EvoLucin · 400 Million Years of Symbiosis: Host-microbe interactions in marine lucinid clams from past to present

The widespread recognition that interactions with microbes drive animal health, development and evolution is transforming biology, but we so far understand the underlying mechanisms in very few systems. Considering that virtually every animal on Earth evolved with and among the microbes in its environment, there is still immense potential for discovering fundamentally new mechanisms of interaction among the staggering diversity of animals and their microbial symbionts in nature. The ancient and exclusive association between marine lucinid clams and chemosynthetic symbiotic bacteria is ideal for investigating these interactions. Lucinidae is one of the most widespread and species-rich animal families in the oceans today, and has lived in symbiosis for more than 400 million years. The clam’s outstanding ability to select one specific symbiont from the trillions of bacteria in its environment challenges widely held assumptions about the function and specificity of the innate immune system. Symbiont-free juveniles can be raised in the lab, and experimentally infected, allowing unmatched insights into the early development of this symbiosis. Although the symbiont infection is specific to gill cells, symbiont-encoded proteins can be found in distant parts of the animal that are symbiont-free. I will combine cutting-edge molecular tools and experimental infection to better understand three key aspects of host-microbe interactions in these clams: 1) Acquisition and selection of microbes during animal development, 2) Maintenance along animal lifetimes through molecular communication and exchange, and 3) Emergence and perpetuation over evolution. I hypothesize that intracellular bacterial symbionts fundamentally alter host biology, and these effects are not limited to the location where symbionts are housed, but can affect distant organ systems. My overarching goal is to understand the molecular basis for these effects, and their evolutionary history.