By STAN FREEMAN
Added: Sat, 31 May 2008 23:00:00 UTC

Thanks to Larry Clark for the link.

Lizards make adaptive change

AMHERST - In 1971, five pairs of Italian wall lizards were transplanted by biologists from their home island of Pod Kopiste, in the South Adriatic Sea, to the neighboring but subtly different island of Pod Mrcaru, where none lived, as an experiment in evolution.

How, if at all, would these creatures change?

Largely insect eaters, the half-foot long reptiles would find themselves on an island where insects were in short supply but plants were not.

Because of political upheaval in the region - the Adriatic Sea borders Croatia - it was not until 2004 that Duncan J. Irschick, a professor of biology at the University of Massachusetts here, and a team of international biologists could return to find out what had happened to the lizards.

"As a scientist, it was a once in a lifetime opportunity. Historical circumstances prevented people from going back to the island for a very long time. So when we first went out there in 2004, we didn't know what we would find. We chartered a boat out to the island, and it was amazing. It was swarming with lizards," he said.

Pod Mrcaru, just off the west coast of Croatia, is a "tiny rock in the middle of the water," Irschick said.

"You could walk from one end to the other in five minutes. It has a Mediterranean climate - hot and very dry. It's mainly rock with little shrubby plants sticking up out here and there. It looks very inhospitable," he said.

They found on that visit and subsequent trips in 2005 and 2006 that the wall lizards had changed dramatically in the intervening decades. Results of their study were published March 25 in the "Proceedings of the National Academy of Sciences."

Two of the most striking changes were the increase in head size and the change in head shape.

"Individuals on Pod Mrcaru have heads that are longer, wider and taller than those on Pod Kopiste, which translates into a big increase in bite force," Irschick said.

"Because plants are tough and fibrous, high bite forces allow the lizards to crop smaller pieces from plants, which can help them break down the indigestible cell walls," he said.

Most importantly, though, the researchers discovered the digestive tracts of the lizards had changed. They were now divided, creating a fermentation chamber where microbes could break down the toughest portions of the plants.

"What was unique about this study was that the lizards developed brand new structures, a part of their gut called a 'cecal valve' (which separates the chambers). No one had ever documented that kind of change before," Irschick said.

"It's good evidence that not only can evolution happen rapidly, but animals can evolve new structures as well (in a short time span)," he said.

To confirm that the lizards were descendants of the 10 individuals introduced to the island, the researchers conducted a DNA analysis and found they were genetically identical to the original ones.

The research was supported by the National Science Foundation and the Fund for Scientific Research in Flanders. Additional members of the study team included researchers from Harvard University, University of Antwerp, the Royal Belgian Institute of Natural Sciences and the Croatian Natural History Museum.

TAGGED: BIOLOGY, EVOLUTION