Rapid Global Spread of wRi-like Wolbachia across Multiple Drosophila

Abstract

Maternally transmitted Wolbachia, Spiroplasma, and Cardinium bacteria are common in insects [1], but their interspecific spread is poorly understood. Endosymbionts can spread rapidly within host species by manipulating host reproduction, as typified by theglobal spread of wRi Wolbachia observed in Drosophila simulans [2, 3]. However, because Wolbachia cannot survive outside host cells, spread between distantly related host species requires horizontal transfers that are presumably rare [4-7]. Here, we document spread of wRi-like Wolbachia among eight highly diverged Drosophila hosts (10-50 million years) over only about 14,000 years (5,000-27,000). Comparing 110 wRi-like genomes, we find ≤0.02% divergence from the wRi variant that spread rapidly through California populations of D.simulans. Thehosts include both globally invasive species (D.simulans, D.suzukii, and D.ananassae) andnarrowly distributed Australian endemics (D.anomalata and D.pandora) [8]. Phylogenetic analyses that include mtDNA genomes indicate introgressive transfer of wRi-like Wolbachia between closely related species D.ananassae, D.anomalata, and D.pandora but no horizontal transmission within species. Our analyses suggest D.ananassae as theWolbachia source for the recent wRi invasion ofD.simulans and D.suzukii as the source of Wolbachia in its sister species D.subpulchrella. Although six of these wRi-like variants cause strong cytoplasmic incompatibility, two cause no detectable reproductive effects, indicating that pervasive mutualistic effects [9, 10] complement the reproductive manipulations for which Wolbachia are bestknown. "Super spreader" variants like wRi may beparticularly useful for controlling insect pestsand vector-borne diseases with Wolbachia transinfections [11].