Biology Now, 2e

Fast Lizards, Slow Corals ■ 233

process of natural selection that enables a good

match between a population of organisms and

their environment. If the population of lizards

was going to survive, it would need to adapt to

its new environment.

When Irschick and his team landed on Pod

Mrcˇaru in 2004, they set to work catching

lizards. It wasn’t hard; the island was swarming

with them. Irschick could sit on a rock and simply

pick up lizards as they ran by. There were several

thousand lizards on the 7-acre island. When

Irschick and his team looked closely, they real-

ized that all the lizards were P. sicula. The ten

transplants had wiped out the other two species

of lizards. What’s more, the adapted lizards

looked strange compared to P. sicula lizards on

other islands nearby (Figure 13.3). “They were

these really big, chunky lizards,” recalls Anthony

Herrel, then a postdoctoral fellow in Irschick’s

lab and now a researcher at the French National

Centre for Scientific Research in Paris. “They

were unlike lizards on any of the other islands.”

Twice a year for 3 years, the group returned to

Pod Mrcˇaru to collect, weigh, and measure the

lizards. They also took small pieces of the tails

(which grow back) to test the lizards’ DNA and

compare it to the original population of P. sicula

on Pod Kopište. Those DNA tests confirmed

that the lizards on Pod Mrcˇaru were indeed

descended from the original ten that Nevo

had transported to the island. In addition to

taking size and weight measurements, the team

tested the strength of the lizards’ bite. They also

dissected two samples of dead lizards.

What the researchers found was unprece-

dented. In about 33 years, from the time Nevo

stepped off the island to the time Irschick

stepped on, the species had evolved dramatically.

The descendant lizards’ heads were larger and

shaped differently, making the lizard’s bite much

stronger than that of the original lizards brought

to the island. The descendant lizards also had a

unique digestive-tract structure called a cecal

valve, a set of muscles between the large and

small intestine that slow down food digestion,

enabling the lizards to better process the cellu-

lose of plants. It’s rare for lizards to have these

structures, says Herrel. Only a few plant-eating

lizard species, like iguanas, have cecal valves.

Figure 13.2

Pod Kopište’s sparse vegetation and

Pod Mrcˇaru’s lush vegetation

Pod Kopište, the island from which the

original ten Podarcis sicula lizards were

taken, is rocky and sparsely vegetated.

Pod Mrcaru is a smaller island

covered with lush vegetation.

Figure 13.3

Podarcis sicula lizard on Pod Mrcˇaru,

33 years after introduction of the

species

Longer, wider head

Thicker body New digestive structure

Duncan Irschick is a biologist at the University of

Massachusetts, Amherst, who studies animal

function and evolution, specializing in research

on animal movement and gecko adhesion.

DUNCAN IRSCHICK