Crabs That Fib

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You talkin' to me? Male fiddler crabs pick fights, even if they know their replacement claws put them at a disadvantage.

Credit: Tanya Detto

Crabs That Fib

By Kelli Whitlock Burton
ScienceNOW Daily News
12 November 2008

When tangling over territories, some male fiddler crabs win by pretending to be stronger than they are, a new study reveals. The research adds to earlier findings that suggest animals use dishonesty more often than previously thought.

Male fiddler crabs sport an enormous claw, which can regrow if lost during a fight over a home burrow. Although the replacement looks the same as the original, it is much weaker. The crabs notice the difference in their new claw, because it is lighter and does not pinch or pull as well. However, when faced with a challenger, they act as if nothing's wrong, displaying their feeble--but large--claws threateningly. The bluff usually works, according to a team of Australian ecologists who report their findings this week in Functional Ecology.

The researchers collected Uca mjoebergi fiddler crabs in Darwin, Australia, and identified those with original claws and those with replacements. They measured closing force and pulling force--in territorial fights, invading crabs try to yank residents from their homes. The researchers then released the crabs near their original burrows and watched as other males challenged them.

Homeless crabs with regenerated claws that were searching for a new burrow usually picked on crabs with smaller claws. Most of the time, the resident crabs gave up their burrow without a fight, falling for the bluff. "Male performance traits, such as claw strength and pull-resisting force, are really the key to success in male combat, so much so that the males will pretend to be good performers even if they are not," says lead author Simon Lailvaux, an evolutionary ecologist at the University of New South Wales in Sydney, Australia.

However, resident crabs with new claws defending their homes against homeless crabs had no choice over opponents, because they had to fight whoever attacked. When challenged, residents still tried to bluff, though they weren't as successful as the deceptive invaders. Those whose bluff was called usually lost the fight because of their weaker claw.

Honesty in signaling is a growing area of interest for many scientists who study sexual selection and communication systems in animals. Work such as this--as well as similar research in crayfish, bull frogs, and hermit crabs--goes a long way toward explaining how animals rely on dishonesty to maintain territories and attract mates, says Jonathan Rowell, a biological mathematician at the University of North Carolina, Chapel Hill, who was not part of the study. "The big issue is trying to determine whether a behavioral pattern such as dishonesty is genetically hard-wired into the or if it's just an individual behavior," Rowell says.

Letters

The article "Crabs that Fib" by Kelli Whitlock Burton appears to be an egregious case of anthropomorphization of crabs. The unsubstantiated and arguably meaningless statement is made that crabs with replacement claws "know" they have a weak claw. This leads to the statement that they are therefore "bluffing" when they display the large weak claw to gain advantage over crabs with a smaller claw.

All I read in the article itself is that replacement claws are effective in winning territory because they are large. If combat ensues they are less effective. The fact that they work as displays is reason enough to retain the genes required for replacing claws.

The evolutionary question this casts light on is "do appearances always reflect physical robustness?" not is "dishonesty genetically hard-wired"? How can a mindless crab be dishonest?

Jay Spivack
Chemist, General Electric; Assistant Professor, retired, The State University of New York