Wolbachia in scale insects: A unique pattern of infection prevalence, high genetic diversity, and host shifts

Wolbachia is one of the most successful endosymbiotic bacteria of arthropods. It is a master manipulator,modifying its hosts’ biology in many ways to increase its vertical (maternal) transmission. Wolbachia can also undergo host shifts that can be mediated by ecological vectors such as shared host plants or parasitoids. Here, I screened ۶۸۷ specimens from ۱۵۱ scale insect species that were mostly collected in Asia and Australia for Wolbachia infection. I fitted the distribution of within-species prevalence of Wolbachia to our data and compared it to distributions fitted to an up-to-date dataset compiled from surveys across all arthropods. In contrast to other hemipteran groups, the prevalence of Wolbachia in scale insects follows a distribution similar to exponential decline (most species are predicted to have low prevalence infections). By conducting Illumina pooled amplicon sequencing of ۵۹ infected scale insect samples and ۱۶ direct associates of scale insects (including wasps and ants), I determined ۶۳ Wolbachia strains in these species belonging to supergroup A, B and F. I observed a lack of congruency between Wolbachia and scale insect phylogeny and identified several putative host-shifts events. Finally, I fitted a Generalised Additive Mixed Model (GAMM) to assess factors influencing Wolbachia sharing among scale insect species. I found strong effects of host phylogeny without any significant contribution of host geography. There were high rates of Wolbachia sharing among closely related species (i.e., host-shifting mostly happens between species of the same genus) with a sudden drop-off in sharing with increasing phylogenetic distance. This finding can explain a large number of reported Wolbachia host-shifting among congeneric species.