Wolbachia diversity within species and individuals

The extent of Wolbachia diversity within species has been investigated in two terrestrial isopods: P. pruinosus (Marcade et al ., 1999; Michel-Salzat et al ., 2001) and A. vulgare (Cordaux et al , 2004; Verne et al , 2007) Three distinct Wolbachia strains have been identified within each isopod species . In P. pruinosus, two strains (wPruI and wPruII) exhibit ~5% nucleotide divergence based on the variable wsp gene (Michel-Salzat et al , 2001) In comparison, the third strain (wPruIII) shows ~20% nucleotide divergence with wPruI and wPruII based on the wsp gene . Interestingly, two types of Wolbachia infections are found in the P. pruinosus complex of species (Lefebvre and Marcadé, 2005): (1) populations with Wolbachia in both males and females, with a prevalence of ~90%, and (2) populations with Wolbachia only in females, with a prevalence of ~60% (Marcadé et al ., 1999) . We observed that there is no strong association between Wolbachia strain distribution and infection patterns Indeed, the two most closely related strains wPruI and wPruII were found associated with different infection patterns, whereas the two distantly related strains wPruII and wPruIII were found to exhibit the same infection pattern (Michel-Salzat et al ., 2001) . These results suggest that host genetic backgrounds may play an important role in the expression of Wolbachia phenotypes in P. pruinosus

In A. vulgare, two strains (wVulC and wVulM) exhibiting ~5% nucleotide divergence based on the wsp gene have been shown to induce feminization of genetic males (Cordaux et al ., 2004) . The third strain (wVulP) is essentially identical to wVulC, except for a ~60 bp-long portion of the wsp gene that is more closely related to wVulM, suggesting that wVulP is a recombinant strain between wVulC and wVulM (Verne et al., 2007) . The phenotype induced by wVulP on its hosts is currently unknown, but if it has any effect, it is likely to be a feminizing strain, based on sequence similarity to wVulC . The discovery of the recombinant wVulP strain has interesting evolutionary implications because it implies that two feminizing Wolbachia strains (wVulC and wVulM) have coexisted at some point within the same cytoplasm This is a quite unexpected result because no crustacean individual has been found to harbor multiple Wolbachia strains to date, although multiple strains can coexist within populations (Verne et al , 2007) Thus, infections of single individuals with multiple feminizing Wolbachia strains seem unstable in natural populations, in agreement with theoretical predictions (Caubet et al. 2000) . Overall, these results suggest that the occurrence of multiple Wolbachia strains, as well as other intracellular bacteria such as the pathogenic Rickettsiella (Cordaux et al., 2007) in single isopod individuals, although most likely transient events, may have important evolutionary consequences to reshuffle bacterial genetic diversity through recombination

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