Data files for: Hazardous loss of genetic diversity through selective sweeps in asexual populations

With the two-fold cost of sex, derived asexual organisms have an immediate
reproductive advantage over their sexual sisters.  Yet the
"twiggy'' phylogenetic distribution of asexual lineages
implies that they go extinct relatively quickly over evolutionary time.
 Meanwhile, bacteria and archaea have persisted for billions of
years without requiring sexual reproduction. A simple explanation for this
difference is that prokaryotes have very large population sizes that are
not subject to the accumulation of deleterious mutations, but this implies
that drift and mutational meltdown dominate derived asexual populations.
  We explored a different hazard, quantifying the degree to which
genetic variation is lost in asexual populations experiencing selective
sweeps.  Even though large populations generate diversity by
mutation during sweeps, we find that populations that are safe from
mutational meltdown may still be reduced to dangerous effective population
sizes by sweeps.  Thus, ironically, adaptation itself reduces
further adaptive potential and may predispose asexual populations to
extinction.  Our data give results for the probability of
mutational meltdown across various population sizes, the critical
population size required to avoid meltdown, and the effect of selective
sweeps on heterozygosity.  Analytical predictions are confirmed
by simulation. We also derive a simple approximation for the effective
population size after a hard sweep, and quantify the impact of
recent sweeps on evolutionary rescue. These factors may help to explain
the phylogenetic twigginess of asexuals, the maintenance of sex and
recombination, and the evolutionary persistence of prokaryotes.