Wolbachia Genome Stability and mtDNA Variants in Aedes aegypti Field Populations Eight Years after Release

Abstract

A dengue suppression strategy based on release of Aedes aegypti mosquitoes infected with the bacterium Wolbachia pipientis is being trialed in many countries. Wolbachia inhibits replication and transmission of dengue viruses. Questions remain regarding the long-term stability of virus-suppressive effects. We sequenced the Wolbachia genome and analyzed Ae. aegypti mitochondrial DNA markers isolated from mosquitoes sampled 2-8 years after releases in the greater Cairns region, Australia. Few changes were detected when Wolbachia genomes of field mosquitoes were compared with Wolbachia genomes of mosquitoes obtained soon after initial releases. Mitochondrial variants associated with the initial Wolbachia release stock are now the only variants found in release sites, highlighting maternal leakage as a possible explanation for rare Wolbachia-negative mosquitoes and not migration from non-release areas. There is no evidence of changes in the Wolbachia genome that indicate selection against its viral-suppressive effects or other phenotypes attributable to infection with the bacterium.

Keywords: Biological Sciences; Entomology; Genomics; Parasitology; Virology.

Graphical abstract

Figure 1

Sampling Locations in the Greater Cairns Area, North Queensland Eggs were collected in ovitraps deployed in the suburbs of Gordonvale, Yorkeys Knob, Caravonica, Edge Hill, Cairns North, Paramatta Park, Portsmith, and Bungalow. Note that there were two releases of Wolbachia-infected mosquitoes in two geographically separated zones in Paramatta Park (January 2013 and March 2017) and Cairns North (August 2014 and March 2017). Samples collected from Portsmith were only included in the mitochondrial DNA analysis.

Figure 2

Haplotype Network for COI and Table of Frequencies Each colored node represents an observed haplotype with circle size indicating the number of individuals with each numbered haplotype. Solid black nodes represent a single base change. Abbreviations: G, Gordonvale; YK, Yorkeys Knob; C, Caravonica; EH, Edge Hill; PP/N, Parramatta Park/Cairns North; PP/P, Parramatta Park/Portsmith; BG, Bungalow. (+), wMel infected; (−), uninfected. Note that Haplotype 1 is equivalent to Haplotype 8 in Yeap et al. (2016), which was found in the wMel release strain and Haplotype 2 is equivalent to Haplotype 10 in Yeap et al. (2016), which was at a low frequency in the wMel release strain.