Molly Morris, associate professor of biological sciences, and colleagues found that older female swordtails spent more time with asymmetrically striped males than symmetrical males when offered a choice. These findings are the first to contradict previous studies showing that females tend to prefer males with symmetrical markings, which in this case are black bars on each side of the body. Scientists have suggested that symmetrical markings are a sign of genetic fitness.
The new study provides evidence that visual cues are not the only thing driving mate selection, however. The findings also suggest that "females may not have the same mating preferences throughout their lives," Morris said. Funded by the National Science Foundation and the Research Challenge Program at Ohio University, the paper has been published online in Biology Letters and will appear in next month's print edition.
Morris' findings raise the question of whether there may be a change in mating preference over time in other species as well. In a current study on human attraction, for example, the average age of the females and males tested for preference for symmetrical faces was only 20.3 years and 19.5 years, she said. The swordtail fish used in the latest research are two species of Mexican fish, Xiphophorus cortezi and Xiphophorus malinche. Because the genetic makeup of these fish is well known, researchers often use them to examine genetic causes of behavior.
To conduct the study, Morris and colleagues exposed females of both species to video animations of male fish, one with an equal number of bar markings on each side of the body, and one with an unequal number of bars on each side. The animations simultaneously were projec