Evol Ecol Res 10: 735-746 (2008)     Full PDF if your library subscribes.

Selection for predator resistance varies with resource supply in a model adaptive radiation

Alex R. Hall,¹ Justin R. Meyer² and Rees Kassen³

¹Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, UK,  ²Department of Zoology, Michigan State University, East Lansing, Michigan, USA and  ³Department of Biology and Center for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada

Correspondence: A.R. Hall, Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, West Mains Road, Edinburgh EH9 3JT, UK.
e-mail: alex.hall@ed.ac.uk

ABSTRACT

Background: The bacterium Pseudomonas fluorescens diversifies in static laboratory microcosms, giving rise to distinct broth-colonizing ‘smooth’ and biofilm-forming ‘wrinkly spreader’ morphotypes. Growth in the biofilm confers predator resistance, but is energetically costly and therefore constrained by both the nutrient concentration of the growth medium and competition for those nutrients with the smooth population.

Question: Does the role of predation during adaptive diversification depend upon resource availability?

Organisms: Laboratory populations of Pseudomonas fluorescens and its protozoan predator Tetrahymena thermophila.

Methods: Experimental evolution of bacteria across a gradient of resource supply in the presence and absence of predators. We recorded the effects of predation and resource supply on the frequencies of resistant and susceptible morphotypes at the end of adaptive diversification. Given that there are distinct subclasses within the principal morphological categories, we also recorded changes in total phenotypic diversity.

Results: In resource-poor conditions, the broth-colonizing morphotype is preponderant, but as resource supply increases, the frequency of the biofilm-forming morphotype rises. Predation increased the frequency of wrinkly spreaders, with the largest effect at intermediate resource concentrations.

Conclusions: Predation extends the range of concentrations that support high phenotypic diversity. Co-existence between different prey phenotypes is more likely at intermediate concentrations than at extremes where one type or the other is in the majority.

Keywords: adaptive radiation, competition, experimental evolution, predation, Pseudomonas fluorescens, Tetrahymena thermophila.

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