A Multi-Gene Molecular Systematic Study of the Kickxellomycotina, Including the Examination of Two New Genes (MCM7 and TSR1) for Phylogenetic Inference

Kickxellomycotina is a recently described subphylum of Fungi defined by the presence of a unique disciform septal pore with a lenticular plug. The relationship between members of the group has proven difficult to resolve with traditional methods due to the degree of morphological and ecological variation among taxa within the clade. Furthermore, existing phylogenetic studies have lacked either the taxonomic coverage or had insufficient phylogenetic resolution to reveal the evolutionary history of the group. In chapter one, I investigate the phylogenetic utility of two single-copy protein-coding genes, MCM7 and TSR1, to improve phylogenetic resolution within the clade. Suitable primers were developed and tested for both genes within the Kickxellomycotina and other early-diverging fungal clades. Trees produced with MCM7 and TSR1 were compared to those produced with rDNA, the gene region used in most previously published studies. MCM7 proved to have considerable phylogenetic utility within the group compared to the rDNA results, while TSR1 was found to be less useful, although still potentially valuable for resolving relationships among closely related taxa. In chapter two, I utilize eight genes (18S rDNA, 28S rDNA, 5.8S rDNA, MCM7, TSR1, RPB1, RPB2, and β-tubulin) to produce a phylogenetic tree of the Kickxellomycotina within the greater context of Fungi. The Kickxellomycotina are found to be monophyletic, with the Zoopagomycotina suggested to be their closest relatives. Eight clades were identified within the tree, including the four orders previously defined within the subphylum (Asellariales, Dimargaritales, Harpellales, and Kickxellales). Four genera (Barbatospora, Orphella, Ramicandelabler, and Spiromyces) do not cluster within the order in which they are currently placed, representing novel clades. Dimargaritales and Ramicandelaber are the first groups of Kickxellomycotina to diverge, although the relationship between the two remains unclear. The remaining six clades form a monophyletic grouping, from which Barbatospora diverges first, followed by a split that divides the group into a clade composed of Asellariales and Harpellales, and a clade composed of Kickxellales, Orphella, and Spiromyces. Ancestral character state reconstruction revealed that some characters previously thought to be isolated to single taxonomic clades, such as the endosymbiotic life history of the Asellariales and Harpellales, are instead distributed throughout the tree. This suggests that the evolutionary picture within the Kickxellomycotina is likely more complex than previously thought.