Mastromonaco, Gabriela

The influence of stress exposure on the body temperature of vertebrates has been known for nearly two-thousand years. While the proximate mechanisms supporting this phenomenon are well described, the ultimate mechanisms remain enigmatic. In this thesis, I propose a novel hypothesis which states that changes in body surface temperature (henceforth "surface temperature") following stress exposure occur to reduce energetic expenditure toward thermoregulation, thus freeing energy for use in the stress response (hereafter, the "Thermoprotective Hypothesis"). Using a paired experimental design, I first show that black-capped chickadees (Poecile atricapillus, Linnaeus, 1766) exposed to repeated stressors decrease their surface temperatures at low ambient temperatures, and increase their surface temperatures at high ambient temperatures relative to unstressed controls. These changes in surface temperature contribute to a relative reduction in heat loss in the cold, and a relative increase in heat dissipation in the warmth among stress-exposed individuals, thus reducing their energetic demands toward more costly thermoregulatory strategies. Next, I show that stress-induced changes in surface temperature are most pronounced in chickadees that experience naturally-occurring resource-restrictions, suggesting that this response occurs to balance allocation of energy among the stress response and thermoregulation (i.e. a true energetic trade-off ). Third, I show that the magnitudes of chronic, stress-induced changes in surface temperature are highly variable among, and highly consistent within, chickadees, therefore suggesting that this response could hold adaptive significance if such variation among individuals is heritable. Finally, using domestic pigeons (Columba livia domestica, Gmelin, 1789) as a model species, I show that stress-induced changes in surface temperature are highly pronounced at bare tissues with a critical role in thermoregulation for some avian species (the bill), when compared with responses at surrounding bare tissues (the eye region). Together, these findings strongly support the Thermoprotective Hypothesis and suggest that endotherms may trade energetic investment toward thermoregulation with that toward the stress response in resource-limiting environments.

Author Keywords: heat transfer, infrared thermography, stress physiology, surface temperature, thermoregulation, trade-off

Many facilities attempt to alleviate the risk of chronic stress in captivity by providing environmental enrichment shown to minimize behavioural disorders and stress in several species. One potential form of enrichment used in zoos is training animals to perform rides for guests, however, the effect of this activity on the welfare of individual animals has never been examined. I validated the use of saliva for assessing stress in dromedary camels (Camelus dromedarius) an animal commonly used for rides. I then measured variation in salivary cortisol in four male camels during animal rides for guests at the Toronto Zoo. The camels were sampled during the ride season (from June to August) using four treatments: 1) in their pasture, 2) at the ride area not performing rides, 3) performing a low number of rides (n=50/day) and 4) performing a high number of rides (n=150/day). Furthermore, samples were taken before and after the ride season for comparison. There was a significant difference between the post-ride season treatment and the three treatments involving guest presence during the ride season (ride area, low rides, high rides. This indicates that performing rides is not a stressful experience based on the stress metrics I used, and suggests that rides may be a form of enrichment for dromedary camels.

Author Keywords: ACTH challenge, animal welfare, camels, environmental enrichment, salivary cortisol, stress