Male-killing bacteria are maternally inherited endosymbionts of many insect
species that selectively kill male offspring of their hosts. Using both
analytical techniques and computer simulations, we studied the impact of
these bacteria on the population genetics of their hosts. In particular, we
derived and corroborated formulae for the fixation probability of mutant
alleles, rate of allele substitution, and mean times to fixation and/or
extinction, for varying male-killer prevalence. Our results demonstrate that
infections with male-killing bacteria impede the spread of beneficial
alleles and facilitate the spread of deleterious alleles. The reason for
this lies in the strongly reduced fitness of infected females combined with
no or very limited gene flow from infected females to uninfected
individuals. These two properties of male-killer infected populations reduce
the population size relevant for the initial emergence and spread of
mutations. In contrast, use of Wright’s equation relating sex ratio to
effective population size produces misleading predictions. We discuss the
relevance of our results to the expected level of genetic variation
maintained in male-killer infected populations, the relationship to the
similar effect of background selection, and the impact of other sex-ratio
distorting endosymbionts.
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