Many species, including humans, struggle to survive when temperatures rise too high. But even small increases can affect animals, causing subtle changes in physiology or behaviour that alter how they fare.
For some lizards, the effects of heat may, somewhat literally, be a no-brainer. A new study published in Royal Society Open Science has found that a temperature increase on the scale expected from climate change can make bearded dragons dumber.
Bearded dragons are Australian lizards that have become popular as pets, and like other reptiles, they’re not as dumb as they might seem. “Reptiles were long considered to be sluggish and unintelligent creatures,” said Anna Wilkinson, an animal cognition scientist at the University of Lincoln in the U.K. But that has been changing, as research has showed that many lizards possess complex cognitive skills, from navigation to problem solving.
In a recent study, Wilkinson and her colleagues found that bearded dragons (Pogona vitticeps) can imitate one another to perform new behaviours—a degree of social cognition that not so long ago was considered unique to primates.
“Learning through observing the behaviour of another individual can be a short cut to finding a solution, and can allow animals to solve tasks that they may not be able to solve through trials and error learning,” Wilkinson told National Geographic. Reptiles will need all the learning they can muster, she added, to adapt as the world changes around them.
Reptilian brains, like those of furry and feathered beasts, are moulded during development. That means the conditions an egg is exposed to may have long-lasting effects.
Wilkinson and her colleagues decided to investigate whether incubation temperature affects bearded dragon intelligence. Surveys have found that, despite the best efforts of reptilian mums, nest temperatures generally are on the rise as climate warms.
The researchers took a single clutch of 13 eggs and split them into two groups. Seven eggs were incubated at a toasty 30°C, while the other six were incubated at a milder 27°C. There was an almost even mix of males and females.
Both groups were kept separate but under the same conditions for a year, until the animals were mature. Then they were put to the test. Each one received an individual screening of a video of a dragon opening a sliding door to retrieve a tasty treat, then was given five minutes to try to open the door to get its reward.
While sliding a door might seem like a simple task, in all previous trials with bearded dragons, Wilkinson and her colleagues found that the animals only figure out the trick if they’ve gotten to watch another lizard perform it. So if an animal succeeded, it was considered evidence that it had learned from the tutorial. Each lizard was tested ten times.
The researchers found that lizards exposed to hotter temperatures during development were slightly less likely to succeed. More important, even if they did open the door, it took them about a minute and a half longer on average than the dragons raised at the cooler temperature. To Wilkinson, that suggests that the warmer incubation impaired the animals’ ability to learn from others.
Further research may identify exactly what happens to the dragons’ brains during development to cause this cognitive disparity, and how it in turn affects the animals’ survival and ability to reproduce.
A FEW LIKE IT HOTTER
Wilkinson’s results are similar to those wildlife ecologist Jonathan Webb obtained when he looked at the effects of nest temperatures on spatial learning in velvet geckos (Amalosia lesueurii). The geckos incubated at warmer temperatures were not only slightly duller, they were less likely to survive in the wild.
Velvet geckos also seem to get duller in the heat.
PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
Webb, now an associate professor at University Technology Sydney in Australia, noted that previous studies like his have only tested hatchlings. “This paper breaks new ground by showing that incubation-induced effects on cognitive abilities may persist into adulthood,” he told National Geographic.
“The only weak part of the study is the small sample size,” he said—a limitation noted by cognitive neuroscientist Josh Amiel as well.
Amiel, who currently collaborates with researchers at the University of British Columbia in Canada, found the opposite—a boost of brainpower with incubation heat—when he looked at non-social learning in hatchling three-lined skinks (Bassiana duperreyi). Because dragons are somewhat far away from skinks on the lizard family tree, “it’s not really surprising that it affects them differently than it did the skinks in my studies,” Amiel said.
Reptiles were already facing steep odds from climate change—it’s estimated that one-fifth of all lizard species could be extinct by 2080. Mental dimming could further stack the deck. Amiel suspects that there may be a few winners, like his skinks—and then, there will be the dragons. “They might be losers, and that allows other animals to come in and challenge them for that habitat,” he said.
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Lead Image: Bearded dragons that incubated at warmer temperatures are slower learners as adults. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC CREATIVE