title: Ecotype diversity in the marine picoeukaryote Ostreococcus (Chlorophyta, Prasinophyceae).
abstract: The importance of the cyanobacteria Prochlorococcus and Synechococcus in marine ecosystems in terms of abundance and primary production can be partially explained by ecotypic differentiation. Despite the dominance of eukaryotes within photosynthetic picoplankton in many areas a similar differentiation has never been evidenced for these organisms. Here we report distinct genetic [rDNA 18S and internal transcribed spacer (ITS) sequencing], karyotypic (pulsed-field gel electrophoresis), phenotypic (pigment composition) and physiological (light-limited growth rates) traits in 12 Ostreococcus strains (Prasinophyceae) isolated from various marine environments and depths, which suggest that the concept of ecotype could also be valid for eukaryotes. Internal transcribed spacer phylogeny grouped together four deep strains isolated between 90 m and 120 m depth from different geographical origins. Three deep strains displayed larger chromosomal bands, different chromosome hybridization patterns, and an additional chlorophyll (chl) c-like pigment. Furthermore, growth rates of deep strains show severe photo-inhibition at high light intensities, while surface strains do not grow at the lowest light intensities. These features strongly suggest distinct adaptation to environmental conditions encountered at surface and the bottom of the oceanic euphotic zone, reminiscent of that described in prokaryotes.
authors.affiliation: Station Biologique, UMR 7127 CNRS/INSU/UPMC, BP 74, 29682 Roscoff, France.
authors.forename: Francisco
authors.initials: F
authors.lastname: Rodríguez
authors.forename: Evelyne
authors.initials: E
authors.lastname: Derelle
authors.forename: Laure
authors.initials: L
authors.lastname: Guillou
authors.forename: Florence
authors.initials: F
authors.lastname: Le Gall
authors.forename: Daniel
authors.initials: D
authors.lastname: Vaulot
authors.forename: Hervé
authors.initials: H
authors.lastname: Moreau
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D000460:Chlorophyta / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D021903:DNA, Ribosomal Spacer / Q000032:analysis / Q000235:genetics*; D017753:Ecosystem; D014644:Genetic Variation / Q000235:genetics; D008027:Light; D008386:Marine Biology; D010860:Pigments, Biological / Q000502:physiology; D017422:Sequence Analysis, DNA
chemical_list: D021903:DNA, Ribosomal Spacer; D010860:Pigments, Biological; D002734:Chlorophyll