Adaptation versus Allometry: Population and Body Mass Effects on Hypoxic Metabolism in Fundulus grandis

Hypoxia has significant effects on organisms, from metabolic reduction to death, and could be an important evolutionary force affecting the variation among populations within a species. To determine intraspecific variation in hypoxic metabolism and the effect of body mass, we examine rates of oxygen consumption ((M) over doto(2)) at seven oxygen concentrations among seven populations of Fundulus grandis that inhabit a mosaic of habitats with different frequencies and intensities of hypoxia. For (M) over doto(2), there is a significant interaction (P < 0.05) between body. mass and oxygen concentrations: log(10) body mass : log(10) (M) over doto(2) slopes were steeper at intermediate oxygen partial pressures (Po-2) than either normoxic or lowest Po-2 (ANCOVA, P < 0.001). Additionally, the Po-2crit (Po-2 where (M) over doto(2) can no longer be maintained) was a negative function of body mass (P < 0.04). At the lowest Po-2 (1.8 kPa), there was a significant difference in (M) over doto(2) among populations: one of the populations from environments more frequently stressed by hypoxia has greater (M) over doto(2) at the lowest oxygen concentrations. With few differences among populations, the most important effects were how body mass affected (M) over doto(2) at intermediate Po-2 and the negative relationship between body mass and Po-2crit. These findings suggest that an increase in body size is a useful strategy to minimize the effect of hypoxia.