Résumé
Wolbachia are maternally-inherited bacteria that induce cytoplasmic
incompatibility in many arthropod species. However, the ubiquity of this
isolation mechanism for host speciation processes remains elusive, as only
few studies have examined Wolbachia-induced incompatibilities when host
populations are not genetically compatible. Here, we used three
populations of two genetically differentiated colour forms of the
haplodiploid spider mite Tetranychus urticae to dissect the interaction
between Wolbachia-induced and host-associated incompatibilities, and their
relative contribution to post-mating isolation. We found that these two
sources of incompatibility act through different mechanisms in an additive
fashion. Host-associated incompatibility contributes 1.5 times more than
Wolbachia-induced incompatibility in reducing hybrid production, the
former through an overproduction of haploid sons at the expense of diploid
daugters (ca. 75% decrease) and the latter by increasing the embryonic
mortality of daughters (by ca. 49%). Furthermore, regardless of cross
direction, we observed near-complete F1 hybrid sterility and complete F2
hybrid breakdown between populations of the two forms, but Wolbachia did
not contribute to this outcome. We thus show mechanistic independence and
an additive nature of host-intrinsic and Wolbachia-induced sources of
isolation. Wolbachia may contribute to reproductive isolation in this
system, thereby potentially affecting host differentiation and
distribution in the field.