Hybrid sterility and inviability in the parasitic fungal species complex Microbotryum
DE VIENNE, D.M. | REFRÉGIER, G. | HOOD, M.E. | GUIGUE, A. | DEVIER, B. | VERCKEN, E. | SMADJA, C. | DESEILLE, A. | GIRAUD, T.
Microbotryum violaceum, the anther-smut fungus, forms a complex of sibling species which specialize on different plants. Previous studies have shown the presence of partial ecological isolation and F1 inviability, but did not detect assortative mating apart from a high selfing rate. We investigated other post-mating barriers and show that F1 hybrid sterility, the inability of gametes to mate, increased gradually with the increasing genetic distance between the parents. F2 hybrids showed a reduced ability to infect the plants that was also correlated with the genetic distance. The host on which the F2 hybrids were passaged caused a selection for alleles derived from the pathogen species originally isolated from that host, but this effect was not detectable for the most closely related species. The post-mating barriers thus remain weak among the closest species pairs, suggesting that premating barriers are sufficient to initiate divergence in this system.
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