Major morphological effect of a regulatory gene: Pgm1-t in rainbow trout

Abstract

We have investigated the morphological effects of a genetic locus, Pgml-t, that affects the expression of a phosphoglucomutase locus (Pgml) in liver of rainbow trout (Salmo gairdneri). We have previously shown that embryos with liver Pgml expression hatch earlier than those without liver Pgml expression. We predicted that this difference in developmental rate should cause a reduction in meristic counts in the more rapidly developing fish with liver Pgml expression. Eight meristic (countable) characters in nine full-sib groups segregating for the presence or absence of liver Pgml expression are in agreement with this prediction. In eight of the nine families, there is a significant difference in the multivariate distribution of the eight meristic counts between full sibs with and without liver Pgml expression. This separation in multivariate space is based on a tendency for lower meristic counts in fish liver Pgml expression. The magnitude of these morphological differences is similar to that between two subspecies of cutthroat trout (Salmo clarki) that show substantial genetic divergence at structural loci encoding enzymes (Nei's D=0.34). These data support the view that small changes in the developmental process caused by genetic differences at regulatory genes can have large effects on morphology.