What Are Oviparous and Viviparous Animals? Definitions and Comparison
Animals display a range of reproductive strategies. Understanding viviparous and oviparous modes, as well as the ovoviviparous mode, not only enriches our appreciation for biodiversity but also clarifies essential biological concepts such as fertilisation and embryo development. In this article, we’ll understand viviparous and oviparous animals, explore the key differences between them, understand ovoviviparity, and discover unique facts along the way.
Introduction to Animal Reproductive Strategies
Reproduction ensures the survival of every species on Earth. Animals have evolved distinct methods to create and nurture offspring, primarily through:
External fertilisation, where sperm and egg fuse outside the female’s body.
Internal fertilisation, where fertilisation occurs inside the female’s body.
Depending on where and how the embryo develops, these methods branch out into different reproductive strategies, such as viviparous and oviparous modes, as well as the less common ovoviviparous mode.
If you’d like to explore more about fertilisation within organisms, refer to our article on Internal Fertilisation.
What are Viviparous Animals?
Viviparous animals are those whose offspring develop inside the mother’s body. Both fertilisation and embryo development take place internally. These animals typically possess a well-developed reproductive system, and the mother directly provides nutrients to the growing embryo through specialised structures or organs.
The process in viviparous animals involves:
Internal fertilisation: Male and female gametes fuse inside the female body.
Embryo development: The fertilised egg (zygote) develops into an embryo within the mother’s reproductive tract.
Birth: Once the embryo matures into a fully formed foetus, the mother gives birth to a live young one.
Key Features
The embryo’s nourishment largely comes from the mother (matrotrophy), not just from egg yolk.
Typically, viviparity is seen in most mammals, including humans, dogs, cats, elephants, and so on.
Advantages of Viviparity
The higher survival rate of offspring is due to constant nourishment and protection inside the mother’s body.
Embryos develop in a temperature-controlled environment.
Lower vulnerability to predators or external environmental threats.
Viviparous and Oviparous Animals: Where Do They Differ?
Before we dive deeper into oviparity, let’s clarify the viviparous and oviparous differences. This distinction revolves around whether animals give birth to live offspring or lay eggs.
Viviparous animals: No egg-laying; offspring are born alive.
Oviparous animals: Fertilised eggs are laid; the embryo develops externally.
By understanding this viviparous and oviparous difference, we can better appreciate the diversity of reproductive strategies across the animal kingdom.
What are Oviparous Animals?
Oviparous animals reproduce by laying eggs that complete embryonic development outside the mother’s body. Internal fertilisation generally happens inside the mother, but the embryo’s major development and hatching occur externally. Birds, amphibians like frogs, and many reptiles exhibit oviparity. However, there are variations, as some fish and certain invertebrates also lay eggs that develop outside.
Key Features
Hard or protective egg shells in many species (e.g., calcium-rich shells in birds).
Embryo relies on the yolk within the egg for nourishment until hatching.
Eggs are often laid in safer, concealed, or temperature-suitable places to protect from predators and environmental hazards.
Examples of Oviparous Animals
Birds like hens, ducks, and eagles lay hard-shelled eggs.
Frogs (amphibians) lay soft, gelatinous eggs, usually in water bodies, requiring consistent hydration.
Reptiles like turtles, crocodiles, and most snakes lay eggs, although some snakes show other modes (discussed later).
The mammal's echidna and platypus are exceptions among mammals as they lay eggs instead of bearing live young.
Viviparous and Oviparous Examples
To summarise, let’s list some viviparous and oviparous examples:
Viviparous Animals: Humans, cows, dogs, cats, elephants, tigers, and most other mammals.
Oviparous Animals: Birds (e.g., hens, parrots), most fish (e.g., salmon), amphibians (e.g., frogs), reptiles (e.g., turtles), and egg-laying mammals (e.g., platypus).
For more insights on how eggs develop outside the mother, refer to our detailed breakdown in Embryo Development.
Metamorphosis in Oviparous Animals
A unique phenomenon often observed in oviparous animals (especially amphibians and many insects) is metamorphosis—a dramatic change in form from larva to adult.
Examples:
Frogs: Egg → Tadpole (aquatic larva) → Adult Frog.
Butterflies: Egg → Larva (caterpillar) → Pupa (chrysalis) → Adult Butterfly.
Since viviparous animals usually give birth to a form that closely resembles the adult, the term metamorphosis is rarely applied to them. If you wish to explore this subject further, check out our article on Metamorphosis.
Ovoviviparity: A Blend of Both Worlds
Beyond viviparous and oviparous animals, there is a third category known as ovoviviparous animals, which combine features of both:
Eggs are formed and fertilised internally (internal fertilisation).
Eggs hatch inside the mother’s body.
Embryos derive nourishment from the yolk rather than directly from the mother (no placenta).
The offspring are eventually born as live young, much like viviparous birth.
Notable Ovoviviparous Examples
Many species of snakes (e.g., rattlesnakes), certain sharks (e.g., great white sharks), rays, and some insects exhibit ovoviviparity. These animals develop eggs internally, but the key difference from viviparous animals is the lack of a direct placental connection with the mother.
Comparing oviparous, viviparous ovoviviparous examples:
Oviparous: Chickens laying eggs.
Viviparous: Humans give birth to live babies.
Ovoviviparous: Rattlesnakes, where eggs hatch inside the mother, and fully formed baby snakes are born.
Embryo Development: Inside vs Outside
No matter the mode of reproduction—be it viviparous and oviparous or even ovoviviparous—embryo development follows a basic blueprint:
Fertilisation: Fusion of sperm and egg to form a single-celled zygote. (To learn more, read our article on Internal Fertilisation.)
Cell Division and Growth: The zygote rapidly divides and differentiates into an embryo.
Embryonic Nutrition:
In viviparous animals, the embryo obtains nourishment directly from the mother (placental mammals) or via other maternal structures.
In oviparous animals, the embryo depends on the egg yolk and the external environment.
In ovoviviparous animals, embryos also depend mostly on the yolk; however, they remain in the mother’s body until they hatch.
Birth or Hatching:
Viviparous animals give birth to live young.
Oviparous animals lay eggs that hatch externally.
Ovoviviparous animals hatch eggs internally and then deliver live young.
Detailed Comparison: Viviparous and Oviparous Difference
Here’s a quick reference table summarising the essential distinctions among the three major categories:
Quick Quiz
Put your knowledge to the test with this short quiz:
Which among the following is not an oviparous animal?
A. Crow
B. Duck-billed Platypus
C. Whale
D. Tortoise
Metamorphosis is commonly associated with which category of animals?
A. Viviparous
B. Oviparous
C. Ovoviviparous
D. None of the above
Which best defines an ovoviviparous organism?
A. Lays eggs externally with no internal fertilisation.
B. Retains eggs internally but nourishes the embryo via the placenta.
C. Retains eggs internally; offspring receive nourishment from the yolk.
D. No egg formation at all.
Quick Quiz: Answers
C. Whale – Whales are viviparous (live birth).
B. Oviparous – Metamorphosis is often seen in oviparous animals like frogs and insects.
C. Retains eggs internally; offspring receive nourishment from the yolk – This is the definition of an ovoviviparous organism.
Additional Interesting Facts
Some sharks (like the sand tiger shark) may practise intrauterine cannibalism, where a stronger embryo consumes weaker siblings for survival before birth (a form of ovoviviparity).
Certain lizards can switch from being oviparous to viviparous in response to environmental stresses such as cooler climates.
Marsupials (e.g., kangaroos) are viviparous, but their young complete development in a pouch after a brief internal gestation.
FAQs on Oviparous and Viviparous Animals Explained: Key Differences, Traits & Examples
1. What is the main difference between oviparous and viviparous animals?
The primary difference lies in how their young develop. Oviparous animals, like birds and fish, lay eggs, and the embryo develops outside the mother’s body, nourished by the yolk. Viviparous animals, like humans and dogs, give birth to live young that develop inside the mother’s body and receive nourishment directly from her through a placenta.
2. Can you give some common examples of oviparous, viviparous, and ovoviviparous animals?
Certainly! Here are some common examples for each type:
- Oviparous (Egg-laying): Most insects, fish, amphibians, reptiles, and all birds (e.g., chickens, frogs, snakes, eagles).
- Viviparous (Live-bearing): Most mammals, including humans, elephants, cats, and whales.
- Ovoviviparous (Eggs hatch inside the mother): Some species of sharks (like the great white), rays, vipers, and guppies.
3. What exactly are ovoviviparous animals, and how are they different from the other two types?
Ovoviviparous animals are a unique middle ground. Like oviparous animals, the embryo develops inside an egg and is nourished by its yolk. However, like viviparous animals, the egg is not laid. Instead, it is retained and hatches inside the mother's body. The key difference is that there is no placental connection for nourishment from the mother; the young are simply born live after the egg hatches internally.
4. Why do animals like frogs lay eggs in water, while birds lay them on land?
This is due to the structure of their eggs. Frog eggs are soft and lack a protective outer shell, so they would dry out and die on land. They need a moist environment like water to survive. In contrast, bird eggs have a hard, protective shell that prevents water loss, allowing the embryo to develop safely in a terrestrial environment.
5. Is it true that some mammals lay eggs?
Yes, it is true! A small and ancient group of mammals called monotremes are oviparous, meaning they lay eggs. The most famous examples are the platypus and the echidna, found in Australia.
6. What are the main survival advantages of being viviparous?
The primary advantage of viviparity is the increased chance of offspring survival. The developing embryo is well-protected from predators and environmental changes by being inside the mother's body. It also receives a constant supply of nutrients and oxygen, ensuring stable and complete development before birth.
7. Is a chicken considered oviparous, viviparous, or ovoviviparous?
A chicken is a classic example of an oviparous animal. It lays a hard-shelled egg, and the chick develops entirely outside the mother's body, getting all its nutrition from the yolk until it is ready to hatch.
8. How do the young of ovoviviparous animals get food if they develop inside the mother?
Even though they develop inside the mother, the young of ovoviviparous animals do not get food from her directly. All their nutrition comes from the yolk of the egg, just like in oviparous animals. The mother’s body primarily offers a safe, protected place for the egg to develop and hatch.
