For butterflies, flashy wings get the girl

YALE (US) — Female butterflies are wired to identify males of their species by the spots on their wings, but new research shows they can learn to like males that evolve flashier patterns.

A new study published online June 11 in Proceedings of the National Academy of Sciences gives a partial explanation of an evolutionary mystery.

Biologists used to think that preference for certain traits such as wing spots are hardwired into insects. But that left scientists wondering how butterflies managed to evolve such great diversity in their wing coloration.


The researchers were surprised to find that an insect species like the butterfly actually can learn to favor some wing patterns more than others. (Credit: William Piel and Antónia Monteiro)

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Researchers studied the butterfly species Bicyclus anynana, which in the wild has two spots on its wings. The researchers found that female butterflies of the species learn to prefer males with four spots on their wings over those with two spots.

“What surprised us was that females learn this preference after being in the presence of males for just a very short period of time,” says Erica L. Westerman of Yale University‘s Department of Evolutionary Biology and Ecology (EEB) and the study’s lead author. “The male did not have to court them or engage in flashy behavior.”

While other studies have found that invertebrates can learn new preferences, the researchers were surprised to find that an insect species like the butterfly actually can learn to favor some wing patterns more than others.

When exposed to butterflies with four brilliant ultraviolet-reflecting spots for only three hours, females no longer show preference for the type of males found in the wild. But females initially exposed to drabber males with one or zero spots did not change their original preferences.

“There is a bias in what females learn, and they learn extra ornamentation is better,” says Antónia Monteiro, EEB professor and senior author of the paper.

The findings that social environment can change mating preference of female butterflies helps explain how novel wing patterns evolve, say the researchers. Now Westerman wants to discover how female butterflies learn to make these choices.

“What we have found is a previously unexplored mechanism for biasing the evolution of morphological diversity,” Westerman says. “We are now investigating what other cues are being evaluated during the learning period and what prevents females from mating with members of other species.”

The study was funded by the National Science Foundation and Yale.

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