egg-laying animals, where the young hatch from the eggs that have been expelled from the body. Fertilization in oviparous animals can be external or internal, but the young hatch outside of their body.
Oviparous animals include birds, amphibians, reptiles, and fish. While in animals like snakes and sharks, ovoviviparity is seen where the young hatch from eggs inside the female body itself.
What is Oviparous?
Oviparous comprises an evolutionary strategy where eggs are produced by females. Eggs are the gamete contributed by the females. The males supply their genetic material in form of sperm that must find and fertilize the egg. The egg on fertilization after many cleavages and divisions form an embryo.
Most of the oviparous organisms produce many fragile small eggs, while others will produce few large hard eggs. Both of these strategies are advantageous to organisms. If a large number of eggs are produced, then a large number of offspring can overcome predators.
Whereas, larger eggs that are strong, help in their survival and development till birth, then after hatching is able to escape from predators. But there are disadvantages of this reproductive strategy.
Oviparous animals must protect the eggs by hiding them well before they hatch as they do not carry their developing embryos like ovoviviparous and viviparous animals.
They also must warm the eggs by sitting on them, till they hatch, for instance, penguins often sit on their eggs constantly to warm them. The eggs are vulnerable to predator attacks.
Oviparous Examples
Oviparous Birds: Chickens are an example of oviparous birds that releases an egg from one of the ovaries that will be laid irrespective of whether it is fertilized or unfertilized. If it is fertilized then the embryo develops by feeding on the nutrition-rich yolk present in the egg. Once the young are developed it hatches and is now capable of feeding and walking. Generally, all birds are considered oviparous and lay internally fertilized eggs that have a hard shell. The young produced are precocial and can walk and feed on hatching
Oviparous Reptiles: Reptiles are also oviparous and their reproductive strategy is similar to birds, the difference occurs in the shells of their eggs. Reptiles lay eggs that have a softer shell as opposed to birds. These eggs have a leathery texture and are incubated in mounded nests or burrows for warmth and to provide a stable temperature. This mechanism is known as temperature-dependent sex determination.
Oviparous Fish: Fishes also exhibit oviparity as they lay their eggs in a nest where they are fertilized by the sperms that are released in the water by males. The fertilization process is thus external. The sperm swims towards the eggs by chemotaxis. Other various mechanisms may be species-specific that ensures mating in these organisms. Some fishes employ mating dance or moves to release their gametes simultaneously to increase the probability of fertilization.
Oviparous Amphibians: Amphibians also lay their eggs in standing water and are thus oviparous. They also exhibit external fertilization but the eggs hatch at larval stages. The larval stages are equipped with appendages like tail and gills, that facilitate the rest of the development in water. These larvae will develop into an adult by metamorphosis.
Oviparous Citations
Lipids of the eggs and neonates of oviparous and viviparous lizards. Comp Biochem Physiol A Mol Integr Physiol . 2000 Dec;127(4):453-67.
The restricted ovulator chicken strain: an oviparous vertebrate model of reproductive dysfunction caused by a gene defect affecting an oocyte-specific receptor. Anim Reprod Sci . 2012 Dec;136(1-2):1-13.
Incubation temperature induced phenotypic plasticity in oviparous reptiles: Where to next? J Exp Zool A Ecol Integr Physiol . 2018 Jul;329(6-7):343-350.
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