Data from: Parasite infection induces size-dependent host dispersal: consequences for parasite persistence

Host dispersal is now recognized as a key predictor of the landscape-level persistence and expansion of parasites. However, current theories treat post-infection dispersal propensities as a fixed trait, and the plastic nature of host’s responses to parasite infection has long been underappreciated. Here, we present a mark-recapture experiment in a single-host parasite system (larval parasites of the freshwater mussel Margaritifera laevis and its salmonid fish host Oncorhynchus masou masou) and provide the first empirical evidence that parasite infection induces size-dependent host dispersal in the field. In response to parasite infection, large fish become more dispersive, whereas small fish tend to stay at the home patch. The observed plasticity in dispersal is interpretable from the viewpoint of host fitness: expected benefits (release from further infection) may exceed dispersal-associated costs for individuals with high dispersal ability (i.e., large fish) but are marginal for individuals with limited dispersal ability (i.e., small fish). Indeed, our growth analysis revealed that only small fish hosts incurred dispersal costs (reduced growth). Strikingly, our simulation study revealed that this plastic dispersal response of infected hosts substantially enhanced parasite persistence and occupancy in a spatially structured system. These results suggest that dispersal plasticity in host species is critical for understanding how parasites emerge, spatially spread, and persist in nature. Our findings provide a novel starting point for building a reliable, predictive model for parasite/disease management.

宿主扩散现已被认为是预测寄生虫在景观尺度上存续与扩散的关键指标。然而，现有理论均将感染后的宿主扩散倾向视为固定性状，而宿主对寄生虫感染的响应所具有的可塑性本质长期以来未得到足够重视。本研究针对单宿主寄生虫系统（淡水蚌类Margaritifera laevis的幼虫寄生虫及其鲑科鱼类宿主Oncorhynchus masou masou）开展了标记重捕实验（mark-recapture experiment），并首次提供了野外实证证据，证明寄生虫感染会诱导宿主产生体型依赖型的扩散行为。受寄生虫感染后，体型较大的鱼类扩散意愿更强，而体型较小的鱼类则倾向于留在原栖息地斑块中。从宿主适合度的视角来看，本次观测到的扩散可塑性可以得到合理解释：对于扩散能力较强的个体（即体型较大的鱼类），其预期收益（免受再次感染）将超过扩散相关的成本；而对于扩散能力有限的个体（即体型较小的鱼类），该收益则微不足道。诚然，我们的生长分析结果显示，仅有小型鱼类宿主会承担扩散带来的成本（生长速率降低）。值得注意的是，我们的模拟研究表明，受感染宿主的这种可塑性扩散响应，可大幅提升寄生虫在空间结构化系统中的存续能力与占据范围。上述结果表明，宿主物种的扩散可塑性，对于理解寄生虫在自然环境中如何出现、空间扩散以及存续至关重要。本研究结果为构建用于寄生虫/疾病管理的可靠预测模型提供了全新的切入点。