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The biologist Thierry Lodé proposed (2001, 2012) five modes of reproduction based on the relationship between the zygote (fertilised egg) and the parents: [1] [2] Ovuliparity: fertilisation is external, the oocytes being released into the environment and fertilised outside the body by the male. [1]
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring.
The traditional modes of reproduction include oviparity, taken to be the ancestral condition, traditionally where either unfertilised oocytes or fertilised eggs are spawned, and viviparity traditionally 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.
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual. In asexual reproduction, an organism can reproduce without the involvement of another organism.
While rare, mostly abortive, parthenogenesis is not unknown in birds and eggs can be diploid, automictic and results in male offspring. [101] Birds are solely gonochoric, [102] meaning they have two sexes: either female or male. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in mammals.
Parental care is any behaviour that contributes to offspring survival, such as building a nest, provisioning offspring with food, or defending offspring from predators. Reptiles may produce self-sufficient young needing no parental care, while some hatchling birds may be helpless at birth, relying on their parents for survival.
The word is most often used for the offspring of mammals, but can be used for any animal that gives birth to multiple young. In comparison, a group of eggs and the offspring that hatch from them are frequently called a clutch, while young birds are often called a brood. Animals from the same litter are referred to as littermates.
In birds, which have a ZW sex-determination system, the W chromosome carries factors responsible for female development, and default development is male. [58] In this case, ZZ individuals are male and ZW are female. It is the female gamete that determines the sex of the offspring. This system is used by birds, some fish, and some crustaceans. [9]