What is it about?
We studied tiny marine worms that move toward light because they live with algae that feed them. The worms chose brighter areas in a balanced way, following a general rule seen in many animals, "matching law'" which is observed in various taxa including vertebrates and arthropods. But after long exposure to light, they showed less interest in light, meaning even simple creatures adjust their behavior depending on their internal state.
Featured Image
Photo by Richard Lin on Unsplash
Why is it important?
This work extends a core behavioral rule, the matching law, into an understudied lineage with a distinctive body plan and photosymbiotic biology, showing that group distributions in a light choice task track relative brightness. By altering internal state through one day of light exposure that changes nutritional status via algal photosynthesis, we show that phototaxis weakens when state changes, which challenges simple reflex accounts. Because sunlight is not depleted by use, the group level matching we observe is independent of consumptive competition, offering a rare test of distribution principles in a nonconsumptive resource context. These results speak to current discussions of minimal cognition by indicating that state based control are broadly shared features of life.
Perspectives
For us, this study reinforced the idea that cognition should not be reserved for animals with large or complex brains. By showing that flatworms display state dependent behavior, our work connects directly with the growing view of minimal cognition, the idea that the roots of perception, decision, and adaptation run deep across the tree of life. To me, the most exciting part is realizing that even small and often overlooked creatures can broaden our understanding of what it means to act, choose, and adapt in the living world.
Hiroshi Matsui
Osaka Daigaku
Read the Original
This page is a summary of: Group-level matching behavior in phototaxis of acoel flatworm Praesagittifera naikaiensis., Journal of Comparative Psychology, September 2025, American Psychological Association (APA),
DOI: 10.1037/com0000430.
You can read the full text:
Contributors
The following have contributed to this page
