title: A well-sampled phylogenetic analysis of the polystichoid ferns (Dryopteridaceae) suggests a complex biogeographical history involving both boreotropical migrations and recent transoceanic dispersals.
abstract: Intercontinental disjunctions in ferns have often been considered as the result of long-distance dispersal (LDD) events rather than of vicariance. However, in many leptosporangiate groups, both processes appear to have played a major role in shaping current geographical distribution. In this study, we reconstructed the phylogenetic relationships and inferred the ancestral distribution areas of the polystichoid ferns (Cyrtomium, Phanerophlebia, and Polystichum), to evaluate the relative impact of vicariance and LDD on the biogeography of this group. We used a molecular dataset including 3346 characters from five plastid loci. With 190 accessions our taxon coverage was about three times as large as any previous worldwide sampling. Biogeographical analyses were performed using S-DIVA and S-DEC and divergence times were estimated by integrating fossil and secondary calibrations. The polystichoid ferns are a monophyletic clade that may have originated in East Asia during the Eocene, an age much younger than previously estimated. Three transoceanic disjunctions between East Asia and New World were identified in the Paleogene: one for Phanerophlebia during late Eocene (34Ma, 19-51Ma), and two in Polystichum at the Eocene-Oligocene boundary (30Ma, 18-43Ma; 28Ma, 19-39Ma respectively). During the Neogene, further range expansions took place from Asia to Africa, Hawaii, and the Southwestern Indian Ocean region. Our results indicate that early transfers between the Old and the New World are compatible with a boreotropical migration scenario. After evolving in Asia during the Eocene, the polystichoid ferns reached the New World in independent migrations at the Eocene-Oligocene boundary through the boreotropical belt. However, although less likely, the alternative hypothesis of independent transoceanic dispersals from the Old to the New World cannot be ruled out. Further range expansion during the Neogene was most likely the result of long-distance dispersal (LDD).
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, Chengdu, Sichuan 610041, China; School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa. Electronic address: tlepechon@gmail.com.
authors.forename: Timothée
authors.initials: T
authors.lastname: Le Péchon
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, Chengdu, Sichuan 610041, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Biology, Chongqing Normal University, Shapingba, Chongqing 400047, China.
authors.forename: Hai
authors.initials: H
authors.lastname: He
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, Chengdu, Sichuan 610041, China.
authors.forename: Xin-Mao
authors.initials: XM
authors.lastname: Zhou
authors.affiliation: School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa.
authors.forename: Benny
authors.initials: B
authors.lastname: Bytebier
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, Chengdu, Sichuan 610041, China. Electronic address: xfgao@cib.ac.cn.
authors.forename: Xin-Fen
authors.initials: XF
authors.lastname: Gao
authors.affiliation: Missouri Botanical Garden, P.O. Box 299, S. Louis, MO 63166-0299, USA. Electronic address: Libing.Zhang@mobot.org.
authors.forename: Li-Bing
authors.initials: LB
authors.lastname: Zhang
mesh_terms: D000349:Africa; D001208:Asia; D032491:Dryopteridaceae / Q000145:classification* / Q000235:genetics*; D005580:Fossils; D006254:Hawaii; D019156:Indian Ocean; D009792:Oceans and Seas; D010802:Phylogeny; D058974:Phylogeography; D018087:Plastids / Q000235:genetics; D058614:Seed Dispersal
keywords: Ancestral ranges; Boreotropical hypothesis; Fern biogeography; Long-distance dispersal; Transoceanic disjunction; Vicariance