In animal behaviour, a gens (pl. gentes) or host race is a host-specific lineage of a brood parasite

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. Brood parasites, such as

cuckoo Cuckoos are birds in the Cuculidae family, the sole taxon in the order Cuculiformes . The cuckoo family includes the common or European cuckoo, roadrunners, koels, malkohas, couas, coucals and anis. The coucals and anis are sometimes separ ...

s, which use multiple

host species In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' ( symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

to raise their chicks evolve different gentes, each one specific to its host species. This specialisation allows the parasites to lay eggs that

mimic MIMIC, known in capitalized form only, is a former simulation computer language developed 1964 by H. E. Petersen, F. J. Sansom and L. M. Warshawsky of Systems Engineering Group within the Air Force Materiel Command at the Wright-Patterson AFB in ...

those of their hosts, which in turn reduces the chances of the eggs being rejected by the hosts, with about 5% of well-matched eggs compared to 72% of mismatched eggs rejected. The exact mechanisms of the evolution and maintenance of gens is still a matter of some research. However, it is believed that in

common cuckoo The common cuckoo (''Cuculus canorus'') is a member of the cuckoo order of birds, Cuculiformes, which includes the roadrunners, the anis and the coucals. This species is a widespread summer migrant to Europe and Asia, and winters in Africa. I ...

s, gens-specific properties are

sex-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). In humans, these are termed X-linked recessive, ...

and lie on the W chromosome of the female. Male cuckoos, which, like all male birds, have no W chromosome, are able to mate with females of any gens, and thereby maintain the cuckoo as one species. This is not the case in other brood parasites, such as

cowbird Cowbirds are birds belonging to the genus ''Molothrus'' in the family Icteridae. They are of New World origin, and are obligate brood parasites, laying their eggs in the nests of other species. The genus was introduced by English naturalist Will ...

s, in which both the male and female imprint on their preferred host. This leads to speciation, such as the indigo bird, which is suggested by the fact they have a more recent evolutionary origin than their hosts.

References

*Davies, N. (2000) ''Cuckoos, Cowbirds and other Cheats''. T. & A. D. Poyser: London *Dawkins, R. (1982) ''

The Extended Phenotype ''The Extended Phenotype'' is a 1982 book by the evolutionary biologist Richard Dawkins, in which the author introduced a biological concept of the same name. The main idea is that phenotype should not be ''limited'' to biological processes such ...

''.

Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...

: Oxford {{ISBN, 0-19-288051-9 Brood parasites Parasitology