Abstract
BackgroundNest parasitism by cuckoos (Cuculus spp.) results in enormous reproductive failure and forces hosts to evolve antiparasitic strategies, i.e., recognition of own eggs and rejection of cuckoo eggs. There are often sexual conflicts between male and female individuals in the expression of antiparasitic behavior due to the differences in reproductive inputs and division of labor.MethodsBy adding a foreign egg made of blue soft clay to the host nest during early incubation period in the field, and by removing several host eggs and adding experimental eggs to control the proportion of two egg types in the nest, we examined egg rejection ability, egg recognition mechanism and sexual difference in egg rejection of the Oriental Reed Warbler (Acrocephalus orientalis), one of the major hosts of Common Cuckoos (Cuculus canorus).ResultsOur results indicated that Oriental Reed Warblers can recognize and reject nearly 100% (73/75) of the non-mimetic eggs made of blue soft clay, and they could reject foreign eggs with 100% accuracy, regardless of the ratio of experimental eggs and its own eggs in the nest. Furthermore, all cases of egg rejections recorded by videos were only carried out by females.ConclusionsOriental Reed Warblers have a high egg recognition ability and show a true recognition mechanism. Only female warblers perform egg rejection, suggesting that the sex for host egg incubation seems to play an important role in the evolution of egg recognition mechanisms.
Highlights
Nest parasitism by cuckoos (Cuculus spp.) results in enormous reproductive failure and forces hosts to evolve antiparasitic strategies, i.e., recognition of own eggs and rejection of cuckoo eggs
Egg rejection Egg recognition experiments with non-mimetic blue model eggs were performed in 75 nests of Oriental Reed
Sex roles in egg recognition Egg rejections were recorded on videos in 30 nests lasting about two hours until the power run out, including 19 nests for recognition mechanism experiments, and 11 nests in which one foreign egg was added for egg recognition experiments
Summary
Nest parasitism by cuckoos (Cuculus spp.) results in enormous reproductive failure and forces hosts to evolve antiparasitic strategies, i.e., recognition of own eggs and rejection of cuckoo eggs. Successful nest parasitism results in significant reproductive losses to the host, prompting the host to evolve a range of antiparasitic strategies (Davies 2000; Soler 2014). Egg recognition and egg rejection are among the most common antiparasitic strategies and are important indicators of host adaptation to nest parasitism (Davies and Brooke 1989a; Moksnes et al 1991b; Soler et al 2017; Yang et al 2020, 2021). The level of host egg recognition ability is subject to variation under different parasitic pressure and coevolutionary time, with inter- and intra-specific variations in recognition and rejection of foreign eggs among hosts in the same area or among geographic populations of the same host
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