Evolution of defences against cuckoo (<Emphasis Type="Italic">Cuculus canorus</Emphasis>) parasitism in bramblings (<Emphasis Type="Italic">Fringilla montifringilla</Emphasis>): a comparison of four populations in Fennoscandia |
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Authors: | Johan Reinert Vikan Bård Gunnar Stokke Jarkko Rutila Esa Huhta Arne Moksnes Eivin Røskaft |
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Institution: | (1) Department of Biology, Norwegian University of Science and Technology (NTNU), Realfagbygget, 7491 Trondheim, Norway;(2) Department of Biology, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland;(3) Finnish Forest Research Institute, Kolari Research Unit, Muoniontie 21, 95900 Kolari, Finland;(4) Centre for Advanced Study, CAS, Drammensveien 78, 0271 Oslo, Norway |
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Abstract: | The brood parasitic common cuckoo Cuculus canorus has a history of coevolution that involves numerous passerine hosts, but today only a subset is known to be regularly parasitised
in any area. In some hosts, there is significant variation in the occurrence of parasitism between populations, but still
individuals in non-parasitised populations show strong antiparasite defences. In the present study we compared the strength
of egg rejection of four distant Fennoscandian brambling Fringilla montifringilla populations experiencing different levels of cuckoo parasitism (0–6%). Egg rejection ability was in general very well developed
and we did not find any population differences in the relationship between egg rejection probability and similarity between
host and experimental parasitic eggs. Furthermore, bramblings very rarely made errors in rejection, indicating that selection
against rejection behaviour is likely to be very weak. The brambling-cuckoo system therefore differs from other well studied
systems which are characterised by pronounced spatial and temporal variation in the host’s level of defence. This result is
unlikely to reflect independent replication of the same evolutionary trajectory because the weak breeding site tenacity of
bramblings should result in an extreme amount of gene flow within the distribution area and thus strongly impede localised
responses to selection. Instead, lack of geographic variation has more likely arisen because bramblings respond to selection
as one evolutionary unit, and because the average parasitism pressures have been high enough in the past to cause regional
fixation of rejection alleles and evolution of clutch characteristics that facilitate cost free egg recognition. |
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