Figure 1.

Conceptual view of the relative numbers of (A) within-pair offspring (WPO) and (B–D) extra-pair offspring (EPO) conceived by females and males with low or high additive genetic liabilities for extra-pair reproduction (EPR) and within-pair paternity success (WPPS), respectively, assuming (B) negative, (C) positive, or (D) zero genetic covariance between male within-pair paternity success and extra-pair reproductive success. Circle sizes indicate relative numbers of offspring. Dark and light shading indicates assortative reproduction that would, respectively, generate negative and positive genetic covariance between female liability for extra-pair reproduction and male liability for within-pair paternity success in offspring. These figures are intended to illustrate conceptual points not to be quantitatively accurate: absolute offspring numbers might differ across panels A versus B–D depending on the mean extra-pair reproduction rate, female and male genetic values will vary continuously rather than dichotomously, and offspring proportions will also depend on any assortative pairing or correlated variation in female fecundity.