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The effects of competition and predation on diversification in a model adaptive radiation


Much of life’s diversity is thought to have arisen through successive rounds of adaptive radiation—the rapid diversification of a lineage into a range of ecologically and phenotypically distinct species1,2,3. Both resource competition and predation have been suggested as mechanisms driving this process4,5, although the former is better studied than the latter6,7. Here we show experimentally how predation by a protist, Tetrahymena thermophila, affects diversification in a model adaptive radiation of the bacterial prey, Pseudomonas fluorescens. We estimate the frequency-dependent fitness functions of competing niche-specialist prey in the presence and absence of predation, and use these to test hypotheses about the extent (measured as the number of new genotypes) and rate of diversification. Competition and predation independently generated diversifying selection that we show is capable of driving prey diversification to similar extents but at different rates, diversification being markedly delayed in the presence of predators. The cause of this delay stems from weaker diversifying selection due to the reduction in prey density caused by predation. Our results suggest that predation may play an under-appreciated role in driving adaptive radiations.

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Figure 1: Frequency-dependent fitness functions due to competition (dashed line and filled circles), predation (dotted line and open circles) and their interaction (solid line and triangles).
Figure 2: The effect of predation on the diversification of wrinkly spreaders in minimal media.
Figure 3: Dynamics of diversification in the presence and absence of predators.


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We thank S. Remold for advice on statistics, P. Rainey for experimental guidance, N. Hairston Jr and H. Rundle for conceptual help, E. Orias and D. Cassidy-Hanely for T. thermophila strains, T. Uy for algebraic derivations, and G. Schroeder, J.-N. Jasmin, T. Boland and M. Al-Azzabi for assistance in the laboratory. T. Fukami and L. Harmon provided comments on a draft of the manuscript. This work was supported by an NSERC (Canada) Discovery Grant (to R.K.).

Author Contributions J.R.M. designed and performed all experiments and wrote the paper; R.K. discussed the research, performed statistical analyses, and helped with the writing.

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Correspondence to Justin R. Meyer.

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Meyer, J., Kassen, R. The effects of competition and predation on diversification in a model adaptive radiation. Nature 446, 432–435 (2007).

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