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
