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Global Warming Produces Smarter Young Lizards
Amiel, J.J. and Shine, R. 2012. Hotter nests produce smarter young lizards. Biology Letters 8: 372-374.

The authors state that a hatchling reptile's sex, body size and shape, as well as its locomotor performance, "can be influenced not only by its genes, but also by the temperature that it experiences during incubation." But what they really wanted to know was if incubation temperature can also affect a hatchling's cognitive skills.

What was done
In an experiment designed to answer this intriguing question, Ameil and Shine examined "whether incubation temperature affects lizards' ability to learn the location of a safe retreat site during a predatory attack," because, as they continue, mastering this cognitive task "is directly relevant to individual survival and therefore fitness," citing the work of Paulissen (2008). This they thus did, working with the scincid lizard Bassiana duperreyi, by first "randomly dividing eggs from each clutch between two incubation treatments ('hot' = diel cycle of 22 7.5°C; 'cold' = diel cycle of 16 7.5°C)," which treatments "mimic thermal regimes typical of natural nests at low (hot) versus high (cold) elevations," after which they conducted the specific test they designed to evaluate the young lizards' cognitive skills and their abilities to act appropriately to escape the perceived danger to them.

What was learned
The two Australian researchers report that "hot-incubated lizards achieved higher learning scores than did cold-incubated lizards," and that "the number of errors they made decreased more from the first to the second half of the trials than was the case for cold-incubated lizards." As for what the mechanism behind this phenomenon might be, they speculate - based on the work of Ahmad and Zamenhof (1978), Rissman et al. (2002), Valenzuela and Lance (2004) and Radder et al. (2008) - that "thermal effects on hormone levels during incubation may induce structural variation in parts of the brain that control behaviors such as learning."

What it means
Amiel and Shine conclude, in general, that "climate change may simultaneously generate novel challenges for post-hatching organisms, while also modifying their ability to respond flexibly to such challenges," and specifically opining that "in B. duperreyi, hotter natural nests over recent decades (due to climate change) probably have produced hatchling lizards with enhanced learning abilities."

Ahmad, G. and Zamenhof, S. 1978. Serotonin as a growth factor for chick embryo brain. Life Sciences 22: 963-960.

Paulissen, M.A. 2008. Spatial learning in the little brown skink, Scincella lateralis: the importance of experience. Animal Behavior 76: 135-141.

Radder, R., Quinn, A.E., Georges, A., Sarre, S.D. and Shine, R. 2008. Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard. Biology Letters 4: 176-178.

Rissman, E.F., Heck, A.L., Leonard, J.E., Shupnik, M.A. and Gustafsson, J. 2002. Disruption of estrogen receptor ß gene impairs spatial learning in female mice. Proceedings of the National Academy of Sciences USA 99: 3996-4001.

Valenzuela, N. and Lance, V. (Eds.). 2004. Temperature-Dependent Sex Determination in Vertebrates. Smithsonian Institution, Washington, DC, USA.

Reviewed 17 October 2012