Zoology - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemThermal advantages of colour change in bearded dragon lizards, Pogona vitticeps( 2014)Many animals possess the remarkable ability to change colour, and this ability has several potential functions, including communication, social signalling, and camouflage. However, the functional significance and drivers of colour change are still poorly understood in many taxa. In this study, I applied laboratory and field approaches to examine an important, but understudied potential function of colour change in terrestrial ectotherms: thermoregulation. I quantified colour change in response to temperature in wild-caught bearded dragon lizards (Pogona vitticeps), which are known for their marked individual colour change and geographic colour variation. For comparison, I also quantified the extent of non temperature-dependent colour change from dark to light states elicited during social interactions and at different times of the day. I found that lizards showed substantial animal-visible (UV-Vis) and near infrared (NIR) skin reflectance change in response to temperature for dorsal but not ventral body regions. By contrast, lizards showed the greatest capacity for colour change on the ventral body regions under other (non temperature-dependent) circumstances. I then used biophysical models to predict the thermal benefit of colour change to a bearded dragon lizard, and found that in the morning, under environmental conditions characteristic of the field site during the breeding season, the maximum temperature-dependent change in dorsal reflectivity would result in a 9% increase in the rate of heating. Although this temperature-dependent colour change may therefore aid thermoregulation, colour change is likely to be less important as a mechanism for bearded dragons to thermoregulate than other mechanisms such as behavioural changes in posture and shuttling between sun and shade. Therefore, colour change may have primarily evolved to enhance social signalling or camouflage, but subsequently been co-opted for thermoregulation. To further understand the relative importance of the different functions of colour change to a bearded dragon in the wild, and how they accommodate these functions when they conflict, I quantified colour change in 11 free-ranging bearded dragons (Pogona vittceps) over an 8-week period during the breeding season (October 9th– November 28th, 2013). In addition to taking daily snapshots of multiple lizards over the entire field study, I followed a single lizard through an entire day (‘day in the life’), and modelled the effect of different thermoregulatory behaviours on core body temperature. From this, I found that lizards showed a significant and consistent relationship between their dorsal skin coloration and both background coloration and either core body temperature or skin temperature. However, background colour explained the most variation in lizard colour, and there was no evidence that these lizards exhibit temperature-dependent background choice. Furthermore, the focal lizard that was followed through the entire day behaved very similarly to a predicted modelled “thermoregulating” lizard, suggesting that in the wild, behavioural thermoregulation may be more important for regulating body temperature than colour change. Overall, the data presented in this thesis shows that colour change in bearded dragons functions in thermoregulation but that this is likely to be secondary to its use for communication and camouflage. These data contribute significantly to our understanding of the evolutionary drivers of colour change in terrestrial ectotherms.