title: Shifting barriers and phenotypic diversification by hybridisation.
abstract: The establishment of hybrid taxa relies on reproductive isolation from the parental forms, typically achieved by ecological differentiation. Here, we present an alternative mechanism, in which shifts in the strength and location of dispersal barriers facilitate diversification by hybridisation. Our case study concerns the highly diverse, stenotopic rock-dwelling cichlids of the African Great Lakes, many of which display geographic colour pattern variation. The littoral habitat of these fish has repeatedly been restructured in the course of ancient lake level fluctuations. Genetic data and an experimental cross support the hybrid origin of a distinct yellow-coloured variant of Tropheus moorii from ancient admixture between two allopatric, red and bluish variants. Deficient assortative mating preferences imply that reproductive isolation continues to be contingent on geographic separation. Linking paleolimnological data with the establishment of the hybrid variant, we sketch a selectively neutral diversification process governed solely by rearrangements of dispersal barriers.
authors.affiliation: Institute of Zoology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
authors.forename: Kristina M
authors.identifier: 0000-0001-8108-8339
authors.initials: KM
authors.lastname: Sefc
authors.affiliation: Institute of Zoology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
authors.forename: Karin
authors.initials: K
authors.lastname: Mattersdorfer
authors.affiliation: Institute of Zoology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
authors.forename: Angelika
authors.initials: A
authors.lastname: Ziegelbecker
authors.affiliation: Institute of Zoology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
authors.forename: Nina
authors.initials: N
authors.lastname: Neuhüttler
authors.affiliation: Institute of Chemistry - Analytical Chemistry, University of Graz, Universitätsplatz 1, 8010, Graz, Austria.
authors.forename: Oliver
authors.initials: O
authors.lastname: Steiner
authors.affiliation: Institute of Chemistry - Analytical Chemistry, University of Graz, Universitätsplatz 1, 8010, Graz, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Goessler
authors.affiliation: Institute of Zoology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
authors.forename: Stephan
authors.initials: S
authors.lastname: Koblmüller
mesh_terms: D000818:Animals; D023681:Cichlids / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism; D014644:Genetic Variation; D006824:Hybridization, Genetic; D010641:Phenotype; D010802:Phylogeny; D010858:Pigmentation; D017422:Sequence Analysis, DNA / Q000662:veterinary; D015024:Zambia
chemical_list: D004272:DNA, Mitochondrial; D029941:Fish Proteins
keywords: Carotenoid coloration; Cichlidae; Lake Tanganyika; Tropheus; climate change; colour pattern; environmental fluctuations; genetic admixture; hybrid speciation; mate choice