ABSTRACT
In fungi, gametes are expressed as mating types and sexuality as homo- and hetero-thallisms. In the 23,975 species Basidiomycota, complementary mating types are formed from the same homothallic basidium followed by external fertilization. Contrastingly, female and male mating spores are generated from ascogonium and antheridium, and internal fertilization is accomplished in the 77,083 speciose pezizomycotines. The combination of heterothallism and safer internal fertilization accelerates species diversity but that of homothallism and risky external fertilization decelerates it. To neutralize the potential loss of spores, the basidiomycotes generate billions of them but pezizomycotines a few millions only. Based on the potential cost of bringing the ‘gametes’ together, five modes of fusion are recognized. Of them, the diversity decreases from zoosporic fusion in 2.9% (2,603 species) aquatic fungi to 3.2% (2,854 species) yeast conjugation in a few parasitic pucciniomycetes, 15.8% (14,178) hyphal conjugation in Agaricomycetes and Zygomycota 31.3% (28,141 species), 46.9% (42,133 species) spermatization involving the internal male spore penetrating oogonium followed by aerial dispersal. The last one is cheaper than in lower fungi and basidiomycetes. In conjugation, the ‘gametes’ are grown toward each other at a higher cost.
