Experimental support for the cost–benefit model of lizard thermoregulation: the effects of predation risk and food supply

Abstract

Huey and Slatkin's (Q Rev Biol 51:363-384, 1976) cost-benefit model of lizard thermoregulation predicts variation in thermoregulatory strategies (from active thermoregulation to thermoconformity) with respect to the costs and benefits of the thermoregulatory behaviour and the thermal quality of the environment. Although this framework has been widely employed in correlative field studies, experimental tests aiming to evaluate the model are scarce. We conducted laboratory experiments to see whether the common lizard Zootoca vivipara, an active and effective thermoregulator in the field, can alter its thermoregulatory behaviour in response to differences in perceived predation risk and food supply in a constant thermal environment. Predation risk and food supply were represented by chemical cues of a sympatric snake predator and the lizards' food in the laboratory, respectively. We also compared males and postpartum females, which have different preferred or "target" body temperatures. Both sexes thermoregulated actively in all treatments. We detected sex-specific differences in the way lizards adjusted their accuracy of thermoregulation to the treatments: males were less accurate in the predation treatment, while no such effects were detected in females. Neither sex reacted to the food treatment. With regard to the two main types of thermoregulatory behaviour (activity and microhabitat selection), the treatments had no significant effects. However, postpartum females were more active than males in all treatments. Our results further stress that increasing physiological performance by active thermoregulation has high priority in lizard behaviour, but also shows that lizards can indeed shift their accuracy of thermoregulation in response to costs with possible immediate negative fitness effects (i.e. predation-caused mortality).

Thermal plasticity in young snakes: how will climate change affect the thermoregulatory tactics of ectotherms?

“…This result reflects behavioural buffering, where cool-treatment snakes emerged to bask earlier in the day, and kept basking for longer as well as closer to the heating lamp (F. A., personal observation). Comparable buffering behaviour has been described in lizards where sub-optimal temperatures led to longer basking periods -but these lizards often foraged at sub-optimal temperature with lower sprint speeds and predatory efficiency (Bennett, 1980;Christian and Tracy, 1981;Avery et al, 1982;Herczeg et al, 2008). In our study, bodytemperature regimes were unaffected by our experimental manipulations (at least outside of feeding periods); thus, showing that lower growth rates [as also seen in lizards kept at unfavourable thermal regimes (Avery, 1984;Sinervo and Adolph, 1994;Martin and Lopez, 1999)] may be elicited by ambient thermal challenges even if body-temperatures are unaffected.…”

A cold-adapted reptile becomes a more effective thermoregulator in a thermally challenging environment

“…It has to be noted that we did not try to test the cost-beneWt model of thermoregulation proposed by Huey and Slatkin (1976) which predicts that an ectotherm should stop thermoregulating when the costs of thermoregulation outweigh the beneWts. Although the model has been considered extensively in the past 10 years (Blouin-Demers and Weatherhead 2001;Blouin-Demers and Nadeau 2005;Herczeg et al 2006Herczeg et al , 2008, estimating the costs and beneWts of thermoregulation is diYcult as it requires knowledge of the costs of energy expenditure (based on the frequency distribution and the spatial distribution of T e ), the costs associated with missed opportunities and predation risks, as well as the interaction between these costs (Angilletta 2009). Furthermore, the quality of the three thermal treatments we oVered to tuatara did not diVer in their thermal quality (d e was the same in all three treatments) but in the length of time that T sel was available; therefore, we manipulated thermal constraint rather than energetic cost.…”

Maternal exposure to predator scents: offspring phenotypic adjustment and dispersal

“…At birth, juveniles born to mothers exposed to predator cues also selected lower temperatures, reflecting a diminution in basking behaviour (less time spent in the hottest part of the temperature gradient). Previous studies found that when in the presence of predator cues, common lizards reduce their basking behaviour [31,60,61], presumably because lizards are particularly vulnerable to predation while basking in the open. Our study adds to these findings by demonstrating that maternal exposure to predator cues during gestation is sufficient to trigger a change in juvenile thermoregulation behaviour even in the absence of actual predation stimulus in the natal environment.…”