Data from: Natural enemy ecology: comparing the effects of predation risk, infection risk and disease on host behavior

1. Growing interest in unifying the field of natural enemy ecology has revealed similarities between predation and parasitism. In parallel with predation, parasite infection – and even the threat of infection – can alter host traits and indirectly affect community interactions. Nonetheless, few studies have considered multiple mechanisms of natural enemy-induced behavioural alteration in parallel (e.g. effects before and after enemy contact) or the factors that drive variation in behavioural responses. 2. We first evaluated how the threat of infection by a virulent trematode (Ribeiroia ondatrae) compared to the well studied risk of predation in triggering inducible defences in amphibian hosts, prior to direct contact with either enemy. We then evaluated five separate factors that influenced the magnitude of parasite-induced behavioural changes after successful transmission. 3. In both the laboratory and an outdoor mesocosm experiment, we found no evidence that tadpoles of two species (Pseudacris regilla and Anaxyrus boreas) altered their activity levels in response to chemical cues from uninfected host snails, trematode-infected snails, or from conspecifics actively becoming infected. In contrast, tadpoles sharply reduced their activity in response to lethal predation risks posed by caged dragonfly larvae. 4. After infection, however, Ribeiroia caused strong decreases in host activity and escape distance that correlated positively with infection intensity and negatively with host size and developmental stage. Five days after infection with a one-time pulse exposure, hosts recovered to near-normal activity levels. Hosts exposed to a chronic daily exposure of equal intensity, however, continued to decrease activity. Unlike Ribeiroia, two less virulent trematodes had no detectable effects on host behaviour. 5. Our results highlight key distinctions between predation and parasitism. The contrasting effects prior to enemy contact may stem from the fact that unlike predation, the consequences of macroparasite infection are intensity-dependent and unpredictable. In contrast, the strong changes in host behaviour after infection are more similar to non-consumptive predator effects in terms of their potential influences on host fitness and community interactions.

1. 学界对统一天敌生态学（natural enemy ecology）研究范畴的兴趣日益浓厚，这一趋势揭示了捕食（predation）与寄生（parasitism）之间存在诸多共性。与捕食类似，寄生虫感染——乃至感染威胁——均可改变宿主性状（host traits），并间接影响群落互作（community interactions）。然而，鲜有研究同时考虑天敌诱导的行为改变的多种机制（例如天敌接触前后的效应），或是探究驱动行为响应变异的相关因素。
2. 本研究首先在未直接接触任何天敌的前提下，评估了强毒力吸虫（trematode）瑞氏吸虫（Ribeiroia ondatrae）的感染威胁，与已被广泛研究的捕食风险，在触发两栖动物宿主（amphibian hosts）诱导型防御（inducible defences）方面的差异。随后，本研究评估了成功传播（transmission）后，影响寄生虫诱导的行为变化幅度的5个独立因素。
3. 在实验室及野外中型实验生态系统（mesocosm）实验中，我们未观测到两种蝌蚪（Pseudacris regilla与Anaxyrus boreas）的活动水平因暴露于未感染宿主螺、感染吸虫的螺，或是正发生感染的同种个体（conspecifics）的化学信号（chemical cues）而发生改变。与之形成鲜明对比的是，当暴露于笼养蜻蜓幼虫构成的致死捕食风险时，蝌蚪的活动水平显著降低。
4. 然而，感染发生后，瑞氏吸虫会导致宿主活动水平与逃逸距离显著下降，且该效应与感染强度（infection intensity）呈正相关，与宿主体型及发育阶段（developmental stage）呈负相关。在一次性脉冲暴露（pulse exposure）感染后的第5天，宿主的活动水平恢复至接近正常状态。但暴露于同等强度的每日慢性暴露（chronic daily exposure）的宿主，其活动水平仍持续下降。与瑞氏吸虫不同，另外两种低毒力吸虫未对宿主行为产生可检测到的影响。
5. 本研究结果凸显了捕食与寄生之间的关键差异。天敌接触前的效应差异可能源于以下事实：与捕食不同，大型寄生虫（macroparasite）感染的后果依赖于感染强度且难以预测。与之相对，感染后宿主行为的剧烈变化，在其对宿主适合度（host fitness）与群落互作的潜在影响方面，与非消耗性捕食效应（non-consumptive predator effects）更为相似。