Sticklebacks infected by the parasitic flatworm Schistocephalus solidus show dramatic changes in phenotype, including a loss of species-typical behavioural responses to predators. The timing of host behaviour change coincides with the development of infectivity of the parasite to the final host (a piscivorous bird), making it an ideal model for studying the mechanisms of infection-induced behavioural modification. However, whether the loss of host anti-predator behaviour results from direct manipulation by the parasite, or is a by-product (e.g. host immune response) or side effect of infection (e.g. energetic loss), remains controversial. To understand the physiological mechanisms that generate these behavioural changes, we quantified the behavioural profiles of experimentally infected fish and attempted to replicate these in non-parasitized fish by exposing them to treatments including immunity activation and fasting, or by pharmacologically inhibiting the stress axis. All fish were screened for the following behaviours: activity, water depth preference, sociability, phototaxis, anti-predator response and latency to feed. We were able to change individual behaviours with certain treatments. Our results suggest that the impact of S. solidus on the stickleback might be of a multifactorial nature. The behaviour changes observed in infected fish might result from the combined effects of modifying the serotonergic axis, lack of energy and activation of the immune system.
The authors declare no competing or financial interests.
L.G. designed the study with input from N.A.-H. and I.B. L.G. and C.S.B. pretested treatment concentrations. L.G. performed the manipulation experiments under the supervision of the licence holder (I.B.), carried out the statistical analysis and extracted RNA from the worms. F.-O.H. performed the transcriptomic analyses to confirm the infectivity status of the worms. I.B. provided experimental aquarium and laboratory facilities. L.G. and N.A.-H. drafted the manuscript with input from F.-O.H., C.S.B. and I.B.
This study was funded through a Fonds de Recherche du Québec - Nature et Technologies (FRQNT) Programme de Recherche en Équipe grant to N.A.-H.; a Natural Sciences and Engineering Research Council of Canada (CRSNG) grant through the Discovery grant program to N.A.-H.; funding from the University of Leicester to I.B., a Vanier Canada Graduate Scholarship from the Natural Sciences and Engineering Research Council of Canada to F.-O.H.; a Ressources Aquatiques Québec (RAQ) travel fellowship to L.G., and a Explo'RA Sup de la région Rhône-Alpes fellowship to C.S.B.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.151456.supplemental
- Received October 12, 2016.
- Accepted October 23, 2016.
- © 2017. Published by The Company of Biologists Ltd