Figure 1.

Illustration of the occurrence of extra‐pair paternity within a breeding attempt, viewed as a single joint “emergent” trait expressed by a focal socially paired female and male. In this example, two offspring are sired by the female's socially paired male (gray, within‐pair offspring, WPO), and one offspring is sired by an extra‐pair male (black, extra‐pair offspring, EPO). The degree of extra‐pair paternity observed at the brood level (in this case 1/3) is the focal binomial trait and can be envisaged as a joint outcome of two sex‐specific latent traits: female liability for extra‐pair reproduction and male liability for paternity loss.