title: Egg color variation, but not egg rejection behavior, changes in a cuckoo host breeding in the absence of brood parasitism.
abstract: Interactions between parasitic cuckoos and their songbird hosts form a classical reciprocal "arms race," and are an excellent model for understanding the process of coevolution. Changes in host egg coloration via the evolution of interclutch variation in egg color or intraclutch consistency in egg color are hypothesized counter adaptations that facilitate egg recognition and thus limit brood parasitism. Whether these antiparasitism strategies are maintained when the selective pressure of parasitism is relaxed remains debated. However, introduced species provide unique opportunities for testing the direction and extent of natural selection on phenotypic trait maintenance and variation. Here, we investigated egg rejection behavior and egg color polymorphism in the red-billed leiothrix (Leiothrix lutea), a common cuckoo (Cuculus canorus) host, in a population introduced to Hawaii 100 years ago (breeding without cuckoos) and a native population in China (breeding with cuckoos). We found that egg rejection ability was equally strong in both the native and the introduced populations, but levels of interclutch variation and intraclutch consistency in egg color in the native population were higher than in the introduced population. This suggests that egg rejection behavior in hosts can be maintained in the absence of brood parasitism and that egg appearance is maintained by natural selection as a counter adaptation to brood parasitism. This study provides rare evidence that host antiparasitism strategies can change under parasite-relaxed conditions and reduced selection pressure.
authors.affiliation: Ministry of Education Key Laboratory for Tropical Animal and Plant Ecology, College of Life Sciences, Hainan Normal University Haikou, 571158, China.
authors.forename: Canchao
authors.initials: C
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Biocontrol and School of Life Sciences, Sun Yat-sen University Guangzhou, 510275, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Biology, University of California Riverside, California, 92521, USA.
authors.forename: Lijin
authors.initials: L
authors.lastname: Zeng
authors.affiliation: Ministry of Education Key Laboratory for Tropical Animal and Plant Ecology, College of Life Sciences, Hainan Normal University Haikou, 571158, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liang
keywords: Brood parasitism; Leiothrix lutea; cuckoo, egg color variation; egg rejection ability; natural selection