<P> Homothallic species may likely have evolved from heterothallic ancestors (Lin and Heitman 2007). In Basidiomycota homothallism is not very common and in Agaricomycotina it is estimated that only 10% of species have homothallic mating behavior . For example, one subspecies of the ectomycorrhizal Basidiomycete Sistotrema brinkmannii is homothallic, although other subspecies have maintained their ability to outcross . Also, a variety of the edible mushroom Agaricus bisporus, (A. bisporus var . eurotetrasporus) produces haploid self - fertile basidiospores . Additionally, in the human pathogen C. neoformans known to outcross under laboratory conditions, both mating types are not normally distributed in natural populations, with the α mating type much more commonly found (> 99%), suggesting homothallism is the most prevalent mode of sexual reproduction in _́ C. neoformans in nature . Finally, the fungus causing witches' broom in cacao, Moniliophthora perniciosa, has a primarily homothallic biology despite having A and B mating type - like genes in its genome . </P> <P> Among the 250 known species of aspergilli, about 36% have an identified sexual state Among those Aspergillus species that exhibit a sexual cycle the overwhelming majority in nature are homothallic (self - fertilizing). Selfing in the homothallic fungus Aspergillus nidulans involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self - fertilization does not bypass required pathways for outcrossing sex but instead requires activation of these pathways within a single individual . Fusion of haploid nuclei occurs within reproductive structures termed cleistothecia, in which the diploid zygote undergoes meiotic divisions to yield haploid ascospores . </P>

Why is it important that the mating hyphae are of different organisms