Date of Award

Winter 12-27-2018

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)




Danielle Levesque

Second Committee Member

Kristy Townsend

Third Committee Member

Leonard Kass


Endothermic organisms such as mammals and birds rely on high energy budgets to regulate body temperature. Many studies have previously investigated the thermo-regulation of mammals under the lower critical temperature of the thermoneutral zone, yet our knowledge in determining the upper critical limits is still scarce. As an endotherm, lab mice (Mus musculus) are perfect models to determine the cost to maintain constant body temperature as ambient temperature increases. The upper critical temperature of the thermoneutral zone of this species has been estimated to be above 32°C and below 34°C. By utilizing different genetic backgrounds of lab mice in this study will help us to understand how genetic variation may impact thermoregulation. My research, questions were: 1) Is the upper critical limit similar for all mice, regardless of genetic background? And 2) Do resting metabolic rate (RMR), body temperature (Tb) and evaporative water loss (EWL) increase similarly all mice as ambient temperature increases? To investigate the upper critical temperature between the standard inbred lab strain C57BL6/JUM (N =12) and mice with a mixed genetic background (N=8), I used flow through respirometry which measured VCO2, evaporative water loss and body temperature over a range of ambient temperatures from 25-38°C. Body mass was measured on a 0.1g scale and there was a significant difference in body mass between both strains of mice, which is well documented. Break points in resting metabolic rate and body temperature were higher C57BL6/JUM mice compared to the mixed strain. On the other hand, evaporative water loss was higher in the mixed strain. The results were not statistically significant since I had a low degree of freedom due to exclusion of data points based on activity of the mice, which confounded data collection in those samples and the goal was to determine the resting metabolic rate, not active metabolic rate. However, my results do indicate differences in RMR, Tb and EWL due to genetic differences. This information could be important for understanding the most efficient way mammals spend their metabolic energy to maintain a tightly balanced energy budget. Future work needs to be done to understand what causes these variations in upper critical limits.