title: Postprandial heat increment does not substitute for active thermogenesis in cold-challenged star-nosed moles (Condylura cristata).
abstract: The postprandial increase in metabolic rate associated with consuming, assimilating and excreting a meal is often termed the heat increment of feeding (HIF). The metabolic heat production of star-nosed moles, Condylura cristata, held at thermoneutrality was monitored for 4 h following a single 10 min session of feeding on a ration consisting of 0 g (controls), 3.5 g or 10 g of earthworms. Coefficients for metabolizable energy digestibility and digesta passage rate of earthworms fed to C. cristata were also determined. We then tested whether feeding-induced thermogenesis substitutes partially or completely for thermoregulatory heat production in these animals exposed to sub-thermoneutral air temperatures (9-24 degrees C). A single feeding on earthworms had both short- and long-term effects on the metabolic rate and respiratory exchange ratio of C. cristata. The observed short-term (0-65 min) rise in metabolic rate, assumed to be associated primarily with the physical costs of nutrient digestion, absorption and excretion, was similar to the calculated mean retention time (66.7+/-7.8 min; mean +/- s.e. m., N=5) of this species. This component of the HIF represented 2.9 % of the food energy ingested by moles fed a single 3.5 g (13.21 kJ) meal of earthworms and 1.4 % of the food energy ingested by moles fed a single 7.5 g (28.09 kJ) meal of earthworms. At all test temperatures, resting metabolic rate typically remained above fasting levels for 1-4 h following ingestion of the high-protein earthworm diet. This protracted rise in metabolic rate, presumably associated with the biochemical costs of amino acid oxidation/gluconeogenesis and ureagenesis, averaged 12.8 % of the metabolizable energy and 8.7 % of the gross energy intake. Despite the potential thermoregulatory benefit, we found no evidence that biochemical HIF substitutes for facultative thermogenesis in star-nosed moles exposed to low air temperatures.
authors.affiliation: Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2. campbelk@zoology.ubc.ca
authors.forename: K L
authors.initials: KL
authors.lastname: Campbell
authors.forename: I W
authors.initials: IW
authors.lastname: McIntyre
authors.forename: R A
authors.initials: RA
authors.lastname: MacArthur
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D004032:Diet; D004734:Energy Metabolism; D005247:Feeding Behavior / Q000502:physiology; D008971:Moles / Q000378:metabolism / Q000502:physiology*; D009835:Oligochaeta; D019518:Postprandial Period / Q000502:physiology*