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. 当前学界对统一天敌生态学研究框架的兴趣日益浓厚，这一研究取向揭示了捕食与寄生之间的诸多共性。与捕食作用相仿，寄生虫感染——甚至仅为感染威胁——均可改变宿主性状，并间接调控群落互作关系。尽管如此，目前鲜有研究同时兼顾天敌诱导行为改变的多重机制（如天敌接触前后的效应差异），以及驱动行为响应产生变异的影响因素。 2. 本研究首先在未直接接触两类天敌的前提下，评估了强毒性吸虫（trematode）里氏拟钉吸虫（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产生诱导防御反应方面的差异。随后，本研究又评估了成功感染宿主后，影响寄生虫诱导行为变化幅度的五项独立因素。 3. 在实验室与室外中宇宙（mesocosm）实验中，我们未发现两种蝌蚪——拟蝗蛙（Pseudacris regilla）与西部蟾蜍（Anaxyrus boreas）——会因未感染宿主螺、吸虫感染螺，或正处于感染过程中的同种个体释放的化学信号而改变其活动水平。与之形成鲜明对比的是，当面临由笼养蜻蜓幼虫带来的致命捕食风险时，蝌蚪会显著降低其活动强度。 4. 但在成功感染后，里氏拟钉吸虫（Ribeiroia ondatrae）会使宿主活动水平与逃逸距离显著下降，且该效应与感染强度呈正相关，与宿主体型及发育阶段呈负相关。在单次脉冲暴露感染后的第五天，宿主的活动水平便可恢复至接近正常状态；但每日接受同等强度慢性暴露的宿主，其活动水平则会持续下降。与里氏拟钉吸虫不同，另外两种毒性较弱的吸虫并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作用间的关键差异。天敌接触前的效应差异，可能源于与捕食作用不同的是，大型寄生虫（macroparasite）感染的后果取决于感染强度且难以预测。与之相反，感染后宿主行为的剧烈变化，就其对宿主适合度与群落互作的潜在影响而言，与非消耗性捕食效应（non-consumptive predator effects）更为相似。