Indirect trophic interactions with an invasive species affect phenotypic divergence in a top consumer
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While phenotypic responses to direct species interactions are well studied, we know little about the consequences of indirect interactions for phenotypic divergence. In this study we used lakes with and without the zebra mussel to investigate effects of indirect trophic interactions on phenotypic divergence between littoral and pelagic perch. We found a greater phenotypic divergence between littoral and pelagic individuals in lakes with zebra mussels and propose a mussel-mediated increase in pelagic and benthic resource availability as a major factor underlying this divergence. Lakes with zebra mussels contained higher densities of large plankton taxa and large invertebrates. We suggest that this augmented resource availability improved perch foraging opportunities in both the littoral and pelagic zones. Perch in both habitats could hence express a more specialized foraging morphology, leading to an increased divergence of perch forms in lakes with zebra mussels. As perch do not prey on mussels directly, we conclude that the increased divergence results from indirect interactions with the mussels. Our results hence suggest that species at lower food web levels can indirectly affect phenotypic divergence in species at the top of the food chain.
KeywordsIndirect effects Morphological response Food web Phenotypic plasticity Disruptive selection
We thank M. Amcoff, A. Kellerman, R. Naddafi, A. Rice, S. South and Andrew Hendry and one anonymous reviewer for helpful comments on the manuscript; K. Bergström, H. Enderskog, R. Fransson, E. Geibrink, J. Malmberg, M. Puffer, and U. Westerlund for help in the field and in the lab; and P. Bartels, H. Peter, P. Innocenti, C. Michel, and B. Rogell for statistical advice. This study was financed by grants from the Swedish Research council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) to P. E.; the Swedish Research Council (VR) to P. E. and R. S.; and the Malméns stiftelse to P. E. H.
Conflict of interest
The authors declare that they have no conflict of interest.
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