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Schmickl, Roswitha [1], Oberlander, Kenneth [2], Zeisek, Vojtěch [1], Liston, Aaron [3], Schneeweiss, Hanna [4], Záveská, Eliška [5], Emshwiller, Eve [6], Dreyer, Leanne [7], Suda, Jan [2].

Massive polyploidization but no obvious role for polyploids in the radiation of southern African Oxalis L.: insights from phylogenomics and cytogenetics.

Every extant angiosperm species has undergone multiple rounds of whole genome duplication (WGD), which implies a major role for polyploidy in the evolutionary history of the clade. Paradoxically, recently originated polyploids seem to have lower diversification rates compared to their diploid congeners. The flora of the extremely diverse Greater Cape Floristic Region (Cape) in southern Africa is particularly polyploid-poor compared to non-Cape floras. An exception is the species-rich eudicot genus Oxalis, a lineage of extraordinary vegetative diversity and karyological complexity. The southern African (SoA) Oxalis lineage accounts for nearly half the species diversity (230 spp.) of the genus and is thus a prime candidate to address the following questions: What is the frequency of WGDs in SoA Oxalis? Are the polyploids of relatively recent origin? How have WGDs influenced the radiation of SoA Oxalis? We answered these questions based on a phylogenomic hypothesis using a targeted sequence capture approach involving >1100 genes and flow cytometric data for >2200 accessions of 122 SoA Oxalis species. We first tested if phylogenetic relationships were indeed tree-like rather than reticulate and then modeled chromosome number evolution and addressed ploidy-associated diversification rate shifts on reconstructed phylogenetic trees. WGD in SoA Oxalis is rife, with ca. 53% of sampled species containing polyploids. Despite this, we find very little evidence for allopolyploidy, almost all sampled species contain diploids, reconstructed WGD events occur almost entirely along the tips of the tree, and polyploids are almost always inferred to have lower diversification rates than diploids. Consequently, despite being present in over half of present-day species, polyploids have played a remarkably small role in the evolution of SoA Oxalis. More generally, SoA Oxalis fits in well in a polyploid-poor Cape flora and our findings agree with hypotheses considering WGD to be mostly an evolutionary dead end.

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1 - The Czech Academy of Sciences, Institute of Botany, Zámek 1, Průhonice, 252 43, Czech Republic
2 - Charles University, Faculty of Science, Department of Botany, Benátská 2, Prague, 12800, Czech Republic
3 - Oregon State Univ, Department Of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, United States
4 - University of Vienna, Department of Botany and Biodiversity Research, Rennweg 14, Vienna, 1030, Austria
5 - University of Innsbruck, Department of Botany, Sternwartestraße 15, Innsbruck, 6020, Austria
6 - University of Wisconsin-Madison, Department of Botany, 321 Birge Hall, Madison, WI, 53706, United States
7 - Stellenbosch University, Botany And Zoology, Private Bag X1, Matieland, Stellenbosch, 7600, South Africa

whole genome duplication
Greater Cape Floristic Region.

Presentation Type: Oral Paper
Session: 1, Phylogenomics I
Location: 114/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 9:15 AM
Number: 1006
Abstract ID:239
Candidate for Awards:None

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