Sexual dimorphism and the evolution of sex-biased gene expression in the brown alga ectocarpus.
Males and females often have marked phenotypic differences, and the expression of these dissimilarities invariably involves sex differences in gene expression. Sex-biased gene expression has been well characterized in animal species, where a high proportion of the genome may be differentially regulated in males and females during development. Male-biased genes tend to evolve more rapidly than female-biased genes, implying differences in the strength of the selective forces acting on the two sexes. Analyses of sex-biased gene expression have focused on organisms that exhibit separate sexes during the diploid phase of the life cycle (diploid sexual systems), but the genetic nature of the sexual system is expected to influence the evolutionary trajectories of sex-biased genes. We analyze here the patterns of sex-biased gene expression in Ectocarpus, a brown alga with haploid sex determination (dioicy) and a low level of phenotypic sexual dimorphism. In Ectocarpus, female-biased genes were found to be evolving as rapidly as male-biased genes. Moreover, genes expressed at fertility showed faster rates of evolution than genes expressed in immature gametophytes. Both male- and female-biased genes had a greater proportion of sites experiencing positive selection, suggesting that their accelerated evolution is at least partly driven by adaptive evolution. Gene duplication appears to have played a significant role in the generation of sex-biased genes in Ectocarpus, expanding previous models that propose this mechanism for the resolution of sexual antagonism in diploid systems. The patterns of sex-biased gene expression in Ectocarpus are consistent both with predicted characteristics of UV (haploid) sexual systems and with the distinctive aspects of this organism's reproductive biology.
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France.
Agnieszka
A
Lipinska
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France.
Alexandre
A
Cormier
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France.
Rémy
R
Luthringer
Bezhin Rosko, Santec, France.
Akira F
AF
Peters
Abims Platform, CNRS-UPMC, FR2424, Station Biologique de Roscoff, Roscoff, France.
Erwan
E
Corre
Microbial and Molecular Biology Department, Scottish Marine Institute, Scottish Association for Marine Science, Oban, United Kingdom.
Claire M M
CM
Gachon
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France.
J Mark
JM
Cock
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France coelho@sb-roscoff.fr.
Susana M
SM
Coelho
D019143:Evolution, Molecular; D020440:Gene Duplication; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D016678:Genome; D055993:Germ Cells, Plant / Q000502:physiology; D006238:Haploidy; D059014:High-Throughput Nucleotide Sequencing; D008957:Models, Genetic; D000459:Phaeophyceae / Q000235:genetics* / Q000502:physiology; D012641:Selection, Genetic; D017423:Sequence Analysis, RNA
UV sex chromosomes; brown algae; haploid–diploid life cycle; sex-biased gene expression