Kenji Yukuhiro

Exploring the molecular phylogeny of phasmids with whole mitochondrial genome sequences

Phasmids are remarkable mimics of twigs, sticks, and leaves. This extreme adaptation for crypsis can easily lead to the convergent evolution of morphology, making it difficult to establish a taxonomic system of phasmids. Accordingly, there are multiple phylogenetic hypotheses that conflict with each other. Phylogenetic arrangements suggested by molecular data disagree with the morphology-based taxonomy in some instances. We collected 13 phasmatodean species, sequenced their mitochondrial genomes, and recovered their molecular phylogeny. Our analyses did not support the monophyly of Areolatae or Anareolatae, two major infraorders of Phasmatodea. The position of Neohirasea was also quite different from the conventional taxonomic systems, thus challenging the previously assumed monophyly of the subfamily Lonchodinae. The enigmatic taxon, Timema, was shown to be distantly related to other phasmatodeans.

Wolbachia-induced meiotic drive and feminization is associated with an independent occurrence of selective mitochondrial sweep in a butterfly.

Maternally inherited Wolbachia endosymbionts manipulate arthropod reproduction in various ways. In the butterfly Eurema mandarina, a cytoplasmic incompatibility-inducing Wolbachia strain wCI and the associated mtDNA haplotypes are known to originate from the sister species Eurema hecabe, which offered a good case study for microbe-mediated hybrid introgression. Besides wCI, some females with the Z0 karyotype harbour a distinct Wolbachia strain wFem, which causes all-female production by meiotic drive and feminization. We report that a considerable proportion of E. mandarina females (65.7%) were infected with both wCI and wFem (CF) on Tanegashima Island. While females singly infected with wCI (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 E. hecabe but not with uninfected E. mandarina. This suggests that CF matrilines also, but independently, experienced a selective sweep after hybrid introgression from E. hecabe. Distinct evolutionary forces were suggested to have caused C and CF matrilines to diverge, which would be irreversible because of the particular phenotype of wFem.