For years, scientists have said global warming will doom most lizards. Rising temperatures in some of their habitats are already wearing them down, limiting their search for food and putting a damper on their mating, earlier studies have shown.
But a new study of the sleek little brown anolis lizard in the Bahamas is challenging the notion that tropical lizards can’t stand the heat. Yes, researchers at Dartmouth College and University of Virginia say, the expected two-degree rise in temperatures over the remainder of the century will likely do a number on lizards. However, they said, researchers should give more consideration to the lizard’s ability to adapt and evolve.
The scientists moved male lizards from the cooler and more forested end of a Bahamian island to a peninsula that baked under the sun. The results showed that nearly a quarter of them didn’t wilt under the heat of an environment that was two degrees warmer than their native habitat.
The surviving lizards were robust — fast enough to catch prey, digest it quickly and race away from predators. In other words, they adapted. The evolution of these reptiles — a sort of micro-evolution — challenges the idea that lizards won’t be able to tolerate a rapidly warming climate and won’t have time to adapt over generations.
The findings surprised the researchers, who concluded that science doesn’t yet know enough about the biology of some organisms to neatly predict what will become of them when the world warms.
“I think we were blown away,” said Ryan G. Calsbeek, an associate professor at Dartmouth and a co-author of the study. “The prediction is that these animals are hosed. If the climate warms a couple of degrees as climate scientists predict, we can kiss these animals goodbye.” This study shows “there probably is some salvation for them. ”
Calsbeek isn’t convinced that lizards will survive, so he added a caveat: “We’re not saying climate change isn’t a huge problem with massive negative consequences.” But, he added, scientists need to consider that “in some cases we may see some potential positive outcomes, and in other cases very negative outcomes.”
The study was published this week in the journal Proceedings of the National Academy of Sciences. The lead author is Michael L. Logan, a doctoral candidate at Dartmouth when the research was conducted. Robert M. Cox, an associate professor at the University of Virginia, is another co- author.
The outcome was grim for the majority of anolis lizards — they sprinted fastest when their body temperatures were cooler in the warmer environment.
The lizards that survived sprinted fastest when their body temperatures were high, showing that they were better equipped for a warmer climate. “It was a selection event,” the point at which one group lives and the other dies, Logan said.
The scientists studied lizards in 2011 and 2012. Nearly half of the 100 lizards selected and observed in a cooler habitat, Kidd Cay in Great Exuma, survived long enough to procreate in the May breeding season.
Fewer than a quarter of the 100 that were captured in a forested area of another island, Eleuthera, and transplanted to a harsher, hotter area on the same island lived long enough to mate and produce more lizards. But that 22 percent was a breed apart, already evolved in a way that was thought to take eons.
A study published four years ago in the journal Science argued that the rising temperatures were killing off lizards. The study was conducted after researchers realized that some European lizards were going extinct but couldn’t figure out why. They found that populations of lizards had disappeared from several continents over at least 20 years and predicted that 20 percent of lizard species would be wiped out before 2100.
It was a key finding because lizards help feed an ecosystem. Even in the best conditions, life is tough for lizards. Herons swoop from the sky and pluck them up with sharp beaks, snakes squeeze the life out of them, and they kill each other in battles over turf and food.
“Life is brutal out there, and if you’re not well suited to your environment, chances are you’re going to get smoked,” Calsbeek said.
Calsbeek is attached to the brown anolis lizards, calling them “God’s perfect creature.” With the help of another author, he caught nearly 200, studied their reactions and speed as they ran across dowels in a climate-controlled lab, then stuck half of them back in a hotter environment.
The researchers focused on the sprint speed of lizards because it’s the key to their survival and because it forces their bodies into a higher thermal state, demonstrating how well they perform at an elevated temperature.
An ability to be active at elevated temperatures for “longer periods of the day” permitted more time “for energy intake and increasing their chances of surviving to the breeding season,” the study said, meaning those males could eat more and possibly mate more.
“What I think this work demonstrates is that, as scientists, we need to consider all the avenues that a species can adapt to in its climate,” Logan said. “They can deal with temperatures in their same life span. We see that many species do have more resilience to a situation than what we give them credit for. We should see how they respond even to these incredibly rapid shifts.”