Genetic Study Complicates a Classic Case of Mimicry

It's hard to believe that these 3 Heliconius butterflies are completely different species. They have very similar wing shape, color, and patterns, and are all perched on passion flower vines, their food source and a cozy place to lay their eggs. Heliconius have a good reason for resembling each other: predators know that bright butterflies make a really foul-tasting meal (the good-tasting ones just mimic the bad-tasting ones so they won't get eaten.)

Evolutionary biologists have studied Heliconius butterflies for more than a century--the first paper on Heliconius mimicry came out in 1879 and is a classic example of convergent evolution, environmental pressure causing different species to look or behave increasingly alike.  Today, genetics inform new studies, but might change the way we think about their evolution.

A recent study reveals an amazing thing about Heliconius wing color: the evolution of only one gene is responsible for Heliconius mimicry across dozens of species. Little tweaks in one gene, over generations, are responsible for making dozens of different species similar. "This is our first peek into how mimicry and convergent evolution happen at a genetic level," researcher Robert Reed said in the press release. "We discovered that the same gene controls the evolution of red color patterns across remotely related butterflies." 

Though these species look alike, we have to remember that they are classified as different species, and thus their genes are arranged and/or regulated differently. Which makes it astonishing that the same gene is responsible for changes in each species. "This is in line with emerging evidence from various animal species that evolution generally is governed by a relatively small number of genes," says Dr. Reed. "Out of the tens of thousands in a typical genome, it seems that only a handful tend to drive major evolutionary change over and over again."

But...if only one gene is involved...is this a case of convergent evolution or homology? Reed asks the same question in the abstract of his study's paper, commenting that it"blur[s] the distinction between convergence and homology."

Do these butterfly species come from a different-enough lineage so we can say they evolved to converge on wing color? Years ago, a study showed that non-sterile hybrids of Heliconius species were possible. These hybirds were first noticed in their habitat outside the lab, and so are an example of what scientists once though was mimicry but was really hybridization. The Reed study uses "distantly related species," though, and still finds the same gene involved.

The other possibility is that the wing color gene comes from a common ancestor of all Heliconius butterflies, and since evolution is acting that single gene to change wing color, it's an example of homology. Who knows--maybe Heliconius wing color is like whale flippers and human arms: they all come from the same ancestral part, tweaked, regulated, deregulated, and changed completely since they last had a common ancestor.

Maybe it's homology then convergence...the butterflies first evolved into different species and then converged on wing color. Truth is, I'm not really qualified to speculate. Any takers?

 SOURCE -- Heliconius.org, UCI

Reed RD, Papa R, Martin A, Hines HM, Counterman BA, Pardo-Diaz C, Jiggins CD, Chamberlain NL, Kronforst MR, Chen R, Halder G, Nijhout HF, & McMillan WO (2011). Optix Drives the Repeated Convergent Evolution of Butterfly Wing Pattern Mimicry. Science (New York, N.Y.) PMID: 21778360

Treehoppers: the Princess Beatrice of the Insect World

Insects called "treehoppers"sport hats as crazy as Princess Beatrice, except it's possible the insects are more fashion-forward. They're much more beautiful to my taste, anyway. Treehopper hats are actually thorn-like projections of their own body, and are permanently attached between their head and wings (the body is the small yellowish legs and light brown midsection below this Cladonota species' expressionistic "C") 

You'd think these oddly large and awkwardly shaped pronouncements would be too cumbersome for scuttling around on tree branches and eating sap; Princess Beatrice is quite happy that she doesn't have to wear that ludicrous nonsense for the rest of her life for fear of hitting her head on every doorframe she walks through. But, the 2-inch-long treehoppers are positively chuffed. They probably use their adornments as camouflage or as intimidation, or at least that's what it looks like to us humans. 

You can imagine this intimidating treehopper, whose hat looks like the lethal claws of a European rhinoceros beetle, leaving predators running scared: 

....or a group of Costa Rican treehoppers impersonating the local bird of paradise foliage to blend in:

....this treehopper looks just like an ant:

 

 ...many different ways to impersonate a stick, a leaf, or another animal:

The creative headgear comes in an astonishing number of variations, and is actually like a third wing, growing alongside the wings as the insects matures. In the treehopper's nymph stag--before their final molt to adulthood--the insects' Hox gene, responsible for making sure their head, segments, and wings end up in the right place, assists making these wild sculptures attached to the first segment of their body, between the head and wings. The Hox protein activates and deactivates genes involved in making wings, and the wild treehopper helmets probably evolved because of a deactivation of a long-time repressed wing-making gene for the first body segment. Here's the developing treehopper nymph, from a recent paper (red is where the helmet is growing, blue is where the wings grow):

In nature, it's rare to find an insect that evolves to add and appendage or enlarge a feature of the body--most often you see wings and body getting smaller as these bugs evolve over thousands of years. The treehopper is truly an eccentric bug.

SOURCE: Nature, Live Science