Butterflies distinguish between plants to lay eggs

London: The tropical butterfly Heliconius erato distinguishes between shapes to use them as a cue for choosing the plants on which to feed and lay eggs, shows a new research.

Heliconius erato, the red passionflower butterfly, is a large (five to eight cm wingspan), white-red-black butterfly that occurs throughout Central America and tropical South America. 

Female Heliconius develop a learned preference -- a "search image" for passionflowers with common leaf shapes and lay their eggs exclusively on these plants, which then suffer damage from caterpillars. Passionflowers (Passiflora) is a genus of tropical vines with extreme variation in leaf shape.

This would drive a cycle in which passionflowers with rare leaf shapes tend to do better and have more offspring -- until over the next generations they become more common in turn and lose their competitive advantage.

"Here we show for the first time that female Heliconius erato use shape as a cue for selecting the passionflowers on which they feed and lay eggs," said Denise Dell'Aglio, researcher at the University of Cambridge, in a statement.

The researchers used artificial flowers and leaves, made out of foam sheet, to test the preferences of Heliconius erato females for particular shapes. 

The first study showed that the butterflies have an innate preference for feeding on star-like flowers with three and five petals over flowers with simpler shapes. But they can quickly learn to reverse this preference if the simpler flowers reliably contain a food reward, showed the researchers. 

The second experiment showed that Heliconius erato prefers to lay eggs on leaves with a familiar shape, and tend to avoid laying on leaves with a shape that they have not previously encountered. 

These results indicate that the butterflies develop search images for familiar leaf and flower shapes, in support of the theory.

"These findings have implications for ecological theory, because they support a decades-old hypothesis that the butterflies could drive so-called 'negative frequency dependent selection' on the leaf shape of passionflowers, that is, natural selection where the rarest forms always have a competitive advantage. This could explain the extraordinary diversity of leaf shapes found in passionflowers," added Dell'Aglio.