Saturday, May 21, 2011

A nickname in biology: domino for whale shark

We all know the game domino, consisting of tiles with their front side divided into faces that are dotted with spots to represent number values. Dot patterns are common in the world of human design as well as in the natural world. The whale shark, a polka-dotted gentle giant living in tropical and warm-temperate seas, is nicknamed domino for the spots on its back [1].  A Mexican conservation group, which works on studying and protecting whale sharks, is accordingly called Proyecto Dominó.

The whale shark (Rhincodon typus) is a filter feeder, living of plankton and small fish [2]. Divers often get near dominoes. A diver swimming next to a domino is a good measuring unit. Peter Klimley reports [3]: a whale shark was five times longer than a diver with long flippers, 8 feet total, suggesting a fish length of 40 feet. The whale-like appearance and feeding behavior makes a domino a peaceful diving fellow, but carnivorous sharks such as hammerheads and blacktip reef sharks can be nearby, as Peter Klimley experienced on a diving trip in the waters above the Gorda Seamount off the tip of the peninsula of Baja California.

Domino spots are variously described as white, yellow or blue. Most intriguing, the spot patterns are unique and allow scientists to identify an individual domino per computer program—kind of a natural bar code system. Certainly, these “dot codes” didn't evolve for human- or computer-based pattern recognition. But what kind of advantage do they provide? Better mutual recognition, greater sex appeal or camouflage?

References and suggested reading
[1] Juliet Eilperin: Swimming with Sharks. Smithsonian June 2011, 42 (3), pp. 34-40.
[2] National Geographic: Whale Shark (Rhinocodon typus) [].
[3] A. Peter Klimley: The Secret Life of Sharks. Simon & Schuster, New York, 2003; pages 77 and 110.

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