title: Chromosome number evolution in Hymenophyllum (Hymenophyllaceae), with special reference to the subgenus Hymenophyllum.
abstract: With about 100 species distributed worldwide, Hymenophyllum subg. Hymenophyllum is the largest subgenus of filmy ferns. It also displays morphological disparity and extreme chromosome numbers variation, with n=11, 12, 13, 14, 18, 21, 22, 26, 28, and 34. We use DNA sequences from the genes rbcL, part of accD, rps4, and the intergenic spacers rbcL-accD, rps4-trnS, and trnG-trnR to infer relationships within Hymenophyllum, with a focus on this subgenus. In the subgenus Hymenophyllum, two main clades are retrieved together with several minor clades whose placement within the subgenus remains ambiguous. We then investigate the evolution of chromosome numbers in the genus and the subgenus, using a maximum likelihood approach taking into account phylogenetic uncertainty. We provide evidence that Hymenophyllum experienced descending aneuploidy during its evolutionary history, especially within the subgenus Hymenophyllum. Reduction in chromosome numbers is particularly extreme in one clade of the subgenus, with the lowest number reported for homosporous ferns. In addition, this group of species displays a high instability in its chromosome number. Both the reduction and the instability in chromosome number may coincide with the distribution of these species in either temperate areas or at high elevations.
authors.affiliation: Department of Botany, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. Electronic address: shennequ@snv.jussieu.fr.
authors.forename: Sabine
authors.initials: S
authors.lastname: Hennequin
authors.affiliation: Department of Botany, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba 305-0005, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ebihara
authors.affiliation: UMR 7207 CNRS MNHN UPMC, "Centre de recherche sur la paléobiodiversité et les paléoenvironnements", Bâtiment de Géologie CP 48, 43 rue Buffon, 75005 Paris, France.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Dubuisson
authors.affiliation: Department of Botany, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Harald
authors.initials: H
authors.lastname: Schneider
mesh_terms: D000782:Aneuploidy; D032461:Chromosomes, Plant; D018744:DNA, Plant / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D019143:Evolution, Molecular; D029624:Ferns / Q000145:classification / Q000235:genetics*; D016013:Likelihood Functions; D010802:Phylogeny; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer