CONSEQUENCES OF WOLBACHIA TRANSMISSION PROCESS ON THE INFECTION DYNAMICS

In some species displaying Wolbachia-induced cytoplasmic incompatibili ty, the intensity of incompatibility depends on the density of symbion ts in both parents. Although modalities of the transmission process ar e poorly known, it appears that the density of Wolbachia within the of fspring of a female is variable and is correlated with that of the mot her. Assuming that the infection level of an host is a continuous trai t, we examine some theoretical consequences of the Wolbachia transmiss ion process on the evolution of the infection level within a populatio n. The hypotheses of this model concern two main points: the transmiss ion of Wolbachia is affected by stochastic processes and a determinist ic bias, and the bacterial load of the parents of a cross affects thei r compatibility relationships. It is shown that the variance of the nu mber of bacteria transmitted induced by the stochastic processes tends to counteract the effect of bacterial curing on the dynamics of infec tion. A general consequence of the model is that the extinction of Wol bachia is possible even if there is strong incompatibility and no sele ctive disadvantage for the host to bear the bacteria. The model indica tes that the evolution of bacterial mutants does not depend on the lev el of incompatibility they induce, but that mutants with higher transm ission variance can be selected for. Moreover, the mean infection leve l of the host population increases in the presence of such bacteria.