TY - JOUR T1 - Environment, antecedents and climate change: lessons from the study of temperature physiology and river migration of salmonids JF - Journal of Experimental Biology JO - J. Exp. Biol. SP - 3771 LP - 3780 DO - 10.1242/jeb.023671 VL - 212 IS - 23 AU - Farrell, A. P. Y1 - 2009/12/01 UR - http://jeb.biologists.org/content/212/23/3771.abstract N2 - Animal distributions are shaped by the environment and antecedents. Here I show how the temperature dependence of aerobic scope (the difference between maximum and minimum rates of oxygen uptake) is a useful tool to examine the fundamental temperature niches of salmonids and perhaps other fishes. Although the concept of aerobic scope has been recognized for over half a century, only recently has sufficient evidence accumulated to provide a mechanistic explanation for the optimal temperature of salmonids. Evidence suggests that heart rate is the primary driver in supplying more oxygen to tissues as demand increases exponentially with temperature. By contrast, capacity functions (i.e. cardiac stroke volume, tissue oxygen extraction and haemoglobin concentration) are exploited only secondarily if at all, with increasing temperature, and then perhaps only at a temperature nearing that which is lethal to resting fish. Ultimately, however, heart rate apparently becomes a weak partner for the cardiorespiratory oxygen cascade when temperature increases above the optimum for aerobic scope. Thus, the upper limit for heart rate may emerge as a valuable, but simple predictor of optimal temperature in active animals, opening the possibility of using biotelemetry of heart rate in field situations to explore properly the full interplay of environmental factors on aerobic scope. An example of an ecological application of these physiological discoveries is provided using the upriver migration of adult sockeye salmon, which have a remarkable fidelity to their spawning areas and appear to have an optimum temperature for aerobic scope that corresponds to the river temperatures experienced by their antecedents. Unfortunately, there is evidence that this potential adaptation is incompatible with the rapid increase in river temperature presently experienced by salmon as a result of climate change. By limiting aerobic scope, river temperatures in excess of the optimum for aerobic scope directly impact upriver spawning migration and hence lifetime fecundity. Thus, use of aerobic scope holds promise for scientists who wish to make predictions on how climate change may influence animal distributions. CaO2concentration of oxygen in arterial bloodCvO2concentration of oxygen in venous bloodCTmaxthe critical thermal maximum that a fish can tolerateCTminthe critical thermal minimum that a fish can tolerateFry curvethe relationship between aerobic scope and temperatureHbhaemoglobinPaO2partial pressure of oxygen in arterial bloodPO2partial pressure of oxygenPvO2partial pressure of oxygen in venous bloodTcritthe temperature at which a fish has no aerobic scopeToptthe temperature at which a fish has maximum aerobic scoperate of oxygen uptake ER -