Ovoviviparity

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Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in which there is internal fertilization and the young are born live, but differ in that there is no placental connection and the unborn young are nourished by egg yolk; the mother's body does provide gas exchange (sharks and rays). The terms "ovoviviparity" or "aplacental viviparity" have been deprecated because they encompass several unrelated modes of reproduction. In some species, the internally developing embryos rely solely on yolk. This is known as "yolk-sac viviparity" and is regarded as a type of lecithotrophy (no maternal provisioning).

Other species exhibit matrotrophy, in which the embryo exhausts its yolk supply early in gestation and mother provides additional nutrition. This additional provisioning may be in the form of unfertilized eggs (intrauterine oophagy), uterine secretions (histotrophy), or it may be delivered through a placenta. The first two of these modes were categorized under aplacental viviparity.[1]

Amphibians[edit]

The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother. Five modes of reproduction can be differentiated [2] based on relations between zygote and parents:

  • Ovuliparity: fecundation (fertilisation) is external (in arthropods and bony fishes, most 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 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.[3]
  • Histotrophic viviparity: the zygotes develop in the female's oviducts, but find their nutriments by oophagy or adelphophagy (intrauterine cannibalism in some sharks or in the black salamander Salamandra atra).
  • Hemotrophic viviparity: nutriments are provided by the female, often through a placenta. In the frog Gastrotheca ovifera, embryos are fed by the mother through specialized gills. The lizard Pseudomoia pagenstecheri and most mammals exhibit a hemotrophic viviparity.

Ovolarviparity[edit]

Some insects, notably tachinid flies are ovolarviparous, which means the embryos develop into the first larval stage (instar) within eggs while still in the female's oviduct. As a result, larvae hatch more rapidly, sometimes immediately after egg deposition, and can begin feeding right away. A similar phenomenon is larviparity, in which larvae hatch before the female delivers them, although this may be mistakenly identified in species with very thin and transparent egg membranes.[4][5]

References[edit]

  1. ^ Carrier, J.C.; Musick, J.A.; Heithaus, M.R., ed. (2012). Biology of Sharks and Their Relatives. CRC Press. pp. 296–301. ISBN 1439839247. 
  2. ^ Thierry Lodé 2001. Les stratégies de reproduction des animaux (reproduction strategies in animal kingdom). Eds Dunod Sciences, Paris
  3. ^ Tyler, M. J. (1994). Australian Frogs: A Natural History. Chapter 12, Gastric Brooding Frogs pp;135–140 Reed Books
  4. ^ Capinera, John L. (2008). "Tachinid Flies (Diptera: Tachinidae)". Encyclopedia of entomology (2nd ed.). Dordrecht: Springer. pp. 3678–3679. ISBN 9781402062421. 
  5. ^ Wiman, Nik G.; Jones, Vincent P. (2012). "Influence of oviposition strategy of Nemorilla pyste and Nilea erecta (Diptera: Tachinidae) on parasitoid fertility and host mortality". Biological Control 64 (3): 195–202. doi:10.1016/j.biocontrol.2012.12.008.