Sample information from <i>Wolbachia</i>-induced meiotic drive and feminization is associated with an independent occurrence of selective mitochondrial sweep in a butterfly

Maternally inherited <i>Wolbachia</i> endosymbionts manipulate arthropod reproduction in various ways. In the butterfly <i>Eurema mandarina</i>, a cytoplasmic incompatibility inducing <i>Wolbachia</i> strain <i>w</i>CI and the associated mtDNA haplotypes are known to originate from the sister species <i>Eurema hecabe</i>, which offered a good case study for microbe-mediated hybrid introgression. Besides <i>w</i>CI, some females with the Z0 karyotype harbour a distinct <i>Wolbachia</i> strain <i>w</i>Fem, which causes all-female production by meiotic drive and feminization. We report that a considerable proportion of <i>E. mandarina</i> females (65.7%) were infected with both <i>w</i>CI and <i>w</i>Fem (CF) on Tanegashima Island. While females singly infected with <i>w</i>CI (C) produced offspring at a 1 : 1 sex ratio, CF females produced only females. Although Z-linked sequence polymorphism showed no signs of divergence between C and CF females, mtDNA split into two discrete clades; one consisted of C females and the other CF females, both of which formed a clade with <i>E. hecabe</i> but not with uninfected <i>E. mandarina</i>. This suggests that CF matrilines also, but independently, experienced a selective sweep after hybrid introgression from <i>E. hecabe</i>. Distinct evolutionary forces were suggested to have caused C and CF matrilines to diverge, which would be irreversible because of the particular phenotype of <i>w</i>Fem.