The overall dissociability of locomotion from head dipping is supported by an analysis of covariance, in which the proportion of variation in head dipping that can be accounted for by locomotion is removed before any potential difference in head-dipping due to the selected lines is considered. At generation 5, a significant main effect of selected line on the number of head dips was still present by analysis of covariance (F1,127 = 8.03; P < 0.01).
