Song similarity predicts hybridization in flycatchers

Authors

  • A. QVARNSTRÖM,

    1. Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
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  • J. HAAVIE,

    1. Evolutionary Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
    2. Department of Biology, University of Oslo, Oslo, Norway
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  • S. A. SÆTHER,

    1. Evolutionary Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
    2. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, Heteren, The Netherlands
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  • D. ERIKSSON,

    1. Ajtte, Swedish Mountain and Sami Museum, Jokkmokk, Sweden
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  • T. PÄRT

    1. Department of Conservation Biology, Swedish University of Agricultural Sciences, Uppsala, Sweden
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Anna Qvarnström, Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.
Tel.: +46 18 471 2662; fax: +46 18 471 6484;
e-mail: anna.qvarnstrom@ebc.uu.se

Abstract

Given that population divergence in sexual signals is an important prerequisite for reproductive isolation, a key prediction is that cases of signal convergence should lead to hybridization. However, empirical studies that quantitatively demonstrate links between phenotypic characters of individuals and their likelihood to hybridize are rare. Here we show that song convergence between sympatric pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) influence social and sexual interactions between the two species. In sympatry, the majority of male pied flycatchers (65%) include various parts of collared flycatcher song in their song repertoire (but not vice versa). Playback experiments on male interactions demonstrate that male collared flycatchers respond similarly to this ‘mixed’ song as to conspecific song. Long-term data on pairing patterns show that males singing a converged song attract females of the other species: female collared flycatchers only pair with male pied flycatchers if the males sing the mixed song type. From the perspective of a male pied flycatcher, singing a mixed song type is associated with 30% likelihood of hybridization. This result, combined with our estimates of the frequency of mixed singers, accurately predicts the observed occurrence of hybridization among male pied flycatchers in our study populations (20.45% of 484 pairs; predicted 19.5%). Our results support the suggestion that song functions as the most important prezygotic isolation mechanism in many birds.

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