Wolbachia Infection in Wild Mosquitoes (Diptera: Culicidae): Implications for Transmission Modes and Host-Endosymbiont Associations

Abstract

Background: Wolbachia is an intracellular bacterial endosymbiont found in most insect lineages. In mosquitoes, the endosymbiont’s influence on host reproduction and arboviral transmission has spurred numerous studies aimed at using Wolbachia-infection as a vector control technique. However, there exist several gaps in the literature regarding the natural Wolbachia infection across species, modes of transmission as well as the associations between various Wolbachia lineages and their hosts. This study aims to address these by exploring mosquito-Wolbachia associations and their evolutionary implications.Methods: We conducted tissue-specific PCR screening of Wolbachia infection in wild mosquitoes from Singapore using the wsp molecular marker. Tissues examined include leg, gut, and reproductive tissues. We also explored mosquito-Wolbachia associations using three methods – a tanglegram, distance-based, and event-based method, and inferred instances of vertical transmission and host shifts. Results: We screened 271 adult mosquitoes (41 species and 14 genera) for Wolbachia and found that 43.9% of all individuals harboured Wolbachia. Eight out of the 21 infected species were not previously reported. We detected Wolbachia infections predominantly in the reproductive tissues, a strong indication of vertical transmission. Despite this, Wolbachia infection rates vary widely within a mosquito host species. There was no clear signal of co-phylogeny between the mosquito hosts and the twelve putative Wolbachia strains observed in our study. Host shift events were also observed. Conclusions: Our results suggest that the mosquito-Wolbachia relationship is complex and that a combination of transmission modes and multiple evolutionary events likely explain the distribution of Wolbachia diversity observed across mosquito hosts. This has implications towards understanding Wolbachia’s diversity, ecology, and utility as a biocontrol method.