Résumé
Although the diversity of bacterial endosymbionts in arthropods is well
documented, whether and how such diversity is maintained remains an open
question. We investigated the temporal changes occurring in the prevalence
and composition of endosymbionts after transferring natural
populations of Tetranychus spider-mites from the field
to the laboratory. These populations, belonging to three
different Tetranychus species (T. urticae, T.
ludeni and T. evansi) carried variable infection
frequencies of Wolbachia, Cardinium,
and Rickettsia. We report a rapid change of the infection status
of these populations after only 6 months of laboratory rearing, with an
apparent loss of Rickettsia and Cardinium,
while Wolbachia apparently either reached fixation or
was lost. We show that Wolbachia had variable
effects on host longevity and fecundity, and induced variable levels of
cytoplasmic incompatibility (CI) in each fully infected population,
despite no sequence divergence in the markers used and full CI rescue
between all populations. This suggests that such effects are largely
dependent upon the host genotype. Subsequently, we used these data to
parameterize a theoretical model for the invasion of CI-inducing symbionts
in haplodiploids, which shows that symbiont effects are sufficient to
explain their dynamics in the laboratory. This further suggests
that symbiont diversity and prevalence in the field are likely maintained
by environmental heterogeneity, which is reduced in the laboratory.
Overall, this study highlights the lability of endosymbiont infections
and draws attention to the limitations of laboratory studies to
understand host-symbiont interactions in natural populations.