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要旨

Background: Host-parasite coevolution is generally believed to follow Red Queen dynamics consisting of ongoing
oscillations in the frequencies of interacting host and parasite alleles. This belief is founded on previous theoretical
work, which assumes infinite or constant population size. To what extent are such sustained oscillations realistic?
Results: Here, we use a related mathematical modeling approach to demonstrate that ongoing Red Queen
dynamics is unlikely. In fact, they collapse rapidly when two critical pieces of realism are acknowledged: (i) population
size fluctuations, caused by the antagonism of the interaction in concordance with the Lotka-Volterra relationship;
and (ii) stochasticity, acting in any finite population. Together, these two factors cause fast allele fixation. Fixation is not
restricted to common alleles, as expected from drift, but also seen for originally rare alleles under a wide parameter
space, potentially facilitating spread of novel variants.
Conclusion: Our results call for a paradigm shift in our understanding of host-parasite coevolution, strongly
suggesting that these are driven by recurrent selective sweeps rather than continuous allele oscillations.