PolyPro3: Ecology and evolution of the tripartite symbioses between polychaetes and their protistan parasites

PolyPro3: Ecology and evolution of the tripartite symbioses between polychaetes and their protistan parasites

Marine polychaete worms (Annelida) are key organisms in marine benthic ecosystems. They have important roles from decomposers to consumers and due to their burrowing lifestyle, they actively participate in oxygenation of sediments maintaining benthic ecosystem health. Polychaetes are known to host protistan symbionts (gregarines), which themselves are infected my microsporidian parasites, forming a tripartite symbiosis. Symbiotic interactions have been of fundamental importance in ecological and evolutionary processes through the history of life, and have ultimately shaped the biodiversity we witness today. However, the polychaete-gregarine-microsporidian tripartite interaction has not been studied before and it is unclear how these interactions affect the polychaetes. Consequently, it is unclear how the the tripartite symbiosis might affect the functioning of benthic ecosystems. One reason behind this knowledge gap is the difficulty of applying experimental approaches with marine hosts and symbionts that are unculturable. With PolyPro3 specifically aiming to resolve the nature of the tripartite symbiosis and the diversity of the interaction by using state-of-the-art molecular methods combined with traditional ecological fieldwork, I will bring a significant step forward in addressing this key gap of knowledge. I will use differential transcriptomics and quantitative methods to disentangle the interaction, and a large spatial scale field sampling across the opening of the Baltic Sea combined with metabarcoding approach to describe the diversity and specificity of polychaete-gregarine-microsporidian tripartite symbiosis. PolyPro3 will also provide novel insights into the impacts of the tripartite symbiosis on the functioning and stability of important benthic habitats and provide effective means for investigation of other marine symbioses. Lastly, PolyPro3 significantly adds to the knowledge on neglected biodiversity of polychaete associated marine protists.