Variation in mutational (co)variances

Because of pleiotropy, mutations affect the expression and inheritance of multiple traits and are expected to determine the structure of standing genetic variation and phenotypic evolution. It is thus important to find if the M matrix, describing mutational (co)variances between traits, varies between genotypes. We here estimate the M matrix for six locomotion behavior traits in two genotypes of the nematode Caenorhabditis elegans . We find significant mutational variance along at least one phenotypic dimension of the M matrix, but its size and orientation was similar between genotypes. We then tested if the M matrices were similar to one G matrix describing the standing genetic (co)variances of a domesticated population derived by the hybridization of several genotypes and adapted to a lab defined environment for 140 generations. M and G are different in part because the genetic covariances caused by mutational pleiotropy in the two genotypes are smaller than those caused by standing linkage disequilibrium in the lab population. If generalized to other genotypes, these observations indicate that selection is unlikely to shape the evolution of the M matrix for locomotion behavior and suggests that the genetic restructuring due to the hybridization of C. elegans genotypes allows for selection in the lab on new phenotypic dimensions of locomotion behavior, phenotypic dimensions which are inaccessible to natural populations.