Fine-scale landscape genomics helps explain the slow spread of Wolbachia through the Aedes aegypti population in Cairns, Australia

Abstract

The endosymbiotic bacterium Wolbachia suppresses the capacity for arboviral transmission in the mosquito Aedes aegypti, and can spread through wild mosquito populations following local introductions. Recent introductions in Cairns, Australia have demonstrated slower than expected spread, that could be due to: i) barriers to Ae. aegypti dispersal; ii) leptokurtically distributed dispersal distances; and iii) intergenerational loss of Wolbachia. We investigated these three potential causes using genome-wide single-nucleotide polymorphisms (SNPs) and an assay for the Wolbachia infection wMel in 161 Ae. aegypti collected from Cairns in 2015. We observed a significant barrier effect of Cairns highways on Ae. aegypti dispersal using distance-based redundancy analysis and patch-based simulation analysis. We detected putative full-siblings in ovitraps 1312m apart, suggesting long-distance female movement likely mediated by human transport. Finally, we found a pair of full-siblings of different infection status, suggesting loss of Wolbachia in the field. While the long-distance movement and Wolbachia loss currently represent single observations, these findings together with the identified dispersal barriers can contribute to the slow spread of Wolbachia through the Ae. aegypti population in Cairns. Our landscape genomics approach can be extended to other host/symbiont systems that are being considered for biocontrol.