Wolbachia infection alters olfactory-cued locomotion in Drosophila spp

Abstract

Wolbachia pipientis is an endosymbiotic bacterium present in diverse insect species. Although it is well studied for its dramatic effects on host reproductive biology, little is known about its effects on other aspects of host biology, despite its presence in a wide array of host tissues. This study examined the effects of three Wolbachia strains on two different Drosophila species, using a laboratory performance assay for insect locomotion in response to olfactory cues. The results demonstrate that Wolbachia infection can have significant effects on host responsiveness that vary with respect to the Wolbachia strain-host species combination. The wRi strain, native to Drosophila simulans, increases the basal activity level of the host insect as well as its responsiveness to food cues. In contrast, the wMel strain and the virulent wMelPop strain, native to Drosophila melanogaster, cause slight decreases in responsiveness to food cues but do not alter basal activity levels in the host. Surprisingly, the virulent wMelPop strain has very little impact on host responsiveness in D. simulans. This novel strain-host relationship was artificially created previously by transinfection. These findings have implications for understanding the evolution and spread of Wolbachia infections in wild populations and for Wolbachia-based vector-borne disease control strategies currently being developed.

FIG. 1.

Drosophila diet-baited trap (a) and capture arena containing a trap (b). After overnight starvation, individual flies representing the different host-strain combinations were placed inside capture arenas with either baited or unbaited traps. The time that individual flies took to enter the trap was recorded during a 220-min assay period.

FIG. 2.

Cumulative mean proportion of D. melanogaster flies captured ± standard error of the mean (SEM) per 20-min period in baited traps. Means represent three replicate assay dates each, based on the performance of 50 individual flies. Infected (solid lines) and uninfected (dashed lines) flies were tested at each of three adult ages (5, 15, and 35 days). Significant differences between the performances of infected and uninfected flies for each adult age were determined by the log-rank test. *, P ≤ 0.01.

FIG. 3.

Cumulative mean proportion of D. simulans flies captured ± SEM per 20-min period in baited traps. Means represent three replicate assay dates, each based on the performance of 50 individual flies. Infected (solid lines) and uninfected (dashed lines) flies were tested at each of three adult ages (5, 15, and 35 days). Significant differences between performances of infected and uninfected flies for each adult age were determined by the log-rank test. *, P ≤ 0.01.

FIG. 4.

Cumulative mean proportion of D. melanogaster and D. simulans flies captured ± SEM per 20-min period in unbaited traps. Means represent three replicate assay dates, each based on 50 individual flies. Infected (solid lines) and uninfected (dashed lines) flies were tested at a single adult age (15 days). Significant differences between performances of infected and uninfected flies were determined by the log-rank test. *, P ≤ 0.01.