Abstract
Genetic covariance between two traits generates correlated responses to selection, and may either enhance or constrain adaptation. Silene latifolia exhibits potentially constraining genetic covariance between specific leaf area (SLA) and flower number in males. Flower number is likely to increase via fecundity selection but the correlated increase in SLA increases mortality, and SLA is under selection to decrease in dry habitats. We selected on trait combinations in two selection lines for four generations to test whether genetic covariance could be reduced without significantly altering trait means. In one selection line, the genetic covariance changed sign and eigenstructure changed significantly, while in the other selection line eigenstructure remained similar to the control line. Changes in genetic variance–covariance structure are therefore possible without the introduction of new alleles, and the responses we observed suggest that founder effects and changes in frequency of alleles of major effect may be acting to produce the changes.
Highlights
Genetic covariance between two traits generates correlated responses to selection, and may either enhance or constrain adaptation
TA B L E 3 Additive genetic variance and covariance for flower number and specific leaf area in males for plants in the base generation, the control line after four generations of random mating, and selection line 1 and selection line 2 after four generations of selection to reduce the correlation between the traits
Note: To determine whether the lines deviated from the base generation, and whether the selection lines differed significantly from the control line, we conducted randomization tests that generated a null distribution of 1,000 iterations from a combined dataset, and p-values were calculated from the number of iterations that were more extreme than the observed values
Summary
Silene latifolia (Caryophyllaceae) is a short-lived perennial herb native to Europe and widely common as an introduced species in the United States. TA B L E 3 Additive genetic variance and covariance for flower number (logtransformed and multiplied by 50) and specific leaf area (cm2/g) in males for plants in the base generation, the control line after four generations of random mating, and selection line 1 and selection line 2 after four generations of selection to reduce the correlation between the traits. Selection line 1 Selection line 2 p < .001 n.s. Note: To determine whether the lines deviated from the base generation, and whether the selection lines differed significantly from the control line, we conducted randomization tests that generated a null distribution of 1,000 iterations from a combined dataset, and p-values were calculated from the number of iterations that were more extreme than the observed values. The asterisk indicates the correlation that showed significant similarity between the two matrices
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