A tiny crab carrying two living “pom-poms.”
Research begun in high school and continuing today at the University of Tokyo.
Lybia tessellata is only one to two centimetres across. Its defining behaviour is carrying a small sea anemone in each claw, raising them like a pair of cheerleading pom-poms when threatened.
The animal is also called a pom-pom crab—an appealing appearance that conceals a remarkably complex relationship between two species.
Behind its charming appearance is a largely unexplored system of tool use, physical adaptation and interspecies dependence.
It uses sea anemones as weapons and tools, and can divide them to preserve a matched pair.
Repeatedly being held in a claw changes the anemone's colour and shape.
Whether both organisms benefit, or one is primarily being used by the other, has long remained unclear.
I first encountered the crab in a National Geographic feature. With fellow members of the Salesio Gakuin biology club, I then spent three years keeping, observing and experimenting with the species as the lead author of our paper.
The crab accepted an anemone whose natural range does not overlap its own, suggesting it may take whatever suitable anemone is locally available rather than relying on one fixed species.
Tissue sections showed that areas held most tightly contained fewer symbiotic algae. The evidence indicates that bleaching is driven primarily by continuous physical stress.
Starved crabs ate the anemones they carried; removed anemones showed little remaining regenerative capacity; and no food transfer was detected. Together, the experiments point to commensalism with little benefit for the anemone, or a relationship approaching predator and prey.
The current research plan is to sequence the nuclear genome of the genus Lybia. The published reference identified in the project so far is mitochondrial-genome data (Gries et al. 2023).
A nuclear genome sequence could provide a new basis for investigation and bring the project closer to questions about tool use and life with an anemone. The scope, specimens and analytical process are still being planned.
This section records work in progress and preparations at meaningful milestones. Plans that are still under discussion are clearly separated from confirmed results.
Preparations are under way for a possible collaboration to advance the nuclear genome research. The scope, specimens and analytical framework are still being discussed.
IN PREPARATIONThe current goal is to establish a path from DNA extraction through sequencing and analysis for the nuclear genome of the genus Lybia.
PLANNINGObservations of behaviours such as dividing anemones and using them as food now inform questions that can be explored at the genetic level.
ONGOING RESEARCHA selection of interviews and reports about the research and the path behind it.