Assessing temperature related variation in routine metabolic rate across the geographic range of the Bluntnose Minnow (Pimephales notatus)

Background/Question/Methods

Predicted changes in climate may affect aquatic taxa, in part, through metabolic impacts associated with increasing water temperatures.  Understanding the potential effects of climate change on aquatic species requires an approach that integrates physiological trait data and local environmental conditions among populations.  Routine metabolic rate (RMR) is a reasonable measure of minimal daily activity and represents an important population-level trait to consider when assessing the potential impacts of changes in temperature.  We investigated whether variation in RMR is correlated with mean annual water temperature among sites across the geographic range of Pimephales notatus, a common North American freshwater fish species.  Individuals were collected from ten populations representing a range of latitudes throughout the Midwestern United States.   Routine metabolic rate data were collected using intermittent flow through respirometry for individuals from each population which were acclimatized to three temperature treatments (9°C, 18°C, and 27°C).  Mean annual temperature experienced by each population was calculated from data collected from temperature loggers deployed at each collection location or by using established air and water temperature relationships for a particular stream.  Regression analyses were performed to determine the relationships between temperature and both RMR and Q₁₀ (a measure of sensitivity to thermal variation).

Results/Conclusions

Routine metabolic rate increases with increasing temperature treatment for all populations.  At the 9°C treatment, results indicate a positive correlation between RMR and mean annual water temperature at the collection location, with northern populations exhibiting a higher RMR than southern populations.  The results also indicate a negative correlation between the Q₁₀ measures of thermal sensitivity and mean annual water temperatures.  Southern populations exhibit higher Q₁₀ values than northern populations, indicating that temperature has a larger effect on RMR for low latitude populations than for high latitude populations over the range of tested temperatures.  These results suggest the importance of understanding population-level responses to predicted changes in climate when considering potential future distributions of aquatic taxa.