Oviparity


Oviparity

Oviparous animals are animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, reptiles, all birds, the monotremes, and most insects, some molluscs and arachnids.

With more scientific rigor, five modes of reproduction can be differentiated [1] based on relations between zygote and parents:

  • Ovuliparity : fecundation is external (in arthropods and fishes, most of frogs)
  • Oviparity : fecundation is internal, the female lays zygotes as eggs with important vitellus (typically birds)
  • Ovo-viviparity : or oviparity with retention of zygotes in the female’s body or in the male’s body, but there are no trophic interactions between zygote and parents. (Anguis fragilis is an example of ovo-viviparity.) In the sea horse, zygotes are retained in the male’s ventral "marsupium". In the frog Rhinoderma darwinii, the zygotes developed in the vocal sac. In the frog Rheobatrachus, zygotes developed in the stomach.
  • Histotrophic viviparity : the zygotes developed in the female’s oviducts, but find their nutriments by oophagy or adelphophagy (intra-uterine cannibalism in some sharks or in the black salamander Salamandra atra).
  • Hemotrophic viviparity : nutriments are provided by the female, often through placenta. In the frog Gastrotheca ovifera, embryos are fed by the mother through specialized gills. The lizard Pseudomoia pagenstecheri and most of mammals exhibit a hemotrophic viviparity.

Land-dwelling animals that lay eggs, often protected by a shell, such as reptiles and insects, do so after having completed the process of internal fertilization. Water-dwelling animals, such as fish and amphibians, lay their eggs before fertilization, and the male lays its sperm on top of the newly laid eggs in a process called external fertilization.

Almost all non-oviparous fish, amphibians and reptiles are ovoviviparous, i.e. the eggs are hatched inside the mother's body (or, in case of the sea horse inside the father's). The true opposite of oviparity is placental viviparity, employed by almost all mammals (the exceptions being marsupials and monotremes).

There are only five known species of oviparous mammals: four species of Echidna and the Platypus.

See also

References

  1. ^ Thierry Lodé 2001. Les stratégies de reproduction des animaux (reproduction strategies in animal kingdom). Eds Dunod Sciences, Paris

External links



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Look at other dictionaries:

  • Oviparity — O vi*par i*ty, n. [See {Oviparous}.] (Biol.) Generation by means of ova. See {Generation}. [1913 Webster] …   The Collaborative International Dictionary of English

  • oviparity — production of eggs that hatch and develop outside the body …   Dictionary of ichthyology

  • oviparity — See oviparous. * * * ▪ biology       expulsion of undeveloped eggs rather than live young. The eggs may have been fertilized before release, as in birds and some reptiles, or are to be fertilized externally, as in amphibians and many lower forms …   Universalium

  • oviparity — noun The condition of being oviparous …   Wiktionary

  • oviparity — The quality of being oviparous. [ovi + L. pario, to bear] * * * ovi·par·i·ty .ō və par ət ē n, pl ties the quality or state of being oviparous * * * ovi·par·i·ty (o″vĭ parґĭ te) the quality of being oviparous …   Medical dictionary

  • oviparity — əʊvɪ pærÉ™tɪ n. laying of eggs …   English contemporary dictionary

  • oviparity — ovi·par·i·ty …   English syllables

  • oviparity — ˌōvəˈparəd.ē noun ( es) Etymology: probably from (assumed) New Latin oviparitat , oviparitas, from Latin oviparus oviparous + itat , itas ity : the quality or state of being oviparous …   Useful english dictionary

  • multiple oviparity — a system in sharks where females retain several pairs of egg cases in the oviducts, the embryo growing to an advanced stage. The eggs may hatch within a month of laying, e.g. in the scyliorhinid Halaelurus in aquaria, although not known in the… …   Dictionary of ichthyology

  • oviparous — oviparity /oh veuh par i tee/, oviparousness, n. oviparously, adv. /oh vip euhr euhs/, adj. Zool. producing eggs that mature and hatch after being expelled from the body, as birds, most reptiles and fishes, and the monotremes. [1640 50; < L… …   Universalium


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