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Interpreting fossils of fly-speck fungi using comparative anatomy and phylogenetics

University of British Columbia

Critical interpretations of fossil fungi combined with phylogenies of living species have the potential to reveal patterns of character evolution and to inform estimates of the geological timing of fungal radiations. Some of the best fungal fossils are of thyriothecia, formed by fly-speck fungi. A thyriothecium is a minute fungal sporulating structure, with a flat scutellum and a shield-like upper surface. Scutella have distinctive cell patterns that are formed by a sequence of hyphal branching and septation. However, for thyriothecial species, phylogenies from DNA sequence data and illustrations of scutella remain have been limited. In Chapter 2, I present a comprehensive phylogeny of thyriothecial Dothideomycetes based on 4251 nucelotides for 320 taxa, contributing new nuclear rDNA sequence data for 14 thyriothecial fungi. I code character states for taxa including 60 thyriothecial species and then estimate ancestral character states using the Bayesian posterior distribution of topologies from my dataset to account for phylogenetic uncertainty. Radiate thyriothecia are only found in Class Dothideomycetes, where they seem to have evolved independently at least three times. In Chapters 3, 4 and 5, I describe new species of Cretaceous scutellum fossils. Scutella can be abundant on fossilized leaf cuticles and are well documented in deposits of Eocene age and younger (<45 Ma). To better sample earlier fossils, I studied thyriothecia from clays from Early Cretaceous Dutch Gap Canal beds (dated 125–113 Ma). I dissolved the inorganic matrix and selected organic, fossilized fragments of plant cuticle showing signs of fungal colonization. Of hundreds of fungal reproductive structures on 281 cuticle fragments, I describe thyriothecia that were preserved well enough to be coded for their characters. Chapter 3 describes Protographum luttrellii, a fossil that shares characters with extant Aulographaceae. Chapters 4 and 5 describe thyriothecial taxa with character combinations not seen in extant species. The most common Cretaceous thyriothecia differ substantially from their extant relatives. My work demonstrates that it is possible to extend fossil evidence of lineages of Dothideomycetes further back in time, by surveying fungi on fossilized plant cuticles and integrating comparative anatomy and phylogeny in their interpretation.

Text

2020-01-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73153

Botany

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/