Male crabs bluff to scare rivals away

November 17th, 2008 - 1:00 pm ICT by IANS  

Sydney, Nov 17 (IANS) Dishonesty helps male fiddler crabs scare rivals away. They grow claws that are seemingly powerful but actually weak and puny. The signals they send one another about their fighting prowess - and the honesty of these signals - is a long-standing problem in evolutionary biology.

Just two centimetres across - fiddler crabs are ideal for studying dishonesty in signalling. One claw they have is massively enlarged (to attract females or fight rival males), which can be regrown if lost in fights.

In most species the new claw is identical to the lost one, but some species “cheat” by growing a new claw that looks like the original but is cheaper to produce because it is lighter and toothless.

Simon Lailvaux of the UNSW School of Biological, Earth and Environmental Sciences (SBEES), who studied the subject, said “what’s really interesting about these ‘cheap’ claws is that other males can’t tell them apart from the regular claws.

“Males size each other up before fights, and displaying the big claw is a very important part of this process.”

Lailvaux and colleagues from the Australian National University measured the size of the major claw in male fiddler crabs, and two elements of fighting ability - claw strength and ability to resist being pulled from a tunnel.

They found that while the size of an original claw accurately reflects its strength and the crab’s ability to avoid being pulled out of its burrow, this relationship does not hold true for a regenerated claw, according to a release of SBEES.

“This means that while males can gain an idea of the performance abilities of males with original claws from the size of those major claws, regenerated claws don’t reveal any information on performance capacities.”

Males with regenerated claws can ‘bluff’ their fighting ability. They’re not good fighters, but the deceptive appearance of their claw allows them to convince other males that it’s not worth picking a fight with them, Lailvaux explained.

These findings were published in the British Ecological Society’s journal Functional Ecology.

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