Unidirectional and Heterogenous Wolbachia Transfer Rates Among Insect Host Orders

Abstract

Background Wolbachia are highly prevalent endosymbiotic bacteria infecting more than two-thirds of arthropods. While Wolbachia are mainly transmitted vertically through the female germline, experiments and phylogenetic studies have suggested that horizontal transmission between hosts is not uncommon. In this study, we aim to get a better understanding of horizontal transfer events between hosts of different orders and between continents using a large database containing nucleotide sequences of the genes wsp and ftsZ. Results Our results show a high frequency of horizontal Wolbachia transmission between host orders and continents, but nevertheless detectable signals of the host phylogeny and geography in the Wolbachia phylogeny. Two different approaches for estimating transition rates between host orders from phylogenies produced evidence that Wolbachia transition rates between some insect orders are unidirectional. Furthermore, the phylogenies and transition rate estimates differed between the genes, suggesting that not all genes are equally likely to spread in a new host following horizontal transmission. This discrepancy between genes, however, is more evident on a larger timescale because highly similar sequences were grouped in the same clades on both genes. Conclusions Together, these results contribute to understanding the dynamics and patterns of Wolbachia host shifts and generate new hypotheses about factors that might prevent horizontal Wolbachia transfer. These insights have important implications for controlling disease vectors or understanding the coevolution of hosts and their associated microbes.

Frequent intertrophic transmission ofWolbachiaby parasitism but not predation

“…Although previous research has demonstrated that parasitoids can acquire Wolbachia from their hosts, the reverse direction of transmission, from host to parasitoid, has been largely overlooked and lacks supportive experimental evidence. One possible reason for this oversight is that all parasitoids emerge from their hosts, but hosts are eventually killed by the parasitism of parasitoid wasps ( 17, 23, 24 ). However, parasitoid wasps’ success in parasitizing their hosts does not always reach 100% ( 34 ).…”

“…However, it remains uncertain whether Wolbachia can be transferred from parasitoid wasps to their hosts. Some have argued that the transfer of Wolbachia between parasitoid wasps and their hosts is unidirectional, from host to wasp, as all parasitoid wasps emerge from their hosts, but parasitized hosts are eventually killed or castrated if not killed immediately ( 17, 23, 24 ).…”