Mitochondrial mismatch: Nasonia hybrid mortality and rescue

Nuclear and mitochondrial genomes evolve at different rates, and yet their products must interact intimately in order to produce functional mitochondria and to allow eukaryotic cells to survive. Hybrids of the wasp genus Nasonia suffer from significant mortality in a maternal/mitochondrial-specific pattern and they exhibit deficits in their mitochondrial function. In hybrids between N. vitripennis and N. giraulti, the N. vitripennis allele at one nuclear locus results in ~98% mortality when paired with N. giraulti mitochondria. This locus contains a divergent gene encoding one of the proteins of the oxidative phosphorylation pathway, making it a prime candidate for mortality due to mitochondrial disruption. In order to study the nuclear-mitochondrial mismatch at this locus, we have produced an introgression strain that has isolated the matching N. giraulti locus in an otherwise completely N. vitripennis nuclear and mitochondrial background. Hybrids produced using males of this matching introgression strain have increased survival relative to hybrids produced using purely N. vitripennis males, indicating a major rescue of mortality. Hybrid mortality represents a significant barrier to gene flow and can serve to reinforce the speciation process, and this work provides further evidence for the role of nuclear-mitochondrial interactions in the evolution of species.