Activity metabolism of the toad (Bufo americanus): Ecological consequences of ontogenetic change

Abstract

Following metamorphosis, juvenile toads form dense, heliothermic aggregations on the margins of the ponds from which they emerge. After a period of growth and development, during which body mass increases ten-fold, the juveniles disperse from the pond and assume the solitary, nocturnal habits that characterize adult toads. The dispersal of the toads coincides with the culmination of ontogenetic changes in activity metabolism. Unlike adults, juvenile toads exhaust rapidly when exercised and exhibit a low aerobic component of total metabolic scope. Values of aerobic scope for sustained activity ranged from 0.5 ml O2/(g•h) for the smallest juveniles to 1.0 ml O2/(g•h) for adults. The capacity of juveniles for oxygen consumption increases rapidly with growth, reaching the level of mature animals immediately prior to dispersal. In contrast to aerobic metabolism, anaerobic scope was independent of body size. Whole body lactate content after a 1 min bout of vigorous activity was elevated above the resting level by 0.14 mg lactate/g for both juvenile and adult animals. The elevated body temperatures that are achieved by basking juvenile toads probably hasten their physiological development and increase their capacity for aerobic metabolism.