Lizards Rapidly Evolve On Island In Only Decades

Lizards Rapidly Evolve After Introduction to Island
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.

Lizard Swarm

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.

Fast-Track Evolution

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—muscles 
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 do***ented 
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.

(Related news: "Komodo Dragon's Bite Is 'Weaker Than a House Cat's'" 
[April 18, 2008].)

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 im****tant 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.

Dramatic Changes

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."

© 1996-2008 National Geographic Society. All rights reserved.

http://news.nationalgeographic.com/news/pf/49841077.html

[
In the sci-fi novel "When Worlds Collide," published in 1933, scientists 
frantically prepare to leave Earth for another planet when Earth is 
facing collision with another planet.  Their space****p only has room to 
take a few select species of plants and animals with them to another 
world.  But they hope that, once those Earthly life forms are released 
on the new world, differentiation and evolution will quickly set in and 
a diverse biota will form there in time for human colonization, rather 
than taking millions of years.

Not bad thinking for 1933.
]


-- 
Steven L.
Email:  sdlitvin@[EMAIL PROTECTED]
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