Physiological Differentiation of Vertebrate Populations

INTRODUCTlON ,. . The foundation of most evolutionary theory rests upon inferences drawn from geographic variation or upon the verification of predictions made about it. The study of geographic variation occupies a central position in evolutionary biology. .. because geographic variation is ordinarily the smallest amount of evolution that can be detected in nature and because evolutionary theory, in its strongest form, applies only to small evolutionary change. Although studies of geographic variation are relatively common, the vast majority have dealt with morphometric or meristic traits (13, 120, 297, 327), allozymes (150, 233, 327), or most recently, mitochondria1 DNA (9). The relative rarity of studies of geographic variation in physiological traits (see 42, 245, 312 for reviews of early studies) is somewhat surprising, considering that a major focus within vertebrate "physiological ecology," "comparative physiology," "environmental physiology," and "biophysical ecology" is the Of course, populations may show differentiation on other than large geographic scales, such as "microgeographic"