title: Molecular Evolution of Freshwater Snails with Contrasting Mating Systems.
abstract: Because mating systems affect population genetics and ecology, they are expected to impact the molecular evolution of species. Self-fertilizing species experience reduced effective population size, recombination rates, and heterozygosity, which in turn should decrease the efficacy of natural selection, both adaptive and purifying, and the strength of meiotic drive processes such as GC-biased gene conversion. The empirical evidence is only partly congruent with these predictions, depending on the analyzed species, some, but not all, of the expected effects have been observed. One possible reason is that self-fertilization is an evolutionary dead-end, so that most current selfers recently evolved self-fertilization, and their genome has not yet been strongly impacted by selfing. Here, we investigate the molecular evolution of two groups of freshwater snails in which mating systems have likely been stable for several millions of years. Analyzing coding sequence polymorphism, divergence, and expression levels, we report a strongly reduced genetic diversity, decreased efficacy of purifying selection, slower rate of adaptive evolution, and weakened codon usage bias/GC-biased gene conversion in the selfer Galba compared with the outcrosser Physa, in full agreement with theoretical expectations. Our results demonstrate that self-fertilization, when effective in the long run, is a major driver of population genomic and molecular evolutionary processes. Despite the genomic effects of selfing, Galba truncatula seems to escape the demographic consequences of the genetic load. We suggest that the particular ecology of the species may buffer the negative consequences of selfing, shedding new light on the dead-end hypothesis.
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France concetta.burgarella@gmail.com.
authors.forename: Concetta
authors.initials: C
authors.lastname: Burgarella
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Gayral
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Ballenghien
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bernard
authors.affiliation: CEFE/CNRS Campus du CNRS 1919, Montpellier, France.
authors.forename: Patrice
authors.initials: P
authors.lastname: David
authors.affiliation: CEFE/CNRS Campus du CNRS 1919, Montpellier, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Jarne
authors.affiliation: MIVEGEC (Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution, Contrôle), UMR (UM1-UM2-CNRS 5290-IRD224), IRD, Montpellier, France.
authors.forename: Ana
authors.initials: A
authors.lastname: Correa
authors.affiliation: MIVEGEC (Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution, Contrôle), UMR (UM1-UM2-CNRS 5290-IRD224), IRD, Montpellier, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Hurtrez-Boussès
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Juan
authors.initials: J
authors.lastname: Escobar
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Galtier
authors.affiliation: Institut des Sciences de l'Evolution, UMR, CNRS 5554, Université Montpellier II, Montpellier, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Glémin
mesh_terms: D000818:Animals; D003062:Codon; D019143:Evolution, Molecular; D005260:Female; D040961:Genetic Drift; D014644:Genetic Variation; D008297:Male; D010802:Phylogeny; D011110:Polymorphism, Genetic; D012098:Reproduction / Q000235:genetics; D012641:Selection, Genetic; D057945:Self-Fertilization / Q000235:genetics; D012908:Snails / Q000235:genetics*
chemical_list: D003062:Codon
keywords: base composition; freshwater snails; mating systems; molecular evolution; selection; selfing