Abstract
The arms race between avian brood parasites and their hosts is one of the best known examples of antagonistic coevolution, and thus has long attracted the attentions of behavioural and evolutionary biologists. In such a system, brood parasites impose great fitness costs on their hosts, thus selecting for hosts with an ability to discriminate against parasitism. As a result, mimicry has evolved among parasites, which further favours higher discrimination abilities among hosts. In this review, I summarize both theoretical and empirical studies of brood parasitism and suggest the direction in which future studies should advance, considering the paradigm shift that brood parasitism studies have experienced over the last decade, and present the newly invented techniques that have been introduced in recent studies. Numerous studies have revealed how Common Cuckoo Cuculus canorus hosts detect parasitic eggs by taking full advantage of their cognitive abilities. However, it is well known that most parasitic chicks do not resemble host chicks, unlike highly mimetic parasitic eggs. Such a lack of mimicry in parasitic chicks has been explained by constraints on the host's learning and recognition processes, which have resulted in the common understanding that hosts can never recognize parasitic chicks. Recent studies have shown that some hosts are in fact able to discriminate against brood parasitic chicks, hence triggering the evolution of chick mimicry; in this process learning the appearance of parasitic chicks is presumably involved, resulting in a paradigm shift. I suggest that cuckoo-host systems in tropical regions can provide a clue to understand this issue.
