Evolution of reproductive systems in filamentous ascomycetes. I. evolution of mating types

Abstract

In the ascomycete family of Sordariaceae both heterothallism (with two mating types) andhomo- thallism (without mating types) are common. A population genetic model is made in an attempt to find out under which conditions evolution from one system to the other is conceivable. Analysis shows that evolution from hetero- to homothallism is possible but evolution from homo- to heterothallism is improbable. As in these haploid fungi self-fertilization has other consequences than in diploid organisms, homothallism seems to have little disadvantage. It is found that polymorphism in homo- andheterothallism can be stable, although this has not yet been found in Sordariaceae in nature. © 1992 The Genetical Society of Great Britain.