EFFECT OF GENOTYPE ON CYTOPLASMIC INCOMPATIBILITY BETWEEN 2 SPECIES OF NASONIA

Cytoplasmically inherited bacteria cause bidirectional incompatibility between two species of the parasitoid wasp genus Nasonia. These bacteria belong to the alpha sub-division of the Proteobacteria. Normally, hybrid (female) offspring are not produced in interspecific crosses. Elimination of the cytoplasmically-inherited bacteria by antibiotic treatments restores compatibility, i.e. hybrid females are produced. Bidirectional incompatibility could be caused directly, by differences between the bacteria of the two species, or indirectly, by the different interactions of the bacteria with host species genomes. To distinguish between these two possibilities, genetic crosses were set up to introduce the nuclear genome of each wasp species into the cytoplasmic (microbial) background of the other. These strains were then tested for compatibility to the infected parental species. Individuals from both reciprocal introgressions were only compatible with individuals that had the same cytoplasm, independent of nuclear background. This indicates that compatibility type is independent of the host genotype and is based on differences between cytoplasmic bacteria of the two Nasonia species. However, compatibility differences from interactions between the bacteria and the other cytoplasmically inherited elements (e.g. mitochondria) have not been ruled out.