Quantitative genetics and the evolution of ontogeny. II. Genetic and environmental correlations among age-specific...

In this study, phenotypic, genetic, maternal and residual environmental correlations among all pairs of six ages (17, 24, 31, 38, 45 and 52 days) were calculated for each of five morphometric characters (body weight, head length, trunk length, trunk circumference, and tail length) in ICR randombred house mice. The maternal correlations between ages averaged nearly unity for all characters, and the overall level (and integration, I) of the genetic correlations (mean level = 0.82, mean I = 0.85) was greater than that for the residual environmental correlations (mean level = 0.26, mean I = 0.32). The patterns of the phenotypic and genetic correlations were similar, with the highest correlations being between contiguous ages and a relatively smooth decrease in correlations for increasingly distant ages. Nearly all of the genetic covariation among ages was explained by the first (average = 86%) and second (average = 14%) components derived from principal components analysis of the genetic correlations. Genes with basically equal pleiotropic effects presumably generated the first component, genes with different effects among ages the second component. From the patterns of genetic correlations, it is predicted that direct selection on any given age would result in a moderate, positive response at most other ages, with more change in the height relative to the shape of the growth curve for each characteristic.