| Summary: | ATLAS work package 1 & 4 presentation at ATLAS 3rd General Assembly. Aim: To infer cold-water corals post-glacial biogeographical history and assess the role of Mediterranean Sea glacial refugia as the origin for the recolonisation of the North-eastern Atlantic Ocean. Location: North-eastern Atlantic Ocean and Mediterranean Sea. Taxon: Lophelia pertusa, Madrepora oculata. Methods: We sampled cold-water corals using remotely operated vehicles and performed one geological corer for coral and sediment dating. We characterized spatial genetic patterns (microsatellites and a nuclear gene fragment) using networks, clustering and measures of genetic differentiation. Results: Microsatellite and sequence data were congruent, and together they showed a contrast between the two species. Populations of L. pertusa present a lack of genetic structure across the North-eastern Atlantic, a dominant pioneer haplotype, local haplotype radiations and a majority of endemic variation in lower latitudes. Surprisingly, sharply genetically differentiated population units were revealed across the North-eastern Atlantic for M. oculata. The genetic lineages are poorly admixed, even along neighbouring sites. Main conclusions: Our study shows contrasting post-glacial colonisation pathways for two main habitat-forming species in the deep-sea. The cold-water coral L. pertusa has likely undertaken a recent (post-glacial) recolonisation of the North-eastern Atlantic from Mediterranean refugial populations. Contrastingly, the strong genetic differentiation of M. oculata populations mirrors the effects of long-term isolation in multiple refugia. We suggest that these distinct and genetically diverged, refugial populations initiated the post-glacial recolonization of North-eastern Atlantic margins, leading to a secondary contact in the northern range. Incipient reproductive isolation may reduce or prevent present day gene flow among divergent but co-occurring M. oculata lineages. This study highlights the need to disentangle the influence of ...
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