Relaxed trait covariance in interspecific cichlid hybrids predicts morphological diversity in adaptive radiations

Authors

  • O. M. Selz,

    Corresponding author
    1. Department of Fish Ecology and Evolution, EAWAG Swiss Federal Institute of Aquatic Science and Technology, Center for Ecology, Evolution and Biogeochemistry, Kastanienbaum, Switzerland
    2. Division of Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
    • Correspondence: Oliver M. Selz, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland. Tel.: +41 (0)58 765 21 46; fax: +41 (0)58 765 21 68; e-mail: oliver.selz@eawag.ch

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  • K. Lucek,

    1. Department of Fish Ecology and Evolution, EAWAG Swiss Federal Institute of Aquatic Science and Technology, Center for Ecology, Evolution and Biogeochemistry, Kastanienbaum, Switzerland
    2. Division of Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
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  • K. A. Young,

    1. Environment Agency, Cardiff, UK
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  • O. Seehausen

    1. Division of Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
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Abstract

The process of adaptive radiation involves multiple events of speciation in short succession, associated with ecological diversification. Understanding this process requires identifying the origins of heritable phenotypic variation that allows adaptive radiation to progress. Hybridization is one source of genetic and morphological variation that may spur adaptive radiation. We experimentally explored the potential role of hybridization in facilitating the onset of adaptive radiation. We generated first- and second-generation hybrids of four species of African cichlid fish, extant relatives of the putative ancestors of the adaptive radiations of Lakes Victoria and Malawi. We compared patterns in hybrid morphological variation with the variation in the lake radiations. We show that significant fractions of the interspecific morphological variation and the major trajectories in morphospace that characterize whole radiations can be generated in second-generation hybrids. Furthermore, we show that covariation between traits is relaxed in second-generation hybrids, which may facilitate adaptive diversification. These results support the idea that hybridization can provide the heritable phenotypic diversity necessary to initiate adaptive radiation.

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