scientists have discovered that female butterflies can be taught to
prefer mates with more spots on their wings. (Image created by William
Piel and Antónia Monteiro)
If female butterflies are
programmed to identify males of their species by the patterns of spots
on their wings, how can new wing patterns evolve in males?
answer is that while females are predisposed to prefer a specific
pattern, they learn to like flashier ones more, according to a new Yale
The study published online the week of June 11
in the 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 Yale team studied the butterfly species Bicyclus anynana, which
in the wild has two spots on its forewings (the tops of the wings). The
researchers found that female butterflies of the species learn to
prefer males with four spots on their forewings over those with two
The male Bicyclus anaynana found in the wild has two eyespots on its forewings (left), while the Spotty type has four.
surprised us was that females learn this preference after being in the
presence of males for just a very short period of time,” said Erica L.
Westerman of Yale’s Department of Evolutionary Biology and Ecology
(EEB) and 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 Yale researchers were
surprised to find that an insect species like the butterfly actually
can learn to favor some wing patterns more than others.
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,” said Antónia Monteiro, EEB professor and senior author of the paper.
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 said. “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.”
Study was funded by the National Science Foundation and Yale.
Yale’s Andrea Hodgins-Davis and April Dinwiddie were co-authors of the paper.