Metabolic interrelations underlying the physiological and evolutionary advantages of genetic diversity

Abstract

SYNOPSIS. Past findings have established how the faster growth, greater reproductive output and/or longer survival that are associated with heterosis and genoinic diversity measured as multi-locus heterozygosity stem from slower intensities with which proteins are renewed and replaced (=protein turnover). Slower turnover results in lower energy requirements and reduced metabolic sensitivity to environmental change, representing a mechanistic basis for evolutionary consequences of genetic polymorphism. To determine the genetic and functional basis of differences in whole-body protein turnover, we have begun to resolve different proteolytic pathways, searching for genetic polymorphisms with a direct effect upon proteolysis, and assessing the metabolic and physiological consequences of those genetic influences in the mussel Mytilus cdulis. Our recent work has established the physiological importance of Ij sosomal enzymes under normal conditions of basal proteolysis, and shown that associated effects on energy flux may vary according to functional differences between separate enzymes. Data are presented here which compare metabolic consequences of polymorphism in the lysosomal aminopeptidases Lap-1 and Lap-2. Findings establish that metabolic and phenotypic effects of genetic polymorphism result directly from genetic variation at the loci coding for these peptidases, rather than from linked loci. They also illustrate the complexity of interrelations that ultimately influence the evolutionary consequences of genomic diversity, including associated influences of both Lap-1 and Lap-2 on energy requirements and animal condition. We impress that energy requirements for protein turnover may represent a functional basis for epistasis, including associations whereby advantages of genetic polymorphism are greatest at loci that code for enzymes acting in both protein catabolism and energy provision.