title: Morphological and Phylogenetic Characterization of New Gephyrocapsa Isolates Suggests Introgressive Hybridization in the Emiliania/Gephyrocapsa Complex (Haptophyta).
abstract: The coccolithophore genus Gephyrocapsa contains a cosmopolitan assemblage of pelagic species, including the bloom-forming Gephyrocapsa oceanica, and is closely related to the emblematic coccolithophore Emiliania huxleyi within the Noëlaerhabdaceae. These two species have been extensively studied and are well represented in culture collections, whereas cultures of other species of this family are lacking. We report on three new strains of Gephyrocapsa isolated into culture from samples from the Chilean coastal upwelling zone using a novel flow cytometric single-cell sorting technique. The strains were characterized by morphological analysis using scanning electron microscopy and phylogenetic analysis of 6 genes (nuclear 18S and 28S rDNA, plastidial 16S and tufA, and mitochondrial cox1 and cox3 genes). Morphometric features of the coccoliths indicate that these isolates are distinct from G. oceanica and best correspond to G. muellerae. Surprisingly, both plastidial and mitochondrial gene phylogenies placed these strains within the E. huxleyi clade and well separated from G. oceanica isolates, making Emiliania appear polyphyletic. The only nuclear sequence difference, 1bp in the 28S rDNA region, also grouped E. huxleyi with the new Gephyrocapsa isolates and apart from G. oceanica. Specifically, the G. muellerae morphotype strains clustered with the mitochondrial β clade of E. huxleyi, which, like G. muellerae, has been associated with cold (temperate and sub-polar) waters. Among putative evolutionary scenarios that could explain these results we discuss the possibility that E. huxleyi is not a valid taxonomic unit, or, alternatively the possibility of past hybridization and introgression between each E. huxleyi clade and older Gephyrocapsa clades. In either case, the results support the transfer of Emiliania to Gephyrocapsa. These results have important implications for relating morphological species concepts to ecological and evolutionary units of diversity.
authors.affiliation: Marine Biological Association of the UK, Plymouth, UK. Electronic address: elmben@mba.ac.uk.
authors.forename: El Mahdi
authors.initials: el M
authors.lastname: Bendif
authors.affiliation: Université Pierre et Marie Curie (Paris VI), Station Biologique de Roscoff, Roscoff, France; Centre National de la Recherche Scientifique, FR2424, Roscoff Culture Collection, Station Biologique de Roscoff, Roscoff, France.
authors.forename: Ian
authors.initials: I
authors.lastname: Probert
authors.affiliation: Department of Earth Sciences, University College London, Gower St., London, UK.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Young
authors.affiliation: Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile; UMI 3614, Evolutionary Biology and Ecology of Algae, CNRS-UPMC Sorbonne Universités, PUCCh, UACH, Station Biologique de Roscoff, Roscoff, France; Instituto Milenio de Oceanografía, Chile.
authors.forename: Peter
authors.initials: P
authors.lastname: von Dassow
mesh_terms: D044822:Biodiversity; D002677:Chile; D017125:Genes, Protozoan / Q000235:genetics; D058087:Haptophyta / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure*; D010140:Pacific Ocean; D010802:Phylogeny; D013045:Species Specificity
keywords: Coccolithophores; Emiliania huxleyi; Gephyrocapsa muellerae; Gephyrocapsa oceanica; hybridization; phylogeny.; species concept