Butterfly Mimicry Still a Challenge for Evolution - Evolution News & Views

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Butterfly Mimicry Still a Challenge for Evolution

butterfly mimicry

Earlier this year, Casey Luskin wrote that butterfly mimicry is a "huge" problem for evolutionary biology. Has anything changed since then? No. A new study published in Nature takes just one baby step beyond "preliminary" in providing a genetic basis for this wonder of the living world.

A glimpse of the problem is found in the paper. The first figure shows seven species of Melinaea, a genus of butterflies in Peru, and seven morphotypes of Heliconius numata, a "distantly related genus" that are spittin' images of Melinaea, down to coloration, wing shape and precise locations of bars, stripes and spots. How lepidopterists are able to tell them apart is astonishing in itself. But how can evolutionary theory explain this remarkable mimicry?

Heliconius_mimicry-WikimediaCommons.pngPhoto: Four Forms of H. numata, Two Forms of H. melpomene, and the Two Corresponding Mimicking Forms of H. erato. Source: Repeating Patterns of Mimicry. Meyer A, PLoS Biology, Vol. 4/10/2006, e341 http://dx.doi.org/10.1371/journal.pbio.0040341, via Wikimedia Commons.

Evolutionists have a number of classifications of mimicry, such as Batesian mimicry, Müllerian mimicry, etc., with just-so stories behind them. A satisfactory explanation, though, will need a genetic basis. In the Nature paper this week, "Chromosomal rearrangements maintain a polymorphic supergene controlling butterfly mimicry," by Joron et al., a team of 23 researchers appeals to "supergenes" as a partial explanation. These are collections of genes that remain linked as a unit, avoiding crossover and transposition. "Supergenes are tight clusters of loci that facilitate the co-segregation of adaptive variation, providing integrated control of complex adaptive phenotypes," they begin. Polymorphic supergenes are those that maintain specific combinations of genes within the supergene, giving rise to discrete phenotypes that can be maintained within a population.

By studying genetic markers in hundreds of Heliconius numata butterflies, the team noticed that each morphotype maintains a specific combination of traits in the supergene named P, a region of about 400 kilobases. They identified and compared these with another species, Heliconius melpomene, and with the reference genome Bombyx mori, the silkworm moth (currently the only published lepidopteran genome):

H. melpomene and the silk moth Bombyx mori, separated by about 100  million years of evolution, share a generally conserved gene order across this region. This supports the hypothesis that the gene rearrangements are evolutionarily derived and associated with the evolution of this locus in the H. numata lineage.
The evolutionary inference should be the least of their concerns, however. One hundred million years with no change? Such remarkable stasis is common in biology. It's hard to support the notion that conservation, the opposite of evolution, leads to any "hypothesis" that butterfly genes are "evolutionary derived and associated with ... evolution." What's more, the researchers have to account for the discrete morphotypes of H. numata persisting for millions of years along with their mimics, unless they believe they evolved very recently. One would think that in all that time, their mimic targets would have changed significantly, or predators caught on to the trick. (Notice, too, that these seven morphotypes are all members of the same species H. numata - i.e., no "origin of species" occurred.)

What's worse, the specific combinations of alleles in the P supergene act as genetic switches between phenotypes that allow for rapid adaptation within the same species, within the same population.

Our results indicate that allelic combinations at known wing-patterning loci have become locked together in a polymorphic rearrangement at the P locus, forming a supergene that acts as a simple switch between complex adaptive phenotypes found in sympatry. These findings highlight how genomic rearrangements can have a central role in the coexistence of adaptive phenotypes involving several genes acting in concert, by locally limiting recombination and gene flow.
Switches, concerts, roles -- those sound downright un-evolutionary. Maybe even designed. (In an aside, the scientists noted that "P seems to be a hotspot of adaptation in several other species, including the melanic peppered moth" -- the old evolutionary icon.)

Interesting as this result is, and praiseworthy for the fieldwork that went into it, it does not even begin to account for the wing patterns themselves. Simple combinatorial elements within a supergene leave unanswered how spots, bars, and stripes, with the precise coloration needed, could arise from an early Heliconius butterfly on its way to becoming a look-alike for Melinaea. Under Darwinian assumptions, the best that the team could say is this:

The P supergene architecture, associated with mimicry polymorphism under balancing selection in H. numata, is thus evolutionarily characterized by non-recombining co-adapted blocks that capture distinct wing-pattern genes that are known to recombine in other species of the clade.
In other words, the combinations in the supergene became locked together somehow in H. numata, maintaining discrete associations with specific morphotypes within this one species: "the rearrangements lock together distinct elements involved in wing-pattern evolution," they said. Well, what is it? Locking or evolution? A theory that explains fluid change and stasis in the same breath explains neither well.

As Casey Luskin noted, evolutionists are nowhere near explaining in mechanistic terms these remarkable look-alike patterns. And as we indicated in an earlier article ("Divining Darwin in Butterfly Genes"), some scientists seem obsessed with searching for genetic data to incorporate into their preconceived evolutionary scenarios when perhaps they should be tackling the really big issues about butterflies -- their amazing life cycles. Illustra's beautiful new documentary Thumbnail image for metamorphosis-bluray.jpgMetamorphosis does just that, using MRI technology and superb animation to advance the science by revealing the transformation that takes place inside the chrysalis, then asking (without assuming Darwinian evolution) the obvious question: how did this arise?

To learn more about butterflies and the evidence they reveal for intelligent design, visit Metamorphosisthefilm.com, where you can watch the trailer and order this outstanding film, now available in both DVD and Blu-Ray formats.