An introgression breakthrough left by an anthropogenic contact between two ascidians

• Published in: Molecular Ecology
• Main Authors: Moan, Alan, Roby, Charlotte, Fraisse, Christelle, Daguin-Thiébaut, Claire, Bierne, Nicolas, Viard, Frédérique
• Other Authors: Adaptation et diversité en milieu marin (ADMM), Institut national des sciences de l'Univers (INSU - CNRS)-Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Tjarno Marine Biological Laboratory, Évolution, Écologie et Paléontologie (Evo-Eco-Paleo) - UMR 8198 (Evo-Eco-Paléo (EEP)), Université de Lille-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Institut de recherche pour le développement IRD : UR226-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Biological introductions; non-indigenous species; anthropogenic hybridization; introgression hotspots; population genomics; tunicates; [SDV.GEN.GPO]Life Sciences [q-bio]/Genetics/Populations and Evolution [q-bio.PE]; [SDV.BID.EVO]Life Sciences [q-bio]/Biodiversity/Populations and Evolution [q-bio.PE]; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.MCG]Environmental Sciences/Global Changes; Pacific; North East Atlantic
• Online Access: https://hal.science/hal-03355754; https://hal.science/hal-03355754/document; https://hal.science/hal-03355754/file/LeMoan_2021_AcceptedMolecularEcology.pdf; https://doi.org/10.1111/mec.16189

International audience Human-driven translocations of species have diverse evolutionary consequences such as promoting hybridization between previously geographically isolated taxa. This is wellillustrated by the solitary tunicate, Ciona robusta, native to the North East Pacific and introduced in the North East Atlantic. It is now co-occurring with its congener C. intestinalis in the English Channel, and C. roulei in the Mediterranean Sea. Despite their long allopatric divergence, first and second generation crosses showed a high hybridization success between the introduced and native taxa in the laboratory. However, previous genetic studies failed to provide evidence of recent hybridization between C. robusta and C. intestinalis in the wild. Using SNPs obtained from ddRAD-sequencing of 397 individuals from 26 populations, we further explored the genome-wide population structure of the native Ciona taxa. We first confirmed results documented in previous studies, notably i) a chaotic genetic structure at regional scale, and ii) a high genetic similarity between C. roulei and C. intestinalis, which is calling for further taxonomic investigation. More importantly, and unexpectedly, we also observed a genomic hotspot of long introgressed C. robusta tracts into C. intestinalis genomes at several locations of their contact zone. Both the genomic architecture of introgression, restricted to a 1.5 Mb region of chromosome 5, and its absence in allopatric populations suggest introgression is recent and occurred after the introduction of the non-indigenous species. Overall, our study shows that anthropogenic hybridization can be effective in promoting introgression breakthroughs between species at a late stage of the speciation continuum.