Viviparous and Oviparous Examples - Introduction to Animal Reproductive Strategies
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 Viviparous, Oviparous and Ovoviviparous Animals: A Comprehensive Guide
1. What are viviparous and oviparous animals?
Viviparous animals give birth to live young, with internal fertilisation and foetal development within the mother’s body. Oviparous animals lay eggs, where embryo development mainly occurs outside the mother’s body.
2. Why do amphibians often lay eggs in water?
Amphibians, which are typically oviparous, lay their eggs in water to keep them hydrated. Their eggs lack a hard shell and need moisture to prevent desiccation and facilitate development.
3. Do all reptiles lay eggs?
Most reptiles are oviparous, but certain reptiles (e.g., some snakes) are ovoviviparous, and they retain eggs internally. While very rare, there are also viviparous lizards.
4. Is there a mammal that lays eggs?
Yes, the platypus and the echidna are egg-laying mammals (monotremes). They are classified as oviparous animals despite being mammals.
5. How can you tell if an animal is ovoviviparous?
If the eggs hatch within the female’s body, and there is no placental connection—meaning no direct maternal nourishment beyond the egg’s yolk—then the animal is ovoviviparous. The offspring are born alive, but the mother does not provide nutrients directly as viviparous animals do.
6. Are humans strictly viviparous, or can there be exceptions?
Humans are strictly viviparous, as fertilisation and full foetal development occur inside the mother’s uterus, and the mother directly nourishes the embryo through the placenta.
