Discovery of chemoautotrophic symbiosis in the giant shipworm Kuphus polythalamia (Bivalvia: Teredinidae) extends wooden-steps theory

Certain marine invertebrates harbor chemosynthetic bacterial symbionts, giving them the remarkable ability to consume inorganic chemicals such as hydrogen sulfide (H₂S) rather than organic matter as food. These chemosynthetic animals are found near geochemical (e.g., hydrothermal vents) or biological (e.g., decaying wood or large animal carcasses) sources of H₂S on the seafloor. Although many such symbioses have been discovered, little is known about how or where they originated. Here, we demonstrate a new chemosynthetic symbiosis in the giant teredinid bivalve (shipworm) Kuphus polythalamia and show that this symbiosis arose in a wood-eating ancestor via the displacement of ancestral cellulolytic symbionts by sulfur-oxidizing invaders. Here, wood served as an evolutionary stepping stone for a dramatic transition from heterotrophy to chemoautotrophy.