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Hybrid sterility and inviability in the parasitic fungal species complex Microbotryum

D M De Vienne1, G Refrégier, M E Hood

  • 1Ecologie, Systématique et Evolution, Université Paris-Sud, Orsay Cedex, France.

Journal of Evolutionary Biology
|February 21, 2009
PubMed

Insights

Post-mating barriers in Microbotryum violaceum, the anther-smut fungus, increase with genetic distance. These barriers are weak in closely related species, suggesting premating isolation drives initial divergence.

Area of Science:

  • Evolutionary Biology
  • Mycology
  • Speciation

Background:

  • Microbotryum violaceum, the anther-smut fungus, comprises sibling species specializing on different host plants.
  • Previous research indicated partial ecological isolation and F1 inviability but no significant assortative mating beyond high selfing rates.

Purpose of the Study:

  • To investigate post-mating reproductive barriers in the Microbotryum violaceum species complex.
  • To assess the role of genetic distance in F1 hybrid sterility and F2 hybrid infectivity.
  • To evaluate host-mediated selection on F2 hybrids.

Main Methods:

  • Assessed F1 hybrid sterility in relation to parental genetic distance.
  • Evaluated the infectivity of F2 hybrids on host plants.
  • Investigated host-specific allele selection in F2 hybrids after host passaging.

Main Results:

  • F1 hybrid sterility increased gradually with increasing genetic distance between parent species.
  • F2 hybrid infectivity was reduced and correlated with genetic distance.
  • Host passaging selected for pathogen alleles specific to the original host, but this was not observed for the most closely related species.

Conclusions:

  • Post-mating barriers in Microbotryum violaceum are generally weak, especially among closely related species.
  • Genetic distance plays a role in F1 sterility and F2 infectivity.
  • Premating barriers are likely sufficient to initiate divergence in this fungal system.

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