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Your cheatin’ claw

Cheat! I call shenanigans.jpgThe distinguishing feature of a male fiddler crab is the giant claw that he waves in a suggestive fashion at females or in a threatening fashion at other males. But it turns out that some males’ claws may be rather less distinguished than they appear. Some of them are faking it!

If a male loses his massive pinching device in a fight or to a predator he can grow a new one. Some species, though, grow new claws that look impressive but are basically useless.

“Males size each other up before fights, and displaying the big claw is a very important part of this process,” says Simon Lailvaux of the University of New South Wales (press release). “What’s really interesting about these ‘cheap’ claws is that other males can’t tell them apart from the regular claws.”

Lailvaux and colleagues have just published a study in Functional Ecology showing that regenerated claws of Uca mjoebergi fiddler crabs are “dishonest signals” as they have less closing force and less pull-resisting force. Both are crucial in fights.

“This study is among the first to show that male armaments can dishonestly signal performance traits that are likely important for winning fights, and is the first to show evidence for dishonest signalling of multiple components of fighting ability,” they say in their paper.

On the Loom blog, Carl Zimmer says:

It’s not clear why male crabs don’t regenerate strong claws again. There may be some limit to their powers of regeneration. It’s conceivable that the crabs have evolved not to waste a lot of energy building a big new claw, since their opponents have such trusting natures.

It’s also intriguing to consider why crabs keep on trusting claw size as a reliable clue to how they’ll fare in a fight. There’s good reason to think that while the rule isn’t perfect, it works well enough. The chances are low that a male crab will encounter a bluff. It’s better to err on the side of safey in a fight than to err on the side of distrust. And so the crabs allow deception to thrive.

Of course, here in Ye Olde England ‘fiddle’ has long been another word for scam.


Crab’s “Fighting Claw” Often Fake – National Geographic

Crabs lie to look tough – London free paper Metro

Image: Tanya Detto


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