Investigations on population genetics and the influence of hydrothermal activity on bivalve growth at MAR hydrothermal vents
Final Report Abstract
This proposal included two research complexes aiming at investigating (i) patterns of microgrowth markers and isotopic signatures in shells of hydrothermal vent mussels in two contrasting hydrothermal vent settings and (ii) biogeographic patterns of vent endemic symbiotic bivalves along the Mid-Atlantic Ridge (MAR) on the basis of gene flow data obtained from geographically separated populations. Both thematic complexes addressed key questions of SPP 1144 related to bio-geo-coupling and biogeography on the MAR, in particular with respect to a previously hypothesized disconnection of a northern from a southern biogeographic province by large equatorial transform faults. Phylogenetic analysis of Bathymodiolus and Vesicomyid host species and their symbiotic bacteria were based on the mitochondrial cytochrome c oxidoreductase subunit I (COI) and bacterial 16S rDNA genes. The material included Bathymodiolus azoricus and B. puteoserpentis from the northern MAR (NMAR), two Bathymodiolus populations collected at 5° S and 9° S, and Abyssogena southwardae (Vesicomyidae) collected at the Logatchev hydrothermal vent field (NMAR) and at 5° S. Initial results indicated geographically structured isolation of all four Bathymodiolus host populations evidenced by sufficient fixed nucleotide substitutions and genetic distances large enough to suggest that all four populations warrant consideration as separate species. This result let the value of comparing growth patterns and isotopic signatures between different species at different physicochemical environments appear questionable, and it was decided to postpone theme (i) and concentrate on in-depth population genetic analyses (ii). Population genetics used Bathymodiolus spp. of each of the four northern and southern MAR (SMAR) sites. The genes selected combine a wide range of different functions and are subjected to different levels of selective pressure resulting in different levels of allele differentiation. These included COI, six nuclear genes coding for proteins and the non-coding nuclear ribosomal Internal Spacer 2. Uni-locus analyses included e.g. analyses of sequence polymorphisms, estimates on the sizes, structures, distributions and divergence times of populations, tests for neutral evolution, tests for changes of population size, and others. Multilocus analyses infer the existence of gene flow in the process of divergence using statistical tests for natural selection and the “Isolation with Migration Model”. In contrast to COI all nuclear genes showed intermixing of alleles on various levels among the populations. Preliminary results of the project can be summarized as follows: • Phylogenetic relationships among MAR Bathymodiolus and Abyssogena suggest that the equatorial transform faults do not represent a strict dispersal barrier of symbiotic bivalves. Gene flow happened in the past and may possibly be ongoing. Our data do not support disconnection of two separate biogeographic provinces on the northern and southern MAR. • Phylogenies of thiotrophic and methanotrophic Bathymodiolus symbionts are incongruent. They do not reflect possible dispersal pathways of the hosts and are currently of low value for answering the questions of this study. Conversely, Abyssogena symbionts on the northern and southern MAR are genetically identical and support a hypothesized unhindered dispersal along the equatorial MAR. • Nuclear gene loci of Bathymodiolus hosts suggest that a geographic structuring of the populations is due to distance rather than isolating effects of biogeographic barriers. Observations of identical alleles in particular at Logatchev and the SMAR sites indicate intense gene flow in the recent past at the MAR mainly from south to north across the equatorial region. This suggests that speciation among MAR Bathymodiolus may be not yet terminated. • Based on preliminary results, we suggest that MAR Bathymodiolus radiated from a common ancestor that diverged into B. azoricus and an ancestor of the B. puteoserpentis and SMAR populations. The first separation happened ~0.6 Ma ago and further radiation of B. puteoserpentis and SMAR lineages may have started soon after that time.
Publications
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Evolution and Biogeography of mussels of the family Bathymodiolus. EGU annual meeting, Vienna, Austria, April 2008
Karina Röse, Christian Borowski, Nicole Dubilier
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Phylogentic relationships of bathymodiolin mussels on the basis of COI. ChEss workshop on chemosynthetic bivalves, Roscoff, France, September 2008
Christian Borowski, Karina Roese, Nicole Dubilier
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Biogeography of hydrothermal vent key species along the Mid-Atlantic Ridge: Diversity, Function and Ecological Significance. SPP1144 workshop, Etelsen, Germany. September 2009
Christian Borowski, Karina van der Heijden, Jillian Petersen, Mirjam Perner, Olav Giere and Nicole Dubilier
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Biogeography of Mid Atlantic Ridge hydrothermal vent communities. 4th International Symposium on Chemosynthesis-Based Ecosystems (4th CBE), Okinawa, Japan Juni 2009
Karina van der Heijden, Christian Borowski, Jillian S. Petersen, Nicole Dubilier
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Biogeography of hydrothermal vent symbioses on the Mid-Atlantic Ridge. Workshop on Symbiotic Interactions, Würzburg, October 2010
Karina van der Heijden, Christian Borowski, Jillian S. Petersen, Nicole Dubilier
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Hydrothermal vent fauna on the Southern Mid-Atlantic Ridge and biogeographic association with other chemosynthetic habitats. 12th International Deep-Sea Biology Symposium, Reykjavík, Iceland, June 2010
Karina van der Heijden, Christian Borowski, Jillian M. Petersen and Nicole Dubilier
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Symbiont transmission in bathymodiolin mussels from deep-sea hydrothermal vent and cold seep habitats. VAAM Anual Meting, Hannover, March 2010
Karina van der Heijden, Julie Huang, Christian Borowski and Nicole Dubilier
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Biogeography of Mid-Atlantic Ridge hydrothermal vent mussels and associated bacterial symbionts. Chemosynthetic Molluscs Workshop, London, April 2011
Karina van der Heijden, Jillian M. Petersen, Christian Borowski and Nicole Dubilier
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Biogeography of Mid-Atlantic Ridge hydrothermal vent mussels and associated bacterial symbionts. Invitational Seminar, Department of Geobiology, University Göttingen, April 2011
Karina van der Heijden, Jillian M. Petersen, Christian Borowski and Nicole Dubilier
