Doctoral Programme on Marine Ecosystem Health and Conservation
 The MARES Researchers and their Research
Dispersal capabilities and symbiont acquisition in deep-sea chemosynthetic metazoans
PhD Code: MARES_16_2010:
Mobility
  • Host institute 1: P11 - Université Pierre et Marie Curie (UPMC)
  • Host institute 2: P13 - University of Aveiro
Research fields:
  • T2 - Understanding biodiversity effects on the functioning of marine ecosystems
Promotor(s):
  • Sébastien Duperron
  • Marina Cunha
Contact Person and email: Sébastien Duperron - sebastien.duperron@snv.jussieu.fr

Subject description
Deep-sea metazoans colonizing chemosynthesis-based ecosystems (i.e. hydrothermal vents, cold seeps, organic falls…) are often endemic to these remote and fragmented habitats. The main peculiarity of these ecosystems is indeed the dominance of metazoans such as siboglinid polychaetes and bathymodiolin bivalves (Duperron, 2010) which have evolved complex symbiotic relationships with chemosynthetic bacteria, often sulphur- or methane-oxidizers. Bacteria sustain at least part of their hosts’ nutritional needs, while they benefit from shelter and access to their substrates. How metazoans, along with their associated bacteria, colonize and disperse between these sometimes distant habitats, and how symbionts are acquired is not yet fully understood. Documenting larval dispersal strategies, colonization, and connectivity among populations of hosts and bacteria is mandatory if we are to understand biodiversity, biogeographic patterns and evolution in these unusual ecosystems.
The project proposes an integrative study of reproduction and larval biology of several metazoans such as bivalves (e.g. Idas spp.) and polychaetes (e.g. Lamellibrachia spp.) associated with chemosynthetic habitats to study their identity, characteristics, dispersal potential, symbioses and nutritional strategies. Colonization devices for the recovery of metazoan larvae and free-living bacteria (CHEMECOLIs) (Gaudron et al. 2010) have been developed in our team and successfully deployed and recovered at deep-sea floor including reducing habitats (hydrothermal vents and cold seeps) and samples are available in the lab from the Mid Atlantic Ridge vents, Norwegian sea, eastern Mediterranean, gulf of Guinea and gulf of Cadiz. Further devices are currently deployed which will be recovered in forthcoming cruises, and others will be deployed in the near future such as in the western Mediterranean in cooperation with N. Le Bris (Obs. Banyuls-sur-mer, France).
Larvae will be sorted and identified using molecular approaches, namely marker gene sequencing and detection of larvae using specific, labelled, oligonucleotidic probes. Their morphological features, as well as the reproductive status of adult specimens, will be investigated using light and electron microscopy to point out eventual seasonality and dispersal potential of the larvae (lecitotrophy, planktotrophy or teloplany). In Banylus and during cruises, in vitro fertilization experiments will be performed both onboard and in situ at the seafloor to study early developmental steps by induction of spawning of reproductive adults.
Symbionts will be investigated in larval tissues using fluorescence in situ hybridization (FISH) and electron microscopy techniques (MEB & TEM) to determine whether bacteria are transmitted vertically from parent to offspring or environmentally acquired, or both (Vrijenhoek, 2010). Free- living forms of the symbionts will be searched in the environment using symbiont-specific PCR approaches and FISH.
The nutritional (heterotrophy vs. symbiotic) strategies will be investigated using stable isotope approaches. Carbon, nitrogen and sulphur isotopes will help understand the role of food sources, while oxygen isotopes (δ18O) will be employed on the larval shell (Lietard and Pierre, 2009), to estimate the temperature (and thus potentially depth) to which larvae were exposed during dispersal.
Connectivity among populations of hosts and bacterial symbionts will be investigated using multiple marker gene sequencing approaches. The level of entanglement between evolutionary histories of metazoans and their associated bacteria will thus be estimated. For bacteria, 16S rRNA has been used as the main marker gene although it failed to resolve phylogenetic relationships among closely related bacteria, so we will employ several additional marker genes (COI, 23S rRNA, APS…).
The final step of the project will consist in an integration of data about larval biology, reproduction status, symbioses and connectivity into a model aiming at describing the dispersal of chemosymbiotic metazoans.
Overall results should improve our understanding of the specificities of chemosynthetic fauna in terms of dispersal capabilities, and the complex interplay between hosts and their bacterial symbionts. This will also help evaluating how these specificities lead to vulnerability in the context of global change and anthropogenic impact.

References: 
Arellano SM, Young CM (2009) Spawning, development, and the duration of larval life in a Deep-sea cold-seep mussel. Biological Bulletin 216:149-162
Duperron S. (2010) The diversity of deep-sea mussels and their bacterial symbioses, chapter 6:, The Vent and Seep biota. Kiel, S. (ed): Springer, pp. 137-167.
Gaudron SM et al. (2010) Colonization of organic substrates deployed in deep-sea reducing habitats by symbiotic species and associated fauna. Marine Environmental Research 70:1-12
Lietard C, Pierre C (2009) Isotopic signatures (d18O &d13C) of bivalve shells from cold seeps and hydrothermal vents. Geobios 42:209-219
Vrijenhoek RC.  (2010) Genetics and evolution of deep-sea chemosynthetic bacteria and their invertebrate hosts, chapter 2: The Vent and Seep biota. Kiel, S. (ed): Springer, pp. 15-49.


Expected outcomes
The expected outcomes which should translate into papers are 1) identification and morphological documentation of the reproductive features and early life stages of chemosymbiotic bivalves and annelids; 2) characterization of the vertical or environmental acquisition of the symbionts, and identification of free-living forms of associated bacteria; 3) evaluation of larval dispersal strategies and 4) implementation of biological data into a model of larval dispersal.

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