As climate change alters the temperatures of reptile habitats around the globe, tests of one lizard species suggests warmer nests could make some reptiles smarter.
When researchers incubated the eggs of Bassiana duperreyi, a mountain-dwelling Australian skink, at warmer-than-usual temperatures, they grew up to perform especially well on a learning task.
Herpetologists knew reptiles incubated in warmer nests developed differently, but linking hotter egg temperatures to increased intelligence is a first.
"We have 16 to 17 years of data on the effects of incubation temperature on skinks. We know the hotter guys are bigger, faster, absorb more [egg] yolk," said herpetologist Joshua Amiel of the University of Sydney, whose research was published Jan. 11 in Biology Letters. "But hardly anyone has given a look at the effect on reptile learning."
Reptiles are cold-blooded animals. Unlike mammals or birds, which burn through calories to maintain body temperature, they use sunlight or other environmental sources of heat.
Because reptiles rely so much on environmental temperatures to survive, researchers have wondered how temperature affects their early development.
Cooler incubation temperatures in the Eastern three-lined skink, for example, produce smaller, less-agile hatchlings that are more likely to be male. Similar effects are seen in turtles. In crocodiles, extremes of temperature produce more females.
Thanks to their reduced metabolism and lumbering, sun-bathing behaviors, reptiles are rarely viewed as intelligent animals. Research on their mental ability, much less the effects of climate upon it, is lacking.
Amiel and colleague Richard Shine developed a simple predator avoidance test: At each end of a rectangular tub, they placed an upside-down flower pot into which skinks could run and hide. The entrance to one pot was blocked by clear plastic.
After incubating two different sets of eggs at different temperatures – the warmer set mimicking natural incubation settings of skinks at lower elevations, the cooler set mimicking higher elevations – Amiel and Shine tested the hatchlings.
They sent each lizard running by touching its tail, then measured how long it took to find the open shelter and how often it tried to enter the blocked door. Warm-incubated lizards learned to find the open flower pot much more readily than their cool-incubated siblings. In the wild, improved learning abilities likely increase chances of survival.
As global temperatures continue to shift, Amiel thinks some reptile species living in warming climates may become innately smarter. In cooling climates, they could become less intelligent.
The mechanism by which intelligence shifts is unclear, but Amiel suspects warm temperatures alter the production of hormones that regulate reptilian brain development.
"Now that we've seen this in one context, it will be nice to do some different trials, like a maze or food-encouraged learning, maybe even try some other species and see if this is generally true of reptiles," he said.
Images: Melanie Elphick/University of Sydney