Modes of reproduction

Animals make use of a variety of modes of reproduction to produce their young. Traditionally this variety was classified into three modes, oviparity (embryos in eggs), viviparity (young born live), and ovoviviparity (intermediate between the first two).

However, each of those so-called traditional modes covered a wide range of diverse reproductive strategies. The biologist Thierry Lodé has accordingly proposed five modes of reproduction based on the relationship between the zygote (the fertilised egg) and the parents. His revised modes are ovuliparity, with external fertilisation; oviparity, with internal fertilisation of large eggs containing a substantial nutritive yolk; ovo-viviparity, that is oviparity where the zygotes are retained for a time in a parent's body, but without any sort of feeding by the parent; histotrophic viviparity, where the zygotes develop in the female's oviducts, but are fed on other tissues; and hemotrophic viviparity, where the developing embryos are fed by the mother, often through a placenta.

The three traditional modes of reproduction are:

It can be seen that so defined, these traditional modes each covered a range of reproductive strategies.

The biologist Thierry Lodé proposed (2001, 2012) five modes of reproduction based on the relationship between the zygote (fertilised egg) and the parents:

Thus the definition of oviparity is narrower in the revised scheme, as it does not include the "ovuliparity" found in most fish, most frogs and many invertebrates.

Ovuliparity: frog development inside soft egg (frogspawn) in pond water, fertilised outside body

Oviparity: bird development inside shelled egg, with large food supply in yolk, after internal fertilisation

Ovoviviparity: slow worm gives birth to live young, after retaining the eggs inside her body

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