Research

Butterfly Sex Determination Manipulated by Wolbachia Symbionts

As predicted by evolutionary theory, female-biased sex ratios are favored by maternally transmitted intracellular symbionts. Male-specific lethality induced by these symbionts (male killing) has been widely documented across diverse arthropod taxa. In Lepidoptera, the alphaproteobacterium Wolbachia causes male killing by interfering with the host sex-determination pathway. To elucidate the underlying mechanisms, we have established a cell culture system that allows us to dissect how Wolbachia manipulates host sex determination (1,2). In parallel, we investigate a unique butterfly system, Eurema mandarina, in which Wolbachia-induced meiotic drive appears to operate in addition to the disruption of sex determination (3).

References (1) Herran et al. (2022) PNAS Nexus (2) Arai et al. (2024) PNAS Nexus (3) Kageyama et al. (2017) Evol. Lett.

Embryonic Arrest by Wolbachia-Induced Maternal Effect 

We found that a specific Wolbachia strain, when transinfected into the somatic tissues of a new host species via injection, can induce embryonic arrest in the subsequent generation, even though the transferred Wolbachia is not vertically transmitted (1). This effect has been observed in multiple insect species across at least three different orders: Lepidoptera, Hymenoptera, and Hemiptera. We aim to determine the uniqueness or generality of this effect and to elucidate its underlying mechanism and implications.

References (1) Kageyama et al. (2017) J. Invertebr. Pathol.

Vertically Transmitted Viruses that Kill Male Hosts

While maternally inherited bacteria such as Spiroplasma and Wolbachia are well known to induce male killing, it is not well understood how viruses, which have much smaller genomes, can do so. We have identified a double-stranded RNA virus belonging to the family Partitiviridae that induces male killing in Drosophila (1,2). The virus has only four genes, and a protein encoded by one gene was found to be necessary and sufficient to induce male killing (2). We also discovered a new virus belonging to an entirely different taxon induces male killing in the moth Spodoptera litura (3). These discoveries suggests that symbiotic viruses play an important role in arthropod evolution and could be used to control arthropod populations.

References (1) Kageyama et al. (2017) Biol. Lett. (2) Kageyama et al. (2023) Nat. Commun. (3) Nagamine et al. (2023) Proc. Natl. Acad. Sci. U.S.A.

Evolutionary Arms Race between Sex-Ratio-Distorting Symbionts and Hosts

If maternally transmitted sex ratio distorters such as feminizers or male killers spread within host populations, the host will be at risk of extinction due to lack of males. Genetic suppressors of the host that restore the normal sex ratio will then be strongly selected for and can spread rapidly in the population (1,2).

References (1) Hayashi et al. (2018) Proc. R. Soc. B (2) Hornett et al. (2022) Proc. R. Soc. B

Effects of Wolbachia on Host Population

References (1) Miyata et al. (2017) Biol. Lett. (2) Kageyama et al. (2020) bioRxiv (3) Miyata et al. (2024) Curr. Biol.