The UB researchers altered wing-pattern elements through carefully painting the wings or by pairing males displaying traits of different size and color. They then tested female preference for wing size, eyespot size, quantity of eyespots on the wing, eyespot and pupil color, and pupil reflectivity.
"Once we found a trait that appeared to be important, we then would exaggerate it or reduce it to pin it down," said Monteiro.
None of the variations induced on the ventral side appeared to have any affect on the females' mating decisions, leading the researchers to conclude that the ventral side of the wing does not play a role in the decision making.
But when the researchers painted the white pupil on the dorsal side with black paint, thereby eliminating the pupil, these males were much less desirable to females by a ratio of two to one, demonstrating clearly that females preferred the presence of the white pupil.
However, a large white pupil, about twice the diameter of a natural pupil, also was not found desirable by females, indicating strong sensitivity to a set of rather narrowly defined features, such as eyespot pupils that measure approximately half of one millimeter.
The most conclusive finding resulted when the researchers painted the white pupils in male eyespots on the dorsal side with a plant extract, rutin, which maintained the pupils' whiteness, but eliminated their ultraviolet reflectivity.
"When there was no UV reflectivity, which butterflies can see, females registered a strong distaste," said Monteiro. "Selection against the absence of UV reflectivity was as strong as selection against the absence of a pupil altogether."
The reasons for this phenomenon are complex, but Robertson noted that the UV reflectivity may be important in what is known as photic stimulation -- a flashing light effect -- during the series of eve
Source:University at Buffalo