Oviparity

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

In traditional usage, most insects, molluscs, and arachnids are also described as oviparous.

Adolphe Millot oeufs-fixed
Eggs of various animals (mainly birds)

Modes of reproduction

The traditional modes of reproduction include oviparity, taken to be the ancestral condition, traditionally where either unfertilised oocytes or fertilised eggs are spawned, and viviparity traditionally including any mechanism where young are born live, or where the development of the young is supported by either parent in or on any part of their body.[1]

However, the biologist Thierry Lodé recently divided the traditional category of oviparous reproduction into two modes that he named ovuliparity and (true) oviparity respectively. He distinguished the two on the basis of the relationship between the zygote (fertilised egg) and the parents :[1][2]

  • Ovuliparity, in which fertilisation is external, is taken to be the ancestral condition as a rule; the eggs that the female releases into the environment contain unfertilised oocytes, and the male fertilises them outside her body. In whichever form they are laid, the eggs of most ovuliparous species contain a substantial quantity of yolk to support the growth and activity of the embryo after fertilisation, and sometimes for some time after hatching as well.[1] Among the Vertebrata ovuliparity is common among fishes and most Amphibia. It occurs among Cnidaria, Ctenophora, Echinodermata, Mollusca, and several other phyla as well.[1]
  • (True) oviparity, in which fertilisation is internal. This is taken to be the derived condition, whether the male inserts the sperm into the female intromittently or whether she actively or passively picks it up—the female lays eggs containing zygotes with a substantial quantity of yolk to feed the embryo while it remains in the egg, and in many species to feed it for some time afterwards. The egg is not retained in the body for most of the period of development of the embryo within the egg, which is the main distinction between oviparity and ovoviviparity.[1] Oviparity occurs in all birds, most reptiles, some fishes, and most Arthropoda. Among mammals, the monotremes (four species of echidna, and the platypus) are oviparous.

In all but special cases of both ovuliparity and oviparity the overwhelming source of nourishment for the embryo is the yolk material deposited in the egg by the reproductive system of the mother (the vitellogenesis); offspring that depend on yolk in this manner are said to be lecithotrophic (opposed to matrotrophic), which literally means "feeding on yolk".

Distinguishing between the definitions of oviparity and ovuliparity necessarily reduces the number of species whose modes of reproduction are classified as oviparous, as they no longer include the ovuliparous species such as most fish, most frogs and many invertebrates. Such classifications are largely for convenience and as such can be important in practice, but speaking loosely in contexts in which the distinction is not relevant, it is common to lump both categories together as "oviparous".

References

  1. ^ a b c d e Lode, Thierry (2012). "Oviparity or viviparity? That is the question ...". Reproductive Biology. 12: 259–264. doi:10.1016/j.repbio.2012.09.001.
  2. ^ Thierry Lodé (2001). Les stratégies de reproduction des animaux (Reproduction Strategies in Animal Kingdom). Eds. Dunod Sciences. Paris.

External links

Anomochilus

Common names: dwarf pipe snakes.The Anomochilidae, or anomochilids, are a monotypic family of snakes, created for the genus Anomochilus, which currently contains three species.

Blackbelly rosefish

The blackbelly rosefish, Helicolenus dactylopterus, is a marine bony fish from the family Sebastidae, also known as bluemouth rockfish, and bluemouth seaperch. This Atlantic species is a typical sit-and-wait predator with a highly cryptic coloration.

Bothrocophias

Bothrocophias is a genus of venomous snakes in the subfamily Crotalinae of the family Viperidae. The genus is endemic to northern South America.

Causus

Causus is a genus of venomous vipers found only in sub-Saharan Africa. It is a group considered to be among the most primitive members of the family Viperidae based on head scalation, oviparity, venom apparatus, and because they have round pupils. However, this is contradicted by recent molecular studies. Seven species are currently recognized. They are commonly known as night adders.

Egg

The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own; at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates (excluding mammals), and mollusks lay eggs, although some, such as scorpions do not.

Reptile eggs, bird eggs, and monotreme eggs are laid out of water, and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e. breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering.

The largest recorded egg is from a whale shark, and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size. Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects and other invertebrates can be even smaller.

Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells".

Egg case (Chondrichthyes)

An egg case or egg capsule is the casing that surrounds the eggs of oviparous sharks, skates, and chimaeras. Egg cases typically contain one embryo, except for big skate and mottled skate egg cases, which contain up to 7 embryos. Oviparity is completely absent in the superorder Squalomorphii.

Euselachii

Euselachii are an infraclass of a class of cartilaginous fish. This group includes sharks and rays.

Fish reproduction

Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused. There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.

Galeus

Galeus is a genus of catshark, belonging to the family Scyliorhinidae, commonly known as sawtail catsharks in reference to a distinctive saw-toothed crest of enlarged dermal denticles, found along the upper edges of their caudal fins. They are found in the Atlantic, the western and central Pacific, and the Gulf of California, inhabiting deep waters at or close to the sea floor. Members of this genus are rather small, slim sharks with firm bodies and thick, rough skin. Their heads are usually fairly long and pointed, and have large mouths with well-developed furrows at the corners. They have large pectoral and anal fins, and two similar dorsal fins placed well back. Many species are ornately patterned with dark saddles and/or blotches. Sawtail catsharks feed on various invertebrates and fishes, and may be either egg-laying or live-bearing. These harmless sharks are sometimes caught as bycatch but are of minimal commercial value.

Gestation

Gestation is the period of development during the carrying of an embryo or fetus inside viviparous animals. It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time for example in a multiple birth.

The time interval of a gestation is called the gestation period. In human obstetrics, gestational age refers to the embryonic or fetal age plus two weeks. This is approximately the duration since the woman's last menstrual period (LMP) began.

List of MeSH codes (G08)

The following is a list of the "G" codes for MeSH. It is a product of the United States National Library of Medicine.

Source for content is here. (File "2006 MeSH Trees".)

Matrotrophy

Matrotrophy is a form of maternal care during embryo development.

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.

Ovoviviparity

Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a mode of reproduction in animals in which embryos that develop inside eggs remain in the mother's body until they are ready to hatch. This method of reproduction is similar to viviparity, but the embryos have no placental connection with the mother and receive their nourishment from a yolk sac. In some species, this is supplemented by uterine secretions or other maternal provisioning.

The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother, and in some insect species, such as the tachinid flies, the embryos develop to the first larval instar stage before they are laid and the eggs hatch almost immediately.

Platypux

Platypux is a French Linux distribution of the Slackware family, developed by Pierre-Aimé and Jacques-Olivier.

Saiphos equalis

Saiphos equalis, commonly known as the yellow-bellied three-toed skink or simply three-toed skink, is a species of burrowing skink found in eastern Australia. It is the only species classified under the genus Saiphos.

The lizard has attracted scientific attention due to its dual reproduction habits of producing young via eggs in coastal populations, or via live young in colder mountain regions.

Shark

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans.

Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.Well-known species such as the great white shark, tiger shark, blue shark, mako shark, thresher shark, and hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities.

Suter's skink

Suter's skink or the black shore skink (Oligosoma suteri) is a species of lizard in the family Scincidae. The species is endemic to New Zealand.

Viviparity

Among animals, viviparity is development of the embryo inside the body of the parent, eventually leading to live birth, as opposed to reproduction by laying eggs that complete their incubation outside the parental body.

Viviparity and the adjective viviparous derive from Latin vivus ("living") and parire ("to bear young").

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