Scientists Report New Take On Sexual Signaling

In dangerous environments, females looking for a mate run great risks. Scientists from Seoul National University, Korea, and the Smithsonian Tropical
Research Institute in Panama present a new take on sexual signaling in the May 9th issue of the online, peer-reviewed open-access journal PLoS ONE.
The researchers report that females prefer a male sexual signal that helps them avoid their predators as they sequentially visit and assess potential
mates.


The traditional explanation for the evolution of outrageous sexual signals like the male peacock's plumage is that showy males attract females and
give them better offspring. Showy males escape from predators despite their highly conspicuous ornaments and behaviors - proof of their superiority.


"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, and lead author of the paper.


As the tide recedes, revealing great expanses of Pacific beach, fiddler crabs (Uca terpsichores) segue in and out of their burrows, dodging predatory
shorebirds. Male crabs build hood-like sand castles next to the entrance of their burrows, attracting the attention of females by waving their one,
super-sized claw.


Females prefer males that have built hoods to males that have not. When they run across the beach to check out or mate with a male, they orient
visually to both the waving male and to his hood. In this way they reach the male's burrow quickly and directly and 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, who has studied sexual selection in this group for nearly 35 years. This study
illustrates how the ecology of choosing a mate can shape sexual communication. "Conspicuous male sexual signals need not advertise the quality of
the signaler as a mate," Christy suggests. "Some may simply allow choosy females to stay safe."


The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The Institute furthers
the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation
by increasing public awareness of the beauty and importance of tropical ecosystems.


The study was funded by the Korean Research Foundation and Ewha Women's University.


Kim TW, Christy JH, Choe JC (2007)

"A Preference for a Sexual Signal Keeps Females Safe"

PLoS ONE 2(5): e422. doi:10.1371/journal.pone.0000422

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