The evolution of brood parasitism from host egg predation

Obligate brood parasites pass all their parental duties to foster parents of a host species. While best understood in birds and hymenopteran insects, obligate brood parasitism has evolved independently at least 59 times across many lineages. The ancestors of brood parasites often provided no parental care to their offspring. Instead, a trophic association with their eventual hosts commonly appears to precede the origin of a brood parasitic strategy. Here, we used a game theoretical model to explore the conditions under which brood parasitism can evolve from predation and be maintained in the population. Our model was inspired by the relationship between the cuckoo catfish (Synodontis multipunctatus) parasitizing mouthbrooding cichlid fishes in the African Lake Tanganyika. Our model demonstrates the facilitatory role of host egg predation on the origin and evolutionary maintenance of brood parasitism through the exploitation of the host response to egg predation by brood parasites. We found no conditions under which brood parasitism as a pure strategy is evolutionarily stable, but we describe a range of evolutionarily stable equilibria when predators and parasites coexist. While our model is tailored to the cuckoo catfish, it generally applies to other systems where brood parasitism has evolved from other antagonistic behavior.