Matt P. Ashworth

Bio: Matt P. Ashworth is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Genus & Monophyly. The author has an hindex of 17, co-authored 53 publications receiving 915 citations.

A preliminary multi gene phylogeny of the diatoms (Bacillariophyta): Challenges for future research

Abstract: 1Texas Natural Science Center, 2400 Trinity Street, University of Texas, Austin TX 78619, U.S.A. 2Section of Integrative Biology, The University of Texas at Austin, 1 University Station (A6700), Austin, TX 78712, U.S.A. 3Plant Biology Graduate Program, The University of Texas at Austin, 1 University Station (A6700), Austin, TX 78712, U.S.A. 4Institute of Cellular and Molecular Biology, The University of Texas at Austin, 1 University Station (A6700), Austin, TX 78712, U.S.A. *Author for correspondence: etheriot@austin.utexas.edu

Revisiting Ross and Sims (1971): toward a molecular phylogeny of the Biddulphiaceae and Eupodiscaceae (Bacillariophyceae).

Abstract: The ocellate and pseudocellate diatoms in the Eupodiscaceae and Biddulphiaceae (respectively) are common inhabitants of the marine littoral (and plankton zone) with a rich fossil history making them important components of marine stratigraphic studies and good candidates for molecular dating work These diatoms are important for un-derstanding the phylogeny of the diatoms as a whole, as molecular phylogenies have blurred the traditional distinction between the pennate and multipolar non-pennate diatoms However, the convoluted taxonomic history of these groups has the potential to disrupt both stratigraphic and molecular dating studies Although efforts have been made to examine frustule morphology of several ocellate and pseudocellate diatoms and develop a morphological scheme to define genera, very little work has been done to determine how these groups are interrelated In this study, we use nuclear and chloroplast molecular markers to construct a phylogeny of a diverse sampling of Eupodiscaceae and Biddulphiaceae taxa The ocellus-bearing taxa (Eupodiscaceae) are monophyletic, and thus the ocellus may be a useful character in delimiting the Eupodiscaceae, the Biddulphiaceae are polyphyletic and scattered across a number of lineages of multipolar non-pennate diatoms Hypothesis testing aimed at assessing the likeliness of several morphology based hypotheses against the molecular data highlights uncertainty in both types of data We present evidence that there are monophyletic genera within both the Biddulphiaceae and Eupodiscaceae, and recommend the taxa within the Odontella mobilensis/sinensis/regia clade be transferred to a new genus: Trieres Ashworth & Theriot

A revision of the genus Cyclophora and description of Astrosyne gen. nov. (Bacillariophyta), two genera with the pyrenoids contained within pseudosepta

Abstract: Ashworth M.P., Ruck E.C., Lobban C.S., Romanovicz D.K., and Theriot E.C. 2012. A revision of the genus Cyclophora and description of Astrosyne gen. nov. (Bacillariophyta), two genera with the pyrenoids contained within pseudosepta. Phycologia 51: 684–699. DOI: 10.2216/12-004.1 The araphid pennate diatom genus Cyclophora is characterized by an elliptical to circular pseudoseptum at the centre of one valve; C. tenuis is the only commonly reported species. New species have included some with pseudosepta on both valves, and we emended the generic description to accommodate these. Three species of Cyclophora were described from light and scanning electron microscopy: C. castracanei sp. nov., C. tabellariformis sp. nov. and C. minor sp. nov. Of these, C. castracanei was isovalvar with a pseudoseptum on both valves; C. tabellariformis was heterovalvar but differed in shape from the type species; and C. minor was very small and had both iso- and heterovalvar frustules. Other differences included stria density and...

Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes

Abstract: This revision of the classification of eukaryotes follows that of Adl et al., 2012 [J. Euk. Microbiol. 59(5)] and retains an emphasis on protists. Changes since have improved the resolution of many ...

Phylogeny and Molecular Evolution of the Green Algae

Abstract: The green lineage (Viridiplantae) comprises the green algae and their descendants the land plants, and is one of the major groups of oxygenic photosynthetic eukaryotes. Current hypotheses posit the early divergence of two discrete clades from an ancestral green flagellate. One clade, the Chlorophyta, comprises the early diverging prasinophytes, which gave rise to the core chlorophytes. The other clade, the Streptophyta, includes the charophyte green algae from which the land plants evolved. Multi-marker and genome scale phylogenetic studies have greatly improved our understanding of broad-scale relationships of the green lineage, yet many questions persist, including the branching orders of the prasinophyte lineages, the relationships among core chlorophyte clades (Chlorodendrophyceae, Ulvophyceae, Trebouxiophyceae and Chlorophyceae), and the relationships among the streptophytes. Current phylogenetic hypotheses provide an evolutionary framework for molecular evolutionary studies and comparative genomics. This review summarizes our current understanding of organelle genome evolution in the green algae, genomic insights into the ecology of oceanic picoplanktonic prasinophytes, molecular mechanisms underlying the evolution of complexity in volvocine green algae, and the evolution of genetic codes and the translational apparatus in green seaweeds. Finally, we discuss molecular evolution in the streptophyte lineage, emphasizing the genetic facilitation of land plant origins.

The timescale of early land plant evolution

Abstract: Establishing the timescale of early land plant evolution is essential for testing hypotheses on the coevolution of land plants and Earth's System. The sparseness of early land plant megafossils and stratigraphic controls on their distribution make the fossil record an unreliable guide, leaving only the molecular clock. However, the application of molecular clock methodology is challenged by the current impasse in attempts to resolve the evolutionary relationships among the living bryophytes and tracheophytes. Here, we establish a timescale for early land plant evolution that integrates over topological uncertainty by exploring the impact of competing hypotheses on bryophyte-tracheophyte relationships, among other variables, on divergence time estimation. We codify 37 fossil calibrations for Viridiplantae following best practice. We apply these calibrations in a Bayesian relaxed molecular clock analysis of a phylogenomic dataset encompassing the diversity of Embryophyta and their relatives within Viridiplantae. Topology and dataset sizes have little impact on age estimates, with greater differences among alternative clock models and calibration strategies. For all analyses, a Cambrian origin of Embryophyta is recovered with highest probability. The estimated ages for crown tracheophytes range from Late Ordovician to late Silurian. This timescale implies an early establishment of terrestrial ecosystems by land plants that is in close accord with recent estimates for the origin of terrestrial animal lineages. Biogeochemical models that are constrained by the fossil record of early land plants, or attempt to explain their impact, must consider the implications of a much earlier, middle Cambrian-Early Ordovician, origin.