• Characterising Behavioural Thermoregulation in the Bearded Dragon: The Role of TRPM8

      Berman, Jacob; Department of Biological Sciences (Brock University, 2013-05-06)
      Temperature regulation is a necessary part of maintaining life, as most biological processes are influenced by temperature. ThermoTRP channels are considered the primary thermosensors in endotherms, but little is known regarding their function in ectotherms. The goal of this study is to establish TRPM8, a cold sensing channel, as a participant in normal thermoregulation of the bearded dragon (Pogona vitticeps), an ectotherm. Animals were placed inside a ramping temperature shuttle box to assess the common behavioural thermoregulatory strategy of shuttling. Shuttling involves the periodic movement between cold and warm environments to maintain body temperature at moderate levels. The temperatures for cold and warm escapes represent sensory thresholds for inducing the shuttling thermoeffector. Animals were administered with: 1) an injection of the TRM8 antagonist capsazepine, 2) an injection of the TRPM8 agonist menthol, and 3) menthol applied topically. No effect was observed with injected drugs, but topical menthol resulted in a 2-3oC rise in the ambient temperature threshold and 1-2oC rise in skin temperature threshold for escape from the cold compartment. In an additional experiment, gaping behaviour, a warm temperature thermoregulatory strategy, was assessed. No effect was observed in this behaviour when the same dose of menthol was applied topically. These results point to a role for TRPM8 only in thermoregulation as it relates to cold temperature sensation in lizards, since it does not participate in regulating warm temperature behaviours such as gaping.
    • Orientation Preference and Behavioural Thermoregulatory Coordination in Pogona vitticeps.

      Black, Ian; Department of Biological Sciences
      Regulating body temperature is a critical function for vertebrates and many invertebrates. Vertebrates that rely on ambient temperature as a heat source (ectotherms) make use of multiple voluntary and involuntary behaviours to thermoregulate, including body orientation. The purpose of this work was to examine orientation behaviour in bearded dragons (Pogona vitticeps) as well as possible coordination between thermoregulatory responses. Both adult and two week old neonatal bearded dragons were placed in a thermal gradient and left to thermoregulate behaviourally in order to observe the presence of a thermoregulatory orientation preference. Since a thermal orientation bias could manifest from a preference for favoring rostral versus caudal traits, animals were subsequently subjected to a separate experiment, in which either heat exchange across the tail or respiratory heat exchange from gaping was inhibited. Changes in thermoregulatory behaviour were then observed in the manipulated bearded dragons in order to assess the potential contributors to thermal preferences as well as isolate potential coordination between behaviours. Both adult and two week old neonatal dragons displayed a non-random orientation preference for facing a heat source that strengthened with time exposed to a thermal gradient, supporting this behaviour as a thermoregulatory response. Bearded dragons also exhibited changes in orientation preference and gaping behaviour when the tail was insulated and when gaping was inhibited, but no changes to selected ambient temperature, indicating that the changes to gaping and orientation behaviours are compensatory responses that support the presence of coordination between thermoregulatory behaviours.