Abstract
Parasites can induce behavioural changes in their host organisms. Several parasite species are known to infect bumblebees, an important group of pollinators. Task allocation within bumblebee colonies can also cause differences in behaviour. Thus, task allocation may lead to context-dependent impacts of parasites on host behaviour. This study uses Bombus terrestris and its gut trypanosome Crithidia bombi, to investigate the effects of parasitism, task allocation (foraging or nest-work) and their interactions, on olfactory learning. Prior to undergoing the olfactory learning task, bees were orally infected with a field-realistic dose of C. bombi, and observed to determine task allocation. Parasitism did not significantly affect olfactory learning, but task allocation did, with foragers being significantly more likely to learn than nest bees. There was no significant interaction between parasitism and task. These results suggest that C. bombi is unlikely to affect pollination services via changes in olfactory learning of its host if bees are under no environmental or nutritional stress. However, wild and commercial colonies are likely to face such stressors. Future studies in the field are needed to extrapolate our results to real world effects.
Highlights
Parasites are highly prevalent in ecosystems with approximately 50% of all animal species thought to be parasitic[1,2]
Context is key for understanding parasite impacts on host behaviour, and as C. bombi displays context-dependent virulence, with virulence increasing during periods of food stress or during energetically demanding stages of the host’s life cycle[30,31], behavioural impacts may be modified by host context
Infection with the parasite C. bombi had no significant effect on the olfactory learning ability of B. terrestris
Summary
Parasites are highly prevalent in ecosystems with approximately 50% of all animal species thought to be parasitic[1,2]. One way that parasites can impact hosts is through behavioural alteration[3,4,5] Such parasite-induced behavioural changes may be manipulative and enhance the fitness or transmission of the parasite, but they can be non-manipulative, benefitting host rather than parasite fitness[5]. Understanding such manipulations is increasingly important, as parasites have been implicated in population declines of numerous taxa[6,7,8,9]. Trade-offs with immunocompetence, could be sufficient for context-dependent behavioural impacts to be induced by the parasite
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