Mutualism Enhances Wolbachia Infection Rates in Ant-attended Tuberculatus Aphid Species (Hemiptera: Aphididae)

Abstract

Wolbachia are intracellular bacteria, the infection of which alters host reproductive characteristics. Wolbachia are estimated to infect more than half of arthropod species and some species of nematodes, and Wolbachia major genotypes are classified into 17 supergroups (A to S except G and R). It has been documented that the distribution and infection rate of Wolbachia on insects in the wild varies intra- or inter-species through competitions between infected and uninfected hosts. Aphid species within the genus Tuberculatus feed on Fagaceae leaves and exhibit two contrasting ecological characteristics, ant-attendance and non-attendance. This study compared Wolbachia infection rates between 11 ant-attended and 12 non-attended Tuberculatus aphid species, which were collected throughout Japan and around Mt. Kariwangsan in South Korea. Mean infection rates of Wolbachia were 30.3% in ant-attended species and 3.1% in non-attended species. Wolbachia haplotypes detected were classified into supergroups B, M, N, and O. Phylogenetic trees of Tuberculatus aphids constructed from a mitochondrion gene of cytochrome oxidase subunit I (COI) and nuclear gene of 18S rRNA showed that mutualistic interactions between Tuberculatus aphids and ants have evolved at least five times. The phylogenetic comparative method showed that Wolbachia infection rates were significantly higher in ant-attended species. Possible Wolbachia infection routes were discussed in terms of the differences in the ecological characteristics between ant-attended and non-attended aphid species. Based on the phylogenetic comparative method, this study first revealed that the spread of microorganisms was affected by species interactions of hosts, and would contribute a profound understanding of the evolution of mutualistic interactions.