Paternity-parasitism trade-offs: a model and test of host-parasite cooperation in an avian conspecific brood parasite

Efforts to evaluate the evolutionary and ecological dynamics of conspecific brood parasitism in birds and other animals have focused on the fitness costs of parasitism to hosts and fitness benefits to parasites. However, it has been speculated recently that, in species with biparental care, host males might cooperate with parasitic females by allowing access to the host nest in exchange for copulations. We develop a cost-benefit model to explore the conditions under which such host-parasite cooperation might occur. When the brood parasite does not have a nest of her own, the only benefit to the host male is siring some of the parasitic eggs (quasi-parasitism). Cooperation with the parasite is favored when the ratio of host male paternity of his own eggs relative to his paternity of parasitic eggs
exceeds the cost of parasitism.

BRUCE E. LYON, WESLEY M. HOCHACHKA, AND JOHN M. EADIE, Evolution, 56(6), 2002, pp. 1253-1266