Effects of host nutrition on the Host-parasite interactions of Schistocephalus solidus infections in sticklebacks

Dietary factors – including the quantity or quality of the food ingested – potentially impact the outcome of host-parasite interactions, through a variety of mechanisms. In this project, host nutritional content is manipulated qualitative and quantitatively, and the influence on host and parasites are examined. The consequences of either quantitative changes in food intake or qualitative changes in diet (i.e. type of food) may potentially benefit the host fish or parasites. The first part of the thesis results (Chapters 3 and 4) documents experiments conducted to evaluate the effect of food type, dietary protein content and ration on host-parasite interactions, focusing on the health, growth and development of fish, and the growth rate of Schistocephalus solidus plerocercoids in experimentally infected three-spined sticklebacks Gasterosteus aculeatus. The results of these studies indicate that the level of dietary protein had a significant effect on the performance of both infected and non-infected fish in the study and suggest that dietary protein plays an important role in determining the emergent phenotypes of infected fish. The level of host alimentation (i.e. ration) also played an important role in determining fish health indices and suggests that the availability of food might have a significant effect on the performance of both infected and non-infected fish in parasitized populations. The second part of this thesis (Chapter 5) therefore investigated the effect of infection on the preferences of sticklebacks for a certain type of diet; (Artemia, bloodworm and Artificial diet). The results of this showed that S. solidus infection reduces the proportion of time spent in the Artemia zone. In addition, behavioural studies showed that sticklebacks tend to prefer bloodworm as their first choice of food. The third part of this thesis (Chapter 6) therefore investigates the effect of a dietary supplement – carotenoids on host-parasite interactions in sticklebacks. Carotenoids appeared to influence three-spined sticklebacks’ investment in splenosomatic index and haematocrit. Female reproductive investment was also influenced by these dietary supplements. S. solidus-infected sticklebacks showed a significant increase in their splenosomatic index. This research has demonstrated that the influence of factors such as variation in nutritional composition, level of feeding and additive nutrients in diet have a significant effect on the performance of both infected and non-infected fish in the study.