the Latin word gens
, plural gentes
, meaning 'clan' (see Webster below, and not to be confused with 'genus
'), is used for the lineage
s through the female line that enables members of the same species to specialize in parasitizing
different kinds of bird.
A number of cuckoo species show the well-known parasitic behaviour, though not all do. Within a single species, they can lay their eggs in the nests of various birds, each of which has strikingly different sizes or colours of eggs: that is, they don't just parasitize those birds that happen to have eggs resembling their own, but match their cuckoo egg to the host egg.
This is surprising if you think of mimicry as having evolved within the cuckoo species: you'd expect one species to have only one kind of egg. In fact egg type has continued to evolve within each gens. This is not a subspecies, because only females transmit gens membership. Daughters born in, say, a dunnock nest, belong to the dunnock gens, and like their mother they lay eggs only in dunnock nests. But a son has no gental affiliation and will mate with a female from any gens, which means the species doesn't split into subspecies based on their chosen host.
Clearly this mimicry of different eggs must be controlled by genes on the female-only chromosome. Birds generally have chromosomes analogous to the mammalian X and Y, but it's the female bird that has two different ones and the male that has two the same. So the female line can continue to evolve host-specific egg shape on her equivalent of the Y chromosome.