LOSS OF MEIOSIS IN ASPERGILLUS

If strictly mitotic asexual fungi lack recombination, the conventional view predicts that they are recent derivatives from older meiotic lin eages. We tested this by inferring phylogenetic relationships among cl osely related meiotic and strictly mitotic taxa with Aspergillus conid ial (mitotic) states. Phylogenies were constructed by using DNA sequen ces from the mitochondrial small ribosomal subunit, the nuclear riboso mal internal transcribed spacers, and the nuclear 5.8S ribosomal gene. Over 990 bp of sequence was analyzed for each taxon. Phylogenetic ana lysis of both the mitochondrial and nuclear data sets showed at least four clades that possess both meiotic and strictly mitotic taxa. These results support the hypothesis that strictly mitotic lineages arise f requently from more ancient meiotic lineages with Aspergillus conidial states. Many of the strictly mitotic species examined retained charac ters that may be vestiges of a meiotic state, including the production of sclerotia, sclerotium-like structures, and hulle cells.