Nighttime activities and peripheral clock oscillations depend on Wolbachia endosymbionts in flies

Abstract

Wolbachia are ubiquitous bacterial endosymbionts of arthropods and affect host gene expression. Although Wolbachia infections were suggested to modulate sleep in flies, their influence on the circadian clock remained obscure. Here, we screened bacterial symbionts in a laboratory Drosophila melanogaster colony, and observed widespread infections of wMel strain Wolbachia. We established a Wolbachia-free strain from a clock gene reporter strain, period-luciferase (per-luc). Temperature (19–29 °C)-compensated free-running periods were detected regardless of infections which may reflect the lack of wMel infections in central circadian pacemaker neurons. However, locomotor activity levels during the night or subjective night were significantly amplified in uninfected flies. Moreover, the behavioral phenotype of F1 offspring of an uninfected female and infected male resembled that of uninfected flies. This trait is consistent with maternal transmission of Wolbachia infection. Interestingly, per-luc activities in headless bodies, as an index of peripheral circadian oscillators, were severely damped in uninfected flies. Additionally, circadian amplitudes of PER immunoreactivities in Malpighian tubules were reduced in uninfected flies. These results demonstrate that Wolbachia boost fly peripheral clock oscillations and diurnal behavioral patterns. Genetic mechanisms underlying behavioral rhythms have been widely analyzed using mutant flies whereas screening of Wolbachia will be necessary for future studies.

The effect of Wolbachia on gene expression in Drosophila paulistorum and its implications for symbiont-induced host speciation

“…Hence, the expression pattern of the serine and glycine metabolism genes in heads of GFR flies, rather than WT flies, mimic starvation conditions. Interestingly, in line with this observation, a recent study showed an increase in nighttime activities in non- Wolbachia infected D. melanogaster flies compared to infected [58].…”

The effect of the endosymbiont Wolbachia on the behavior of insect hosts

“…This is consistent with the observation that Wolbachia infection resulted in an increase of the number of nighttime sleep bouts (Bi et al, 2018), indicating that Wolbachia infection could decrease the sleep quality in D. melanogaster. Morioka et al (2018) also demonstrated that D. melanogaster carrying Wolbachia exhibited an increase in nocturnal activities relative to uninfected flies, which may reflect a decrease in arousal threshold during the nighttime. Moreover, we also found that Wolbachia infection caused an increase in sleep latency as the night progresses (Bi et al, 2018).…”

Pervasive effects ofWolbachiaon host activity

“…Alternatively, hosts may be modifying their own behavior as a response to Wolbachia infection. Several studies indicate that w Mel alters circadian activity and sleep patterns of D. melanogaster [52,54–56]. For example, Bi et al [55] report that w Mel increases sleep time, which could represent a host immune response to infection [19].…”