2 Physiological Adjustments to Fluctuating Thermal Environments: An Ecological and Evolutionary Perspective

Abstract

I. INTRODUCTION
The physical environment of organisms is not constant but changes through time and space. Major environmental changes cause stress, damage, or even death to organisms, but even minor changes may hamper the physiological capacities of organisms to grow, reproduce, or interact socially. Not surprisingly, organisms have evolved a variety of adjustments (e.g., behavior, acclimation, heat stress response) that help buffer the physiological impact of environmental change. These adjustments, which can have a profound effect on evolutionary fitness, can be studied from diverse perspectives. For example, what molecular and physiological bases underlie a given adjustment? What ecological and physiological circumstances favor its evolution and use?

In this paper, we adopt an ecological and evolutionary framework that has been developed to study general adjustments that organisms use to buffer natural environmental variation (Levins 1968; Slobodkin and Rapoport 1974; Hochachka and Somero 1984). We apply this framework in an analysis of adjustments specifically associated with heat stress. We begin with a brief discussion of the general effects of temperature on organisms. Then, for each class of adjustment to stress, we evaluate the ecological circumstances favoring its use, describe some organismal examples from the comparative literature, and also evaluate its relevance to studies of induced aspects of the heat stress response. Our primary goal is to encourage an expanded dialogue between biologists studying the heat stress response and those interested in ecological and evolutionary physiology. As we will argue, both groups have much to contribute to each other.

That organisms are sometimes...