Viviparity

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An aphid giving viviparous birth, an unusual mode of reproduction among insects Aphid-giving-birth.jpg
An aphid giving viviparous birth, an unusual mode of reproduction among insects

In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juvenile that is at least metabolically independent. This is opposed to oviparity, where the embryos develop independently outside the mother in eggs until they are developed enough to break out as hatchlings; [1] and ovoviviparity, where the embryos are developed in eggs that remain carried inside the mother's body until the hatchlings emerge from the mother as juveniles, similar to a live birth.

Contents

Etymology

The term "viviparity" and its adjective form "viviparous" both derive from the Latin vivus, meaning "living"; and pario, meaning "give birth to". [2]

Reproductive mode

Hemotrophic viviparity: a mammal embryo (centre) attached by its umbilical cord to a placenta (top) which provides food Elements of the comparative anatomy of vertebrates (1886) (21057027940).jpg
Hemotrophic viviparity: a mammal embryo (centre) attached by its umbilical cord to a placenta (top) which provides food

Five modes of reproduction have been differentiated in animals [3] based on relations between zygote and parents. The five include two nonviviparous modes: ovuliparity, with external fertilisation, and oviparity, with internal fertilisation. In the latter, the female lays zygotes as eggs with a large yolk; this occurs in all birds, most reptiles, and some fishes. [4] These modes are distinguished from viviparity, which covers all the modes that result in live birth:

At least some transport of nutrients from mother to embryo appears to be common to all viviparous species, but those with fully developed placentas such as found in the Theria, some skinks, and some fish can rely on the placenta for transfer of all necessary nutrients to the offspring and for removal of all the metabolic wastes as well once it has been fully established during the early phases of a pregnancy. In such species, there is direct, intimate contact between maternal and embryonic tissue, though there also is a placental barrier to control or prevent uncontrolled exchange and the transfer of pathogens.

In at least one species of skink in the large genus Trachylepis , placental transport accounts for nearly all of the provisioning of nutrients to the embryos before birth. In the uterus, the eggs are very small, about 1 mm 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. [8] In several respects, the phenomenon is of considerable importance in theoretical zoology. Blackburn & Flemming (2011) [8] remark that such an endotheliochorial placenta is fundamentally different from that of any known viviparous reptile. [8]

There is no relationship between sex-determining mechanisms 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 viviparous reptiles. Therefore, marine viviparous species, including sea snakes and, it now appears, the mosasaurs, ichthyosaurs, and plesiosaurs of the Cretaceous, use genotypic sex determination (sex chromosomes), much as birds and mammals do. [9] Genotypic sex determination is also found in most reptiles, including many viviparous ones (such as Pseudemoia entrecasteauxii), whilst temperature dependent sex determination is found in some viviparous species, such as the montane water skink ( Eulamprus tympanum ). [10]

Evolution

In general, viviparity and matrotrophy are believed to have evolved from an ancestral condition of oviparity and lecithotrophy (nutrients supplied through the yolk). [11] One traditional hypothesis concerning the sequence of evolutionary steps leading to viviparity is a linear model. According to such a model, provided that fertilization was internal, the egg might have been retained for progressively longer periods in the reproductive tract of the mother. Through continued generations of egg retention, viviparous lecithotrophy may have gradually developed; in other words the entire development of the embryo, though still with nutrients provided by the yolk, occurred inside the mother's reproductive tract, after which she would give birth to the young as they hatched. The next evolutionary development would be incipient matrotrophy, in which yolk supplies are gradually reduced and are supplemented with nutrients from the mother's reproductive tract. [12]

In many ways, depending on the ecology and life strategy of the species, viviparity may be more strenuous and more physically and energetically taxing on the mother than oviparity. However, its numerous evolutionary origins imply that in some scenarios there must be worthwhile benefits to viviparous modes of reproduction; selective pressures have led to its convergent evolution more than 150 times among the vertebrates alone. [13]

There is no one mode of reproduction that is universally superior in selective terms, but in many circumstances viviparity of various forms offers good protection from parasites and predators and permits flexibility in dealing with problems of reliability and economy in adverse circumstances. Variations on the theme in biology are enormous, ranging from trophic eggs to resorption of partly developed embryos in hard times or when they are too numerous for the mother to bring to term, but among the most profoundly advantageous features of viviparity are various forms of physiological support and protection of the embryo, such as thermoregulation and osmoregulation. [1] Since the developing offspring remains within the mother's body, she becomes, in essence, a walking incubator, protecting the developing young from excessive heat, cold, drought, or flood. This offers powerful options for dealing with excessive changes in climate or when migration events expose populations to unfavourable temperatures or humidities. In squamate reptiles in particular, there is a correlation between high altitudes or latitudes, colder climates and the frequency of viviparity. The idea that the tendency to favour egg-retention selectively under cooler conditions arises from the thermoregulatory benefits, and that it consequently promotes the evolution of viviparity as an adaptation, is known as "the cold climate hypothesis". [14]

Reversion of viviparity

Through ancestral state reconstruction, scientists have shown that the evolution of viviparity to oviparity may have occurred a maximum of eight times in the genus Gerrhonotus of anguid lizards. [15] Advanced ancestral state reconstruction was used to more accurately prove that the reverse evolution of viviparity to oviparity is true. [16] In the analysis, the authors use a maximum likelihood tree to reveal that parity mode is a labile trait in the Squamata order. [16] They also further show through analysis that viviparity is also strongly associated with cooler climates which suggests the previously stated "cold-climate hypothesis" is true. [16]

However, others directly refute this notion that parity is a labile trait. [17] In their critique, they show that ancestral state reconstruction analyses are reliant on the underlying phylogenetic information provided. [17] The use of a maximum likelihood tree which is vulnerable to phylogenetic error may cause an artificial inflation of the number of viviparity to oviparity occurrences. [17] Additionally, they state that the previous study does not take into account the morphological and behavioral modifications that would have to occur for reversion to occur. [17] Some of these modifications would be the redevelopment of uterine glands to synthesize and secrete shell fibers, the restoration of the careful timing of oviposition due to eggshell thickness, etc. [17] The degradation and loss of function of oviparous genes during viviparous evolution suggests that these genes would have to re-evolve in order for the reversion of this evolution to occur. [17] Since this re-evolution is near impossible due to the complexity of oviparous reproductive mode, the simple labile characteristic of parity cannot be sufficiently supported. [17]

See also

Related Research Articles

<span class="mw-page-title-main">Gestation</span> Period during the carrying of an embryo

Gestation is the period of development during the carrying of an embryo, and later 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.

<span class="mw-page-title-main">Livebearers</span> Fish that give birth to free swimming offspring

Livebearers are fish that retain their eggs inside the body and give birth to live, free-swimming young. They are especially prized by aquarium owners. Among aquarium fish, livebearers are nearly all members of the family Poeciliidae and include: guppies, mollies, platies and swordtails.

<span class="mw-page-title-main">Poeciliidae</span> Family of fishes

The Poeciliidae are a family of freshwater fishes of the order Cyprinodontiformes, the tooth-carps, and include well-known live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail. The original distribution of the family was the Southeastern United States to north of Río de la Plata, Argentina, and Africa, including Madagascar. Due to release of aquarium specimens and the widespread use of species of the genera Poecilia and Gambusia for mosquito control, though, poeciliids can today be found in all tropical and subtropical areas of the world. In addition, Poecilia and Gambusia specimens have been identified in hot springs pools as far north as Banff, Alberta.

<span class="mw-page-title-main">Uterus</span> Female sex organ in mammals

The uterus or womb is the organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic and fetal development of one or more embryos until birth. The uterus is a hormone-responsive sex organ that contains glands in its lining that secrete uterine milk for embryonic nourishment.

<span class="mw-page-title-main">Birth</span> Process of bearing offspring

Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.

<span class="mw-page-title-main">Chorion</span> Outermost fetal membrane around the embryo in amniotes

The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida, known as the vitelline membrane in other animals. In insects, it is developed by the follicle cells while the egg is in the ovary. Some mollusks also have chorions as part of their eggs. For example, fragile octopus eggs have only a chorion as their envelope.

<span class="mw-page-title-main">Ovoviviparity</span> Gestation type

Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that remain in the mother's body until they are ready to hatch.

<span class="mw-page-title-main">Egg</span> Organic vessel in which an embryo first begins to develop

An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches.

<span class="mw-page-title-main">Viviparous lizard</span> Species of lizard

The viviparous lizard, or common lizard, is a Eurasian lizard. It lives farther north than any other species of non-marine reptile, and is named for the fact that it is viviparous, meaning it gives birth to live young. Both "Zootoca" and "vivipara" mean "live birth", in (Latinized) Greek and Latin respectively. It was called Lacerta vivipara until the genus Lacerta was split into nine genera in 2007 by Arnold, Arribas & Carranza.

<span class="mw-page-title-main">Claire Weekes</span>

Doctor Hazel Claire Weekes MBE was an Australian general practitioner and health writer; she also had an early career as a research scientist working in the field of comparative reproduction. Doctor Weekes is considered by many as the pioneer of modern anxiety treatment and has written several books on dealing with anxiety disorders. Many of today's self-help books on anxiety continue to cite her work.

<span class="mw-page-title-main">Internal fertilization</span> Union of an egg and sperm to form a zygote within the female body

Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For internal fertilization to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract.

<span class="mw-page-title-main">Fish reproduction</span> Reproductive physiology of fishes

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 can often be determined by the shape of its papilla.

<span class="mw-page-title-main">Oviparity</span> Animals that lay their eggs, with little or no other embryonic development within the mother

Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings known as hatchlings with little or no embryonic development within the mother. This is the reproductive method used by most animal species, as opposed to viviparous animals that develop the embryos internally and metabolically dependent on the maternal circulation, until the mother gives birth to live juveniles.

<span class="mw-page-title-main">Placentation</span> Formation and structure of the placenta

Placentation refers to the formation, type and structure, or arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to remove waste from the embryo. Placentation is best known in live-bearing mammals (theria), but also occurs in some fish, reptiles, amphibians, a diversity of invertebrates, and flowering plants. In vertebrates, placentas have evolved more than 100 times independently, with the majority of these instances occurring in squamate reptiles.

<i>Pseudemoia entrecasteauxii</i> Species of lizard

Pseudemoia entrecasteauxii, also known commonly as Entrecasteaux's skink, the southern grass skink, the tussock cool-skink, and the tussock skink, is a species of lizard in the family Scincidae. The species is endemic to Australia.

<i>Saiphos</i> Species of reptile

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.

Histotrophy is a form of matrotrophy exhibited by some live-bearing sharks and rays, in which the developing embryo receives additional nutrition from its mother in the form of uterine secretions, known as histotroph. It is one of the three major modes of elasmobranch reproduction encompassed by "aplacental viviparity", and can be contrasted with yolk-sac viviparity and oophagy.

<i>Cryptasterina hystera</i> Species of starfish

Cryptasterina hystera is a species of starfish. It is found in a limited region of the coast of Australia and is very similar in appearance to Cryptasterina pentagona. The two appear to have diverged from a common ancestral line a few thousand years ago.

<span class="mw-page-title-main">Pregnancy in fish</span>

Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish, e.g. Consistent with this definition, there are several modes of reproduction in fish, providing different amounts of parental care. In ovoviviparity, there is internal fertilization and the young are born live but there is no placental connection or significant trophic (feeding) interaction; the mother's body maintains gas exchange but the unborn young are nourished by egg yolk. There are two types of viviparity in fish. In histotrophic viviparity, the zygotes develop in the female's oviducts, but she provides no direct nutrition; the embryos survive by eating her eggs or their unborn siblings. In hemotrophic viviparity, the zygotes are retained within the female and are provided with nutrients by her, often through some form of placenta.

<span class="mw-page-title-main">Modes of reproduction</span>

Animals make use of a variety of modes of reproduction to produce their young. Traditionally this variety was classified into three modes, oviparity, viviparity, and ovoviviparity.

References

  1. 1 2 3 Blackburn, D.G. (1999). "Viviparity and oviparity: Evolution and reproductive strategies". Encyclopedia of Reproduction. 4. Academic Press: 994–1003.
  2. ↑ Schuett, G.W. (2002). Biology of the Vipers. Eagle Mountain, UT: Eagle Mountain Publications.
  3. ↑ Lodé, Thierry (2001). Les stratégies de reproduction des animaux[Reproduction strategies in the animal kingdom] (in French). Paris, FR: Eds Dunod Sciences.
  4. 1 2 Blackburn, D.G. (2000). Classification of the Reproductive Patterns of Amniotes. Herpetological Monographs. pp. 371–377.
  5. ↑ Capinera, John L. (2008). Encyclopedia of Entomology. Springer Reference. p. 3311. ISBN   9781402062421 – via Google Books.
  6. ↑ Costa, James T. (2006). The Other Insect Societies. Belknap Press. p. 151.
  7. ↑ Newbern, E. (26 January 2016). "Mom Genes: This cockroach species' live births are in its DNA". LiveScience . Purch. Retrieved 26 January 2016.
  8. 1 2 3 Blackburn, D.G.; Flemming, A.F. (2011). "Invasive implantation and intimate placental associations in a placentotrophic African lizard, Trachylepis ivensi (scincidae)". Journal of Morphology. 273 (2): 37–159. doi:10.1002/jmor.11011. PMID   21956253. S2CID   5191828.
  9. ↑ Organ, Chris L.; et al. (2009). "Genotypic sex determination enabled adaptive radiations of extinct marine reptiles". Nature. 461 (7262): 389–392. doi:10.1038/nature08350. PMID   19759619. S2CID   351047.
  10. ↑ Robert, Kylie A.; Thompson, Michael B. (2001). "Sex determination: Viviparous lizard selects sex of embryos". Nature. 412 (6848): 698–699. doi:10.1038/35089135. PMID   11507628. S2CID   4420854.
  11. ↑ Griffith, OW; Blackburn, DG; Brandley, MC; Van Dyke, JU; Whittington, CW; Thompson, M.B. (2015). "Ancestral state reconstructions require biological evidence to test evolutionary hypotheses: A case study examining the evolution of reproductive mode in squamate reptiles". J Exp Zool B. 324 (6): 493–503. doi:10.1002/jez.b.22614. PMID   25732809.
  12. ↑ Blackburn, D. G. (1992). "Convergent evolution of viviparity, matrotrophy, and specializations for fetal nutrition in reptiles and other vertebrates". Am. Zool. 32 (2): 313–321. doi: 10.1093/icb/32.2.313 .
  13. ↑ Blackburn, Daniel G (2014). "Evolution of vertebrate viviparity and specializations for fetal nutrition: A quantitative and qualitative analysis". Journal of Morphology. 276 (8): 961–990. doi:10.1002/jmor.20272. PMID   24652663. S2CID   549574.
  14. ↑ Lambert, S. M.; Wiens, J. J. (2013). "Evolution of viviparity: a phylogenetic test of the cold-climate hypothesis in phrynosomatid lizards". Evolution. 67 (9): 2614–2630. doi:10.1111/evo.12130. PMID   24033171. S2CID   3890276.
  15. ↑ Fraipont, M.D.; Clobert, J.; Barbault, R. (1996). "The evolution of oviparity with egg guarding and viviparity in lizards and snakes: A phylogenetic analysis". Evolution. 50 (1): 391–400. doi: 10.1111/j.1558-5646.1996.tb04501.x . PMID   28568867. S2CID   205780092.
  16. 1 2 3 Pyron, R. A.; Burbrink, F. T. (2013). "Early origin of viviparity and multiple reversions to oviparity in squamate reptiles". Ecology Letters. 17 (1): 13–21. doi: 10.1111/ele.12168 . PMID   23953272.
  17. 1 2 3 4 5 6 7 Griffith, O.W.; Blackburn, D.G.; Brandley, M.C.; Dyke, J.U.V.; Whittington, C.M.; Thompson, M.B. (2015). "Ancestral state reconstructions require biological evidence to test evolutionary hypotheses: A case study examining the evolution of reproductive mode in squamate reptiles". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 324 (6): 493–503. doi:10.1002/jez.b.22614. PMID   25732809.
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