How butterflies got their spots: A 'supergene' controls wing pattern diversity
Butterflies are known to employ some interesting convergent evolutionary tactics to survive--some nonpoisonous species have similar wing patterns to those of noxious species that predators avoid. In a new study published online today in the open access journal PLoS Biology, Mathieu Joron, Chris Jiggins, and colleagues investigate the underlying genetic mechanisms of such molecular mimicry in three species of Heliconius butterflies.
In this study, the authors investigate two distantly related species (H. melpomene and H. erato) that have similar wing patterns and a third species, H. numata, that is closely related to H. melpomene, but displays very different wing patterns. Each of these three species is also known to mimic a different species within another butterfly genus, Melinaea. Several genomic loci are already known to be responsible in part for encoding the wing patterns and colorings. To explore the genetic backgrounds of each of these species, the authors crossed different races of each species and genotyped the offspring in order to identify genes responsible for the color patterns. Thus, they were able to map the color pattern controlling loci in each species: N, Yb, and Sb for H. melpomene; Cr for H. erato; and P for H. numata. Using molecular markers within the pattern encoding genic regions, the authors then found that the loci controlling color pattern variation for each species lie within the same genomic equivalent locations.
This "supergene" region therefore seems to be responsible for producing wing pattern diversity in Heliconius butterflies. Such a locus plays what researchers call a "jack-of-all-trades flexibility" rather than a constraining role. Under natural selection, this region presumably functions as a "developmental switching mechanism" by responding to a wide range of mimetic pressures to produce radially divergent, locally adapted wing patterns.
Citation: Joron M, Papa R, Beltrán M, Chamberlain N, Mavárez J, et al. (2006) A conserved supergene locus controls colour pattern diversity in Heliconius butterflies. PLoS Biol 4(10): e303. DOI: 10.1371/journal.pbio.0040303.
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