Dragons like to face the heat

At long last, my former MSc student, Ian Black’s first paper has been published!  (Citation below)  Ian graduated last year and moved to Ottawa, but has been maintaining contact and working with me to write his work up (so far, we have a book chapter in review and a second manuscript being edited now).

To many that keep lizards as pets, the results of this study might not be so surprising, as articulated by this meme:

 

From a scientific perspective, however, these results might not have been predicted.  So, what did we show? In a nutshell, we demonstrated that bearded dragons prefer to keep their heads facing toward the heat when given a choice.

To thermoregulatory biologists, this is intriguing.  Why? It is often stated in the herpetology literature that lizards are either heliothermic (i.e. they bask in the sun) or thigmothermic (i.e. they warm up via contact with the substrate), and an implicit corollary is that if a species is known to be heliothermic, it cannot respond to contact based thermal cues (i.e. they cannot sense heat via the skin).  Thus one might not expect them to orient toward or away from this kind of heat source or thermal gradient if they are heliothermic/baskers.

We conducted this study by creating an artificial thermal gradient to allow the lizards the chance to move and select different temperatures throughout the day.

Banner in gradient

Thermal image of a bearded dragon in a temperature gradient (~15C on left, ~42C on right) orienting toward the warm end.

Our paper clearly demonstrates that bearded dragons are very capable of orienting their body along a gradient of temperature, and thus are quite thermally “aware” of the environment around them.  We also demonstrate that both adults and neonates show this behaviour.  Finally, as the lizards choose warmer temperatures later in the day (i.e. move up the gradient), they orient less and less toward the heat, suggesting that they are capable of using their orientation to keep their heads from getting too warm.  Therefore, orientation behaviour is used to fine-tune their thermoregulatory control.  This is analogous to how Galapagos marine iguanas use sky-pointing orientation to maximise solar absorption int he early morning and maximise convective cooling later in the day to prevent overheating (Bartholomew, 1966. Copeia. p 241-250).

 

Please find links to the study below and consider sharing our findings.

Citation and Links

Black, IRG and Tattersall, GJ. 2017.  Thermoregulatory behavior and orientation preference in bearded dragons.  Journal of Thermal Biology. 69: 171-177. doi:doi:​10.​1016/​j.​jtherbio.​2017.​07.​009

For a limited time (until Sept 13, 2017) the paper is available for free for anyone that does not have a subscription here:

https://authors.elsevier.com/a/1VRVT15hXtsbUW

but I will provide permanent links to the pre-print version: Post Review Version or from the Brock University Respository.

 

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