Testing the potential contribution of Wolbachia to speciation when cytoplasmic incompatibility becomes associated with host‐related reproductive isolation

Endosymbiont induced cytoplasmic incompatibility (CI) may play an important role in arthropod speciation. However, whether CI consistently becomes associated or coupled with other host-related forms of reproductive isolation (RI) to impede the transfer of endosymbionts between hybridizing populations and further the divergence process remains an open question. Here, we show varying degrees of pre- and post-mating RI exist among allopatric populations of two interbreeding cherry-infesting tephritid fruit flies (Rhagoletis cingulata and R. indifferens) across North America. These flies display allochronic and sexual isolation among populations, as well as unidirectional reductions in egg hatch in hybrid crosses involving southwestern USA males. All populations are infected by a Wolbachia strain, wCin2, whereas a second strain, wCin3, only coinfects flies from the Southwest USA and Mexico. Strain wCin3 is associated with a unique mtDNA haplotype and unidirectional postmating RI, implicatin...