Branching Worm - Sponge Holobionts: Interactions and Evolution

Branching syllids of the genus Ramisyllis live entirely within the intricate canal systems of their sponge hosts, forming a striking holobiont, a tightly integrated unit of worm, sponge, and their associated microbial communities. These worms display a unique architecture: a single head giving rise to multiple posterior branches that grow without a fixed orientation inside the sponge’s three-dimensional labyrinth.
This unusual environment may have relaxed typical developmental constraints, allowing a novel branched body plan to evolve and persist. Studying these systems reveals how ecological conditions can shape development and drive evolutionary innovation.
Our research focuses on the dynamics of this tripartite association: understanding how Ramisyllis initiates new branches during post-embryonic development, exploring the population structure and co-evolution of worms, sponges, and microbiomes, and uncovering the trophic strategies that sustain this complex partnership. These investigations provide key insights into symbiosis, adaptation, and the evolutionary consequences of life within a holobiont.