Lizards Rapidly Evolve After Introduction to Island (Italian Wall Lizards On Island off the Coast of Croatia)

Kimberly Johnson
for National Geographic News
April 21, 2008

Italian wall lizards introduced to a tiny island off the coast of Croatia are evolving in ways that would normally take millions of years to play out, new research shows.

In just a few decades the 5-inch-long (13-centimeter-long) lizards have developed a completely new gut structure, larger heads, and a harder bite, researchers say.

In 1971, scientists transplanted five adult pairs of the reptiles from their original island home in Pod Kopiste to the tiny neighboring island of Pod Mrcaru, both in the south Adriatic Sea. Genetic testing on the Pod Mrcaru lizards confirmed that the modern population of more than 5,000 Italian wall lizards are all descendants of the original ten lizards left behind in the 1970s. While the experiment was more than 30 years in the making, it was not by design, according to Duncan Irschick, a study author and biology professor at the University of Massachusetts, Amherst.

After scientists transplanted the reptiles, the Croatian War of Independence erupted, ending in the mid-1990s. The researchers couldn't get back to island because of the war, Irschick said.

In 2004, however, tourism began to open back up, allowing researchers access to the island laboratory.

"We didn't know if we would find a lizard there. We had no idea if the original introductions were successful," Irschick said. What they found, however, was shocking. The island was swarming with lizards," he said. The findings were published in March in the journal Proceedings of the National Academy of Sciences. The new habitat once had its own healthy population of lizards, which were less aggressive than the new implants, Irschick said. The new species wiped out the indigenous lizard populations, although how it happened is unknown, he said.

The transplanted lizards adapted to their new environment in ways that expedited their evolution physically, Irschick explained.
Pod Mrcaru, for example, had an abundance of plants for the primarily insect-eating lizards to munch on. Physically, however, the lizards were not built to digest a vegetarian diet. Researchers found that the lizards developed cecal valves¡ªmuscles between the large and small intestine that slowed down food digestion in fermenting chambers, which allowed their bodies to process the vegetation's cellulose into volatile fatty acids.

"They evolved an expanded gut to allow them to process these leaves," Irschick said, adding it was something that had not been documented before. "This was a brand-new structure." Along with the ability to digest plants came the ability to bite harder, powered by a head that had grown longer and wider. The rapid physical evolution also sparked changes in the lizard's social and behavioral structure, he said. For one, the plentiful food sources allowed for easier reproduction and a denser population. The lizard also dropped some of its territorial defenses, the authors concluded.

Such physical transformation in just 30 lizard generations takes evolution to a whole new level, Irschick said. It would be akin to humans evolving and growing a new appendix in several hundred years, he said. "That's unparalleled. What's most important is how fast this is," he said.

While researchers do know the invader's impact on its reptile brethren, they do not know how the species impacts local vegetation or insects, a subject of future study, Irschick said. The study demonstrates that a lot of change happens in island environments, said Andrew Hendry, a biology professor at Montreal's McGill University.

What could be debated, however, is how those changes are interpreted whether or not they had a genetic basis and not a "plastic response to the environment," said Hendry, who was not associated with the study. There's no dispute that major changes to the lizards' digestive tract occurred. "That kind of change is really dramatic," he added. "All of this might be evolution," Hendry said. "The logical next step would be to confirm the genetic basis for these changes."

Reptilman´s comment:

is´nt that awesome - cool results and some scientists playing god, introducing a foreign species onto a small island (which is probably unique and therefore vulnerable) and they happily wiped out the local lizard population! congratulation friends, well done! thats a perfect example, how stupid even university graduates can be....

Mario Lutz wrote:

Reptilman´s comment:

is´nt that awesome - cool results and some scientists playing god, introducing a foreign species onto a small island (which is probably unique and therefore vulnerable) and they happily wiped out the local lizard population! congratulation friends, well done! thats a perfect example, how stupid even university graduates can be....

First of all, the scientists who obtained the results reported there are not the same ones who introduced the lizards 36 years ago! They followed up on an experiment started in the early 1970s by others, that's all. I guess the sort of experiment done in the 1970s would not get ethics approval today, but that does not mean that we should not look at the results of that experiment

Second, the island concerned was the size of a couple of football fields, one of hundreds like that off the coast of Croatia, and the P. melisellensis there have been isolated for no more than a few thousand years - since the end of the ice age at the absolute maximum - very unlikely that anything special was lost there.

Third, P. sicula is not a "foreign" species there - P. melisellensis and P. sicula are both widespread and common all over the Dalmatian coast and on the various islands, the interesting feature being that on the islands, you generally get one or the other, but not both (that was part of the interest of the initial experimental introduction).

Fourth, given how close these islands are to each other and the mainland, I would expect to see considerable turnover by natural processes (extinctions, recolonizations etc.) in any case (and let's not even mention unintended human transport of lizards and other fauna and flora all over the place which happens al the time). So all in all, in the grand scheme of things, it's pretty trivial (and in any case, a short herping trip to S. Florida will demonstrate how much more damage herpetoculture and the herp trade do when it comes to wrecking ecosystems through the introduction of invasive aliens).

Given the constant assault on evolution by creationists etc., that study is a major achievement in demonstrating real-time evolution, even of major features such as a complete change in gut architecture, and opens up a whole series of new questions using that particular introduction as a model system.

Cheers,

WW

everyone has his own point of view on stories like this...

"The new species wiped out the indigenous lizard populations," is enough for me to know, it cant be right at all. who ever is been in charge for this action earlier..

its not up to them, not up to you and not up to me to judge what population of what species on what island in this world can be lost because of the higher target of science. its the same, to see the stuff happen in florida, at least - their where most animals escaped from some facility or released by stupid folks.... how ever this introductions around the world has happened in the first place - to me it sounds just wrong. sorry, my 2 cents...

Homo sapiens has always introduced species some places they not belong, results are visible all over the world.. i spare to mention them.. that does not make it right to do the same for any reason what so ever....



cheers
Mario