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Butterfly Wing Pattern Diversification by Non-Darwinian Mechanisms


Yesterday, Evolution News looked at findings about butterflies that fit a design perspective better than a Darwinian one. Now for some surprising and complementary news about these delightful insects, showing how they can diversify by introgression. 

For background, see an earlier post, “More Ways of Information Sharing Found in Living Things.” As noted there, this is like sharing books, not by writing new books — the Darwinian method. Could this explain the divergent wing patterns found in Heliconius butterflies, long a favorite of Darwinians to show speciation? If so, it would simultaneously undermine the Darwinian narrative for peppered moths. An international team of 29 researchers from Harvard, Cornell, and Brigham Young University revealed widespread sharing of genetic information in members of this genus:

In a paper published today in Science, the researchers shed light on the rapid speciation of these exceptional butterflies and describe an evolutionary history rampant with introgression, wherein species exchange genes due to interbreeding between genetically divergent individuals. On a grand scale, the findings provide evidence that the model of an evolutionary tree first famously drawn by Darwin may need some adjusting.

“The traditional way of looking at evolution as a bifurcating tree doesn’t capture the complexity of the evolutionary process,” said study co-author Paul Frandsen, professor of plant and wildlife sciences at BYU. “Instead of a tree, it’s more like a bush or a network. By looking at whole genomes and using our new methods, we can get a much clearer picture of what’s going on.”

In the video, Frandsen speaks of “a lot of genetic exchange after things become distinct species.” He says that rather than seeing a tree pattern, as Darwin predicted,

it resembles more of a bush. There’s genetic information being transferred horizontally. We hope that other people who are studying other groups of animals will start to look for these same types of evolutionary signatures, to understand whether this is a really important evolutionary process among all of life.”

The “bush” metaphor is exactly what Jonathan Wells used in describing the Cambrian explosion. It’s a very different picture from Darwin’s branching tree. Frandsen shows remarkable examples of members within a species looking more diverse than members of other species that mimic them! That seems highly improbable by “convergent evolution,” but makes sense with information sharing.

Harvard University finds in these same Heliconius butterflies “evidence that the process of sharing DNA may be far more common than ever thought.” Completely absent is any mention of random mutation or natural selection.

“DNA sharing had been shown in closely related species, but we wanted to probe deeper into the phylogenetic tree,” [James] Mallet said. “What we found is really astonishing: introgression even among species that are distantly related. ‘Species’ are simply not what we thought they were, and now we have the data to show it. The evolutionary tree of butterflies is a complete morass of interconnectedness.”

Darwinism is getting hit from all directions. Meanwhile, another team of 14 scientists, publishing in PNAS, discovered that “Parallel evolution of ancient, pleiotropic enhancers underlies butterfly wing pattern mimicry.” Heliconius butterflies were the type specimens that led Fritz Müller to propose his model of Müllerian mimicry, the classic case being a butterfly mimicking a toxic species in order to avoid being eaten. What this team found was not classic neo-Darwinian mutation and selection, but “contrary to prior predictions,” introgression and regulation of the optix gene that allowed unrelated species to diversify their wing patterns in parallel. 

Still another study published in Current Biology found wing patterns were affected not by Darwinian selection, but by regulation of the WntA gene. The Smithsonian Tropical Research Institute says that those results “forever changes the way evolution is understood.” Ricardo Papa, a co-author from the University of Puerto Rico, moved from a gene-centric concept to a theme-centric model:

“Distinct species with identical wing-color patterns, such as co-mimetic butterflies, can evolve using different molecular strategies. Imagine the same notes played on different instruments!”

In summary, “Gene regulation gives butterflies their stunning looks,” says The Scientist. Regulation, hybridization, and introgression involve sharing and controlling existing genetic information. This is not neo-Darwinian evolution.

Generalizing the Lesson

The paper in Science tentatively suggests that the “complete morass of interconnectedness may be true for many kinds of related animals that show species diversity. Watch for common Darwinian icons as examples:

Species involved in rapid radiations are prone to hybridization because of frequent geographical overlap with closely related taxa. In both the melpomene and erato clades of Heliconius, introgression has overwritten the original bifurcation history of several species across large swathes of the genome, a pattern also observed in Anopheles mosquitos. This observation is also consistent with genomic analysis of other rapid radiations characterized by widespread hybridization and introgression, including Darwin’s finches and African cichlids. In other radiations, the role of introgression is less clear: in Tamias chipmunks, widespread introgression of mitochondrial DNA was identified, in contrast to an absence of evidence for nuclear gene flow. With few genomic comparisons available to date, it is perhaps too early to say whether introgression is a major feature of adaptive radiations in general, but evidence thus far suggests this to be the case.

If introgression has overwritten the original bifurcation history, you have to ask if that history ever really existed in the first place. These revolutionary findings about information sharing were only made possible by sequencing more butterfly genomes. It will be interesting to see if the findings about information sharing continue for other cases of “adaptive radiation” — cases Darwinians have typically used to proclaim the “fact” of evolution. 

A Golden Opportunity

As evidences for beauty and intelligent design in butterflies continue to grow, and the expectations of neo-Darwinism continue to decline in the face of rampant information sharing, scientists have a golden opportunity. They can show how regulated information is the real stuff of biological change. The capacity for robustness in a changing world shows foresight and planning. Butterflies may be the first well-studied case of non-Darwinian mechanisms that maintain and diversify life — within limits — through regulated sharing of purposeful, robust information.

Photo: Sara longwing, a Heliconius butterfly, by DirkvdM at en.wikipediaLater version(s) were uploaded by Samsara at en.wikipedia. [CC BY 1.0], via Wikimedia Commons.