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Ploidy level and genome size variation in the homosporous ferns Botrychium s.l. (Ophioglossaceae)

Abstract

Recent cytological and molecular studies have investigated genome size variation and evolution in the homosporous ferns, but representatives of the Ophioglossaceae were largely overlooked, despite their evolutionary singularity. Flow cytometry analysis was performed on 41 individuals of eight species of the genera Botrychium (B.), Botrypus, and Sceptridium to estimate their ploidy level variation. In a subset of individuals, we also estimated the absolute genome size and corresponding C values. Additionally, a classical chromosome count was made on the recently described species B. alaskense. Ploidy level and new genome size records were determined for Botrychium alaskense, B. boreale, B. lanceolatum, B. “neolunaria” ined., B. pinnatum, Botrypus virginianus and Sceptridium multifidum. In addition, we confirmed the genome size of B. matricariifolium, B. minganense and B. lunaria. Two of the three major sub-clades of Botrychium differ slightly in their averaged homoploid genome size (subclade Lanceolatum, 24.72 ± 0.40 pg; subclade Lunaria, 27.51 ± 0.47 pg). Flow cytometry and chromosome counting confirmed that B. alaskense is a tetraploid. A new hexaploid cytotype, putatively formed through an autopolyploidization from the sympatric tetraploid cytotype, was detected in a single individual of B. boreale. This is only the second report of hexaploidy in the genus Botrychium and our data highlight the potential to find other ploidy levels within other Botrychium species. Interestingly, no difference within the monoploid genome sizes was detected between ploidy levels, thus supporting the hypothesis of genome size stability after polyploidization and rejecting the scenario of genome downsizing.

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Acknowledgments

This work was supported by the Fonds Marguerite Wüthrich and A. Matthey-Dupraz at the Université de Neuchâtel, the Fonds Dr. Joachim de Giacomi of the Swiss Academy of Natural Sciences, the Bourse de voyages of the Swiss Academy of Natural Sciences, and the Fonds de donations of the Université de Neuchâtel. The authors thank Lennart Stenberg for assistance with fieldwork in Sweden, and Anne-Catherine Pasche and Philippe Küpfer for help with laboratory work.

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Correspondence to Benjamin Dauphin.

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B. Dauphin received research Grants from the Fonds Marguerite Wüthrich and A. Matthey-Dupraz at the Université de Neuchâtel, the Fonds Dr. Joachim de Giacomi of the Swiss Academy of Natural Sciences, the Bourse de voyages of the Swiss Academy of Natural Sciences, and the Fonds de donations of the Université de Neuchâtel.

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The authors declare that they have no conflict of interest.

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Handling editor: Karol Marhold.

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Dauphin, B., Grant, J. & Mráz, P. Ploidy level and genome size variation in the homosporous ferns Botrychium s.l. (Ophioglossaceae). Plant Syst Evol 302, 575–584 (2016). https://doi.org/10.1007/s00606-016-1285-7

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Keywords

  • Botrychium
  • Chromosome
  • Homosporous ferns
  • Flow cytometry
  • Genome size
  • Polyploidy