Stability in flexibility: Shifting alliances stabilize the symbioses of marine animals over 150 million years.

Obligate marine oligochaete symbioses maintain long-term stability despite rapid community changes, with primary symbionts persisting over millions of years.

• Why it matters: Understanding how stable symbiotic relationships persist amid ecological and evolutionary shifts is crucial for grasping the resilience of complex biological systems over deep time.
• What they did: Researchers analyzed 246 individuals from 63 species across 17 marine sites using high-resolution phylogenomics, revealing persistent primary symbionts and frequent acquisition of additional partners.
• The result: Findings show that while core symbionts like "Candidatus Thiosymbion" are maintained over macroevolutionary timescales, symbiont communities can rapidly reshape, illustrating a balance between stability and flexibility that supports diversification.