Metabolic costs of rodents feeding on plant chemical defenses: A comparison between an herbivore and an omnivore

We analysed the combined effect of subchronic dietary cellulose and tannic acid on the metabolic cost in the herbivorous burrowing caviomorph rodent Octodon degus, and the omnivorous Sigmodontine Phyllotis darwini. Both are sympatric rodent species living in open scrub subjected to summer droughts in the Mediterranean communities of northern and central Chile. We measured basal metabolic rate (BMR), maximum metabolic rate of thermoregulation (MMR) and the aerobic scope. As a consequence of the ingestion of comparative higher concentrations of dietary tannic acid and fiber, a higher MMR was observed in P. darwini than in the herbivorous O. degus. Metabolic costs were observed under maximal but not under basal conditions. (C) 1997 Elsevier Science Inc.