A Bassiana duperreyi hatchling. New research has suggested to warmer nest temperatures lead to smarter offspring.
Credit: Joshua Amiel
Bassiana duperreyi lizards basking. The researchers also suggested that 'slow' lizards may catch up with their smarter peers at a later date by basking in the sun.
Credit: Joshua Amiel
LONDON: Eggs hatched in hotter nests produce smarter young lizards than those hatched in cooler environments, new research has suggested.
These findings, published in Biology Letters today, suggest that increasing temperatures due to global warming could actually be of benefit to these reptiles.
"As soon as lizards hatch they must fend for themselves, locating food and avoiding predators. The better a lizard is at remembering the location of resources and shelter the less time it spends exposed to predators; thus increasing its survival," said leaf author Joshua Amiel from the University of Sydney. "Also, when a lizard encounters a predator, the faster it can find a suitable shelter the greater its odds of surviving the encounter."
Why are you so clever?
Previous studies of reptile behaviour have evaluated the ability of different lizard species to learn tasks and looked at differences in the performance of individual lizards when undertaking said tasks.
"Such studies have found that some individuals complete the assigned learning tasks with greater proficiency than others," said Amiel. "Our study looks at incubation temperature as a potential factor driving this variation in lizard learning ability."
Incubation temperature is known to influence reptile sex, shape and body size, but has not previously been linked to learning ability. "There is some evidence that temperature may influence learning ability in honey bees, but to our knowledge no one has tested the effects of incubation temperature on learning behaviour in other lizard species," said Amiel.
Testing hatchlings' smarts
Using predator evasion tests as a means of assessing the hatchlings' ability to learn, Amiel and co-author Richard Shine, also from the University of Sydney, found that lizards born from eggs incubated at 22°C achieved higher learning scores when tested than those hatched at 16°C.
For the learning task, Amiel and Shine placed the hatchlings in opaque plastic containers resembling their normal housing and containing an open and closed 'hide' 24 hours before the first test. The test involved the lizard being placed between the two hides, which remained in the same location throughout the experiment, and then stimulated to run from a 'predator' in the shape of an artist's paintbrush.
Reptile escape artists
The lizards were tested four times a day for four days, allowing them to learn which hide was open and which closed. They were considered to have successfully 'escaped' the predator if they found and hid in the open hide within 30 seconds.
To see whether the lizards were actually learning where the open hide was, the researchers calculated a 'learning score' by subtracting the total number of successful escapes in the first eight tests from the number of successful escapes in the last eight for each reptile. A positive score showed that the lizards were learning where to hide by trial and error.
The hatchlings from 'hot' nests achieved a positive average learning score, but those from the 'cold' nests did not, even after accounting for age, sex and running speed of the lizards.
"Incubation temperature can mediate many different developmental processes (including regulation of hormones), so it is not surprising that it also could influence brain development or function," commented evolutionary biologist and expert on amphibian and reptile development Tobias Uller from the University of Oxford in England. "We know, for example, that temperature affects brain development in species with temperature-dependent sex determination, such as leopard geckos."
Environment-based evolution
Amiel emphasised that their results do not necessarily apply to all lizards. Bassiana duperreyi, the species tested in this experiment, appear to benefit from incubation at higher temperatures, but this may reflect their natural environment. "Lizards that are consistently exposed to cold climates may have evolved means to deal with low temperatures," he said. "This includes low temperature development of lizard embryos. The eggs of these 'cold-adapted' species actually develop better and produce larger and faster offspring when incubated at low temperatures."
Amiel added that it is possible that initially 'slow' lizards may catch up with their smarter peers at a later date. "We are currently investigating the possibility that the variation we saw in learning ability is due to differences in brain development. If this is the case, then lizards incubated at cold temperatures may be able to behaviourally compensate for slow embryonic brain development by eating more food or by maintaining higher body temperatures by basking in the sun for longer periods during the day."
