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The evolution of egg rejection by cuckoo hosts in Australia and Europe




Langmore, Naomi
Kilner, Rebecca
Butchart, S
Maurer, Golo
Davies, Noel
Cockburn, Andrew
Macgregor, Nicholas
Peters, Ann
Magrath, Michael
Dowling, D.

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Oxford University Press


Exploitation of hosts by brood parasitic cuckoos is expected to stimulate a coevolutionary arms race of adaptations and counteradaptations. However, some hosts have not evolved defenses against parasitism. One hypothesis to explain a lack of host defenses is that the life-history strategies of some hosts reduce the cost of parasitism to the extent that accepting parasitic eggs in the nest is evolutionarily stable. Under this hypothesis, it pays hosts to accept cuckoo eggs if (1) the energetic cost of raising the cuckoo is low, (2) there is time to renest, and (3) clutch size is small. We parasitized the nests of host and nonhost species with nonmimetic model eggs to test whether the evolution of egg recognition by cuckoo hosts could be explained by life-history variables of the host. The most significant factor explaining rates of rejection of model eggs was whether or not a species was a cuckoo host, with hosts rejecting model eggs at a higher rate than nonhosts. Egg-rejection rates were also explained by visibility within the nest and by cuckoo mass. We found little support for the life-history model of egg rejection. Our results suggest that parasitism is always sufficiently costly to select for host defenses and that the evolution of defenses may be limited by proximate constraints such as visibility within the nest.



Keywords: brood parasitism; coevolution; egg rejection; evolution; life history; Australasia; Australia; Eastern Hemisphere; Eurasia; Europe; World; Cuculidae; Molothrus Brood parasitism; Coevolution; Cowbirds; Cuckoos; Life-history strategies



Behavioral Ecology


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