Research

We are a research team at the National Agriculture and Food Research Organization (NARO), dedicated to exploring sex-manipulating microbes within arthropod cells and their impact on the evolution of arthropods. These symbiotic microbes manipulate host biology to their advantage, exemplifying what Richard Dawkins described as extended phenotypes. By investigating the mechanisms behind these interactions, we aim to unravel the intricacies of host-symbiont relationships and their evolutionary origins. A deeper understanding of these processes may pave the way for innovative strategies to manage insect pests or enhance the utility of beneficial insects.

Butterfly Sex Determination Manipulated by Wolbachia Symbionts

Male-specific death induced by maternally transmitted symbiotic bacteria (male killing) has often been reported in a wide variety of arthropods. In Lepidoptera, Wolbachia-induced male killing is attributed to interference with the sex determination. We have developed a cell culture system to study the molecular mechanism of the sex determination system (1,2). We also focus on a specific system of a buttefly, Eurema mandarina, in which Wolbachia-induced meiotic drive appears to occur in addition to the interference with sex determination (3).

References

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

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

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

Effects of Wolbachia on Host Population

References

Our research is supported by the Japan Society for the Promotion of Science (JSPS) and National Agriculture and Food Research Organization (NARO).