Rapid Evolution in Real Time

On islands off the coast of Florida, scientists uncover swift adaptive changes among Carolina anole populations, whose habitats were disturbed by the introduction of another lizard species.

By | October 23, 2014

Male Carolina anole (left); male brown anole (right)WIKIMEDIA, R. COLIN BLENIS (L), HANS HILLEWAERT (R)For most of its existence, the Carolina anole (Anolis carolinensis) was the only lizard in the southwestern U.S. It could perch where it wanted, eat what it liked. But in the 1970s, aided by human pet trade, the brown anole (Anolis sagrei)—native to Cuba and the Bahamas—came marching in. In experiments on islands off the coast of Florida, scientists studying the effects of the species mixing witnessed evolution in action: the Carolina anole started perching higher up in trees, and its toe pads changed to enable better grip—all in a matter of 15 years, or about 20 lizard generations.

In a paper published in Science today (October 23), Yoel Stuart of the University of Texas at Austin, Todd Campbell from the University of Tampa, Florida, and their colleagues discuss what happened when the two species converged upon the same habitats.

“It’s a cool paper and I am excited by it,” said Daniel Simberloff, a professor of ecology at the University of Tennessee, Knoxville, who was not involved in the study. “It confirms a couple of theories that I’ve been interested in: rapid evolution and character displacement.”

When closely related species compete, they may evolve to become different from one another. Called “character displacement,” this process can result in evolutionary changes that reduce further interactions between the species. A. carolinensis and A. sagrei have similar ecologies and occupy similar habitats—they both live on trees and eat insects. So it was no surprise that both were changed by their meeting.

Spoil islands in the Mosquito Lagoon off the coast of Florida, a byproduct of dredging in the area to make the Intracoastal Waterway in the 1950s, served as the prime site for this experimental evolution study. By the 1990s, flora and fauna from the mainland—including the Carolina anole—had colonized the islands. In May 1995, Todd Campbell chose six islands with resident populations of the Carolina anole and recorded the height at which the lizards were perched. He then introduced small populations of the brown anole to three of the islands, leaving three land patches undisturbed.

“We had two predictions: one, that perch height would be higher for the Carolina anole in areas where the brown anole was found; two, that there would be an evolutionary consequence to this behavior modification,” said Stuart, who at the time of the study was a PhD student at Harvard University.

The brown anole populations grew rapidly. By August 1995, after just three months, the Carolina anoles began perching at greater heights. On the control islands, however, the Carolina anole was making full use of its typical habitat: the entire tree, from the ground to the crown.

Previous studies had shown that anoles that perch at elevated heights have more adhesive toepads because they have more lamellae, grooves that allow the digits to stick better to surfaces. In 2010, Stuart went about counting lamellae on the longest digits of the Carolina anoles, the fourth toe of each hindleg. He found that Carolina anoles living on the islands where brown anoles were introduced had larger toe pads and more lamellae.

To rule out phenotypic plasticity, the researchers sought to establish whether the larger, stickier toepads were passed on to the next generation. So the team collected gravid females from four invaded and four non-invaded islands in 2011, raising their offspring in identical conditions. The larger, stickier toepads persisted in the lab-bred offspring conceived on the invaded islands.

“The evidence for an evolutionary change surprised me,” said Stuart.  “The pace at which the change was happening surprised me even more.”

“This elegant study adds to a growing body of evidence that evolutionary changes can occur very rapidly, on timescales that we once regarded as far too brief for significant adaptation,” Rick Shine, an evolutionary ecologist at the University of Sydney, who was not involved with the study, told The Scientist in an e-mail.

“Ironically, this new paradigm has come from studies of invading species, organisms that we usually treat as terrible ecological problems,” added Shine.  “Because invaders encounter strong evolutionary forces in their new homes, and impose equally strong pressures on the native species already there, they can experience—and induce—remarkably rapid adaptive changes.”

Y. Stuart et al., “Rapid evolution of a native species following invasion by a congener,” Science, doi: 10.1126/science.1257008, 2014.

Correction (October 24): This article has been updated to reflect that it has been around 15 years since brown anole invaded the Carolina anole habitat, not 10 as originally reported. The Scientist regrets the error.

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Avatar of: James V. Kohl

James V. Kohl

Posts: 349

October 24, 2014

RNA-directed DNA methylation links the epigenetic landscape to the ecological adaptations manifested in the morphology of the toe pads. The changes require epigenetically-effected nutrient-dependent RNA-mediated amino acid substitutions that differentiate cell types. The morphological changes manifested in the cell types linked to larger toepads exemplify cell type differentiation that must be controlled by the physiology of reproduction and properly timed nutrient-dependent reproductive sexual behavior, which probably occurs near the location of the higher perches.

Re: rapid evolution and character displacement

Everything currently known about biophysical constraints; the chemistry of protein folding; and the conserved molecular epigenetics of molecular biology attests to the fact that 1) moving to higher perches and 2) larger toepads require a series of simultaneous nutrient-dependent pheromone-controlled ecological adaptations that obviously have occurred.

The similarities to what also occurs in hummingbirds that ecologically adapt to higher elevations is clear. However, like all similarities manifested in morphological and behavioral phenotypes that arise in the context of nutrient-dependent pheromone-controlled ecological adaptations, these lizards attest to the fact that the differences are due to RNA-mediated events, not to evolutionary events.

Creative use of the term “character displacement” can be compared to what Dobzhansky, a self-proclaimed creationist, wrote about amino acid substitutions in 1973. "...the so-called alpha chains of hemoglobin have identical sequences of amino acids in man and the chimpanzee, but they differ in a single amino acid (out of 141) in the gorilla."

If he was not still dead, Dobzhansky, who was also a self-proclaimed evolutionist, would probably dismiss the observations of others who claim that 'character displacement' is proof of evolution, as he did in (1964) when he wrote:  "...the only worthwhile biology is molecular biology. All else is "bird watching" or "butterfly collecting." Bird watching and butterfly collecting are occupations manifestly unworthy of serious scientists!"

We can expect to see researchers report soon that a single nutrient-dependent RNA-mediated change leads from ecological variation to the morphological and behavioral phenotypes of these lizards, since that is how ecological adaptation occurs in all species. However, we can also expect to see a few more attempts to place ecological adaptations into the context of evolutionary theories, since the theory has become more popular than biological facts.

But Darwin's theory placed 'conditions of life' before natural selection. Only after population geneticists bastardized his theory did it become popular enough to include in the context of:

1) "character displacement"

2) "indirect genetic effects"

and

3) "genome dynamics events."

Avatar of: Roy Niles

Roy Niles

Posts: 88

Replied to a comment from James V. Kohl made on October 24, 2014

October 24, 2014

None of that inane series of non scientific proclamations makes any logical sense at all.  There must be something in that perfume you sell that's unadaptive.

Avatar of: Brent Beach

Brent Beach

Posts: 7

October 24, 2014

The remaining question - how long will it take for these new characteristics to disappear from a population if the competitors are removed?

 

Avatar of: James V. Kohl

James V. Kohl

Posts: 349

Replied to a comment from Brent Beach made on October 24, 2014

October 24, 2014

Once the nutrient-dependent amino acid substitutions are fixed in the organized genome, they are removed only when they are of no further benefit to organism-level thermoregulation, which occurs in the context of themodynamic cycles of protein biosynthesis and degradation.

Mutations may then accumulate that lead from the loss of functional protein structure to loss of tissues, as occurs in eye regression in cave fish. Their nutrient-poor environment leads only to preservation of tissues that are essential for their nutrient-dependent pheromone-controlled physiology of reproduction.

Mutations are not likely to eliminate the newly acquired morphological and behavioral diversity of the lizards that climbed higher into the trees to find food, unless the RNA-mediated changes in their toepads and behavior provided no benefit whatsoever when the congeners were removed.

Avatar of: James V. Kohl

James V. Kohl

Posts: 349

Replied to a comment from Roy Niles made on October 24, 2014

October 24, 2014

You seem to have missed the links that scientifically support the entirety of my claims for RNA-mediated events that link amino acid substitutions to morphological and behavioral phenotypes without the pseudoscientific nonsense of evolutionary theory.

Alternatively, you may simply have not liked the information in the links. Here are two more for you to consider.

Combating Evolution to Fight Disease

RNA and dynamic nuclear organization

Please let others know if you also think these two articles make no sense. Many people may not be aware that nothing you have ever said in your comments about my comments makes any sense. You're like a child who can only say 'Nuh-uh' when confronted with facts.

Avatar of: JMK-Free

JMK-Free

Posts: 7

October 25, 2014

It would have been useful to know the initial range of sizes of the Carolina anole's toe pads - i.e. were there already different populations with different sized footpads at different heights in the trees.

Avatar of: Andries

Andries

Posts: 14

October 25, 2014

THAT IS CALLED ADDAPTION AS THERE IS NO SUCH THING AS EVOLUTION, EVOLUTION IS A MINDLESS THEORY THAT EVOLVES IN TO WORSE AND WORSE MINDLESNESS

Avatar of: mary14889

mary14889

Posts: 5

October 28, 2014

I am disturbed that this researcher intentionally introduced an alien species to these islands.  That seems  like a breach of scientific ethics.  Where was the oversight?

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