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 reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

(embryos in eggs),

viviparity 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 juv ...

(young born live), and

ovoviviparity Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that r ...

(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 A zygote (; , ) is a eukaryote, eukaryotic cell (biology), 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 individ ...

(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 zygote and initiate its development into a new individual organism or of ...

; 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 vertebrates is the passageway from an ovary. In human females, this is more usually known as the fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, or will dege ...

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 (: placentas or placentae) 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 ...

Traditional modes

The three traditional modes of reproduction are: *

Oviparity Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

, taken to be the ancestral condition, where either unfertilised oocytes or fertilised eggs are spawned. *

Viviparity 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 juv ...

, 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 "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that r ...

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

(fertilised egg) and the parents: Thierry Lodé (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 a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s and

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

es, and is found in most

frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...

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

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

, birds and some other reptiles. Among mammals, the monotremes 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''. 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'', 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 Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecology, ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is also well ...

( intra-uterine cannibalism in some sharks or in the black salamander '' Salamandra atra''). * Hemotrophic viviparity: nutrients are provided by the female, often through a

, as in

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s except for

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

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

embryo An embryo ( ) is the initial stage of development for 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 sp ...

s are fed by the mother through specialized

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, 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 r ...

s. The lizard '' Pseudemoia pagenstecheri'' 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 (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

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 bec ...

, after internal fertilisation File:Anguidae.jpg,

: slowworm 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 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 gre ...

embryo at 50 days, feeding in the mother's marsupial pouch (outside the womb) File:Elements of the comparative anatomy of vertebrates (1886) (21057027940).jpg, Hemotrophic viviparity: a mammal embryo (centre) attached by its

umbilical cord In Placentalia, 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 i ...

to a

(top) which provides food

References

{{Authority control Animal reproductive system Oology