November 27, 2012
One Lizard Species Adapts Quickly To Climate Change
April Flowers for redOrbit.com - Your Universe Online
A new study from Duke University shows that one tropical lizard's tolerance for cold is a bit stiffer than scientists had assumed.
"We are not saying that climate change is not a problem for lizards. It is a major problem. However, these findings indicate that the thermal physiology of tropical lizards is more easily altered than previously proposed," said Duke biologist Manuel Leal in a statement.
Previously, scientists have proposed that because lizards are cold-blooded animals, they would not be able to tolerate or adapt to colder temperatures.
A. cristatellus was introduced to Miami around 1975 by human intervention. Although the summer temperatures are similar, winter temperatures in Miami average about 18 degrees Fahrenheit cooler than Puerto Rico.
Leal and his team captured lizards from Miami's Pinecrest area and from northeastern Puerto Rico and brought them back to the lab in North Carolina. They slid a thermometer into each lizard's cloaca and then chilled the air to a series of cooler temperatures. The team observed how easily each lizard was able to right themselves after they were flipped onto their backs.
The Miami lizards flipped themselves over at temperatures 5.4F cooler than the Puerto Rican lizards. Leal said that animals that flip over at lower temperatures have a higher tolerance for cold temperatures. This is likely advantageous when air temperatures drop.
"It is very easy for the lizards to flip themselves over when they are not cold or not over-heating. It becomes harder for them to flip over as they get colder, down to the point at which they are unable to do so," he said.
The point at which the animal is unable to flip is called the critical temperature minimum. The lizards are not dead at this temperature; they have just lost control of their coordination.
"It is like a human that is suffering from hypothermia and is beginning to lose his or her balance or is not capable of walking. It is basically the same problem. The body temperature is too cold for muscles to work properly," Leal said.
A difference of 5.4F is "relatively large and when we take into account that it has occurred in approximately 35 generations, it is even more impressive," Leal explained.
Because most evolutionary changes happen on a time scale of a few hundred, thousands or even millions of years, a change occurring in a mere thirty-five years is noteworthy. This is a time scale that happens within a single human lifetime, making it possible for us to witness this evolutionary change.
The tolerance for cold displayed by the Miami lizards also "provides a glimpse of hope for some tropical species," Leal added. He cautioned, however, that at present scientists don´t know how quickly tolerance to high temperature can evolve.
He and his colleagues are now working on the heat-tolerance experiments. They are also conducting tests to study other lizard species' adjustments to cold temperatures.