SCALING OF ANAEROBIC METABOLISM DURING EXERCISE IN THE ESTUARINE CROCODILE (CROCODYLUS-POROSUS)

The allometry of anaerobic metabolism was examined in wild estuarine crocodiles (Crocodylus porosus) exercised to exhaustion during capture, with the aim of identifying factors underlying the higher anaerobic capacity but possibly lower anaerobic scope in larger animals, Exercise time to exhaustion, and concentrations of lactate and protons in blood and tail muscle, increased with increasing body mass, Muscle glycogen, both before and after exercise, also showed positive allometric sealing, Muscle intracellular pH buffering capacity scaled negatively with body mass, The effects of pH on the activities of muscle phosphorylase and phosphofructokinase were independent of body mass, It is proposed that anaerobic capacity may be limited by the size of muscle glycogen reserves in smaller crocodiles and by glycolytic inhibition at the lower pH values encountered in larger crocodiles, Mean anaerobic scope, and phosphorylase activity in tail muscle, decreased with increasing body mass, while lactate dehydrogenase activity was independent of body mass, Negative allometric scaling of anaerobic scope in crocodiles may relate to changes in predator-prey and social interactions that involve reduced dependence on frequent bursts of anaerobic muscle work with increasing body mass.