Wolbachia plays no role in the one-way reproductive incompatibility between the hybridizing field crickets Gryllus firmus and G. pennsylvanicus

Wolbachia are cytoplasmically inherited alpha-proteobacteria that can cause cytoplasmic incompatibility (CI) in insects. This incompatibility between sperm and egg is evident when uninfected females mate with infected males. Wolbachia-driven reproductive incompatibilities are of special interest because they may play a role in speciation. However, the presence of Wolbachia does not always imply incompatibility. The field crickets Gryllus firmus and G. pennsylvanicus exhibit a very clear unidirectional incompatibility and have been cited as a possible example of Wolbachia-induced CI. Here, we conduct curing experiments, intra- and interspecific crosses, cytological examination of Wolbachia in testes and Wolbachia quantifications through real-time PCR. All of our data strongly suggest that Wolbachia are not involved in the reproductive incompatibility between G. firmus and G. pennsylvanicus.