26 January 2015

Butterflies can change their spots


Every aspect of a butterfly has been shaped by evolutionary processes over the millenia to render the butterfly as perfectly adapted as possible to its favored environment.  The shape of the wings, the wing pattern, the color of the eggs - all are the result of billions of tiny changes.

Some butterfly wing patterns incorporate "eyespots" such as those seen in my photo of an Eyed Brown above.  It has been well understood that one of the purposes these spots serve is to confuse a predator, as shown by the wings of this Common Buckeye I found with multiple beak-shaped defects in the area of the eyespots:


The process is demonstrated in this video by researchers at Oregon State University.  Mantids are shown attacking the head/thorax of butterflies without prominent eyespots, but the wing margins of those with eyespots:


What is most interesting is that the butterflies are the same genus and species, differing only in seasonal appearance.  (data and discussion published here).  The implications are explained at The Scientist:
Prudic and her collaborator found that the dramatic eyespots on the wings of Bicyclus anynana individuals in the wet season were more effective at fooling mantid insects, the butterflies’ main predators during rainy times, than the more diffuse wing spots of the dry season forms, which are preyed upon mostly by birds. The researchers even found that pasting wet-season spots onto dry-season butterflies had the same effect. Conversly, dry-season patterns [less-prominent eyespots] served to conceal the butterflies better from birds in its eastern African woodland habitats. “Having the right type of eyespot in the right season allowed the butterflies to live long enough to lay eggs and have more offspring in the next generation,” Prudic said. “With the wrong eyespot at the wrong time, they were quickly annihilated by the mantids.”
Fascinating.

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