This Lizard Will never bake alive, enjoying the luxuries of air conditioning

From geckos and iguanas to Gila monsters and Komodo dragons, lizards are among the most common reptiles on Earth. They are found on every continent except Antarctica. One even pitches car insurance in TV ads. They seemingly can adapt to a variety of conditions, but are most abundant in the tropics.

However, new research that builds on data collected more than three decades ago demonstrates that lizards living in tropical forests in Central and South America and the Caribbean could be in serious peril from rising temperatures associated with climate change.

In fact, those forest lizards appear to tolerate a much narrower range of survivable temperatures than do their relatives at higher latitudes and are actually less tolerant of high temperatures, said Raymond Huey, a University of Washington biology professor.

“The least heat-tolerant lizards in the world are found at the lowest latitudes, in the tropical forests. I find that amazing,” said Huey, lead author of a paper outlining climate warming’s threat to lizards published in the March 4 Proceedings of the Royal Society B. The Royal Society is Great Britain’s national academy of science.

It has often been assumed that tropical organisms are much better at dealing with high temperatures than those in colder climates because the lowland tropics are always warm. But that assumption is only true to a point, Huey said, because those in the tropical forest experience a much narrower range of temperatures during the year and are rarely, if ever, exposed to extreme high temperatures.

A lizard in Washington, for example, might experience a temperature range of 40 degrees or more between summer and winter, while one in Puerto Rican forests might only experience a range of 20 to 25 degrees.

Forest conditions tend to keep lizards living there at temperatures that allow them to function at or close to their physical peak. A temperature change of just a few degrees can reduce their physical performance greatly.

Lizards are ectotherms, regulating their body temperature by exchanging heat with their surroundings. Huey originally collected data on body temperatures of lizards in a Puerto Rican forest in 1973, and later measured how fast they can sprint at various body temperatures. Sprinting relates directly to survivability because it affects a lizard’s ability to hunt or elude predators.

He found that even at the coolest and warmest parts of the day the forest lizards functioned at least at 90 percent of their maximum ability, because the temperatures varied so little and were optimal then for these lizards. Subsequent laboratory work by Huey and others tested the sprinting speeds for more than 70 species of lizards at varying body temperatures.

“In the 1970s a bunch of us were running around the Caribbean with thermometers taking lizard body temperatures for reasons totally unrelated to climate warming. But we can use our data from a third a century ago as a baseline to now predict how lizards at different latitudes would respond to climate change,” Huey said.

His co-authors are Curtis Deutsch of the University of California, Los Angeles; Joshua Tewksbury of the UW; Laurie Vitt of the University of Oklahoma; Paul Hertz of Barnard College; Héctor Álvarez Pérez of the University of Puerto Rico; and Theodore Garland Jr. of the University of California, Riverside. The work was funded by the National Science Foundation and the UW Program on Climate Change.

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