Figure 1.

How frequency-dependent selection from specialist phage might affect host adaptation when resistance and growth rate are pleiotropically linked. Dots show the location of host strains on an underlying adaptive landscape shown by the contour lines. A: In the absence of phage, resource competition leads to a host population tightly converged on a suboptimal local peak in the adaptive landscape. Although a higher peak exists, hosts are unable to reach it due to an intervening fitness valley. B: Density-dependent phage predation creates frequency-dependent selection that causes hosts to diversify, so that the host community explores the adaptive landscape. Some strains cross the fitness valley and can now adapt to the higher peak.

Williams BMC Evolutionary Biology 2013 13:17   doi:10.1186/1471-2148-13-17
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