Endocrine differences among colour morphs in a lizard with alternative behavioural strategies
Section snippets
Study species
The tawny dragon lizard, C. decresii, is a small, sexually dimorphic agamid lizard found on rocky outcrops of Kangaroo Island, Mt. Lofty Ranges and southern Flinders Ranges of South Australia (Houston, 1974). Males exhibit striking throat colour variation both within and between populations (Houston, 1998). In populations in the Flinders Ranges, males occur in four distinct throat colour morphs: orange, yellow, grey and orange-yellow, which can be objectively classified, independently of the
Factors affecting hormone concentrations
Morphs did not differ in most traits that could influence hormones concentrations. There were no differences between morphs in SVL (F3,112 = 1.74, p = 0.162, η2 = 0.03), the time of day at capture (F3,138 = 2.24, p = 0.086, η2 = 0.06) or the time it took to capture a lizard (F3,139 = 2.52, p = 0.061, η2 = 0.04); however there was a difference between morphs in their body temperature at capture (F3,154 = 4.19, p = 0.007, η2 = 0.15; Fig. 2) with the orange-yellow morph having a higher body temperature than the yellow
Discussion
We predicted that the behavioural strategies of C. decresii colour morphs would be reflected by differences in androgen and corticosterone concentration as well as bite force. All morphs showed a similar increase in corticosterone concentration in response to acute capture stress and did not differ in their adrenal stress response, measured as CSM. However, morphs did differ in baseline levels of androgen, with the orange, more aggressive morph having significantly higher concentrations of
Conclusions
Here we have shown that colour morphs of C. decresii differ in levels of androgen immediately after capture and following acute stress but do not differ in concentration of corticosterone, CSM or bite force. Our findings appear consistent with previously established behavioural differences of morphs (Yewers et al., 2016). The orange morph shows consistently high aggression and has a higher concentration of androgen immediately after capture than the grey or yellow morphs, and maintains high
Acknowledgements
We thank Sarah Pryke, Nina Svendin and Kristal Cain for help with hormone assays at the Australian National University. We are grateful for the field work assistance of Rachael Bartlett, Enrique Cruz, Fran Lyndon-Gee, Sarah Grogan, Jessica Hacking, David Hamilton, Jennifer Hetz, Molly Hunter, Claire McLean, Adnan Moussalli, Montse Sutulov, Tim Tan, Luisa Teasdale, Bryant Turffs and Peter Yewers. This work was funded by the Australian Research Council (DP1092908) to D.S-F., the Nature Foundation
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