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Zeller M.,University of Bern | Lucek K.,Eawag Center for Ecology | Haesler M.P.,Eawag Center for Ecology | Seehausen O.,Eawag Center for Ecology | Sivasundar A.,Eawag Center for Ecology
Evolutionary Ecology Research | Year: 2012

Background: Different predation regimes may exert divergent selection pressure on phenotypes and their associated genotypes. Threespine stickleback Gasterosteus aculeatus have a suite of bony structures, which have been shown to be an effective defence against predation and have a well-known genetic basis. Question: Do different predator regimes induce different selective pressures on growth rates and defence phenotypes in threespine stickleback between different habitats across distinct age classes? Hypothesis: In the presence of predation-induced selection, we expect diverging morphological responses between populations experiencing either low or high predation pressure. Study system: Threespine stickleback were sampled from two natural but recently established populations in an invasive range. One site has a high density of fish and insect predators, while at the other site predation pressure is low. Methods: We inferred predator-induced selection on defence traits by comparing the distribution of size classes, defence phenotypes, and an armour-related genotype between different age classes in a high and a low predation regime. Results: Under high predation, there are indications of directional selection for faster growth, whereas lateral plate phenotypes and associated genotypes show indications for disruptive selection. Heterozygotes at the Eda-gene have a lower survival rate than either homozygote. Neither pattern is evident in the low predation regime. Conclusion: Potential evolutionary responses to divergent predation pressures between sites are apparent in a recently established system. © 2012 Michael Zeller.

Magalhaes I.S.,University of Bern | Magalhaes I.S.,Eawag Center for Ecology | Magalhaes I.S.,CSIC - National Museum of Natural Sciences | Lundsgaard-Hansen B.,University of Bern | And 5 more authors.
Evolutionary Ecology Research | Year: 2012

Questions: (1) Do replicate pairs of ecotypes of cichlid fish represent different stages of ecological speciation? (2) Are phenotypic and genetic divergence correlated with each other and with the steepness of the habitat gradients? Study system: Three replicate pairs of putative ecotypes of cichlid fish in the genus Neochromis from three islands in Lake Victoria. The three pairs present similar trophic polymorphisms. The three islands differ in steepness of the benthic habitat gradients mediated by variation in water clarity, shore slopes, and depths of the rock-sand interface. Analytical methods: We quantified fish body morphology and dentition, typed population samples at nine microsatellite loci, and analysed how phenotypic and neutral genetic variation were distributed among ecotypes and along the habitat gradients. Results: Despite weak or absent genetic differentiation at neutral markers, ecotypes were divergent in phenotypes in a replicated manner, involving from one to many different traits in a nested series. Variation in eco-morphological traits and allelic variation at neutral marker loci were associated with depth of habitat at some islands. © 2012 Ole Seehausen.

Ingram T.,Harvard University | Hudson A.G.,University of Bern | Hudson A.G.,Eawag Center for Ecology | Hudson A.G.,CSIC - National Museum of Natural Sciences | And 4 more authors.
Evolutionary Ecology Research | Year: 2012

Question: Is the extent of genetic divergence between sympatric whitefish ecotypes - a proxy for progress towards speciation - related to the extent of ecological divergence in spawning depth or diet? Study system: Whitefish (Coregonus spp.) that have diversified into two or more sympatric ecotypes in subalpine Swiss lakes. Sympatric ecotypes vary in the extent of reproductive isolation. Analytical methods: We measured the degree of spawning depth differentiation based on the depth-at-capture of different ecotypes. We estimated diet differentiation between ecotypes as Mahalanobis distances from stable isotopes. We compared each of these to genetic differentiation measured from AFLP data, using modified correlation tests and phylogenetically independent contrasts to account for non-independence of comparisons in lakes with more than two ecotypes. Results: We found that the magnitude of divergence in spawning depth was generally - albeit only marginally significantly - associated with the extent of genetic divergence between sympatric ecotypes. This effect was clearly stronger than the effect of diet divergence, which was not associated with genetic differentiation. Furthermore, there was no evidence for an interactive effect of depth and diet divergence on progress towards speciation. © 2012 Travis Ingram.

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