Long-range actin-driven endosymbiont mobility in an animal-algal symbiosis.

Hundreds of Amphidinium sp. dinoflagellate symbionts (10–20 µm) move across Waminoa sp. at ~1 µm/s inside a ~200 nm host parenchymal cell network.

• Why it matters: Established symbionts are often assumed to be niche-confined and immotile after losing appendages, but whether they remain mobile within hosts is unclear.
• What they did: Using long-term tracking, fluorescence, and electron microscopy, the study tests whether host actin machinery drives symbiont transport and examines diel and regeneration-linked distribution changes.
• The result: Symbiont mobility is host-actin driven and occurs faster than comparable actin-based transport systems despite confinement, enabling dynamic homeostasis via diel rhythms and regeneration.