Abstract
Parasitism is ubiquitous in the animal kingdom. Although many fundamental aspects of host-parasite relationships have been unravelled, few studies have systematically investigated how parasites affect organismal movement. Here we combine behavioural experiments of Schistocephalus solidus infected sticklebacks with individual-based simulations to understand how parasitism affects individual movement ability and thereby shapes social interaction patterns. High-resolution tracking revealed that infected fish swam, accelerated, and turned more slowly than did non-infected fish, and tended to be more predictable in their movements. Importantly, the strength of these effects increased with increasing parasite load (proportion of body weight), with more heavily infected fish showing larger changes and impairments in behaviour. When grouped, pairs of infected fish moved more slowly, were less cohesive, less aligned, and less temporally coordinated than non-infected pairs, and mixed pairs were primarily led by the non-infected fish. These social patterns also emerged in simulations of self-organised groups composed of individuals differing similarly in speed and turning tendency, suggesting infection-induced changes in mobility and manoeuvrability may drive collective outcomes. Together, our results demonstrate how infection with a complex life-cycle parasite affects the movement ability of individuals and how this in turn shapes social interaction patterns, providing important mechanistic insights into the effects of parasites on host movement dynamics.
Highlights
Parasitism is ubiquitous in the animal kingdom
Few studies have systematically investigated the mechanistic basis of such potential behavioural m odifications[2,5] or considered the repercussions this may have for social interactions and collective outcomes via self-organising effects[6,7]
We systematically studied the fine-scale movements of individuals and pairs of sticklebacks with different levels of S. solidus infection to get a better understanding of how parasite infection alters host movement dynamics and how that in turn may influence social interaction patterns
Summary
Parasitism is ubiquitous in the animal kingdom. many fundamental aspects of host-parasite relationships have been unravelled, few studies have systematically investigated how parasites affect organismal movement. Pairs of infected fish moved more slowly, were less cohesive, less aligned, and less temporally coordinated than non-infected pairs, and mixed pairs were primarily led by the non-infected fish These social patterns emerged in simulations of self-organised groups composed of individuals differing in speed and turning tendency, suggesting infection-induced changes in mobility and manoeuvrability may drive collective outcomes. Forced swimming tests revealed that infected fish tend to have reduced maximum swim speeds and e ndurance[13,29,30], and exhibit increasingly high metabolic costs when forced to move at greater speeds[12,13,14] It remains unclear if the parasite may impair turning mobility and how these constraints influence individual movement decisions
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