12 January 2016

Fearsome fiddlers?

Photo of a male fiddler crab Uca  from www.arkive.org

Judging a confident male fiddler crab, one can be easily captured by its unique, brightly colored, threatening enlarged claw. Fiddler crabs (Genus Uca) are major inhabitants of mud and sand flats along estuaries and sheltered coasts in the tropics and subtropics [1]. They may be small but their claws appear robust and powerful that you would not even think twice of its combating prowess. Or, should we?

Australian ecologists discovered this “bluff” in a group of fiddler crabs. The crabs use their massively enlarged claws for fighting over turfs as well for attracting females [1].  Once they lose a claw upon battle, they may grow another one, most of the time a replica of the original. The new claw, however, is a far cry to how they physically appear. It is lighter and toothless, rendering them weak and inferior [2].

Fighting ability is measured through major claw size, claw strength and the ability to resist being pulled from a tunnel. Crabs size up each other through their major claws, waving them in the air with surety. This means that physical make-up of the enlarged claw is detrimental in picking fights [2]. 

Now, to advertise one’s sex or to incite fight over territories, a crab will wave its regenerated claw, either up and down, others sideways, during low tide at territories established around their burrows [1]. Now, the wave is done and a fight may ensue. Unfortunately, the potential opponent, which is about to be fooled but is clueless of it, cannot distinguish the regular, powerful authentic claws from the cheap ones. The shining, regenerated claw is unfortunately void of any information on its fighting capacity. The opponent is then deceived and backs off. This remains true unless the crab with the regenerated claw holds territory and is trumped by a stronger opponent, revealing his bluff [2].

Knowing that this kind of dishonesty in the animal kingdom exists may provide an opportunity for ecologists to study dishonest signals. This discovery can also shed light on the individual reproductive success and survival among fiddler crabs by a thorough understanding of dishonesty mechanisms and consequences [2].

To know more about fiddler crabs, visit SeaLifeBase or come be a collaborator!

[1] Castro, P., & Huber, M. E. (2003). Marine Biology (4th ed.). Boston, Massachusetts: McGraw Hill.
[2] British Ecological Society (BES). Fiddler Crabs Reveal Honesty Is Not Always The Best Policy. ScienceDaily. ScienceDaily Retrieved from www.sciencedaily.com/releases/2008/11/081111203501.htm.

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