title: Molecular evolution of candidate male reproductive genes in the brown algal model Ectocarpus.
abstract: BACKGROUND
  Evolutionary studies of genes that mediate recognition between sperm and egg contribute to our understanding of reproductive isolation and speciation. Surface receptors involved in fertilization are targets of sexual selection, reinforcement, and other evolutionary forces including positive selection. This observation was made across different lineages of the eukaryotic tree from land plants to mammals, and is particularly evident in free-spawning animals. Here we use the brown algal model species Ectocarpus (Phaeophyceae) to investigate the evolution of candidate gamete recognition proteins in a distant major phylogenetic group of eukaryotes.
  
  
  RESULTS
  Male gamete specific genes were identified by comparing transcriptome data covering different stages of the Ectocarpus life cycle and screened for characteristics expected from gamete recognition receptors. Selected genes were sequenced in a representative number of strains from distant geographical locations and varying stages of reproductive isolation, to search for signatures of adaptive evolution. One of the genes (Esi0130_0068) showed evidence of selective pressure. Interestingly, that gene displayed domain similarities to the receptor for egg jelly (REJ) protein involved in sperm-egg recognition in sea urchins.
  
  
  CONCLUSIONS
  We have identified a male gamete specific gene with similarity to known gamete recognition receptors and signatures of adaptation. Altogether, this gene could contribute to gamete interaction during reproduction as well as reproductive isolation in Ectocarpus and is therefore a good candidate for further functional evaluation.
authors.affiliation: Phycology Research Group and Center for Molecular Phylogenetics and Evolution, Ghent University, Krijgslaan 281, Building S8, 9000, Ghent, Belgium. ap.lipinska@gmail.com.
authors.forename: Agnieszka P
authors.initials: AP
authors.lastname: Lipinska
authors.affiliation: Department of Molecular Biotechnology, Laboratory of Biochemistry and Glycobiology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium. ElsJM.VanDamme@UGent.be.
authors.forename: Els J M
authors.initials: EJ
authors.lastname: Van Damme
authors.affiliation: Phycology Research Group and Center for Molecular Phylogenetics and Evolution, Ghent University, Krijgslaan 281, Building S8, 9000, Ghent, Belgium. olivier.declerck@ugent.be.
authors.forename: Olivier
authors.initials: O
authors.lastname: De Clerck
mesh_terms: D005075:Biological Evolution; D019143:Evolution, Molecular; D005306:Fertilization / Q000235:genetics*; D056771:Ovule / Q000235:genetics; D000459:Phaeophyceae / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny; D011058:Pollen / Q000235:genetics*; D012641:Selection, Genetic