Abstract
Endosymbiotic bacteria of the genus Wolbachia induce diverse reproductive alterations in their insect hosts. Wolbachia (wSca) infecting the moth Ostrinia scapulalis causes unusual male killing, in which males (genotype: ZZ) selectively die during embryonic and larval development, whereas females (genotype: ZW), in turn, selectively die when cured of infection. To gain insight into the interaction between wSca and the host, we analysed phenotypic and genetic sexes of the embryos and larvae of normal, wSca-infected, and infected-and-cured O. scapulalis by diagnosing the sex-specifically spliced transcripts of Osdsx—a homologue of the sex-determining gene doublesex—and sex chromatin in interphase nuclei, respectively. It was observed that the female-type Osdsx was expressed in the infected male (ZZ) progenies destined to die, whereas the male-type Osdsx was expressed in the cured female (ZW) progenies destined to die. These findings suggest that (i) wSca, a male killer, carries a genetic factor that feminizes the male host, (ii) the sex-determining system of the host is degraded, and (iii) a mismatch between the genetic and phenotypic sexes underlies the sex-specific death.
Highlights
Wolbachia, a group of endosymbiotic bacteria harboured by a wide range of insects [1], is known for various manipulations of host reproduction to expedite their own propagation [2]
Wolbachia infecting the adzuki bean borer moth (Ostrinia scapulalis) causes male killing, the male killing in this Wolbachia – host system is unusual in that females, in turn, selectively died when wSca was eliminated by antibiotic treatment, giving rise to all-male progeny
In an uninfected normal strain of O. scapulalis, the sex ratio of individuals did not deviate significantly from 1 : 1 throughout development, and the type of dsx homologue expressed was in accordance with the genetic sex, that is, the maletype OsdsxM was expressed in individuals with the ZZ genotype, and the female-type OsdsxFL was expressed in individuals with the ZW genotype
Summary
A male-killing Wolbachia carries a feminizing factor and is associated with degradation of the sex-determining system of its host. It was observed that the female-type Osdsx was expressed in the infected male (ZZ) progenies destined to die, whereas the male-type Osdsx was expressed in the cured female (ZW) progenies destined to die. These findings suggest that (i) wSca, a male killer, carries a genetic factor that feminizes the male host, (ii) the sex-determining system of the host is degraded, and (iii) a mismatch between the genetic and phenotypic sexes underlies the sex-specific death
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