Convergent evolution of highly reduced fruiting bodies in Pezizomycotina suggests key adaptations to the bee habitat

Background: Among the understudied fungi found in nature are those living in close association with social and solitary bees. The bee-specialist genera Bettsia, Ascosphaera and Eremascus are remarkable not only for their specialized niche but also for their simple fruiting bodies or ascocarps, which are morphologically anomalous in Pezizomycotina. Bettsia and Ascosphaera are characterized by a unicellular cyst-like cleistothecium known as a spore cyst, while Eremascus is characterized by completely naked asci, or asci not formed within a protective ascocarp. Before molecular phylogenetics the placement of these genera within Pezizomycotina remained tentative; morphological characters were misleading because they do not produce multicellular ascocarps, a defining character of Pezizomycotina. Because of their unique fruiting bodies, the close relationship of these bee-specialist fungi and their monophyly appeared certain. However, recent molecular studies have shown that Bettsia is not cl...