Phylogeny of Laboulbeniales (Ascomycetes)

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9615520 Blackwell The taxonomic order Laboulbeniales includes minute fungi that are obligate ectoparasites on a variety of arthropod hosts. Their bizarre morphology and interesting ecological relationships make them fascinating subjects for evolutionary investigation. Although known in a general sense to mycologists and entomologists, these remarkable ascomycetes have attracted little sustained study, and the taxonomic classification of the c. 2,000 named species is unstable. As a group, the Laboulbeniales are characterized by the absence of the tubular threads (mycelia) typical of the bodies of most fungi, but instead possess few-celled bodies that are initiated by division of the sexual spores, followed by haustoria that grow through the arthropod host cuticle to obtain nutrients. Because they are dispersed through host contact, often during mating, species of Laboulbeniales often have processes and structures that may act as triggers for spore discharge. So unusual is the morphology of this group of fungi that they were once proposed as parasitic descendants of the red algae. The intriguing features of their life cycle provide many morphological characters for phylogenetic analysis, but no such explicit study has yet been undertaken. The current study draws upon Prof. Meredith Blackwell's previous work with putatively related ascomycete fungi with more typical morphology and with life cycles that include parasitic stages on both other fungi and arthropods. The phylogenetic work will include studies of morphological features, of life history stages, and of nucleotide sequence diversity in nuclear ribosomal DNA as a source of characters for taxonomic resolution and genealogical reconstruction. A phylogenetic framework for the genera and families of the order, with consequent improvement in classification, is one major goal. Another goal is to explore hypotheses of host-shifting and speciation among groups of Laboulbeniales on different arthropod hosts.