Metabolic rates of three gazelle species (Nanger soemmerringii, Gazella gazella, Gazella spekei) adapted to arid habitats

The basal metabolic rate of mammals correlates with body mass, but deviations from this regression have been observed and explanations comprise ecological adaptations, reproductive strategies or phylogeny. Certain mammalian groups, adapted to arid environments, show comparatively lower metabolic rates. To expand existing datasets and to investigate metabolic rates in ruminants adapted to arid environments, we conducted respiration measurements with three gazelle species (Gazella spekei, G. gazella and N. soemmerringii, total n = 16). After an adaptation period to a diet of fresh lucerne offered ad libitum, subjects were put separately into respiration boxes for 24 h where they had free access to food and water. Oxygen consumption and carbon dioxide production were measured with a modular system of gas analyzers and pumps. Mean and resting metabolic rate (RMR) were calculated by accounting for the entire measurement phase or the lowest 20 oxygen measurements, respectively. N. soemmerringii had the lowest relative RMR values and the highest respiratory coefficients compared to the other species. Measured values were compared to expected RMR values calculated based on body mass. Gazella spekei and G. gazella showed higher RMR values than expected, while the RMR of N. soemmerringii was in the range of expected values. Our results indicate that not all mammals adapted to aridity have lower metabolic rates under conditions of unlimited resources and that in these cases other physiological adaptations might be of higher importance. Further extensions of the datasets could allow explaining which deviations of metabolic rate from the body mass regressions result from convergent adaptations