Russet Sparrows spot alien chicks from their nests

Juan Huo,Anders Pape Møller,Wei Liang,Tongping Su,Canchao Yang

doi:10.1186/s40657-018-0104-y

Abstract

BackgroundIn coevolutionary interactions between brood parasites and their hosts, host parents are under strong selection to evolve defenses against parasitism. Egg rejection is an efficient and common defense against parasitism, although some apparently suitable hosts do not reject cuckoo eggs.MethodsSparrows Ploceidae are widespread throughout the Old World, and they have a suitable diet for rearing cuckoos, but still they are rarely exploited by brood parasites. To solve such puzzle, we conducted artificial parasitism and cross-fostering experiments in Russet Sparrow (Passer cinnamomeus).ResultsThe present study showed that Russet Sparrows have no egg recognition ability, but recognize their own nestlings and eject alien chicks or starve them to death. They may use visual cues in chick recognition, although they accept sister species Tree Sparrow (Passer montanus).ConclusionsBy rejecting nestlings of foreign species, Russet Sparrows have succeeded to escape from the brood parasitism by cuckoos and other parasites. Our studies shed light on the puzzle why some species are not utilized by cuckoo parasites as hosts.

Highlights

In coevolutionary interactions between brood parasites and their hosts, host parents are under strong selection to evolve defenses against parasitism
This study aims to determine whether egg or chick stage defenses can explain the lack of parasitism of this species by brood parasites
In the cross-fostering experiment, all dead chicks died in Russet Sparrow nests except one case of Tree Sparrow (Passer montanus) chick (Figs. 1, 2)

Summary

Introduction

In coevolutionary interactions between brood parasites and their hosts, host parents are under strong selection to evolve defenses against parasitism. Interactions between brood parasites and their hosts are regarded as a model system for the study of coevolution (Davies 2000; Soler 2014) Brood parasites lay their eggs in hosts’ nests and subsequently transfer the cost of parental care to the hosts. The coevolutionary outcome of an arms race is difficult to elucidate strong indirect evidence has been found to demonstrate that some hosts have defeated brood parasites by maintaining strong anti-parasitism defenses such as egg rejection despite a lack of current parasitism. Such evidence has been obtained for several suspected former hosts of cuckoos. The Hume’s Leaf Warbler (Phylloscopus humei), which is not currently parasitized, shows high inter-clutch variation in egg size and rejects eggs that differ in size to their own clutch, preventing egg matching by the parasite and allowing successful prevention of parasitism (Marchetti 2000)

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Conclusion