Direct calorimetry reveals large errors in respirometric estimates of energy expenditure

Abstract

Knowledge of animal energetics is based largely upon indirect calorimetry, which is estimation of metabolic heat production by an organism from measurement of indices such as oxygen consumption or carbon dioxide production. Remarkably, indirect calorimetry has been validated by comparison to direct measurements of metabolic heat production (direct calorimetry) only for highly restricted conditions, primarily with a few species of medium-to-large mammals. Taxa with differing physiologies are little studied. For birds, for example, validations are limited to chickens and waterfowl exposed to mild environmental conditions and typically fasted for prolonged periods. Workers rely upon these restricted validations when studying animals ranging greatly in activity, phylogeny, body size and nutritional status. We tested the accuracy of respirometric estimates of energy expenditure by simultaneous indirect and direct calorimetry in a small mammal (the kangaroo rat Dipodomys merriami Mearns), a small bird (the dove Columbina inca Lesson) and a medium-sized bird (the quail Coturnix communis Linnaeus). We find that conventional respirometric estimates of energy expenditure may incorporate large errors (up to 38%) that are sufficient to call into question generalizations regarding patterns of animal energy use in many studies.

Summit metabolism and metabolic expansibility in Wahlberg's epauletted fruit bats (Epomophorus wahlbergi): seasonal acclimatisation and effects of captivity

“…We are not aware of published thermal equivalence data suitable for converting respiratory gas exchange to metabolic rate when RER <0.71, and hence assumed RER=0.71 when estimating M sum . Values of RER below the expected range of 0.71-1.00 have been reported by several workers (reviewed by Walsberg and Hoffman, 2005). These authors also pointed out that accepted RER and thermal equivalence values are based largely on data obtained from medium-to largebodied domesticated taxa during the first half of the 20th century, and may not necessarily be expected to apply universally to species from phylogenetically diverse groups operating under a wide variety of thermogenic requirements and exercise intensities.…”

Mean mass-specific metabolic rates are strikingly similar across life's major domains: Evidence for life's metabolic optimum

“…To noticeably alter the results obtained, the applied oxygen energetic equivalent should have been changing in a systematic manner by hundreds of percent across taxa; this differs sharply from the relative constancy of oxygen energetic equivalent revealed in comparisons of direct and indirect calorimetry (46,47). Metabolic rates reported on the dry mass basis [q DM, W (kg DM) Ϫ1 ] were converted to wet mass basis (q, W kg Ϫ1 ) assuming a mean 30% dry matter content: q ϭ qDM ϫ 0.3.…”

Measuring abnormal rotational movements in free-swimming fish with accelerometers: implications for quantifying tag- and parasite-load

“…calorimetry, Walsberg and Hoffman, 2005; or ṀO 2 , Clarke and Johnston, 1999) because of the need to collect data from freeswimming fish. However, given past research, it is reasonable to assume that the dynamic body acceleration, VeDBA (Wright et al, 2014;Gleiss et al, 2010), can be used as a proxy for energy expenditure, as it is assumed to be proportional to energy expenditure.…”