Abstract

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 ( ) at seven oxygen concentrations among seven populations of Fundulus grandis that inhabit a mosaic of habitats with different frequencies and intensities of hypoxia. For , there is a significant interaction ( ) between body mass and oxygen concentrations: log₁₀ body mass:log₁₀ slopes were steeper at intermediate oxygen partial pressures (Po₂) than either normoxic or lowest Po₂ (ANCOVA, ). Additionally, the (Po₂ where can no longer be maintained) was a negative function of body mass ( ). At the lowest Po₂ (1.8 kPa), there was a significant difference in among populations: one of the populations from environments more frequently stressed by hypoxia has greater at the lowest oxygen concentrations. With few differences among populations, the most important effects were how body mass affected at intermediate Po₂ and the negative relationship between body mass and . These findings suggest that an increase in body size is a useful strategy to minimize the effect of hypoxia.