Animals are under increasing pressure as the global climate continues to change at an unprecedented rate. Ectotherms are particularly vulnerable to changes in thermal regimes because they rely on environmental temperatures to maintain the body temperatures necessary for physiological functioning. Multiple competing hypotheses predict different responses to climatic shifts for ectotherms that behaviorally thermoregulate (i.e., maintain a constant body temperature through behavioral modulation). Some suggest behavioral plasticity in thermoregulation will allow individuals to keep pace with climatic changes by avoiding critical temperatures. Conversely, others suggest this plasticity in behavior at the individual level will limit natural selection’s ability to operate on the upper thermal tolerance of populations, thus limiting the population’s ability to respond when temperatures exceed individuals’ capacity to behaviorally adjust. We used greater short-horned lizards (Phrynosoma hernandesi), a species with a demonstrated capacity to quickly respond to new thermal regimes through behavioral plasticity, to determine if behavioral plasticity buffered them from natural selection on upper thermal tolerance. We measured the upper thermal tolerance of the captured lizards, and then transplanted lizards from a high-elevation site to a low-elevation site within their elevational range to test their survival compared to a control group that was maintained at the high-elevation site.
Results/Conclusions
We found that survival did not differ between the transplant group and the control group. However, we found that lizards transplanted down the mountain lost significantly more mass than the control conspecifics. Our results suggest lizards that are able to shift their behaviors in response to changes in the thermal environment may be able to survive for relatively short periods of time after a change in their thermal environment. However, the loss in mass these lizards experienced after the transplant may indicate they experienced energetic changes that are causing them to expend more energy than they are able to renew. This would suggest that at a longer timescale than we measured, behavioral changes in thermoregulation would not fully buffer these animals from selective processes.