In animal

behaviour Behavior (American English) or behaviour ( British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as w ...

, a gens (pl. gentes) or host race is a host-specific

lineage Lineage may refer to: Science * Lineage (anthropology), a group that can demonstrate its common descent from an apical ancestor or a direct line of descent from an ancestor * Lineage (evolution), a temporal sequence of individuals, populatio ...

of a

brood parasite Brood parasites are animals that rely on others to raise their young. The strategy appears among birds, insects and fish. The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were its ow ...

species In biology, a species is the basic unit of Taxonomy (biology), 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 ...

. 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 separat ...

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. It ...

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 rece ...

and lie on the

W chromosome 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, ...

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 Wil ...

s, in which both the male and female imprint on their preferred host. This leads to speciation, such as the

indigo bird __NOTOC__ The indigobirds and whydahs, together with the cuckoo-finch, make up the family Viduidae; they are small passerine birds native to Africa. These are finch-like species which usually have black or indigo predominating in their plumage. ...

, 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 book ...

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