title: Evolutionary processes and cellular functions underlying divergence in Alexandrium minutum.
abstract: Understanding divergence in the highly dispersive and seemingly homogeneous pelagic environment for organisms living as free drifters in the water column remains a challenge. Here, we analysed the transcriptome-wide mRNA sequences, as well as the morphology of 18 strains of Alexandrium minutum, a dinoflagellate responsible for harmful algal blooms worldwide, to investigate the functional bases of a divergence event. Analysis of the joint site frequency spectrum (JSFS) pointed towards an ancestral divergence in complete isolations followed by a secondary contact resulting in gene flow between the two diverging groups, but heterogeneous across sites. The sites displaying fixed SNPs were associated with a highly restricted gene flow and a strong overrepresentation of nonsynonymous polymorphism, suggesting the importance of selective pressures as drivers of the divergence. The most divergent transcripts were homologs to genes involved in calcium/potassium fluxes across the membrane, calcium transduction signal and saxitoxin production. The implication of these results in terms of ecological divergence and build-up of reproductive isolation is discussed. Dinoflagellates are especially difficult to study in the field at the ecological level due to their small size and the dynamic nature of their natural environment, but also at the genomic level due to their huge and complex genome and the absence of closely related model organism. This study illustrates the possibility to identify the traits of primary importance in ecology and evolution starting from high-throughput sequencing data, even for such organisms.
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France. Mickael.Le.Gac@ifremer.fr.
authors.forename: Mickael
authors.initials: M
authors.lastname: Le Gac
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France.|CNRS, PUCCh, UACH, UMI 3614, Evolutionary Biology and Ecology of Algae, Station Biologique de Roscoff, Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Place Georges Teissier, CS90074, 29688, Roscoff Cedex, France.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Metegnier
authors.affiliation: Station de Biologie Marine, IFREMER, 29900, Concarneau, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Chomérat
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France.
authors.forename: Pascale
authors.initials: P
authors.lastname: Malestroit
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Quéré
authors.affiliation: GeT PlaGe, Genotoul, INRA Auzeville, Castanet Tolosan, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Bouchez
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Siano
authors.affiliation: CNRS, PUCCh, UACH, UMI 3614, Evolutionary Biology and Ecology of Algae, Station Biologique de Roscoff, Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Place Georges Teissier, CS90074, 29688, Roscoff Cedex, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Destombe
authors.affiliation: CNRS, UMR 7144, Station Biologique de Roscoff, Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Place Georges Teissier CS90074, 29688, Roscoff Cedex, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Guillou
authors.affiliation: Ifremer, DYNECO PELAGOS, 29280, Plouzané, France.
authors.forename: Annie
authors.initials: A
authors.lastname: Chapelle
mesh_terms: D004141:Dinoflagellida / Q000235:genetics*; D019143:Evolution, Molecular; D051456:Gene Flow; D014644:Genetic Variation; D008957:Models, Genetic; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000235:genetics; D060047:Reproductive Isolation; D012641:Selection, Genetic; D059467:Transcriptome
chemical_list: D012333:RNA, Messenger
keywords: Dinoflagellates; Populations Genomics; Pseudocryptic species; harmful algal blooms; speciation