Cytoplasmic incompatibility associated with Wolbachia strains differing
in the presence of cif genes
Abstract
Wolbachia is a widespread bacterial endosymbiont and its maternal
transmission favours the selfish manipulation of host reproduction to
increases in frequency. One such manipulation is cytoplasmic
incompatibility (CI), where uninfected female’s eggs fail to hatch when
fertilised by an infected male. If variation in infection rates and CI
strength exist, Wolbachia induced CI may reduce gene-flow between
populations. Here, we investigate CI between three populations of the
bulb mite, Rhizoglyphus robini. Our crosses and PCR screening for
Wolbachia of populations with and without antibiotic curing provide
evidence that one population infected with Wolbachia induces and rescues
CI: when males are mated to females either from an uninfected population
or from another population infected with Wolbachia the majority of eggs
fail to hatch, the latter suggesting that different Wolbachia strains
infect different populations. By assembling draft Wolbachia genomes
using a metagenome assembly approach, we find that Wolbachia assemblies
are almost identical in aligned regions, but also find evidence for
possible structural variation by performing coverage analysis. This
structural variation appears to be linked phage regions and the
presence/absence of “cif-like” genes, in a pattern consistent with the
observed CI phenotype. Cif genes have previously be shown to be causal
in inducing and rescuing CI in other species. The causal mechanisms for
this structural variation remains unknown. Interestingly, we find a
large number of hybrid males inheriting the CI inducing Wolbachia
strain, do not themselves induce CI. We suggest this pattern is likely
associated with host variant that acts to suppress CI.