Instead, females are attracted to the "sparkle" created by the ultraviolet reflectivity of the pupils, the white circles at the center of eyespots, according to new research from University at Buffalo biologists.
The research, to be published online June 29 in the Proceedings of the Royal Society B: Biological Sciences, overturns previous work indicating that larger eyespots might be considered more desirable by female butterflies.
The purpose of the research was to explore some of the evolutionary reasons behind butterfly wing patterns in the African satyrid butterfly, Bicyclus anynana.
The findings were surprising in the context of the natural world, where dramatic colors and physical features often win the sexual-selection game, according to the UB researchers.
"This is one of the first studies to show that such a small pattern element really matters in female choice," said Antonia Monteiro, Ph.D. a co-author on the paper and UB assistant professor of biological sciences.
"We always think of something huge or ornamental as determining sexual choice," noted Kendra Robertson, co-author, who recently received her master's degree from the Department of Biological Sciences in the UB College of Arts and Sciences.
In a series of carefully controlled tests on both the dorsal and ventral sides of wings, Robertson induced a dozen subtle variations in the eyespot size and pattern of males and then studied how they influenced female's mating decisions.
"It's very easy to change the size, color composition and shape of these patterns, using artificial selection," said Monteiro. "The question then becomes, 'Why do these populations remain unchanged?' What are the selective forces that maintain these patterns constant through time in any one species in nature?"