Micro-evolutionary change and population dynamics of a brood parasite and its primary host: the intermittent arms race hypothesis |
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Authors: | Manuel Soler Juan J Soler Juan G Martinez Tomás Pérez-Contreras Anders P Møller |
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Institution: | (1) Departamento de Biología Animal y Ecología, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain e-mail: msoler@goliat.ugr.es, fax: +34-58-243238, ES;(2) Laborotaire d'Ecologie, CNRS URA 258, Université Pierre et Marie Curie, Bat. A, 7ème étage, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France, FR |
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Abstract: | A long-term study of the interactions between a brood parasite, the great spotted cuckoo Clamator glandarius, and its primary host the magpie Pica pica, demonstrated local changes in the distribution of both magpies and cuckoos and a rapid increase of rejection of both mimetic
and non-mimetic model eggs by the host. In rich areas, magpies improved three of their defensive mechanisms: nest density
and breeding synchrony increased dramatically and rejection rate of cuckoo eggs increased more slowly. A stepwise multiple
regression analysis showed that parasitism rate decreased as host density increased and cuckoo density decreased. A logistic
regression analysis indicated that the probability of changes in magpie nest density in the study plots was significantly
affected by the density of magpie nests during the previous year (positively) and the rejection rate of mimetic model eggs
(negatively). These results are consistent with a hypothesis (the intermittent arms race hypothesis) of spatially structured
cyclic changes in parasitism. During periods of parasitism, host defences continuously improve, and as a consequence, the
fitness gains for parasites decrease. When host defences against parasites reach a high level, dispersing parasites have a
selective advantage if they are able to emigrate to areas of low resistance. Once parasites have left an area hosts will lose
their defensive adaptations due to their cost in the absence of parasitism. The scene is then set for re-colonization by great
spotted cuckoos.
Received: 7 May 1998 / Accepted: 24 August 1998 |
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Keywords: | Brood parasitism Clamator glandarius Coevolution Parasite counter-defences Pica pica |
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