Breusing, Corinna (2016) Population genetics and contemporaneous connectivity in deep-sea hydrothermal vent mussels of genus Bathymodiolus. (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 171 pp.

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Abstract

Deep-sea hydrothermal vents offer transient, sporadically distributed habitats to lush communities of animal species that live in mutualistic symbioses with chemosynthetic bacteria. While both mineral and genetic resources from these unique ecosystems gain increasing interest in human society, plans for the sustainable management of vent biodiversity are still in their infancies, given that the genetic structure and ecological connectivity of individual vent populations is poorly understood. To address these issues and provide informative data for environmental mitigation strategies, I have studied patterns of contemporaneous gene flow and genetic subdivision in ecologically important deep-sea mussel species (Bathymodiolus spp.) from Indo-Pacific and mid-Atlantic vents by using a combination of molecular and modeling approaches. In disagreement with the expectation that veliger larvae are transported over vast distances of possibly more than 1000 km, my findings show that direct dispersal between vent localities separated by 10s to 1000s of kilometers is improbable, indicating that effective population connectivity can only be maintained via hitherto undiscovered stepping stone sites. Results from biophysical models for the Mid-Atlantic Ridge implied that Bathymodiolus larvae rarely arrive at vent habitats that are more than 70-150 km away from their release positions, while more research is needed to assess whether these estimates apply to other vent taxa and hydrothermal systems as well. Population genetic analyses based on multiple molecular markers indicated the presence of one Bathymodiolus species with broad biogeographic range in the Indo-Pacific region (B. septemdierum) and the existence of four Bathymodiolus species with comparatively restricted distributions on the Mid-Atlantic Ridge (B. azoricus, B. puteoserpentis, B. sp. 5°S, B. sp. 9°S). In addition, investigations of population structure implied the putative evolution of incipient species in both study areas. In the Indo-Pacific Ocean, geographic barriers seemed to favor genetic divergence between two B. septemdierum metapopulations of the Central Indian Ridge and the western Pacific back-arc basins. By contrast, patterns of introgressive hybridization between B. azoricus and B. puteoserpentis suggested differential local adaptation among parental and recombinant genotypes on the Mid-Atlantic Ridge and the potential speciation of a genetically distinct hybrid lineage in the extreme environment of the Broken Spur vent field. These results significantly advance our understanding of contemporary gene flow, evolution and population genetic structure of key invertebrate species from Indo-Pacific and mid-Atlantic hydrothermal vents. Although future population genomic and biophysical modeling studies on other vent organisms and geographic regions are highly warranted, the data presented here will allow the development of initial mitigation measures for the protection of vent biodiversity in the deep sea.

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