Endowed Crabs Flaunt it

Saturday, 12 December 2009

Hermit crabs exaggerate their fighting ability with misleading claw displays

Jane Palmer, Ph.D.

Back off. Male hermit crabs display their claws to intimidate and deter attackers. Credit Hans Hillewaert by courtesy of Wikimedia Commons

Well-endowed hermit crabs are not shy about displaying their claws – especially if showing off will mislead potential opponents. When a crab has unusually large claws for its body size, it will spend more time displaying them, says a new study. The research, which suggests such crabs exaggerate their fighting ability to avoid attack, indicates a more subtle form of dishonesty in animal signaling than has been previously recognized.

To study these crab interactions in detail, a team led by marine biologist Gareth Arnott at Queen’s college in Belfast, collected European hermit crabs, Pagurus bernhardus, from the shores of Ballywalter, Northern Ireland. They selected only male crabs for the study, measured the size of their claws and weighed each crab without its shell. The researchers then staged and videotaped 120 encounters between the crabs.

When the crabs’ claws were disproportionately large, belying the crabs’ true body size, the crabs spent more time displaying them. “It’s like you have got this bigger claw than is predicted by your body size, so you might as well wave it around and use it,” says Arnott. Also, the researchers found that the longer the display, the less likely the crabs were to fight over shells. This result indicates the crabs are signaling they are unwilling to take the role of defender and that opponents should not attack, Arnott said. The results appeared last month in Animal Behaviour.

The researchers argue for a revised perspective on deception in animal signaling. “Rather than a deception, it is an exaggeration: It is kind of making the most of what you have got,” Arnott says. Viewing signals as either honest or deceptive is too simplistic and hinders progress in understanding the function of animal signals, he maintains.

“It is quite interesting in that they have looked at what happens after the displays have been used and whether the individuals that are cheating are gaining an advantage,” says marine biologist Mark Briffa at the School of Marine Science and Engineering in Plymouth, England. Briffa cautions however, that the sample size for the crabs engaged in the shell fights in this study was insufficiently large to draw any conclusions about whether the exaggeration behavior was advantageous.

Source

Arnott, G. and Elwood, R.W. (2009) Signal residuals and hermit crab displays: flaunt it if you have it! Animal Behaviour. Published online 7 November 2009.

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