Using the doubly labeled water method to field metabolic rate in northern red-backed voles, Myodes rutilus.

摘要

Field metabolic rate (FMR) is a measurement of an animal's total daily energy expenditure and can be measured with the doubly labeled water (DLW) method. Northern red-backed voles, Myodes rutilus, are interesting in that they do not hibernate, nor do they store enough fat to sustain their active lifestyles, even in the harsh winters of Alaska. The aim of this study was to test the effects of seasonal and environmental factors on the FMR of captive populations of M. rutilus held in indoor and outdoor enclosures at the Alaska Zoo in Anchorage, Alaska. Data showed that photoperiod did not affect the FMR of the indoor vole population, but there was a seasonal fluctuation in the FMR of outdoor voles. This seasonal change appeared to be linked to ground temperature, which is directly affected by snow depth and ambient temperature.;Several months into the project, a second aim was added to test the validity of DLW samples outside the range of current recommended dosages, as some initial samples had high isotopic concentrations. Highly enriched samples are said to be increasingly difficult to interpret by mass spectrometers, and, if they are too low, they will not be discernible from the natural abundance in the local environment.;To test the validity of the high isotope results, FMR measurements were made over a three month period using DLW doses within the recommended range. These were then compared with the measurements made 12 months earlier using highly enriched DLW. No difference in FMR was found between the two sets of measurements, which supports the validity of the data we obtained using enriched DLW. It also suggests that earlier studies that used higher than recommended enrichments, or failed to specify the levels of enrichment used, are also likely to be valid. Our data further suggest that enriching DLW dosages above the recommended range may be appropriate for studies of small mammals where doses within the recommended range cannot produce discernible results.