Pollo de Aguilucho cenizo (Circus pygargus)

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

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, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

(embryos in eggs),

viviparity Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

(young born live), and

ovoviviparity 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 insi ...

(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 Thierry Lodé (born 1956 in Tarbes) is a French biologist and professor of evolutionary ecology in a CNRS lab at the University of Rennes 1. His work deals mainly with sexual conflict.Göran Arnqvist and Locke Rowe, Eds., "Sexual conflict", Prin ...

has accordingly proposed five modes of reproduction based on the relationship between the

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...

(the fertilised egg) and the parents. His revised modes are ovuliparity, with external

fertilisation Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

; 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

oviduct The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, o ...

s, but are fed on other tissues; and hemotrophic viviparity, where the developing embryos are fed by the mother, often through a

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...

Traditional modes

The three traditional modes of reproduction are: *

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, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

, taken to be the ancestral condition, where either unfertilised

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

s or fertilised eggs are spawned. *

Viviparity Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

, 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. *

Ovoviviparity 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 insi ...

, covering mechanisms which span the modes of oviparity and viviparity. It can be seen that so defined, these traditional modes each cover a range of reproductive strategies.

Revised modes

The biologist

proposed (2001, 2012) five modes of reproduction based on the relationship between the

(fertilised egg) and the parents:

(2001). ''Les stratégies de reproduction des animaux'' (Reproduction Strategies in Animal Kingdom). Eds. Dunod Sciences. Paris. * Ovuliparity:

is external, the oocytes being released into the environment and fertilised outside the body by the male. This is common in

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s and

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

es, and is found in most

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

s. * Oviparity: fertilisation is internal, but the female lays zygotes as eggs with a substantial quantity of yolk to feed the embryo while it remains in the egg. The egg is not retained in the body, or only for a limited time. Oviparity is found in birds. Among mammals, the

monotreme Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals ( Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brai ...

s (four species of ''

Echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...

'', and the ''

Platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...

'') are oviparous. * Ovo-viviparity: or oviparity with retention of zygotes in either the female's or in the male's body, but there are no trophic interactions between zygote and parents. This mode is found in the slowworm, ''

Anguis fragilis The slow worm (''Anguis fragilis'') is a reptile native to western Eurasia. It is also called a deaf adder, a slowworm, a blindworm, or regionally, a long-cripple and hazelworm. These legless lizards are also sometimes called common slowworms. Th ...

''. In the sea horse, zygotes are retained in the male's ventral "marsupium". In the frog '' Rhinoderma darwinii'', the zygotes develop in the vocal sac. In the recently extinct frogs ''

Rheobatrachus The gastric-brooding frogs or platypus frogs (''Rheobatrachus'') is a genus of extinct ground-dwelling frogs native to Queensland in eastern Australia. The genus consisted of only two species, both of which became extinct in the mid-1980s. The ...

'', zygotes developed in the stomach. * Histotrophic viviparity: the zygotes develop in the female's

s, but find their nutriments from other tissues, whether skin or glandular tissue, oophagy or adelphophagy (

intra-uterine cannibalism Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, ...

in some sharks or in the black salamander ''

Salamandra atra The alpine salamander (''Salamandra atra'') is a black salamander that can be found in the French Alps, and through the mountainous range in Europe. It is a member of the genus ''salamandra''. Their species name, ''atra'', may be derived from th ...

''). * Hemotrophic viviparity: nutrients are provided by the female, often through a

, as in

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s except for

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...

s and

s. In the frog '' Gastrotheca ovifera'',

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s are fed by the mother through specialized

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...

s. The lizard ''

Pseudemoia pagenstecheri ''Pseudemoia pagenstecheri'', also known commonly as the southern grass tussock skink or the southern tussock grass skink, is a species of lizard in the family Scincidae. The species is endemic to Australia. Etymology The specific name, ''pa ...

'' and most mammals use this form of viviparity. Thus the definition of oviparity is narrower in the revised scheme, as it does not include the "ovuliparity" found in most fish, most frogs and many invertebrates. File:Rana temporaria eggs 4.JPG, Ovuliparity:

development inside soft egg (frogspawn) in pond water, fertilised outside body File:Schleiden-vogel.jpg,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

development inside shelled egg, with large food supply in

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...

, after internal fertilisation File:Anguidae.jpg,

slowworm The slow worm (''Anguis fragilis'') is a reptile native to western Eurasia. It is also called a deaf adder, a slowworm, a blindworm, or regionally, a long-cripple and hazelworm. These legless lizards are also sometimes called common slowworms. T ...

gives birth to live young, after retaining the eggs inside her body File:CSIRO ScienceImage 2059 A Fiftydayold Kangaroo in Pouch.jpg, Histotrophic

kangaroo Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern ...

embryo at 50 days, feeding in the mother's

marsupial pouch The pouch is a distinguishing feature of female marsupials, monotremes and possibly most extinct non-placental mammals including eutherians like ''Zalambdalestes'' (and rarely in the males as in the water opossumNogueira, José Carlos, et al.Mo ...

(outside the

womb The uterus (from Latin ''uterus'', plural ''uteri'') 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 ut ...

) File:Elements of the comparative anatomy of vertebrates (1886) (21057027940).jpg, Hemotrophic viviparity: a mammal embryo (centre) attached by its

umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...

to a

(top) which provides food

References

{{Authority control Animal reproductive system Oology