Loss of meiosis in Aspergillus

If strictly mitotic asexual fungi lack recombination, the conventional viewpredicts that they are recent derivatives from older meiotic lineages. Wetested this by inferring phylogenetic relationships among closely relatedmeiotic and strictly mitotic taxa with Aspergillus conidial (mitotic)states. Phylogenies were constructed by using DNA sequences from themitochondrial small ribosomal subunit, the nuclear ribosomal internaltranscribed spacers, and the nuclear 5.8S ribosomal gene. Over 920 bp ofsequence was analyzed for each taxon. Phylogenetic analysis of both themitochondrial and nuclear data sets showed at least four clades thatpossess both meiotic and strictly mitotic taxa. These results support thehypothesis that strictly mitotic lineages arise frequently from moreancient meiotic lineages with Aspergillus conidial states. Many of thestrictly mitotic species examined retained characters that may be vestigesof a meiotic state, including the production of sclerotia, sclerotium-likestructures, and hulle cells.