Egg discrimination in the Australian reed warbler (Acrocephalus australis): rejection response toward model and conspecific eggs depending on timing and mode of artificial parasitism |
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Authors: | Welbergen Justin; Komdeur Jan; Kats Romke; Berg Mathew |
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Institution: | a
Department of Zoology, University of Melbourne, Parkville, Victoria 3052,
Australia
b
Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren, The
Netherlands
c
Department of Biology, University of Amsterdam 1098 SM, Amsterdam, The
Netherlands |
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Abstract: | In a coevolutionary arms race between an interspecific broodparasite and its host species, both are expected to evolveadaptations and counteradaptations. We studied egg discriminationin the Australian warbler (Acrocephalus australis). This speciesis currently not significantly parasitized by the seven speciesof cuckoo for which it is a suitable host. However, experimentalbrood parasitism in the warbler revealed a fine tuned egg discriminationresponse towards non-mimetic and conspecific eggs, the firstsuch evidence in an Australian passerine: (1) non-mimetic eggswere significantly more often rejected than conspecific eggs;(2) only non-mimetic dummy eggs were rejected selectively,whereas rejection of conspecific eggs entailed a rejectioncost; (3) replacement of a host's egg with a conspecific eggduring egg laying resulted in a significantly higher rejectionrate than after the day of clutch completion; (4) by contrast,rejection rate after addition of a conspecific egg was independentof nest stage; (5) conspecific eggs introduced into a clutchduring the egg laying period led to a significantly highernest desertion rate and a lower egg ejection rate than afterthe day of clutch completion; and (6) addition of a conspecificegg led to egg ejection while egg replacement with a conspecificegg led to nest desertion. The fact that this species respondsdifferentially toward different modes of artificial parasitismsuggests that its egg discrimination has evolved to minimizethe costs of rejection and parasitism. The ability to rejecthighly mimetic conspecific eggs may explain the current paucityof brood parasitism in this species. The significance of thisfor brood parasite-host coevolution is discussed. |
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Keywords: | egg discrimination egg rejection egg ejection nest desertion brood parasitism coevolutionary arms race |
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