Brood Parasitism in Birds: A Coevolutionary Point of View

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Interspecific brood parasitism is a breeding strategy in which the brood parasite female evades all parental care by laying its eggs in host nests. Fitness costs imposed on hosts by brood parasitic adults or nestlings select for host defences setting the stage for a coevolutionary arms race in which brood parasites evolve counter-adaptations, which subsequently select for better host defences and so on. These so-called coevolutionary interactions have proven to be an excellent system for understanding coevolution. Here I review brood parasite–host interactions from the point of view of coevolutionary theory. After emphasizing the relevance of the costs provoked by brood parasitism, I present the traditional model of coevolution between brood parasites and their hosts, but I also incorporate new discoveries reported during the last two decades, which, frequently, do not support important predictions of coevolutionary theory. Next I describe the current situation of coevolution in brood parasite–host systems emphasizing three points that should be taken into account in studies centred on this subject. Later, I suggest three potentially important topics that have been almost neglected until now: (1) it would be superior to study as many defences as possible at all stages of the nesting cycle, (2) to examine the role of tolerance because this type of host defence contrary to what happen with resistance does not induce coevolutionary arms races and (3) to study the role of hormones in regulating host defensive responses to brood parasitism. Finally, a list of eleven future directions of research is provided.