Figure 1.—

Phenotypic, additive genetic, and residual variance for lamb male traits of (A) horn length, (B) body weight, and (C) parasite load as a function of the environmental quality of their first year (E: distribution shown by solid triangles). Results were obtained from model 1 (see methods), where phenotypic and residual variance was estimated by grouping years on the basis of the quartiles of the distribution of E (1, very poor; 2, poor; 3, good; 4, very good), and error bars show the 95% confidence intervals of the estimates. Additive genetic effects were estimated as a linear function of E and are shown by a solid line, with dashed lines indicating the 95% confidence intervals of the estimates. Significance testing was conducted using a log-likelihood-ratio comparison of model 1 with a model with constant variance across all environments.