Biologists have long observed that females of numerous species will distance themselves from pushy would-be partners, but they have disagreed as to why.
At least one study has shown that when females are more vulnerable to attack -- because size or color, for example -- they may abandon prime feeding grounds, leaving the choicest morsels to males.
Another theory suggests that, for some species, the two sexes digest differently and thus wind up foraging or hunting in separate areas for different plants or prey.
In the case of the guppies, however, Safi Darden and Darren Croft, researchers at Bangor University in Wales, suspected that sexual harassment was the driving force of segregation.
"In nature, as a result of sexual conflict, females often experience harassment from males, which can be costly" for the females, they note.
To test their hypothesis, they devised an experiment with 240 wild guppies -- 120 large females, 60 small females, 60 males -- in a Trinidadian river, creating four zones subject to varying degrees of danger from fish-eating predators.
The results were unambiguous.
"In the presence of males, females actively select areas of high predation risk but low male presence, and thus trade off increased risk against reduced sexual harassment," they concluded.
Take away the males, and the females returned.The study, published in the British Royal Society's Biology Letters, is the first experimental evidence that sex-adled males sometimes drive the objects of their ardor to flee, even into the jaws of danger, the authors say.