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Plasticity of symbiont acquisition throughout the life cycle of the shallow-water tropical lucinid Codakia orbiculata (Mollusca: Bivalvia)

Authors

  • Olivier Gros,

    Corresponding author
    1. UMR-CNRS 7138, Systématique-Adaptation-Evolution, Equipe « Biologie de la mangrove ». Université des Antilles et de la Guyane. UFR des Sciences Exactes et Naturelles, Département de Biologie. B.P. 592. 97159 Pointe-à-Pitre Cedex, Guadeloupe. France
      E-mail olivier.gros@univ-ag.fr; Tel. (+590) 590 48 30 06; Fax (+590) 590 48 32 81.
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  • Nathalie H. Elisabeth,

    1. UMR-CNRS 7138, Systématique-Adaptation-Evolution, Equipe « Biologie de la mangrove ». Université des Antilles et de la Guyane. UFR des Sciences Exactes et Naturelles, Département de Biologie. B.P. 592. 97159 Pointe-à-Pitre Cedex, Guadeloupe. France
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  • Sylvie D. D. Gustave,

    1. UMR-CNRS 7138, Systématique-Adaptation-Evolution, Equipe « Biologie de la mangrove ». Université des Antilles et de la Guyane. UFR des Sciences Exactes et Naturelles, Département de Biologie. B.P. 592. 97159 Pointe-à-Pitre Cedex, Guadeloupe. France
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  • Audrey Caro,

    1. UMR-CNRS 5119, Laboratoire Ecosystèmes Lagunaires, Université Montpellier II, 34095 Montpellier cedex 5, France
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  • Nicole Dubilier

    1. Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359 Bremen. Germany
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E-mail olivier.gros@univ-ag.fr; Tel. (+590) 590 48 30 06; Fax (+590) 590 48 32 81.

Summary

In marine invertebrates that acquire their symbionts from the environment, these are generally only taken up during early developmental stages. In the symbiosis between lucinid clams and their intracellular sulfur-oxidizing bacteria, it has been shown that the juveniles acquire their symbionts from an environmental stock of free-living symbiont forms, but it is not known if adult clams are still competent to take up symbiotic bacteria from the environment. In this study, we investigated symbiont acquisition in adult specimens of the lucinid clam Codakia orbiculata, using transmission electron microscopy, fluorescence in situ hybridization, immunohistochemistry and PCR. We show here that adults that had no detectable symbionts after starvation in aquaria for 6 months, rapidly reacquired symbionts within days after being returned to their natural environments in the field. Control specimens that were starved and then exposed to seawater aquaria with sulfide did not reacquire symbionts. This indicates that the reacquisition of symbionts in the starved clams returned to the field was not caused by high division rates of a small pool of remaining symbionts that we were not able to detect with the methods used here. Immunohistochemistry with an antibody against actin, a protein involved in the phagocytosis of intracellular bacteria, showed that actin was expressed at the apical ends of the gill cells that took up symbionts, providing further evidence that the symbionts were acquired from the environment. Interestingly, actin expression was also observed in symbiont-containing cells of untreated lucinids freshly collected from the environment, indicating that symbiont acquisition from the environment occurs continuously in these clams throughout their lifetime.

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