Resting metabolic rate of Sceloporus grammicus at intermediate and native elevations

Body maintenance energy requirements are measured as minimal metabolic rate (RMR) of inactive, postabsorptive individuals in the laboratory. For mountain-dwelling species, translocation to the laboratory can mean a change in elevation and thus oxygen pressure, which may affect metabolic rates. Here we present resting metabolic rate (RMR) of three populations of the Mesquite lizard (Sceloporus grammicus) at their native elevations (i.e., 2600, 3200 and 4100 m) and at an intermediate elevation (3100 m). Each lizard was tested at 15, 25, 30 and 35ºC. For each test RMR is given in VCO2 ml/min. Data also includes sex, snout vent length (SVL), body mass, and throat color morph.

Methods
We collected five male and five females lizards, Sceloporus grammicus, from three sites (i.e., 2600, 3200 and 4100 m) in April 2018 and April 2019. To perform respirometry tests, in April 2018 lizards were transported to an intermediate elevation (i.e., 3200 m) and in 2019 lizards were transported to a location at a similar elevation to their native elevation. Lizards were fasted for two days and then tested at 15, 25, 30, and 35ºC. Tests for each population took place during two consecutive days, order of the tests was randomized. To measure resting metabolic rate, lizards were placed in a 50ml (in 2018) or 200 ml (in 2019) metabolic chamber, placed in an incubator set at the experimental temperature. Metabolic measures were taken in an open flow respirometry system, pushing CO2-free and dry air at 100 ml/min (in 2018) and 200 ml/min (in 2019) and measuring levels of excurrent CO2 using a FoxBox (Sable Systems International). VCO2 was measured during 20 min and the resting metabolic rate was determined as the lowest average CO2 production over an interval of 100 consecutive seconds.