Evolution of reproductive systems in filamentous ascomycetes. II. Evolution of hermaphroditism and other reproductive strategies.

The evolution of different reproductive systems in filamentous ascomycetes is studied in a population genetic model. These fungi differ essentially from higher plants and animals because mating types can exist in addition to male and female gametes, and the conidia serve as both male gametes and asexual spores; moreover, selfing is genetically equivalent to asexual reproduction in these haploid organisms. A variable fitness of ascospore production is predicted as the explanation for the evolution of two systems that abundantly exist in nature: hermaphroditism in heterothallic species and the formation of both asexual and sexual spores in homothallic species. Imperfect fungi will evolve if sexual spores do not show a remarkably higher fitness than asexual spores.