Adaptive significance of differences in the tissue-specific expression of a phosphoglucomutase gene in rainbow trout.

We have investigated the phenotypic effects of a mutant allele that results in the expression of a phosphoglucomutase locus (Pgm1) in the liver of rainbow trout. Embryos with liver Pgm1 expression hatch earlier than embryos without liver Pgm1 expression. These differences apparently result from increased flux through glycolysis in embryos with liver PGM1 activity while they are dependent on the yolk for energy. Fish with liver PGM1 activity are also more developmentally buffered, as indicated by less fluctuating asymmetry of five bilateral meristic traits. The more rapidly developing individuals begin exogenous feeding earlier and achieve a size advantage that is maintained until sexual maturity. This size advantage produces a significant tendency for earlier age of sexual maturity. These results show that different genotypes at this regulatory gene result in important phenotypic differences that are likely to be of important adaptive significance.