Reproductive Patterns
Reproductive
Patterns
The great majority of invertebrates, as well as many vertebrates, lay their eggs in the environment for development; these animals are called oviparous (“egg-birth”). Fertilization may be either internal (eggs are fertilized inside the body of a female before she lays them) or external (eggs are fertilized by a male after a female lays them). While many oviparous animals simply abandon their eggs rather indiscriminately, others display extreme care in finding places that will provide immediate and suitable sources of food for the young when they hatch.
Some animals retain eggs in their body (usually the oviduct) while they develop, with embryos deriving all their nourishment from yolk stored within the egg. These animals are called ovoviviparous (“egg-livebirth”). Ovoviviparity occurs in several invertebrate groups (for example, various annelids, brachiopods, insects, and gastropod molluscs) and is common among certain fishes and reptiles.
In the third pattern, viviparous (“live-birth”), eggs develop in the oviduct or uterus with embryos deriving their nourishment directly from the mother. Usually some kind of intimate anatomical relationship is established between developing embryos and their mother. In both ovoviviparity and viviparity, fertilization must be internal (within the body of the female) and the mother gives birth to young in an advanced stage of development. Viviparity is confined mostly to mammals and elasmobranch fishes, although viviparous invertebrates (some scorpions, for example), amphibians, and reptiles are known. Development of embryos within the mother’s body, whether ovoviviparous or viviparous, obviously affords more protection to the offspring than egg-laying.
The great majority of invertebrates, as well as many vertebrates, lay their eggs in the environment for development; these animals are called oviparous (“egg-birth”). Fertilization may be either internal (eggs are fertilized inside the body of a female before she lays them) or external (eggs are fertilized by a male after a female lays them). While many oviparous animals simply abandon their eggs rather indiscriminately, others display extreme care in finding places that will provide immediate and suitable sources of food for the young when they hatch.
Some animals retain eggs in their body (usually the oviduct) while they develop, with embryos deriving all their nourishment from yolk stored within the egg. These animals are called ovoviviparous (“egg-livebirth”). Ovoviviparity occurs in several invertebrate groups (for example, various annelids, brachiopods, insects, and gastropod molluscs) and is common among certain fishes and reptiles.
In the third pattern, viviparous (“live-birth”), eggs develop in the oviduct or uterus with embryos deriving their nourishment directly from the mother. Usually some kind of intimate anatomical relationship is established between developing embryos and their mother. In both ovoviviparity and viviparity, fertilization must be internal (within the body of the female) and the mother gives birth to young in an advanced stage of development. Viviparity is confined mostly to mammals and elasmobranch fishes, although viviparous invertebrates (some scorpions, for example), amphibians, and reptiles are known. Development of embryos within the mother’s body, whether ovoviviparous or viviparous, obviously affords more protection to the offspring than egg-laying.
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