THE EVOLUTION OF GENETIC CORRELATIONS - AN ANALYSIS OF PATTERNS

The genetic correlation is a central parameter of quantitative genetic s, providing a measure of the rate at which traits respond to indirect selection (i.e., selection that does not act upon the traits under st udy, but some other trait with which they have genes in common). In th is paper, I review the pattern of variation among four combinations of traits: life history x life history (L x L), morphological x morpholo gical (M x M), life history x morphological (L x M), and behavioral x behavioral (B x B). A few other combinations were investigated, but in sufficient data were obtained for separate analysis. A total of 1798 c orrelations, distributed over 51 different animal and plant species, w ere analyzed. The analysis was conducted at two levels: first by divid ing the data set solely by trait combination, and second by blocking t he data by trait combination and species. Because selection will tend to fix alleles that show positive correlations with fitness traits fas ter than those that are negative and because the latter are expected t o arise more frequently by mutation, correlations between life-history traits are predicted to be more often negative than those between mor phological traits. This prediction was supported, with the ranking in decreasing proportion of negative correlations being: L x L > L x M > B x B > M x M. The mean magnitude of the genetic correlation shows lit tle variation among morphological and life-history combinations, and t he distribution of values is remarkably flat. However, the estimated s tandard errors and the coefficient of variation (SE/r(G)) are large, m aking it difficult to separate biological factors influencing the patt ern of dispersion from experimental error. Analysis of the phenotypic and genetic correlations suggest that for the combinations M x M and L x M, but not L x L or B x B, the phenotypic correlation is an adequat e estimate of the genetic correlation.