Evol Ecol Res 14: 193-205 (2012)     Full PDF if your library subscribes.

Signals of predation-induced directional and disruptive selection in the threespine stickleback

Michael Zeller, Kay Lucek, Marcel P. Haesler, Ole Seehausen and Arjun Sivasundar

Institute for Ecology and Evolution, University of Bern, Bern, Switzerland and Department of Fish Ecology, Eawag Centre for Ecology, Evolution and Biogeochemistry, Kastanienbaum, Switzerland

Correspondence: M. Zeller, Institute for Ecology and Evolution, University of Bern, Baltzerstrasse 6, CH-3012 Bern, Switzerland.
e-mail: mich.zeller@gmail.com


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.

Keywords: age classes, defence traits, disruptive selection, Eda, predation.

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