Crayfish Cheat Their Opponents with Fake Claws
Male Crayfish’s Large Claws May Not be as Dangerous as They Look
Apr 30, 2009
Dr Robbie Wilson and researchers from University of Queensland's Integrative Ecology Lab found male freshwater crayfish with larger claws could trick opponents into believing they were stronger fighters. In fact, many of these specimens were quite weak.
Dr Wilson and his team observed as many as 500 crayfish fights during their research at North Stradbroke Island, over the last few years.
"What we found was that many of the crayfish were winning fights through intimidation alone, and were actually weak-clawed individuals," he said.
The team tested the crustaceans’ claw muscle strength and found claw size was not an accurate indicator of claw strength.
Testing for strength was easy, he said, because of the crayfishes’ aggression. “We get the crayfish to clamp their claws down on a device that measures the gripping strength of the claws. Getting them to grab hold and clamp down is very easy, as they are unbelievably aggressive.”
They found that almost 50 per cent of the male crayfish tested had claws much weaker than their size suggested.
The Benefit of Cheating with Big Claws
By waving their big claws at an opponent a crayfish is sending a signal that he is stronger than the other and could harm or even kill him.
The animal with the smaller front claws, on the basis of this threat, would usually back away to avoid injury.
A cheating crayfish has thus managed to avoid a conflict in which it may actually be beaten by a stronger rival.
Paying the Price of Large Front Claws
However, strong or weak, large front claws can also be a disadvantage, Dr Wilson said.
The large claws prove cumbersome when trying to swim away from predators. “A large set of claws can reduce males’ swimming speeds by as much as 40-50%.
"Whether they are strong or weak, all crayfish with larger claws must pay this extra cost," Dr Wilson said.
Cheating Behaviour in Crayfish Unexpected
This evidence of cheating surprised Dr Wilson and his team, as signals of strength and ferocity were usually thought to be reliable warnings to others to stay clear.
"The roar of a lion, the bark of a dog, or even the fairing fins of a male Siamese fighting fish are all signals between competing individuals," he said.
"These signals are expected, by theory, to be an honest indicator of how strong that individual is and how it could inflict injuries on opponents.”
Yet, it was clear from his team’s research that sending dishonest signals like waving large but weak claws was fairly widespread. Even a few females were cheating.
"We found that dishonest signals can occur and in very high frequencies in nature, which is very cool and very surprising.
“We expect some animals to cheat in a population, but the really surprising thing is that cheating is so common among the males.”
Crayfish Not Alone in Sending Dishonest Signals
Dr Wilson said the practice of cheating was probably more common than originally suspected, especially among crustaceans.
“I suspect that cheating is way more common in nature than has been previously suspected, especially among organisms that have an external skeleton that can effectively hide their muscles inside their shells (i.e. crustaceans).”
The next step will be to try to discover “why males still pay attention to the size of the claws of their competitors when so many males are cheating. It seems silly that males would still make decisions about whether they fight or flee based on relative size of their claws.”
‘Costs and benefits of increased weapon size differ between sexes of the slender crayfish, Cherax dispar’ was published in the Journal of Experimental Biology.
See also: Transvestite Lizards Imitate Females
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