Wolbachia in leafcutter ants: a widespread symbiont that may induce male killing or incompatible matings

Wolbachia is a maternally inherited bacterium that manipulates host reproduction by inducing cytoplasmic incompatibility (CI), parthenogenesis or male killing (MK). Here, we report on a screening of seven leafcutter ant species of the genera Atta and Acromyrmex. Using Wolbachia-specific polymerase chain reaction (PCR) primers we show that all species are infected, usually by double A + B strain infections. For Acromyrmex echinatior and A. octospinosus, a screening across all castes shows that gynes (prospective queens) have higher infection rates than workers and males. The low infection rate of workers suggests that workers lose their infection during development. This we interpret as adaptive, because a heritable symbiont does not benefit from being present in sterile workers. Both CI and MK could potentially account for the low infection rate of males. Formal theoretical models show greater support for the MK scenario in the free living species A. echinatior and A. octospinosus but indicate that Wolbachia in the social parasite A. insinuator may cause CI, supporting a scenario of sympatric speciation of the social parasite. We conclude that Wolbachia represents a previously unrecognized source of reproductive conflict in leafcutter ant colonies.