Avoiding the effects of translocation on the estimates of the metabolic rates across an elevational gradient

Body maintenance costs are often considered a proxy for performance in fitness traits. Maintenance energy requirements are measured as minimal metabolic rate of inactive, postabsorptive individuals in the laboratory. For mountain-dwelling species, translocation to the laboratory often means that they are also moved to another elevation. Due to physiological adaptations to local oxygen pressure, rapid elevational change can alter metabolic rate and translocation may result in erroneous estimates of body maintenance costs. In this study, we measured resting metabolic rate (RMR) of three populations of the Mesquite lizard (Sceloporus grammicus, Wiegmann 1828) at their native elevations (i.e., 2600, 3200 and 4100 m). Our results showed that at native elevations, mass specific RMR of lizards from the high elevation population (4100 m) did not differ from the RMR of the other populations (i.e., 2600 and 3200 m), whereas the lizards from the low elevation (2600 m) had lower RMR than those from the intermediate population. These results differ from a previous study in which the RMR of lizards from the same populations were reported to increase with native elevation when translocated and measured at an intermediate elevation. Hence, our results show that translocation in elevation can affect metabolic measures. We caution researchers that changes in elevation may preclude accurate measures of RMR in some animals and may therefore incorrectly predict performance of fitness-related traits.