Isolement reproductif et architecture génomique de la différenciation chez deux espèces du complexe Jaera albifrons (isopodes marins) - Etude de populations mixtes présentant des niveaux d'isolement interspécifique contrastés

Abstract : Within the field of speciation, sympatric areas with different levels of interspecific genetic differentiation offer a good opportunity to understand the nature and evolution of reproductive barriers between species. Jaera (albifrons) albifrons and Jaera (albifrons) praehirsuta are two species of marine isopods that coexist in sympatry along the northern European coasts. Ecological, behavioral and genetic barriers efficiently isolate these two species, except in a unique region (Normandy, France) where morphological phenotypes were described in the 60's.In this thesis, microsatellites and SNPs obtained from RAD-sequencing allowed me to demonstrate that the level of interspecific isolation varies widely between sites, from introgressive hybridization to quasi-complete isolation. A comparative analysis of these sites combining sampling from natural populations, experimental crosses, and genomic analyses then allowed me to: i) demonstrate the predominant role of sexual isolation (which remains strong in introgressed populations), together with a relatively weaker post-zygotic barrier, ii) discover the presence of Wolbachia bacteria within the two species, iii) demonstrate that the coexistence of these species originate from an allopatric speciation followed by secondary contacts with varying levels of heterospecific gene flow renewal, and iv) show that gene flow varies also strongly along the genome, with an effect of sex chromosomes and rearranged chromosomes apparently limiting introgression.
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Ambre Ribardière. Isolement reproductif et architecture génomique de la différenciation chez deux espèces du complexe Jaera albifrons (isopodes marins) - Etude de populations mixtes présentant des niveaux d'isolement interspécifique contrastés. Evolution [q-bio.PE]. Université Pierre et Marie Curie - Paris VI, 2017. Français. ⟨NNT : 2017PA066397⟩. ⟨tel-01746147⟩

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