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Sympatric colour polymorphisms associated with nonrandom gene flow in cichlid fish of Lake Victoria

Authors

  • I. S. MAGALHAES,

    1. Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, CH-3012 Bern, Switzerland
    2. Fish Ecology and Evolution, Eawag Swiss Federal Institute of Aquatic Science and Technology, Center of Ecology, Evolution and Biogeochemistry, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland
    3. Department of Biological Sciences, University of Hull, Cottingham Road, Hull, HU6 7RX, UK
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  • S. MWAIKO,

    1. Fish Ecology and Evolution, Eawag Swiss Federal Institute of Aquatic Science and Technology, Center of Ecology, Evolution and Biogeochemistry, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland
    2. Tanzanian Fisheries Research Institute, Mwanza Centre, PO Box 475 Mwanza, Tanzania
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  • O. SEEHAUSEN

    1. Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, CH-3012 Bern, Switzerland
    2. Fish Ecology and Evolution, Eawag Swiss Federal Institute of Aquatic Science and Technology, Center of Ecology, Evolution and Biogeochemistry, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland
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Isabel S. Magalhaes, Fax: +44(0) 1482 465458; E-mail: I.Santos-Magalhaes@hull.ac.uk

Abstract

Colour polymorphisms have fascinated evolutionary ecologists for a long time. Yet, knowledge on the mechanisms that allow their persistence is restricted to a handful of well-studied cases. We studied two species of Lake Victoria cichlid fish, Neochromis omnicaeruleus and Neochromis greenwoodi, exhibiting very similar sex-linked colour polymorphisms. The ecology and behaviour of one of these species is well studied, with colour-based mating and aggression preferences. Here, we ask whether the selection potentially resulting from female and male mating preferences and aggression biases reduces gene flow between the colour morphs and permits differentiation in traits other than colour. Over the past 14 years, the frequencies of colour morphs have somewhat oscillated, but there is no evidence for directional change, suggesting the colour polymorphism is persistent on an ecological timescale. We find limited evidence of eco-morphological differentiation between sympatric ancestral (plain) and derived (blotched) colour morphs. We also find significantly nonrandom genotypic assignment and an excess of linkage disequilibrium in the plain morph, which together with previous information on mating preferences suggests nonrandom mating between colour morphs. This, together with negative frequency-dependent sexual selection, found in previous studies, may facilitate maintenance of these polymorphisms in sympatry.

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