Meeting Abstract

P2.21  Thursday, Jan. 5  Stress, Strain, Thermal Environment, and Thermoregulation BAKKEN, G.S.; Indiana State Univ.

Stress is an applied force, while strain is the response of the object to the stress. For example, the weight of a diver (stress) causes a springboard to bend (strain). Stress and strain are related by a filter function, in this case springboard stiffness. In thermoregulatory physiology, the thermal environment determines the stress, while physiological strain is the resulting rate of change of body temperature or the metabolic heat production and evaporative cooling needed to stabilize body temperature. A small armadillo exposed to an arctic winter day is incorrectly described as “cold stressed.” An arctic fox of similar size is equally cold stressed, but is not strained because its filter function (fur) is radically different. Stress vs. strain confusion is evident in some studies using temperature-sensing reptile models to characterize a complex thermal environment. A model with heat storage capacity(filter function) similar to that of the animal estimates strain (body temperature), while a model with minimal heat capacity estimates thermal stress (operative temperature). Strain (body temperature) can easily be computed, even for active animals, given the spatial distribution of stress (operative temperature. In contrast, measured strain applies only to an animal rooted to a particular point. I will describe the construction of free-standing, temperature sensing, low mass reptile models, present data illustrating the effects of model properties on measured operative temperature, and present simple example computation procedures for estimating body temperature given the spatial distribution of operative temperature, movement patterns, and the animal filter function.