Plasticity, repeatability, and phenotypic correlations of aerobic metabolic traits in a small estuarine fish

Standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS), and critical oxygen tension (Pcrit) were determined for the Gulf killifish, Fundulus grandis, an ecologically dominant estuarine fish, acclimated to lowered salinity, elevated temperature, and lowered oxygen concentration. Acclimation to low salinity resulted in a small, but significant, elevation of Pcrit (suggesting lower tolerance of hypoxia); acclimation to elevated temperature increased SMR, MMR, AAS, and Pcrit; acclimation to low oxygen led to a small increase in SMR, but substantial decreases in MMR, AAS, and Pcrit. Variation in these metabolic traits among individuals was consistent and repeatable when measured during multiple control exposures over seven months. Trait repeatability was unaffected by acclimation condition suggesting that repeatability of these traits is not context dependent. There were significant phenotypic correlations between specific metabolic traits: SMR was positively correlated with MMR and Pcrit; MMR was positively correlated with AAS; and AAS was negatively correlated with Pcrit. In general, within-individual variation contributed more than among-individual variation to these phenotypic correlations. The effects of acclimation on these traits demonstrate that aerobic metabolism is plastic and influenced by the conditions experienced by these fish in the dynamic habitats in which they occur; however, the repeatability of these traits and the correlations among them suggest that these traits change in ways that maintains the rank order of performance among individuals across a range of environmental variation.