8. Garland, T., Jr., and P. L. Else. 1987. Seasonal, sexual, and individual variation in endurance and activity metabolism in lizards. American Journal of Physiology 252 (Regulatory, Integrative and Comparative Physiol. 21):R439-R449.

Abstract

Amphibolurus nuchalis were collected in central Australia during mid- (January) and late summer (March). Endurance time at 1 km/h on a motorized treadmill is greater in larger lizards, scaling as M^0.65. Maximal O₂ consumption (VO₂max) scales as M^0.96; standard metabolic rate (SMR) scales as M^0.83. Factorial aerobic scope thus increases ontogenetically (9.4 at 1 g vs. 15 at 50 g). All organ masses scale allometrically; larger lizards have relatively smaller livers, but larger hearts and thigh muscles. Hematocrit and hemoglobin increase during early ontogeny, but are mass independent in adults. Maximal in vitro catalytic rates were determined for citrate synthase (CS) and pyruvate kinase (PK) in liver, heart, and thigh muscle and for lactate dehydrogenase (LDH) (lactate oxidation) in heart. All enzyme activities (expressed per g tissue) scale positively, except CS in heart. Females exhibit lower SMR and heart CS activity. March animals exhibit elevated endurance, VO₂max, heart LDH, and thigh CS and PK activities. Individual variation in endurance correlates with individual differences in heart LDH and thigh CS and/or PK activities. Individual differences in VO₂max are partly related to variation in hematocrit.