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The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
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 breeding pair of Persian leopards. Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals. [1] For example, many birds mate for a breeding season or sometimes for life.
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.
The benefits of cooperative breeding in birds have been well-documented. One example is the azure-winged magpie (Cyanopica cyanus), in which studies found that the offspring's cell-mediated immune response was positively correlated with increase in the number of helpers at the nest. [34]
In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), [28] [29] ZZ (male), or WW (non-viable in most species, [31] but a fertile, [dubious – discuss] viable female in a few, e.g ...
Extra-pair copulation in men has been explained as being partly due to parental investment. [7] Research has suggested [7] that copulation poses more of a risk to future investment for women, as they have the potential of becoming pregnant, and consequently require a large parental investment of the gestation period, and then further rearing of the offspring.
The offspring of males with larger eyespots on their ornamented tails have been shown to weigh more and were more likely to be alive after 2 years than the progeny of males with fewer eyespots. [19] Ornaments that play a role in reproduction develop under the influence of two series of genes. [21]