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) and homothallism (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-and heterothallism can be stable, although this has not yet been found in Sordariaceae in nature.

DNA Sequence Characterization and Molecular Evolution of MAT1 and MAT2 Mating-Type Loci of the Self-Compatible Ascomycete Mold Neosartorya fischeri

“…Theoretically, there is more support for the transition from heterothallism to homothallism among a fungal population (29,30) and for a general unidirectional breeding system shift from obligate outcrossing to partial or predominant self-fertilization (20,28). In the subsection Fumigati, there are nearly 20 additional species with a described sexual cycle, 3 of which are functionally heterothallic while the rest are homothallic.…”

Mating System of the Anther Smut Fungus Microbotryum violaceum : Selfing under Heterothallism

“…The phenomenon was first observed because of the inability to isolate sporidia of one of the two mating types from certain strains of the pathogen (38,63,87,100). This mating-type bias was investigated for a number of possible causes, including spore killers and meiotic drive (83). However, inheritance in experimental crosses showed that the observed mating-type bias does not result from the presence of segregation distorters, but from the exposure of lethal recessive alleles leading to nonviable haploids (87).…”

Cyclical dynamics under constant selection against mutations in haploid and diploid populations with facultative selfing

“…Diploid selfing is common in flowering plants (Charlesworth & Charlesworth, 1987) and in conifers (Sorensen, 1973 ;Sakai et al, 1989;Å gren & Willson, 1991 ;Hitchcock & Cronquist, 1984;Godfrey & Wooten, 1981). Haploid selfing occurs in homosporous ferns (McCauley et al, 1985 ;Soltis & Soltis, 1987) and filamentous ascomycetes (Nauta & Hoekstra, 1992) owing to fusion of gametes produced by the same haploid gametophyte. If selection occurs during the haploid phase, haploid selfing leads to the same population-level consequences as haploid apomixis.…”