Meeting Abstract
Standard metabolic rate (SMR) and maximal metabolic rate (MMR) typically vary 2-3 fold amongst individual animals of the same species, size and life history stage, despite these traits being presumed to have a significant impact on fitness. Yet, the underlying physiological differences that determine such intraspecific variation in metabolism are largely unknown. Here we tested the hypotheses that variability among individuals in SMR and MMR is influenced by mitochondrial functioning, and that if SMR support the cost of maintaining the machinery needed for MMR, their underlying mitochondrial capacities should be shared. We examine the role of variation in mitochondrial respiratory capacities (leak and phosphorylative respiration rates) of key metabolic tissues (liver and white muscle) in brown trout Salmo trutta from the same life stage, environment and nutritional state. Mass-independent MMR and SMR were found to be uncorrelated, indicating that they are under the control of separate physiological processes. Moreover, the leak respiration in liver was significantly greater in high SMR individuals and the difference in MMR between fish was positively related to the leak respiration in the white muscle. Trout with high SMR or high MMR, far from signalling a higher respiratory capacity for mitochondrial ATP synthesis, can be those individuals whose tissue-specific mitochondria have a greater leakage of proton across the mitochondrial inner membrane. These results open up a range of avenues for future research on the consistent variability among individuals in the aerobic metabolism, including the fitness consequence of such variation in mitochondrial function, given the importance of mitochondria in the conversion of resources into ATP.
