How Long Does Wolbachia Remain on Board?

Abstract

Wolbachia bacteria infect about half of all arthropods, with diverse and extreme consequences ranging from sex-ratio distortion and mating incompatibilities to protection against viruses. These phenotypic effects, combined with efficient vertical transmission from mothers to offspring, satisfactorily explain the invasion dynamics of Wolbachia within species. However, beyond the species level, the lack of congruence between the host and symbiont phylogenetic trees indicates that Wolbachia horizontal transfers and extinctions do happen and underlie its global distribution. But how often do they occur? And has the Wolbachia pandemic reached its equilibrium? Here, we address these questions by inferring recent acquisition/loss events from the distribution of Wolbachia lineages across the mitochondrial DNA tree of 3,600 arthropod specimens, spanning 1,100 species from Tahiti and surrounding islands. We show that most events occurred within the last million years, but are likely attributable to individual level variation (e.g., imperfect maternal transmission) rather than population level variation (e.g., Wolbachia extinction). At the population level, we estimate that mitochondria typically accumulate 4.7% substitutions per site during an infected episode, and 7.1% substitutions per site during the uninfected phase. Using a Bayesian time calibration of the mitochondrial tree, these numbers translate into infected and uninfected phases of approximately 7 and 9 million years. Infected species thus lose Wolbachia slightly more often than uninfected species acquire it, supporting the view that its present incidence, estimated here slightly below 0.5, represents an epidemiological equilibrium.

Novel Wolbachia strains in Anopheles malaria vectors from Sub-Saharan Africa

“…mosquitoes from both Burkina Faso and Mali), strain variants observed in An . species A, and the concatenated grouping of the novel Anopheles strains with strains found in different Orders of insects, support the lack of congruence between insect host and Wolbachia phylogenetic trees 80 . …”

Context‐dependent vertical transmission shapes strong endosymbiont community structure in the pea aphid, Acyrthosiphon pisum

“…Nonessential, heritable bacterial symbionts are even more common among the insects (Weinert et al., ; see Mondo, Toomer, Morton, Lekberg, & Pawlowska, for an example in mycorrhizal fungi). And while their impacts in any one lineage have been likely ephemeral (e.g., Bailly‐Bechet et al., ), they can profoundly shape host biology in insects and host taxa beyond (Oliver et al., ). Impacts of protective symbionts on surrounding macro‐organismal communities have been noted (Clay, Holah, & Rudgers, ; Ferrari & Vavre, ; Jaenike & Brekke, ), as has their relevance to the success and management of damaging insect pests (Hedges, Brownlie, O'Neill, & Johnson, ; Hoffmann et al., ; Hosokawa, Kikuchi, Shimada, & Fukatsu, ; Weiss & Aksoy, ).…”

Genome comparisons indicate recent transfer ofwRi‐likeWolbachiabetween sister speciesDrosophila suzukiiandD. subpulchrella

“…Bailly‐Bechet et al. (2017) provide a meta‐analysis of more than 1,000 arthropod species from Tahiti that suggests average durations on the order of 7 million years. However, their molecular data, which involve only two Wolbachia loci and the CO1 mtDNA locus, do not have sufficient power to resolve the issue.…”