Taxa-specific activity loss and mortality patterns in freshwater trematode cercariae under subarctic conditions

A series of laboratory experiments simulating natural subarctic conditions in warmer and colder months (two temperature scenarios, 6 and 13 °C) were conducted to characterise cercarial activity and survival of three trematode genera, represented by four taxa (Diplostomum spp., Apatemon spp., small- and large-sized Plagiorchis spp. that differ in terms of morphology, life history and transmission strategy) parasitizing a freshwater snail species, the lymnaeid Radix balthica. A statistical approach, where activity loss and mortality of cercariae are analyzed as a proxy for activity and survival, was used. The aims of this study were 1) to quantify the effect of the two temperature scenarios on cercarial activity loss and mortality in the different trematode taxa, and 2) to compare cercarial activity loss and mortality among the four trematode taxa and to relate them to specific morphology and behaviour of the cercariae. A strong temperature-dependent response was identified in both activity loss and mortality in all taxa, with Diplostomum spp. cercariae showing the most gradual changes compared to other taxa. Furthermore, whilst activity loss and mortality dynamics could not be divided into “fish- vs invertebrate-infecting cercariae” groups, the detected taxa-specific responses in relation to life-history traits likely indicate the swimming behaviour of cercariae and energy allocation among larvae individuals as the main drivers.

本研究开展了一系列实验室模拟实验，以模拟亚寒带冷暖季的自然环境，设置6℃与13℃两种温度情景，旨在表征三种吸虫（Trematode）属尾蚴（Cercaria）的活动能力与存活状态。实验涉及四个类群，对应三个吸虫属：双穴吸虫属（Diplostomum spp.）、阿帕特吸虫属（Apatemon spp.），以及形态、生活史与传播策略存在差异的小型和大型斜睾吸虫属（Plagiorchis spp.），所有类群均寄生于淡水螺物种巴氏萝卜螺（Radix balthica，椎实螺科）。本研究采用统计学分析方法，以尾蚴的活动衰减率与死亡率作为活动能力与存活状态的替代指标开展分析。本研究的目标为：1）量化两种温度情景对不同吸虫类群尾蚴活动衰减率与死亡率的影响；2）比较四种吸虫类群尾蚴的活动衰减率与死亡率，并将其与尾蚴的特异性形态与行为特征相关联。研究结果显示，所有类群的活动衰减与死亡率均表现出显著的温度依赖性响应，其中双穴吸虫属尾蚴的变化过程相较于其他类群最为平缓。此外，尽管无法将尾蚴的活动衰减与死亡率动态划分为‘感染鱼类’与‘感染无脊椎动物’两类群，但本研究观测到的与生活史特征相关的类群特异性响应，或可表明尾蚴的游泳行为以及幼虫个体间的能量分配是调控其活动与存活的主要驱动因素。