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Ovoviviparity

Ovoviviparity

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Encyclopedia
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s in which embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

s develop inside egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

s that are retained within the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in that there is internal fertilization
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

 and the young are born live, but differ in that there is no placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

l connection and the unborn young are nourished by egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

; the mother's body does provide gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...

 (respiration), but that is largely necessary for oviparous animals as well.

Ovoviviparity is employed by many aquatic life forms such as some fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s, and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s. The young of ovoviviparous amphibians are sometimes born as larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e, and undergo metamorphosis outside the body of the mother.
With more scientific rigor, five modes of reproduction can be differentiated based on relations between zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...

 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 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 oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...

s, but find their nutriments by oophagy
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....

 or adelphophagy (intrauterine cannibalism
Intrauterine Cannibalism
Intrauterine Cannibalism is the first studio album by American brutal death metal band Malignancy.-Track listing:# "Rotten Seed" — 3:16# "Intrauterine Cannibalism" — 1:42# "Intestinal Sodomy" — 2:22# "Internal Corruption" — 1:48...

 in some sharks or in the black salamander Salamandra atra).
- Hemotrophic viviparity : nutriments are provided by the female, often through placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

. In the frog Gastrotheca ovifera, embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

s are fed by the mother through specialized gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s. The lizard Pseudomoia pagenstecheri and most of mammals exhibit a hemotrophic viviparity.

Aplacental viviparity


In sharks and rays
Elasmobranchii
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, that includes the sharks and the rays and skates .-Evolution:...

, the term ovoviviparity has recently been deprecated in favor of aplacental viviparity. Authors may regard the two terms as synonymous, or equate ovoviviparity only with aplacental yolk-sac viviparity, in which the embryos are solely sustained by yolk (as opposed to secondary provisioning by their mother in the form of "uterine milk", such as in the stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...

s, or unfertilized eggs, such as in the mackerel sharks
Lamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...

; the latter is referred to as intrauterine oophagy
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....

).

There is a wide range of forms of intrauterine provisioning however, which could complicate the classification. In at least some sharks the routine intrauterine oophagy is not limited to unfertilised or trophic egg
Trophic egg
A trophic egg is an egg which is not laid for reproduction but for nutrition, often for offspring hatched from regular eggs. Trophic eggs are usually unfertilised....

s, in various forms and in in some the principle extends to actual intrauterine cannibalism
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...

.

Ovolarviparity


Among entomologists
Entomology
Entomology is the scientific study of insects, a branch of arthropodology...

 some authorities prefer the term ovolarviparous for insects that produce hatched or hatching larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e, in contrast to animals such as many snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...

s and lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

s that give birth to young that already largely resemble their adult form.

The idea is not unreasonable in general, but hard to sustain in detail. For one thing there are all sorts of gradations of resemblance between young and mature organisms of the same species, making it hard to draw clear distinctions between young and larvae, and accordingly, between ovoviviparity and ovolarviparity. For another, although there is a clear resemblance between say the newly born aphid, or chameleon (of say, the genus Bradypodion
Bradypodion
Bradypodion is one of six genera of chameleons within the "true" or "typical" chameleons . They are native to southern Africa, and are sometimes collectively called South African dwarf chameleons...

) and the parents, whereas there is a dramatic difference between the newly-born larvae of say, some ovolarviparous tachinid
Tachinidae
Tachinidae is a large and rather variable family of true flies within the insect order Diptera, with more than 8,200 known species and many more to be discovered. There are over 1300 species in North America. Insects in this family are commonly called tachina flies or simply tachinids...

 and Sarcophagid flies and the parents, it is easy to make too much of such resemblances. The differences to be found between say, the chameleons and their offspring (young lacking noticeable crest or bright colours etc.) are clearly functional, inhibiting adult aggression
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...

, so they are not trivial but systematic; the differences between insect larvae and adults might be more dramatic, but one could argue that they are no more significant in principle.

A comparatively small number of species of insects bear larvae already fully grown and ready to pupate. The most dramatic example is probably the Tsetse fly
Tsetse fly
Tsetse , sometimes spelled tzetze and also known as tik-tik flies, are large biting flies that inhabit much of mid-continental Africa between the Sahara and the Kalahari deserts. They live by feeding on the blood of vertebrate animals and are the primary biological vectors of trypanosomes, which...

, but that is an example of vivipary or if one prefers larvipary, because the larva has already shed its skin more than once and emergence from the egg has nothing to do with its birth.

Many other differences between young and mature viviparous or ovoviviparous organisms are clearly adaptive rather than adventitious
Adventitious
Adventitious has various meanings in various disciplines and in general usage.Adventitious is from the Latin root advenire, meaning "to come or be superadded" and in correct English the meanings tend to have connections to accidental or casual occurrence...

; one could make a strong case for regarding human babies as larvae for example, considering the distinct differences in their skeletal and hormonal development and their bodily proportions.