If you have ever had trouble breeding swordtails (Xiphophorus), it may be an indication that your filtration system is highly efficient. Thanks to research funded by the National Science Foundation and the American Livebearer Association, it has been shown that the urine of male swordtails contains chemical messengers called pheromones that serve to attract female swordtails.
This study was based on wild sheepshead swordtails (X. birchmanni), from the Rio Atempa in Huitznopala, Mexico. By administering a fluorescent dye that is visible under ultraviolet light, it was possible to see when the male fish urinated in the aquarium study.
The male swordtails strategically release pheromone-packed urine in the presence of female swordtails as a hidden aspect of their courtship display. This indicates that they have developed both temporal and spatial control when it comes to releasing their pheromones.
The research, led by Texas A&M biologists Dr. Gil Rosenthal and Dr. Heidi Fisher, with assistance from colleagues at Centro de Investigaciones Cientificas de las Huastecas in Hidalgo, Mexico, and Boston University, opens up a new and exciting field of study. In the past, it had been assumed that fish simply released pheromones indiscriminately, but it is now clear that this is not always the case.
In the wild, male swordtails were observed swimming upstream, so that their urine would be carried downstream by the water current to the female swordtails.
“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, who is now based at Harvard University’s Department of Organismic and Evolutionary Biology.
Swordtails are considered an important model system in animal communication and are widely used in female mate-choice research. But while numerous studies have addressed the role of cues ranging from olfactory to visual on the behavior of the swordtail, none has previously investigated exactly how and when chemical cues are released.
“For the first time, we have shown that male swordtails use chemicals in their urine as mating signals,” Rosenthal said. “There’s been relatively little work on how pheromones shape the lives of aquatic creatures.”
Rosenthal added that studying the chemical signals of swordtails is vital not only to understanding how they and similar species communicate, but also because the information could be indicative of several environmental factors that could prove useful in the future. For example, he said, any amount of pollution might disrupt the communication within a species, thereby interfering with the courting and mating process and ultimately affecting the population.
“Since these chemicals are rich in information and because they’re transmitted through the water at very low concentrations, any change in the environment has the potential to shut down communication,” Rosenthal said. “The silver lining is that we might be able to use communication behavior as a bioassay that local communities can use to detect pollutants in the water.”
To read the full research paper, click here.