Meiotic drive is associated with sexual incompatibility in Neurospora

Meiotic drive is the phenomenon whereby selfish elements bias their transmission to progeny at ratios above 50:50, violating Mendels law of equal segregation. The model fungus Neurospora carries three different meiotic drivers, called Spore killers. Two of these, Sk-2 and Sk-3, are multilocus spore killers that constitute large haplotypes and are found in the species N. intermedia. Here we used molecular markers to determine that all N. intermedia isolates from New Zealand in fact belong to the sister species N. metzenbergii. Additionally, we use laboratory crosses to demonstrate that Sk-2 and Sk-3 are involved in sexual incompatibility between N. intermedia and N. metzenbergii.. Our experiments revealed that while crosses between these two species normally produced viable progeny at appreciable rates, when strains of N. intermedia carried Sk-2 or Sk-3 the proportion of viable progeny dropped substantially and in some crosses, no viable progeny were observed. Backcrossings supported that the incompatibility is tightly linked to the Sk haplotype. Finally, it appears that Sk-2 and Sk-3 have accumulated different incompatibility phenotypes when crossed with N. metzenbergii strains, consistent with their independent evolutionary history. This research illustrates how meiotic drive can contribute to reproductive isolation between populations, and thereby speciation.