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Abstract

Wolbachia bacteria infect one third of all arthropod species, and inhabit all ecosystems and geographical regions, making it one of the most common symbiont in the animal world. The dynamics of these bacteria within species are largely relying of efficient vertical transmission, from mothers to offspring. However, from the lack of congruence between the host and symbiont phylogenetic trees beyond the species level, it is evident that horizontal transfer and infection loss are the two processes governing the global Wolbachia distribution. How often do uninfected species get infected through horizontal transfer? And how long does Wolbachia remain on board once it has invaded a new species? Here we address these questions by using a Wolbachia / host cophylogeny approach. We show that uninfected lineages receive Wolbachia at least once every nine million years, and remain infected for about seven million years, with a strong variability between different orders. These estimates support the conjecture that the present global incidence is close to a stable equilibrium between loss and acquisition.