On the Adaptive Significance of Enzyme Polymorphisms in Relation to Environmental Variability

Abstract

Geographic variation in enzyme polymorphisms for a variety of organisms was analyzed in light of Levins' (1965) prediction that genetic variation in fitness should increase with environmental variability. Under the premise that genes evolve in correlated blocks, a matrix of correlations in heterozygosities among loci for each study was analyzed by varimax rotated principal components to discern independent trends of variation. Step-wise multiple regression was used to relate these trends to measures of within-year environmental variability, computed from climate summaries of the United States Weather Bureau. Over the eight sets of data analyzed, including both poikilotherm and homeotherm data, approximately 70% of the geographic variation in heterozygosities could be accounted for by these measures of temporal variation. Therefore, patterns of geographic variation in heterozygosities, for statistically correlated ensembles of loci, may represent adaptive shifts in response to changes in variability of specific components of the environment.