Genomic “Hotspots” Drive Wing Pattern Evolution

Heliconiid butterflies

Heliconiid butterflies

Parallel papers published today in the journal PLoS Genetics upend some of scientists’ common assumptions about how Mullerian mimicry — the convergence of unrelated species toward a common wing pattern — evolves in Heliconius butterflies in Panama.

Scientists had believed that, because there are thousands of genes responsible for wing color and pattern in Heliconius butterflies, it was very unlikely the same set of genes would be responsible for the remarkable similarity of wing color and pattern in the Heliconius butterflies H. melpomene and H. erato.  They also suspected that the genes would be the same ones that are involved in wing pattern evolution for other butterfly species.  Both appear to be wrong, at least in these two species.

Scientists at Cambridge and their colleagues conducted extensive genetic studies of the two butterfly species, which are virtually indistinguishable on the wing. Both have complex, colorful wing patterns that apparently serve to warn bird predators that they are unpalatable.  Evolution favors this kind of development, since the more unpalatable species that sport similar patterns, the more likely it is that birds will learn to avoid them all.

What Chris Jiggins and his fellow researchers found was just the opposite — the same very small part of the genome, a “hotspot” if you will, actually controls the pattern in both species, and this hotspot is different from the genes involved in color and pattern development in other butterflies.

“This tells us something about the limitations on evolution, and how predictable it is. Our results imply that despite the many thousands of genes in the genome there are only one or two that are useful for changing this colour pattern. It seems like evolution might be concentrated in quite small regions of the genome – or hotspots – while the rest of it does not change very much,” Jiggins is quoted as saying in a MediaNewswire release.

The release also notes that the team also found that the obvious candidate genes – such as those involved in colour or wing pattern in other species – do not seem to be involved in the passion-vine butterflies’ mimicry.

According to Jiggins: “We think it’s more likely to be some novel method of cellular signaling, which is quite intriguing and could be important in many other insect species.”

The research is published as two papers from the Cambridge Butterfly Genetics Group in the Feb. 5, 2010 PLoS Genetics.  Read the papers here:

Jiggins et al 2010 PLoS Genetics mullerian mimicry in H melpomene clade

Counterman et al 2010 PLoS mullerian mimicry in Heliconius butterflies

And the MediaNewswire release:

2010 MediaNewsWire genomic hotspots in heliconius butterflies

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