The Relation of Enzyme Heterozygosity to Standard and Active Oxygen Consumption and Body Size of Tiger Salamanders, Ambystoma tigrinum

We addressed the questions concerning what relation exists between enzyme heterozygosity and standard or active oxygen consumption (V̇o2) and whether the genotype at a particular locus could predict differences in body size. Of the 25 enzyme loci evaluated in liver tissue, eight were polymorphic; no individual was heterozygous at more than five loci. Standard V̇o2 was most strongly associated with heterozygosity at the glucose phosphate isomerase and alcohol dehydrogenase (ADH) loci, whereas active V̇o2 was most tightly associated with heterozygosity at the ADH locus. Overall, standard V̇o2 was inversely correlated with multiple-locus heterozygosity at the eight loci, whereas active V̇o2 was positively correlated with heterozygosity. The significant correlation between polymorphism at the ADH locus and both standard and active V̇o2 led us to examine the relation between heterozygosity at the ADH locus and body size in a natural population. Body size in a single age class of larvae was greatest in heterozygotes and smallest in the least common homozygote, suggesting an important role for ADH in whole-body physiology. Analysis of the relation between genotypes and physiological characteristics may reveal some of the causes of variation in physiological performance among individuals. Furthermore, these analyses may generate testable hypotheses concerning the selective advantage of biochemical mechanisms and properties.