Foraging and Transport Costs in the Galapagos Marine Iguana, Amblyrhynchus cristatus

Abstract

Metabolic rates of walking and swimming marine iguanas (Amblyrhynchus cristatus) were measured in order to evaluate the locomotory specialization of this submarine foraging lizard. These data are compared to similar data for walking Galapagos land iguanas (Conolophus subcristatus) and to data for other lizards. Juvenile (mass = 500 g) and adult (mass = 2,900 g) marine iguanas could sustain walking speeds of ≤1 km/h aerobically for at least 20 min at basking temperatures of 35 C. increased linearly with increased walking speed. Amblyrhynchus studied in the field walked at 0.8-1.0 km/h, but were capable of brief bursts in excess of 9.0 km/h. Adaptation to swimming has not resulted in increased transport costs on land. Cost of transport by walking Amblyrhynchus (0.37-0.88 ml O₂/[g·km]) is similar to Conolophus and to other lizards and quadruped mammals. Marine iguanas ( ) swam at velocities up to 1.7 km/h with reduced metabolic rates relative to walking iguanas. Metabolic cost of swimming at 1.0 km/h was found to be one-fourth the cost of walking at the same speed for adult iguanas. Passive reduction of body temperature while in water, coupled with increased speeds attainable by swimming, function to reduce both time and energy spent foraging. Foraging costs are generously estimated to approximate less than 10% of Amblyrhynchus's 24 h energy budget. Hypothetical foraging on land would cost Amblyrhynchus approximately 31% of its 24 h energy budget.