Pervasive effects of Wolbachia on host activity

Heritable symbionts have diverse effects on the physiology, reproduction, and fitness of their hosts. Maternally transmitted Wolbachia are one of the most common endosymbionts in nature, infecting about half of all insect species. We test the hypothesis that Wolbachia alter host behavior by assessing the effects of 14 different Wolbachia strains on the locomotor activity of nine Drosophila host species. We find that Wolbachia alter the activity of six different host genotypes, including all hosts in our assay infected with wRi-like Wolbachia strains (wRi, wSuz, wAur), which have rapidly spread among Drosophila species in only the last 13,000 years. While Wolbachia effects on host activity were common, the direction of these effects varied unpredictably and sometimes depended on host sex. We hypothesize that the prominent effects of wRi-like Wolbachia may be explained by patterns of Wolbachia titer and localization within host somatic tissues, particularly in the central nervous system. Our findings support the view that Wolbachia have wide-ranging effects on host behavior. The fitness consequences of these behavioral modifications are important for understanding the evolution of host-symbiont interactions, including how Wolbachia spread within host populations.