Vivipary
Encyclopedia
Vivipary has two different meanings. In animal
s, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs
. In plant
s, it means reproduction via embryos, such as buds, that develop from the outset without interruption, as opposed to germinating externally from a seed
.
and parents:
A relatively less developed form of animal vivipary is called ovoviviparity
, which, for instance, occurs in most vipers
and most live-bearing bony fishes (Poeciliidae
). The more developed form of vivipary is called placental viviparity
. Placental mammals
are the best example, but other animals have also adapted by incorporating this principle. Examples include some species of scorpion
s and cockroaches, certain genera of sharks and snake
s, and velvet worm
s.
Certain lizards, in particular some species of skink
, also reproduce in this way, referred to as viviparous matrotrophy. Examples include the species Tiliqua rugosa and members of the genus Corucia. In such species the placenta is attached directly to the mother. Viviparous offspring live independently and require an external food supply from birth. This contrasts with some egg laying animals, such as fish and amphibia
in which the recently hatched young bear yolk sacs
. Precocial
birds, such as domestic fowl, typically also bear internal yolk sacs at birth.
Recent investigation has revealed that in at least one species of skink
in the large genus Trachylepis
this process has gone essentially to completion. In several respects the phenomenon is of considerable importance in theoretical zoology. In the uterus the eggs are very small, about 1mm in diameter, with very little yolk and very thin shells. The shell membrane is vestigial and transient; its disintegration permits the absorption of nutrients from uterine secretions. The embryo then produces invasive chorionic tissues that grow between the cells of the uterine lining till they can absorb nutrients from maternal blood vessels. As it penetrates the lining, the embryonic tissue grows aggressively till it forms sheets of tissue beneath the uterine epithelium. They eventually strip it away and replace it, making direct contact with maternal capillaries. The authors remark that such an endotheliochorial placenta is fundamentally different from that of any known viviparous reptile.
There is a relationship between sex-determining mechanism and whether a species bears live young or lays eggs. Temperature-dependent sex determination
which cannot function in an aquatic environment, is seen only in terrestrial reptiles. Therefore, marine viviparous species, including sea snakes and, it now appears, the mosasaur
s, ichthyosaur
s, and plesiosaur
s of the Cretaceous, use genotypic sex determination (sex chromosomes), much like birds and mammals.
Viviparous plants produce seeds that germinate before they detach from the parent. In many mangroves, for instance, the seedling germinates and grows under its own energy while still attached to its parent before dropping into the water in order to transport away. In some trees, like Jackfruit, the seeds can be found already germinated while the fruit goes overripe; this condition cannot be said as vivipary since the moist and humid conditions provided by the fruit mimics a wet soil that encourages germination. However, the seeds can germinate under soil too.
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, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs
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...
. In plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s, it means reproduction via embryos, such as buds, that develop from the outset without interruption, as opposed to germinating externally from a seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
.
In animals
Five modes of reproduction can be differentiated in animals based on relations between zygoteZygote
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 seahorseSeahorseSeahorses compose the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning “sea monster”.There are nearly 50 species of seahorse...
, zygotes are retained in the male’s ventral "marsupium". In the frog Rhinoderma darwinii, the zygotes develop in the vocal sac. In the frog Rheobatrachus, zygotes develop in the stomach. - Histotrophic viviparity : the zygotes develop in the female’s oviductOviductIn 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 oophagyOophagyOophagy , 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 (intra-uterine cannibalism in some sharks or in the black salamander Salamandra atra). - Hemotrophic viviparity : nutriments are provided by the female, often through some form of placentaPlacentaThe 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, embryoEmbryoAn 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 gillGillA 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 skinkSkinkSkinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae , they comprise the superfamily or infraorder Scincomorpha...
PseudemoiaPseudemoiaPseudemoia is a genus of skinks native to south–eastern Australia. For similar skinks see genera Bassiana, Lampropholis, and Niveoscincus.-Species:...
pagenstecheri and most of mammals exhibit a hemotrophic viviparity.
A relatively less developed form of animal vivipary is called ovoviviparity
Ovoviviparity
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...
, which, for instance, occurs in most vipers
Viperidae
The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...
and most live-bearing bony fishes (Poeciliidae
Poeciliidae
Poeciliidae is a family of fresh-water fish which are live-bearing aquarium fish . They belong to the order Cyprinodontiformes, tooth-carps, and include well-known aquarium fish such as the guppy, molly, platy, and swordtail...
). The more developed form of vivipary is called placental viviparity
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...
. Placental mammals
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
are the best example, but other animals have also adapted by incorporating this principle. Examples include some species of scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
s and cockroaches, certain genera of sharks and 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 velvet worm
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
s.
Certain lizards, in particular some species of skink
Skink
Skinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae , they comprise the superfamily or infraorder Scincomorpha...
, also reproduce in this way, referred to as viviparous matrotrophy. Examples include the species Tiliqua rugosa and members of the genus Corucia. In such species the placenta is attached directly to the mother. Viviparous offspring live independently and require an external food supply from birth. This contrasts with some egg laying animals, such as fish and amphibia
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
in which the recently hatched young bear yolk sacs
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. Precocial
Precocial
In biology, the term precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial," where the young are born or hatched helpless. Extremely precocial species may be called...
birds, such as domestic fowl, typically also bear internal yolk sacs at birth.
Recent investigation has revealed that in at least one species of skink
Skink
Skinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae , they comprise the superfamily or infraorder Scincomorpha...
in the large genus Trachylepis
Trachylepis
Trachylepis is a skink genus in the subfamily Lygosominae found mainly in Africa. Its members were formerly included in the "wastebin taxon" Mabuya, and for some time in Euprepis. As defined today, Trachylepis contains the clade of Afro-Malagasy mabuyas. The genus also contains a species from the...
this process has gone essentially to completion. In several respects the phenomenon is of considerable importance in theoretical zoology. In the uterus the eggs are very small, about 1mm in diameter, with very little yolk and very thin shells. The shell membrane is vestigial and transient; its disintegration permits the absorption of nutrients from uterine secretions. The embryo then produces invasive chorionic tissues that grow between the cells of the uterine lining till they can absorb nutrients from maternal blood vessels. As it penetrates the lining, the embryonic tissue grows aggressively till it forms sheets of tissue beneath the uterine epithelium. They eventually strip it away and replace it, making direct contact with maternal capillaries. The authors remark that such an endotheliochorial placenta is fundamentally different from that of any known viviparous reptile.
There is a relationship between sex-determining mechanism and whether a species bears live young or lays eggs. Temperature-dependent sex determination
Temperature-dependent sex determination
Temperature-dependent sex determination is type of environmental sex determination in which the temperatures experienced during embryonic development determine the sex of the offspring. It is most prevalent and common among amniote vertebrates that are classified under the reptile class, but is...
which cannot function in an aquatic environment, is seen only in terrestrial reptiles. Therefore, marine viviparous species, including sea snakes and, it now appears, the mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s, ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s, and plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s of the Cretaceous, use genotypic sex determination (sex chromosomes), much like birds and mammals.
In plants
See also
- ApomixisApomixisIn botany, apomixis was defined by Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. This definition notably does not mention meiosis...
- OviparityOviparityOviparous 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....
- OvoviviparityOvoviviparityOvoviviparity, 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...
- Placental mammals
- MarsupialMarsupialMarsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s - Live-bearing aquarium fishLive-bearing aquarium fishLive-bearing aquarium fish, often simply called livebearers, are fish that retain the eggs inside the body and give birth to live, free-swimming young.-Common aquarium livebearers:...
- False viviparyFalse viviparyFalse vivipary is an abnormal condition found in many types of plants in which a plantlet is produced where the flower should appear. It is not a completely understood topic, but some say it could be caused by a hormonal mistake. The plantlet which appears can be rooted and grown like normal...