title: Lotka-Volterra dynamics kills the Red Queen: population size fluctuations and associated stochasticity dramatically change host-parasite coevolution.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Evolutionary Theory Group, Max Planck Institute for Evolutionary Biology, August Thienemann Str-2, 24306, Plön, Germany. gokhale@evolbio.mpg.de.
authors.forename: Chaitanya S
authors.initials: CS
authors.lastname: Gokhale
authors.forename: Andrei
authors.initials: A
authors.lastname: Papkou
authors.forename: Arne
authors.initials: A
authors.lastname: Traulsen
authors.forename: Hinrich
authors.initials: H
authors.lastname: Schulenburg
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005787:Gene Frequency; D040961:Genetic Drift; D006790:Host-Parasite Interactions; D008957:Models, Genetic; D011156:Population Density