Drosophila species

Sleep is conventionally thought to be “by the brain and for the brain”. Yet, recent laboratory studies suggest sleep, immune system, and gut health regulate each other. This interaction between gut/immunity and sleep is less well understood in the wild. Seasonal and ecological variation exists for Drosophila immune genes1, gut microbiota2, and ecological traits such as body colour3,4. Experiments using the genetic workhorse Drosophila melanogaster have further tied sleep to immune function and microbe control5. Importantly, sleep in the wild requires temporal alignment to annual transitions in photoperiod and temperature, which correlates with seasonal variation in immunity, the microbiota, and body colour. Whether genetic or microbiota variation contributes to seasonal sleep profile, or vice versa, is unclear. 

Temperate Drosophila fly species encounter seasonal transitions of photoperiod and temperature across generations, providing an ideal model for understanding the temporal regulatory mechanisms underlying seasonal adaptation of sleep. Unlike D. melanogaster, D. testacea is a temperate mushroom-breeding fly occurring primarily in the late summer & fall, with different colour morphs showing seasonal3,4 and geographic3 patterns (Fig.1). 

We have isolated wild-caught D. testacea lines with heritable colour variation, suggesting this seasonal body colour involves a genetic component. Recently, Hanson et al showed that D. testacea has lost a crucial immune gene, Diptericin B (DptB), which evolved to supress Acetobacter infection in fruit-feeding Drosophila. This loss may reflect the dietary switch to fungi since Acetobacter is abundant in gut microbiota of fruit-feeders, but almost non-existent in mushroom-feeding Drosophila2. Increased gut Acetobacter is associated with reduced sleep in D. melanogaster. Intriguingly, we have found that DptB mutation in D. melanogaster also causes reduced sleep, and D. testacea sleep profile differs markedly from D. melanogaster.  

Taken together, the Drosophila system boasts the powerful genetic tools of D. melanogaster, as well as natural variation in immune genes, gut microbes, seasonal photoperiod and temporal sleep profile. Using these tools, we will test if the sleep-controlling role of gut microbes relies on interactions with host immune genes and/or other factors. 

To address the knowledge gap, this collaborative PhD project aims to apply behaviour assays, and manipulations of the microbiota and host genetics in D. melanogaster and D. testacea. There are three research aims: