There is a Research Highlights piece (in Nat Rev Gen [Nature Review Genetics]) on a paper entitled Parallel evolutionary dynamics of adaptive diversification in Escherichia coli (in PLoS Biol), which studies the principle of sympatric diversification, which is the “organismal diversification or speciation that occurs without […] geographical separation of [the] diverging populations”.
Background to experiment: the same authors had shown that a single strain grown in the presence of both glucose and acetate diversify into coexisting stable populations that (relatively) specialize in using either glucose/acetate.
Experiment: Same as before, but now conduct whole-genome sequencing from three replicate diverged populations. Sequence not only at end-point, but also use frozen samples collected in intermediate generations.
Results: All three replicates had similar evolutionary trajectories: rare glucose-specialization mutations (100 generations) eventually dominate (300 gen’s), after which acetate-specialization mutations gain frequency, until eventually, both types co-exist at intermediate levels until end of experiment (1045 gen’s).
This is consistent with frequency-dependent selection in which the frequency of one strain causes (and so correlates with) the selective pressure on another strain. Here dominance of glucose metabolizers would create a relative excess of acetate enabling an advantage for acetate metabolizers.
