Genetic and chemical divergence among host races of a socially parasitic ant.

Host-parasite associations facilitate the action of reciprocal selection and can drive rapid evolutionary change. When multiple host species are available to a single parasite, parallel specialization on different hosts may promote the action of diversifying natural selection and divergence via host race formation. Here, we examine a population of the kidnapper ant () that is an obligate social parasite of three sympatric ant species: , , and (formerly ). Behavioral and ecological observations of have shown that individual colonies parasitize only one species of host and that new queens maintain host fidelity when establishing new colonies. To successfully adapt to a particular host, ants may mimic or camouflage themselves with the species-specific chemical cues (cuticular hydrocarbons) that their hosts use to ascertain colony membership. To investigate the extent of host specialization, we collected both genetic and chemical data from that parasitize each of the three different species in sympatry. We show that host-associated genetic structure exists for both maternally inherited mitochondrial DNA data and biparentally inherited microsatellite markers. We also show that can be distinguished by chemical profile according to host due to partial matching with their host. Our results support the hypothesis that host race formation is occurring among lineages of that use different hosts. Thus, this system may represent a promising model for illuminating the early steps of divergence, accumulation of reproductive isolation, and speciation.