Introduction to the Symposium: What is Evolutionary Physiology?

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Organisms in natural populations possess a number of physiological and morphological traits that appear to increase fitness in the natural environment. For example, with regard to cold tolerance these include long fur in Arctic mammals, subcutaneous fat in marine mammals, glycoprotein antifreezes in Antarctic fishes, and the capacity to hibernate in rodents subjected to long winters. Physiological ecologists have long been concerned with elucidating such characters and demonstrating their significance for the survival of organisms in the natural environments (Schmidt-Nielsen, 1990; Bartholomew, 1987). It is assumed that the presence of these traits in extant populations is the result of evolution of the traits in question. It is axiomatic that the adaptive traits evolved under selective pressures favoring organisms that are more fit in the corresponding environment. Considerable insight has been gained over the past two centuries regarding patterns of morphological evolution (Lauder, 1996). Morphological traits are often easily quantified and, if properly chosen, they are accessible in ancestral and extinct species in the form of preserved specimens and fossils. Even with these advantages, the picture emerging from the study of evolution of morphological traits is complex. The importance of genetic pleiotropies and phylogenetic constraints in contorting straightforward evolutionary progress is becoming clear. These present significant challenges to ecologists and evolutionary biologists in their attempts to understand the evolution of life history traits (Rose and Lauder, 1996).