Local adaptation reduces the metabolic cost of environmental warming

Metabolism shapes the ecosystem role of organisms by dictating their energy demand and nutrient recycling potential. Metabolic theory (MTE) predicts consumer metabolic and recycling rates will rise in a warming world, especially if body size declines, but it ignores potential for adaptation. We measured metabolic and nutrient excretion rates of individuals from populations of a globally invasive fish that recently colonized a wide temperature range (19-37°C) on two continents. Fish body size declined across our temperature gradient and MTE predicted large rises in population energy demand and nutrient recycling. However, we found that the allometry and temperature dependency of metabolism varied in a countergradient pattern with local temperature in a way that offset predictions of MTE. Scaling of nutrient excretion was more variable, and did not track temperature. Our results suggest that adaptation can reduce the metabolic cost of warming, increasing the prospects for population persistence under extreme warming scenarios.