Sexual signaling for female protection

May 9, 2007 08:53 GMT  ·  By

Sex can be dangerous. And in some cases the females are the ones putting themselves at risk.

In the case of the fiddler crabs females have to expose themselves to the predators to get some loving moments. That's why they seem to take very seriously the sexual signaling as discovered by a mix team from Seoul National University, in Korea and the Smithsonian Tropical Research Institute in Panama.

The female crabs guide themselves after a male sexual signal that enables them to avoid their predators while going out of their burrows for amorous visits.

Commonly, the showy sexual signals like the male peacock's plumage are believed to function for attracting females and deliver them better genes for their offspring. These males escape from predators despite being extremely conspicuous, thus they have higher fitness.

"In our study of fiddler crabs, the strength of female preference for a male signal that increases her own survival increases with her perceived risk of predation. That a female's choice of a mate is based on sexual signals that benefit her directly is a fundamentally new and perhaps widely applicable idea," said Tae Won Kim, a post-doctoral fellow at Ewha Women's University in Korea.

When the low tides expose the beaches, the fiddler crabs (Uca terpsichores) enter and get out of their burrows, avoiding predatory shorebirds.

The male crabs construct hood-like sand formations next to the hole of their burrows. They attract potential mates by waving their sole super-sized claw. Females clearly choose males which have built hoods over those which have not. While running across the beach looking for a mate, females look for both the waving claw and the hood.

The hoods seem to help them avoid their predators.

"When we bait predatory birds into the area-artificially increasing the risk of predation, females show an even greater preference for males who have built hoods," said STRI staff scientist John Christy.

"Conspicuous male sexual signals need not advertise the quality of the signaler as a mate. Some may simply allow choosy females to stay safe." he added.