title: A haploid system of sex determination in the brown alga Ectocarpus sp.
abstract: BACKGROUND
  A common feature of most genetic sex-determination systems studied so far is that sex is determined by nonrecombining genomic regions, which can be of various sizes depending on the species. These regions have evolved independently and repeatedly across diverse groups. A number of such sex-determining regions (SDRs) have been studied in animals, plants, and fungi, but very little is known about the evolution of sexes in other eukaryotic lineages.
  
  
  RESULTS
  We report here the sequencing and genomic analysis of the SDR of Ectocarpus, a brown alga that has been evolving independently from plants, animals, and fungi for over one giga-annum. In Ectocarpus, sex is expressed during the haploid phase of the life cycle, and both the female (U) and the male (V) sex chromosomes contain nonrecombining regions. The U and V of this species have been diverging for more than 70 mega-annum, yet gene degeneration has been modest, and the SDR is relatively small, with no evidence for evolutionary strata. These features may be explained by the occurrence of strong purifying selection during the haploid phase of the life cycle and the low level of sexual dimorphism. V is dominant over U, suggesting that femaleness may be the default state, adopted when the male haplotype is absent.
  
  
  CONCLUSIONS
  The Ectocarpus UV system has clearly had a distinct evolutionary trajectory not only to the well-studied XY and ZW systems but also to the UV systems described so far. Nonetheless, some striking similarities exist, indicating remarkable universality of the underlying processes shaping sex chromosome evolution across distant lineages.
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France; Medical Biology Centre, Queens University Belfast, Belfast BT9 7BL, Northern Ireland, UK.
authors.forename: Sophia
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: J Mark
authors.initials: JM
authors.lastname: Cock
authors.affiliation: Laboratoire de Biométrie et Biologie Évolutive, UMR 5558, Centre National de la Recherche Scientifique, Université Lyon 1, 69622 Villeurbanne, France.
authors.forename: Eugenie
authors.initials: E
authors.lastname: Pessia
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Remy
authors.initials: R
authors.lastname: Luthringer
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Cormier
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France; Evolutionary Biology and Ecology of Algae, CNRS UMI 3604, Sorbonne Université, UPMC, PUCCh, UACH, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Marine
authors.initials: M
authors.lastname: Robuchon
authors.affiliation: Department of Plant Systems Biology (VIB) and Department of Plant Biotechnology and Bioinformatics (Ghent University), Technologiepark 927, 9052 Gent, Belgium.
authors.forename: Lieven
authors.initials: L
authors.lastname: Sterck
authors.affiliation: Bezhin Rosko, 29250 Santec, France.
authors.forename: Akira F
authors.initials: AF
authors.lastname: Peters
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Dittami
authors.affiliation: ABiMS Platform, FR2424, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Erwan
authors.initials: E
authors.lastname: Corre
authors.affiliation: Evolutionary Biology and Ecology of Algae, CNRS UMI 3604, Sorbonne Université, UPMC, PUCCh, UACH, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Myriam
authors.initials: M
authors.lastname: Valero
authors.affiliation: Commissariat à l'Energie Atomique (CEA), Institut de Génomique (IG), Genoscope, 91000 Evry, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Aury
authors.affiliation: Evolutionary Biology and Ecology of Algae, CNRS UMI 3604, Sorbonne Université, UPMC, PUCCh, UACH, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Roze
authors.affiliation: Department of Plant Systems Biology (VIB) and Department of Plant Biotechnology and Bioinformatics (Ghent University), Technologiepark 927, 9052 Gent, Belgium; Genomics Research Institute, University of Pretoria, Hatfield Campus, Pretoria 0028, South Africa.
authors.forename: Yves
authors.initials: Y
authors.lastname: Van de Peer
authors.affiliation: Medical Biology Centre, Queens University Belfast, Belfast BT9 7BL, Northern Ireland, UK.
authors.forename: John
authors.initials: J
authors.lastname: Bothwell
authors.affiliation: Laboratoire de Biométrie et Biologie Évolutive, UMR 5558, Centre National de la Recherche Scientifique, Université Lyon 1, 69622 Villeurbanne, France.
authors.forename: Gabriel A B
authors.initials: GA
authors.lastname: Marais
authors.affiliation: Integrative Biology of Marine Models, CNRS UMR 8227, Sorbonne Universités, UPMC Université Paris 6, Station Biologique de Roscoff, CS 90074, 29688 Roscoff, France. Electronic address: coelho@sb-roscoff.fr.
authors.forename: Susana M
authors.initials: SM
authors.lastname: Coelho
mesh_terms: D006238:Haploidy; D000459:Phaeophyceae / Q000235:genetics* / Q000254:growth & development*; D019849:Sex Determination Processes