Aquatic Ecology Group, The David Attenborough Building, Department of Zoology, University of Cambridge, CambridgeCB2 3QZ, UK.
Parasitology. 2020 Oct;147(12):1375-1380. doi: 10.1017/S0031182020001213. Epub 2020 Jul 30.
Parasitic castration of bivalves by trematodes is common, and may significantly reduce the reproductive capacity of ecologically important species. Understanding the intensity of infection is desirable, as it can indicate the time that has passed since infection, and influence the host's physiological and reproductive response. In addition, it is useful to know the developmental stage of the trematode, to understand trematode population trends and reproductive success. However, most existing methods (e.g. visually estimating the degree of infection) to assess intensity are approximate only and not reproducible. Here, we present a method to accurately quantify the percentage of bivalve gonad filled with digenean trematode tissue, based on small squashes of gonad tissue rapidly photographed under light microscopy. A maximum of 15 photographs is required to determine the percentage of the whole gonad occupied by trematodes with a minimum of 90% confidence, with smaller mussels requiring fewer. In addition, the stage of trematode infection can be assessed because full sporocysts, spent sporocysts and free cercariae are clearly distinguishable. Although variation exists in the distribution of trematodes in gonad tissue, and thus in the estimate of percentage of the gonad filled with trematodes, this method represents a marked improvement on current coarse assessments of infection which typically focus on binary presence/absence measures. This technique can be used to facilitate a more sophisticated understanding of host-parasite interactions in bivalves, and can inform the conservation and reproductive biology of environmentally crucial species.
双壳类寄生虫的寄生性阉割很常见，可能会显著降低生态重要物种的繁殖能力。了解感染的严重程度是很有必要的，因为它可以指示感染发生的时间，并影响宿主的生理和生殖反应。此外，了解吸虫的发育阶段有助于了解吸虫种群的趋势和繁殖成功。然而，大多数现有的评估感染严重程度的方法（例如，通过目测估计感染程度）只是近似的，并且不可重复。在这里，我们提出了一种基于光镜下快速拍摄的性腺组织小压片来准确量化双壳类动物性腺中被吸虫组织占据的百分比的方法。为了确定 90%置信度下整个性腺中被吸虫占据的百分比，最多需要拍摄 15 张照片，对于较小的贻贝，则需要的照片更少。此外，还可以评估吸虫感染的阶段，因为完整的孢子囊、已耗尽的孢子囊和游离的尾蚴可以清晰区分。尽管吸虫在性腺组织中的分布存在变异，因此在估计被吸虫占据的性腺百分比时存在差异，但与当前通常侧重于二元存在/不存在措施的粗略评估相比，这种方法是一个显著的改进。该技术可用于更深入地了解双壳类动物中的宿主-寄生虫相互作用，并为具有重要环境意义的物种的保护和生殖生物学提供信息。
