Australasian Science: Australia's authority on science since 1938

Neighbours Keep Crabs Honest

By Stephen Luntz

Urban crabs are more honest than their country cousins, new evidence suggests.

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Fiddler crabs put considerable resources into making large fighting claws. Since crabs will often avoid conflict with a larger-clawed opponent, the temptation exists to build large but poorly muscled claws to bluff opponents.

“When there are lots of crabs living in one area, there is lots of competition for resources like females and food. High competition means there is a greater chance of males having to fight each other to win resources compared to when there are not many crabs about. Those crabs might not have to fight at all,” says Candice Bywater, a PhD student in the Performance Lab at the University of Queensland.

“We wanted to have a look at lots of populations that vary in the level of contact they have with other crabs and see if there was an obvious variation in the level of honesty,” says lab head Dr Robbie Wilson. This was indeed what happened, with males from highly populated areas generally having claws whose strength matched their size.

“We found that when there are not many other male crabs in a population (low competition), males produce large but relatively weak claws as they don’t have to fight as often and ultimately can get away with it,” Bywater adds.

Wilson says that not enough data has been collected to determine whether a sharp cut-off exists at a particular crab density, or if the results lie along a continuum.

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The full text of this article can be purchased from Informit.