Meeting Abstract
An organism’s ability to adjust metabolic performance in response to current selective pressures has clear implications for fitness and adaptation. At the lower limit, basal metabolic rate is the energy expenditure required for self-maintenance at rest; while at the upper limit, peak metabolic rate is an individual’s maximum aerobic performance under conditions of physical exertion. The difference between the two, metabolic scope, is an instantaneous measure of an individual’s flexibility to cope with the many energetic demands posed by its environment. Metabolic scope has been shown to linearly increase with increasing absolute latitude across fishes and mammals. This pattern has largely been attributed to underlying latitudinal trends in climatic variability, such that individuals in variable temperate zones are likely to exhibit greater flexibility in their physiological response than do those in the less variable tropics. Alternatively, climatic extremes could drive variation in scope via selective pressure on thermoregulatory performance. To differentiate between these two hypotheses, we characterized patterns in avian metabolic scope using data from the literature and tested for associations with climatic variables using both conventional and phylogenetically informed analyses. We found that climatic extremes (i.e. minimum temperature), not climatic variability, are driving interspecific patterns in avian scope. Moreover, we found a tight correlation between scope and peak metabolic rate, indicating that selection is acting on the upper limits of performance. This represents an important step towards illuminating the mechanisms underlying patterns in avian macrophysiology.
