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Warmer nests make smarter lizards

Skink IQ Lizards hatching from warmer nests are better at learning new things than their counterparts from cooler nests, say Australian researchers.

PhD student Joshua Amiel and Professor Rick Shine from the University of Sydney report their findings today in the Royal Society's Biology Letters.

"We already know that nest temperature affects how fast lizards are able to run, how big they are when they hatch and even their sex," says Amiel.

"So I wondered then whether it also affected how their brains developed."

Amiel studied the effect of temperature on the cognitive skills of a small highland lizard called Bassiana duperreyi, which lives in the Brindabella Range west of Canberra.

Female lizards lay their eggs in nests under rocks and previous studies have found nests lower down the mountain are warmer than those further up, resulting in faster-hatching lizards.

The researchers collected 23 pregnant females from different locations in the field and then incubated their eggs in potting soil in the laboratory, at an average temperature of 16°C and 22°C.

To control for the any genetic effect, they split the clutches up into the different temperature treatments.

When the hatchlings were a few weeks old, the researchers tested their learning ability.

The animals were placed in a large open bin that contained potential shelters in the form of upside down flower pots.

The opening to one pot was blocked by Perspex while the opening to the other pot was unblocked.

Amiel wanted to know how quickly a lizard could learn where to hide when threatened.

To simulate a predator, he tapped the lizards on their tails with a paint brush. Amiel then recorded how many errors they made before identifying the right opening to the shelter, and how long it took them to find it.

"In over 16 trials the hot-incubated lizards made fewer errors," he says.

During the last trial, only one out of the 12 hot-incubated lizards made an error where as five out of the nine cool-incubated lizards made an error.

Amiel says data loggers measuring nest temperatures in the field over the past 16 years have found a mean increase in nest temperatures.

He says while local factors such as the amount of vegetation covering the area can influence nest temperatures, evidence suggests the increase is more likely to be due to climate change.

In the future, Amiel hopes to carry out other ecologically relevant tests of lizard intelligence, including a test that will require the lizard to move an object or navigate a maze, to get food.

"Ideally you would want to see if the lizards that are smarter at one task are also smarter at other tasks."