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Species-specific song convergence in a moving hybrid zone between two passerines

Authors

  • J. SECONDI,

    Corresponding author
    1. Department of Animal Ecology, Ecology building, Lund University, S-223 62 Lund, Sweden
    2. Institute of Evolutionary and Ecological Sciences, Behavioural Biology, PO Box 9516, 2300 RA Leiden, the Netherlands
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  • V. BRETAGNOLLE,

    1. Centre d’Etudes Biologique de Chizé—CNRS, 79360 Beauvoir-sur-Niort, France
    2. GDR 2555 Ecologie Comportementale
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  • C. COMPAGNON,

    1. UMR CNRS 5561, Equipe Ecologie Evolutive, Université de Bourgogne, 6, bvd Gabriel, 21000 Dijon, France
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  • B. FAIVRE

    1. UMR CNRS 5561, Equipe Ecologie Evolutive, Université de Bourgogne, 6, bvd Gabriel, 21000 Dijon, France
    2. GDR 2555 Ecologie Comportementale
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Current address: Laboratory of Animal Ecology, Angers University, Faculté des Sciences, Campus de Belle-Beille, 2 bd Lavoisier, F-49045 Angers, France. E-mail: jean.secondi@univ-angers.fr

Abstract

Moving hybrid zones are receiving increasing attention. However, so far little is known about the proximate mechanisms underlying these movements. Signalling behaviour, by individuals engaged in interspecific sexual and aggressive interactions, may play a crucial role. In this study, we investigated song variation within a moving hybrid zone between two warblers, Hippolais polyglotta and H. icterina. In these species, song is involved in interspecific territoriality and, probably, in mixed pairings. We showed that allopatric populations of the two species are clearly acoustically differentiated. However, interspecific differences faded out in sympatry as a result of an overall pattern of convergence. Unexpectedly, the two species converged for different song parameters, namely temporal parameters for H. icterina and syntax for H. polyglotta. Hybridization and interspecific competition could explain convergence in H. icterina. Instead, in H. polyglotta we suggest that local adaptation to habitat and interspecific learning might contribute to convergence. We particularly stress that cross-species learning, by maintaining high levels of interspecific interactions, may influence the movement of the zone. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 507–517.

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