Tapeworm infection affects sleep behavior in three-spined stickleback

Sleep is a complex and conserved biological process that affects several body functions and behaviors. Evidence suggests that there is a reciprocal interaction between sleep and immunity. For instance, fragmented sleep can increase the probability of parasitic infections and reduce the ability to fight infections. Moreover, viral and bacterial infections alter the sleep patterns of infected individuals. However, the effects of macro-parasitic infections on sleep remain largely unknown. In this study, we investigated whether macro-parasite infections could alter the sleep of their hosts. We experimentally infected three-spined sticklebacks (Gasterosteus aculeatus) with the tapeworm Schistocephalus solidus and used a hidden Markov model to characterize sleep behavior in sticklebacks. One to four days after parasite exposure, infected fish showed no difference in sleep compared with non-exposed fish, whereas fish that were exposed-but-not-infected slept less during daytime. 29-32 days after exposure, infected fish slept more than uninfected fish, while exposed-but-not-infected fish slept less than non-exposed fish. Using brain transcriptomics, we identified immune- and sleep-associated genes that potentially underlie the observed behavioral changes. These results provide insights into the complex association between macro-parasite infection, immunity, and sleep in fish and may thus contribute to a better understanding of reciprocal interactions between sleep and immunity. Stickleback, Gasterosteus aculeatus, were either exposed to the parasite Schistocephalus solidus or not exposed to the parasite ("control"[Con]). Exposed fish were catogorized as "infected"[Inf] (parasite present) or "exposed" [Exp] (parasite not present) based on the presence of the parasite Schistocephalus solidus upon dissection of the fish. Fish were monitored for their activity at different time points and dissection of the brain for RNAseq analysis was performed subsequently of the activity measures.