HOST-RACE FORMATION IN THE COMMON CUCKOO

The exploitation of a new host by a parasite may result in host-race f ormation or speciation. A brood parasitic bird, the common cuckoo, is divided into host races, each characterized by egg mimicry of differen t host species. Microsatellite DNA markers were used to examine cuckoo mating patterns and host usage in an area where a new host has been r ecently colonized. Female cuckoos show strong host preferences, but in dividual males mate with females that Lay in the nests of different ho sts. Female host specialization may Lead to the evolution of sex-linke d traits such as egg mimicry, even though gene flow through the male L ine prevents completion of the speciation process.