Joanna Piercy

MSc Candidate, Zoology (UBC) Directed Studies, Zoology (UBC) BSc (McGill) Contact Info: Department of Zoology University of British Columbia 6270 University Blvd. Vancouver, British Columbia Canada, V6T 1Z4 Tel: (604) 822-5799 FAX: (604) 822-2416 piercy@zoology.ubc.ca

Estimating Metabolic Rate in Tegu Lizards (Tupinambis merianae): Calculating the Correlation between Oxygen Consumption and Heart Rate

There are a number of methods commonly used to estimate metabolic rate in animals, however every method has its limitations. In some cases, the metabolic rate of short-term activities cannot be differentiated, nor can the metabolic rate be monitored over longer periods of time. In other cases, the method used to estimate metabolic rate is disruptive to the animal’s natural behaviour. Indeed, even the high cost of implementing some methods can be a major limitation.

With this in mind, considerable research has been carried out to determine whether heart rate can be used to accurately estimate oxygen consumption, and therefore metabolic rate. The advantage of using heart rate as a proxy for metabolic rate is that heart rate is easily monitored both in the lab and in the field, is sensitive to short-term changes in activity, and can be consistently monitored on the order of weeks or months. In other words, this “heart rate method” of estimating metabolic rate has the potential to increase both the resolution and the scope of studies in energetics, especially in field studies where direct respirometry is not possible.

Past studies have repeatedly confirmed that the accuracy of the heart rate method is at least as great as the doubly-labelled water method in various birds and marine mammals. However, to date only one published study has been performed using reptiles. As an Unclassified student, I performed preliminary studies with tegu lizards and observed that the relationship between oxygen consumption and heart rate varies in a predictable manner with ambient temperature and digestive state. The trend was clear; however, further studies were necessary to refine methodology to reduce experimental error such that a reliable “calibration equation” could be derived, and to validate the generalized use of this “calibration equation”.

I am currently continuing this research for my MSc thesis. Using open-flow respirometry I can determine oxygen consumption in tegu lizards on a breath-by-breath basis, while simultaneously monitoring heart rate. Experiments are conducted at 17°C, 27°C and 37°C (both fasting and during digestion), representing the normal range of temperatures experienced in the wild. With this data, my goal is to determine the equation which best expresses oxygen consumption in terms of heart rate, temperature and digestive state in one population of tegu lizards (i.e. to derive the “calibration equation”). Using another population of tegu lizards I will repeat these experiments to confirm the application of the calibration equation to the species in general (i.e. to validate the calibration equation). My hope is that this study will generate a reliable tool to facilitate the estimation of metabolic rate in future field studies in the energetics of wild and free-range tegus.