Butterflies as imitation offenders

"Supergene Region" regulates mimicry in wing coloration

Heliconius numata Mathieu Joron
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Butterflies are mimicry experts: Often, completely harmless species mimic the wing patterns of inedible or venomous representatives of the butterflies. Now, researchers have found that a particular gene region controls these wing tints and facilitates the adaptation to specific model types with great flexibility.

Butterflies are among the animal species that use the mimicry strategy very successfully: The deterrent eye spots or the bright warning color of the wings signalize: "I do not taste" or even "I'm poisonous". That's true even with many species. But a whole range of butterfly species only mimics these inedible ones, protected by a similar wing pattern. This includes the Heliconius species.

Biologists Mathieu Joron, Chris Jiggins and colleagues have studied the genetic mechanisms of vane patterning in three related Heliconius species. H. melpomene and H. erato are only remotely related, but have a very similar wing outline. The third species, H. numata, although closely related to H. melpomene, shows a quite different wing pattern. All three species each imitate a species of another butterfly genus, Melinea.

So far, some loci are already known, which are responsible for wing patterns and colors. However, how and which genes determine the patterns in these mimetic species was still unclear. To find out, the researchers crossed different breeds of each species and then analyzed the genetic makeup of the parents and offspring. The goal was to identify the genes that generated the respective patterns. In fact, the scientists were able to identify loci of control for each of the three species: N, Yb, and Sb for H. melpomene; Cr for H. erato and P for H. numata.

The surprising thing was the realization that the loci that regulated the color variations of all three species were all in the same "supergene region". Apparently, it concludes, this area in the genome serves as a kind of flexible "case-by-case" reservoir that promotes rapid adaptation and development of new color patterns. In the course of natural selection, this region is believed to function as an evolutionary switching mechanism that responds to a range of external influences that facilitate mimicry. In this way, the typical, adapted to local prototypes wing patterns that protect their wearers from predators. The results of the study have been published in the journal PloS Biology. display

(Public Library of Science, 26.09.2006 - NPO)