Chemicals in male swordtail urine drive females crazy for sex

Last Updated: Fri, Feb 11, 2011 11:20 hrs

The urine of male swordtails is full of pheromones that drive their female counterparts crazy for sex, according to a new research.

Texas A and M biologists Gil Rosenthal and Heidi Fisher and an international team have revealed that the fish use chemical cues in their urine to elicit sexual responses from their downstream female counterparts.

They found that male swordtail fish strategically release pheromone-packed urine in the presence of females as a display of courtship, indicating that they have evolved a temporal and spatial control of their pheromone release.

The findings contradict previous assumptions that male pheromones in fish are passively released, given that most fish lack specialized scent glands or scent-marking behaviour.

"We showed that male swordtail fish use chemicals in the urine as mating signals," said Rosenthal.

The team studied wild-caught swordtail adults from the Rio Atempa in Huitznopala, Mexico, to determine whether females were attracted by passively produced cues or to pheromones as a form of communication.

Using fluorescein dye injections to visualize urine release inside an aquarium, they were able to determine that male swordtails relieved themselves more frequently in the presence and proximity of females than when females were absent altogether.

In the wild, males court females in much the same way, but by swimming further upstream to ensure their scent is detected in the current by the females downstream.

"Our findings show that aquatic species and vertebrates, in particular, can have fine control over their release of chemical cues in the same manner as mammals that mark their territories or advertise their reproductive state, for example," said Fisher.

Rosenthal said that swordtail fish are considered an important model system in animal communication and are widely used in female mate-choice research.

While numerous studies have addressed the role of cues in swordtails - from olfactory to visual - he said none previously have addressed exactly how and when chemical cues are released.

The findings are published in the current issue of the journal PLoS ONE. (ANI)