title: Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores.
abstract: The coccolithophore family Noëlaerhabdaceae contains a number of taxa that are very abundant in modern oceans, including the cosmopolitan bloom-forming Emiliania huxleyi. Introgressive hybridization has been suggested to account for incongruences between nuclear, mitochondrial and plastidial phylogenies of morphospecies within this lineage, but the number of species cultured to date remains rather limited. Here, we present the characterization of 5 new Noëlaerhabdaceae culture strains isolated from samples collected in the south-east Pacific Ocean. These were analyzed morphologically using scanning electron microscopy and phylogenetically by sequencing 5 marker genes (nuclear 18S and 28S rDNA, plastidial tufA, and mitochondrial cox1 and cox3 genes). Morphologically, one of these strains corresponded to Gephyrocapsa ericsonii and the four others to Reticulofenestra parvula. Ribosomal gene sequences were near identical between these new strains, but divergent from G. oceanica, G. muellerae, and E. huxleyi. In contrast to the clear distinction in ribosomal phylogenies, sequences from other genomic compartments clustered with those of E. huxleyi strains with which they share an ecological range (i.e., warm temperate to tropical waters). These data provide strong support for the hypothesis of past (and potentially ongoing) introgressive hybridization within this ecologically important lineage and for the transfer of R. parvula to Gephyrocapsa. These results have important implications for understanding the role of hybridization in speciation in vast ocean meta-populations of phytoplankton.
authors.affiliation: Marine Biological Association of the UK Plymouth, UK.
authors.forename: El Mahdi
authors.initials: el M
authors.lastname: Bendif
authors.affiliation: Université Pierre et Marie Curie (Paris VI), Roscoff Culture Collection, Station Biologique de RoscoffRoscoff, France; Centre National de la Recherche Scientifique, FR2424, Station Biologique de RoscoffRoscoff, France.
authors.forename: Ian
authors.initials: I
authors.lastname: Probert
authors.affiliation: Facultad de Ciencias Biológicas, Pontificia Universidad Católica de ChileSantiago, Chile; Instituto Milenio de OceanografíaConcepcion, Chile; UMI 3614, Evolutionary Biology and Ecology of Algae, Centre National de la Recherche Scientifique-UPMC Sorbonne Universités, PUCCh, UACH, Station Biologique de RoscoffRoscoff, France.
authors.forename: Francisco
authors.initials: F
authors.lastname: Díaz-Rosas
authors.affiliation: Facultad de Ciencias Biológicas, Pontificia Universidad Católica de ChileSantiago, Chile; Instituto Milenio de OceanografíaConcepcion, Chile; UMI 3614, Evolutionary Biology and Ecology of Algae, Centre National de la Recherche Scientifique-UPMC Sorbonne Universités, PUCCh, UACH, Station Biologique de RoscoffRoscoff, France.
authors.forename: Daniela
authors.initials: D
authors.lastname: Thomas
authors.affiliation: Center for Marine Cytometry Concrete, WA, USA.
authors.forename: Ger
authors.initials: G
authors.lastname: van den Engh
authors.affiliation: Departments of Earth Sciences, University College London London, UK.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Young
authors.affiliation: Facultad de Ciencias Biológicas, Pontificia Universidad Católica de ChileSantiago, Chile; Instituto Milenio de OceanografíaConcepcion, Chile; UMI 3614, Evolutionary Biology and Ecology of Algae, Centre National de la Recherche Scientifique-UPMC Sorbonne Universités, PUCCh, UACH, Station Biologique de RoscoffRoscoff, France.
authors.forename: Peter
authors.initials: P
authors.lastname: von Dassow
keywords: Emiliania; Gephyrocapsa; Reticulofenestra; coccolithophores; cyto-nuclear discordance; diversity; evolution; introgressive hybridization