Discussion

While parasitic relationships are globally ubiquitous, the impact of parasitic infection, particularly in the light of a warming climate, is only now becoming clear. Warming temperature is likely to influence host-parasite relationships, especially in cases where parasites are known to modify the behaviour of their hosts. We explore whether parasitism and warming interact to modify energy flow in ecosystems by comparing individual energy budgets of the gammerid amphipod Gammarus duebeni infected with the acanthocephalan parasite Polymorphus minutus with those of uninfected individuals across a broad range of ecologically relevant temperatures. By combining individual energy budgets with experiments on behavioural manipulation across the same temperature range, we see a clear pattern where temperature moderates individual physiology, infection status influences feeding preferences, and both parasitism and temperature modify anti-predator behaviour. These findings highlight the importance of the non-trophic effects of parasites in modifying energy flow through ecosystems and affirm the need for experimental and field studies of the impact of temperature in a warming world.