Chytridiomycosis causes high amphibian mortality prior to the completion of metamorphosis,Environmental Research

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Chytridiomycosis causes high amphibian mortality prior to the completion of metamorphosis
Environmental Research ( IF 7.7 ) Pub Date : 2024-01-18 , DOI: 10.1016/j.envres.2024.118249
Josephine E Humphries ₁ , Chantal M Lanctôt ₂ , Hamish I McCallum ₃ , David A Newell ₄ , Laura F Grogan ₁

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Amphibian populations are undergoing extensive declines globally. The fungal disease chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), is a primary contributor to these declines. The amphibian metamorphic stages (Gosner stages 42–46) are particularly vulnerable to a range of stressors, including Bd. Despite this, studies that explicitly examine host response to chytridiomycosis throughout the metamorphic stages are lacking. We aimed to determine how Bd exposure during the larval stages impacts metamorphic development and infection progression in the endangered Fleay's barred frog (Mixophyes fleayi). We exposed M. fleayi to Bd during pro-metamorphosis (Gosner stages 35–38) and monitored infection dynamics throughout metamorphosis. We took weekly morphological measurements (weight, total body length, snout-vent-length and Gosner stage) and quantified Bd load using qPCR. While we observed minimal impact of Bd infection on animal growth and development, Bd load varied throughout ontogeny, with an infection load plateau during the tadpole stages (Gosner stages 35–41) and temporary infection clearance at Gosner stage 42. Bd load increased exponentially between Gosner stages 42 and 45, with most exposed animals becoming moribund at Gosner stage 45, prior to the completion of metamorphosis. There was variability in infection outcome of exposed individuals, with a subgroup of animals (n = 5/29) apparently clearing their infection while the majority (n = 21/29) became moribund with high infection burdens. This study demonstrates the role that metamorphic restructuring plays in shaping Bd infection dynamics and raises the concern that substantial Bd-associated mortality could be overlooked in the field due to the often cryptic nature of these latter metamorphic stages. We recommend future studies that directly examine the host immune response to Bd infection throughout metamorphosis, incorporating histological and molecular methods to elucidate the mechanisms responsible for the observed trends.

中文翻译：

乳糜菌病在完成之前导致两栖动物的高死亡率

全球两栖动物种群数量正在大幅下降。由病原真菌 Batrachochytrium dendrobatidis （Bd）引起的真菌病乳糜菌病是导致这些下降的主要原因。两栖动物阶段（Gosner 阶段 42-46）特别容易受到一系列压力源的影响，包括 Bd。尽管如此，缺乏明确检查宿主在整个阶段对壶菌病反应的研究。我们旨在确定幼虫阶段的 Bd 暴露如何影响濒临灭绝的 Fleay's barred frog （Mixophyes fleayi）的发育和感染进展。我们在促（Gosner 阶段 35-38）期间将 M. fleayi 暴露于 Bd 并监测整个过程中的感染动态。我们每周进行形态学测量（体重、体长、吻孔长度和 Gosner 分期）并使用 qPCR 量化 Bd 负荷。虽然我们观察到 Bd 感染对动物生长和发育的影响最小，但 Bd 负荷在整个个体发育过程中各不相同，在蝌蚪阶段（Gosner 阶段 35-41）处于感染负荷平台期，在 Gosner 阶段 42 期处于暂时感染清除状态。Bd 载量在 Gosner 第 42 期和第 45 期之间呈指数级增加，大多数暴露的动物在完成之前在 Gosner 第 45 阶段垂死。暴露个体的感染结果存在差异，动物亚群（n = 5/29）显然清除了感染，而大多数动物（n = 21/29）因感染负担高而垂死。这项研究证明了重组在塑造 Bd 感染动力学中的作用，并引起了人们的担忧，即由于这些后期阶段通常具有神秘的性质，因此在该领域可能会忽视大量与 Bd 相关的死亡率。我们建议未来的研究直接检查宿主在整个过程中对 Bd 感染的免疫反应，结合组织学和分子学方法来阐明导致观察到的趋势的机制。

更新日期：2024-01-18

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