Temperature changes affect metabolism on acute, acclimatory and evolutionary time scales. To better understand temperature's affect on metabolism at these different time scales, we quantified cardiac oxidative phosphorylation (OxPhos) in three Fundulus taxa acclimated to 12°C and 28°C and measured at three acute temperatures (12°C, 20°C, and 28°C). The Fundulus taxa (northern Maine and southern Georgia F. heteroclitus, and a sister taxa, F. grandis) were used to identify evolved changes in OxPhos. Cardiac OxPhos metabolism was quantified by measuring six traits: State 3 (ADP and substrate dependent mitochondrial respiration), E State (uncoupled mitochondrial activity), Complex I, II, and IV activities, and LEAK ratio. Acute temperature affected all OxPhos traits. Acclimation only significantly affected State 3 and LEAK ratio. Populations were significantly different for State 3. In addition to direct effects, there were significant interactions between acclimation and population for Complex I and between population and acute temperature for State 3. Further analyses suggest that acclimation alters the acute temperature response for State 3, E State, and Complexes I and II: at the low acclimation temperature, the acute response was dampened at low assay temperatures, and at the high acclimation temperature, the acute response was dampened at high assay temperatures. Closer examination of the data also suggests that differences in State 3 respiration and Complex I activity between populations were greatest between fish acclimated to low temperatures when assayed at high temperatures, suggesting that differences between the populations become more apparent at the edges of their thermal range.
