Ramisyllis - branching marine worms as a holobiont system of annelids interacting with their sponge hosts and the corresponding microbiomes

• Applicants: Professorin Maria Teresa Aguado Molina, Ph.D.; Professor Dr. Harald Gruber-Vodicka
• Subject Area: Systematics and Morphology (Zoology) ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562442721

Branching marine worms, a unique group of annelids, exhibit a remarkable body structure: they possess a single head but undergo continuous branching, leading to multiple posterior ends in a seemingly unlimited pattern. These unusual annelids inhabit a specialized environment - host sponges - where they navigate the sponge’s complex three-dimensional canal system, moving their branches freely without predefined directionality. The worms' size and shape are flexible, likely influenced by the characteristics of the host sponges and their associated microbiomes. The extraordinary capacity of these annelids to form intricate, branching body structures that permeate the canal systems of their sponge hosts presents compelling questions about their growth, movement, feeding strategies, and interactions with their environment. This particular habitat might relax the developmental constraints that typically hinder the evolution of non-bilaterally symmetric forms. This system challenges conventional knowledge of annelid biology while providing invaluable insights into the evolutionary processes that lead to such specialized adaptations. From an evolutionary-ecology standpoint, the intricate, branching body plan of Ramisyllis exemplifies how ecological changes can drive evolutionary innovation by altering the developmental biases that usually restrict variation. Studying Ramisyllis offers a unique opportunity to investigate these remarkable traits from structural, functional, and evolutionary angles, expanding our understanding of symbiosis and morphological diversity within marine ecosystems. In this project, we aim to understand the developmental biology and ecophysiology of branching Syllidae annelids. Specifically, we aim to answer the following questions: 1) How and why does Ramisyllis ramify? (Postembryonic development and external triggers); 2) how does Ramisyllis get its food? (Diet analyses, trophic position and way of feeding); and 3) What are the benefits to the partners? (Symbiotic life style). The sponge, the branching worms, and their microbiomes form a complex, interdependent four-way symbiosis. To fully understand the biology of this multiparters interaction, an integrated research approach is essential. Our teams have united to pursue this comprehensive study. We share multiple work packages (WPs), facilitate student exchanges, and collaborate on student supervision, building a dual-PI project with collective capabilities that exceed those of individual labs. We have structured the project with two PhD students and two master’s students to support balanced research interactions. Leveraging the resources of both labs, the PIs’ networks, and our combined infrastructures, we aim to generate a strong research initiative focused on this evolution, development, ecology, and ecophysiology model system.

• DFG Programme: Research Grants