Have You Ever Seen A Lybia Crab? Often Called Boxer Crabs, Or Pom-pom Crabs, These Tiny Crustaceans Are

Have you ever seen a Lybia crab? Often called boxer crabs, or pom-pom crabs, these tiny crustaceans are easily identified by a unique behavior: they hold anemones on their claws to defend themselves from predators, keeping the anemones small enough to wield by limiting their food intake. But how do they get the anemones in the first place? Researchers think they have an answer: by stealing one from another crab, and then splitting it in half to create two identical clones—one for each claw.

Two graduate students, Yisrael Schnytzer and Yaniv Giman, set out to discover how the Lybia crabs acquire their anemones. They spent years observing and collecting crabs (Lybia leptochelis, specifically) from the Red Sea. Given that Lybia crabs are exceptionally well-camouflaged and only a few centimeters across, this was no easy task, but they managed to observe or collect more than 100 individuals.

Every specimen Schnytzer and Giman found was in possession of a pair of anemones, and each anemone belonged to the genus Alicia. Interestingly, the anemones themselves were not found living by themselves; they were only found already living on the claws of Lybia crabs. The researchers decided to study some of the crabs in a laboratory, to see if more observation would solve the mystery of how they acquired their anemones to begin with.

In the lab, the researchers conducted several experiments, the first of which was to take one anemone away from a crab. When left with just one anemone, the crab solved the problem by splitting the remaining anemone into two. The two halves of the anemone would then regenerate into two identical clones, one for each claw, over the course of several days.

The second experiment involved removing both anemones from one crab and placing it in a tank with a crab that still had both its anemones. The result: the two crabs would fight, with the anemone-less crab usually succeeding in stealing one anemone from the other crab. These fights did not tend to result in injuries to the crabs themselves, and once each crab was in possession of one anemone, both crabs would split their anemone into halves to create a pair of clones.

In addition to these experiments, Schnytzer and Giman examined the genes of the anemones found on the wild crabs. Every crab collected from the wild was holding a pair of identical clones. This might mean that anemone theft is rampant among Lybia crabs in the Red Sea, and that it might be the main way that these crabs acquire their anemones.

At any rate, it is clear that the crabs are frequently splitting anemones in two, inducing asexual reproduction in another species and potentially limiting that species’ genetic diversity in the process—a rarity outside the human world.

Based on materials provided by PeerJ and ScienceDaily

Journal reference: Yisrael Schnytzer, Yaniv Giman, Ilan Karplus, Yair Achituv. Boxer crabs induce asexual reproduction of their associated sea anemones by splitting and intraspecific theft. PeerJ, 2017; 5: e2954 DOI: 10.7717/peerj.2954

Image credit: Yisrael Schnytzer

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