Thomas Marcussen

Thomas Marcussen
University of Oslo · Centre for Ecological and Evolutionary Synthesis

Dr.

About

83
Publications
37,736
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1,639
Citations
Introduction
Interests: Inference of species phylogenies, especially homoploid and polyploid phylogenetic networks, from gene phylogenies under the multispecies coalescent (MSC), ancestral state reconstruction, phylogenetic dating techniques. Research: Taxonomy, evolution of Viola (Violaceae), Geranium (Geraniaceae) and grasses (Poaceae).
Additional affiliations
April 2015 - March 2017
Norwegian University of Life Sciences (NMBU)
Position
  • PostDoc Position
April 2014 - present
Norwegian University of Life Sciences (NMBU)
Position
  • PostDoc Position
Description
  • Origin and evolution of flowering response and 'temperate' traits in Pooideae.
May 2013 - July 2013
Norwegian University of Life Sciences (NMBU)
Position
  • Researcher
Description
  • Inference of ancient homoploid hybrid speciations in the wheat lineage, using multilocus phylogenetic data under the multispecies coalescent.

Questions

Questions (5)
Question
Style shape is a highly important character for identifying species groups within Viola. The published descriptions of the style of the New Zealand endemic V. filicaulis are however insufficient. To give an idea of what I am after, the resolution of the style in the images below is insufficient. I would also need closeups from different angles, preferably from dissected flowers:
I'd be most grateful if someone had good images to share.
Thanks,
Thomas
Question
Hi all,
Does anyone here know where to obtain estimates of paleo land areas for continents? I need data for the Cretaceous-Paleogene boundary and/or early Paleocene for each continent individually. While paleomaps are relatively easy to come by I haven't been able to find estimates for land areas although I assume such estimates exist.
Cheers,
Thomas
Question
Dear all,
I would greatly appreciate if any of you could help me answering the following two questions concerning angiosperm evolution:
(1) What are the oldest whole genome duplications known to have happened by allopolyploidisation?
What I am looking for is the oldest whole genome duplications where one or both parental lineages are known. From my own research on Viola (Violaceae) the oldest event is 20-25 Ma, but I am confident there are older, well-documented allopolyploidisations.
(2) What are the "widest" hybridisations known, i.e. natural hybridisations between the most distantly related parental taxa?
As far as I know, the record is held by a fern where the parents may have diverged ~60 Ma ago (Rothfels et al. 2015, https://pdfs.semanticscholar.org/996a/584749849eec145a23df224bc98967da022e.pdf). Among angiosperms I am aware of a few grasses (Ampelodesmos mauritanicus, Trikeraia pappiformis; Hochbach et al. 2015: https://www.ncbi.nlm.nih.gov/pubmed/25804934) that come close at 40-50 Ma, and Viola (that doesn't come close) at ~17 Ma (Yoshida et al. 2016: https://www.jstage.jst.go.jp/article/apg/67/2/67_201517/_pdf).
It would be interesting to clarify these questions in order to get an idea of how long lineages can exchange genes sexually.
Thanks in advance for any feedback you'd be able to give.
Thomas
Question
Hybridisation and allopolyploidy can happen between lineages that diverged a long time ago. The 'widest' hybrids that I am aware of are a fern (xCystocarpium roskamianum; Rothfels et al. 2015) and a Viola (V. rostrata × violacea; Yoshida et al. 2015) whose parental lineages diverged ~60 and 15-20 Ma ago, respectively. Similarly, the 'widest' allopolyploids that I am aware of are two grasses (Ampelodesmos mauritanicus, Trikeraia pappiformis; Hochbach et al. 2015) which may be recent and whose parental lineages may have diverged >44 Ma ago.
Does anyone here know of other, and possibly more extreme, cases?
Thanks for your help.
Thomas

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Projects

Projects (3)
Project
The most diverse group of Viola L. in South America and the one that requires extensive systematic scrutiny is subgenus Andinium (W. Becker) Marcussen. This group includes approximately 150 species that are distributed in the mountainous habitats of Argentina, Bolivia, Chile, Ecuador and Peru; one of the regions with the greatest taxonomic and morphological diversity of the genus. The species in this section are little known, some only through the type specimen, they are morphologically very similar and the diagnostic characters are imprecise and insufficient to identify and differentiate them. The objective of this project is to contribute to the systematic knowledge of subgenus Andinium to understand the composition, circumscription, evolutionary relationships, and distribution of its species, based on morphological and molecular studies in a phylogenetic and geographical context. It is also planned to clarify the phylogenetic relation with the other South American sections of Viola, taking into account that the genus originated in the Andes. In parallel, we plan to study the morphology and anatomy of pollen and other structures on extant species to provide the basis for future fossil surveys.
Project
The genus Viola was last revised by W. Becker in 1925. The goal of this ongoing project is to provide a comprehensive phylogenetic classification for Viola, with diagnostics for each infrageneric taxon (phylogeny, base chromosome numbers, ploidy, morphology), a key to these taxa, and also a global specs checklist. PRELIMINARY RESULTS: Viola comprises >625 species. Allopolyploidy limits the number and rank of possible monophyletic infrageneric taxa. We recognise two subgenera, subg. Andinium with 10 (new) sections and subg. Viola with 20 sections (Chamaemelanium, Chilenium, Danxiaviola, Delphiniopsis, Erpetion, Leptidium, Melanium, Nosphinium, Plagiostigma, Rubellium, Sclerosium, Tridens, Viola, Xylinosium, plus six new sections). Within the latter, the old, polyphyletic sect. "Nomimium" is split into five sections. New infrasectional classifications are provided for sects. Chamaemelanium, Melanium, Nosphinium, Plagiostigma, and Viola, with a total of 18 subsections. We do not recognise formal taxa below the level of subsection, as these would be non-monophyletic due to allopolyploidy.
Project
We revise the fossil record for the 32 genera of Violaceae and select fossils useful for phylogenetic dating. Chloroplast sequences, fossil calibrations, and ancestral state reconstruction for discrete biogeography and continuous climate parameters will be entered jointly in a Bayesian phylogenetic analysis.