Evolution, speciation, and inbreeding in the parasitic ant genus Epimyrma (Hymenoptera, Formicidae)

Abstract

The ant genus Epimyrma exhibits an evolutionary transition from fully developed slave‐making to a completely workerless parasitic condition. Two of the actively dulotic species, like the closely‐related Myrmoxenus gordiagini, engage in mating and dispersal flights as is usual in ants, whereas in the remaining five species intranidal mating of the sexuals and thus continuous inbreeding is observed; the females shed their wings in the nest and disperse on foot. The inbreeding species are very closely interrelated, as was recently demonstrated with hybridization experiments. The reduction of slave‐making and the evolution of intranidal mating in this group can hardly be explained assuming ordinary models of speciation and spreading of species. I therefore suggest the scenario of an original, widespread, polytypic species with partially isolated, host‐specific races and populations in which genetic dispositions for a reduction of worker numbers and slave‐raiding, and for intranidal mating, were adaptive; the latter, however, encountered problems associated with inbreeding. Such a situation then selected for a sex‐determination mechanism resistant to inbreeding which spread throughout the range of the species, completing the life‐pattern. Due to intranidal mating and inbreeding, however, gene flow between populations is interrupted. The inbreeding system has evidently led to the conservation of a status quo in each population it has reached. The original host‐specific races are morphologically and biologically discrete entities, which should be maintained as species, as they were described, even though they consist of reproductively isolated demes which themselves are built up of isolated, clone‐like lineages. Copyright © 1989, Wiley Blackwell. All rights reserved