Wilson Emily A, Briggs Cheryl J, Dudley Tom L
Marine Science Institute, University of California Santa Barbara, Santa Barbara, California, United States of America.
Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
PLoS One. 2018 Feb 14;13(2):e0191537. doi: 10.1371/journal.pone.0191537. eCollection 2018.
Amphibian species are experiencing population declines due to infection by the fungal pathogen, Batrachochytrium dendrobatidis (Bd). The African clawed frog (Xenopus laevis), an asymptomatic carrier of Bd, has been implicated in the spread of this pathogen through global trade and established invasive populations on several continents. However, research has not explored the relationships of both life stages of this amphibian with Bd. While the post-metamorphic individuals may act as a reservoir, spreading the infection to susceptible species, the filter-feeding larvae may consume the motile Bd zoospores from the water column, potentially reducing pathogen abundance and thus the likelihood of infection. We explore these contrasting processes by assessing Bd prevalence and infection intensities in field populations of post-metamorphic individuals, and performing laboratory experiments to determine if larval X. laevis preyed upon Bd zoospores. The water flea, Daphnia magna, was included in the Bd consumption trials to compare consumption rates and to explore whether intraguild predation between the larval X. laevis and Daphnia may occur, potentially interfering with control of Bd zoospores by Daphnia. Field surveys of three X. laevis populations in southern California, in which 70 post-metamorphic individuals were tested for Bd, found 10% infection prevalence. All infected individuals had very low infection loads (all Bd loads were below 5 zoospore equivalents). Laboratory experiments found that larval X. laevis consume Bd zoospores and therefore may reduce Bd abundance and transmission between amphibians. However, metamorphic and juvenile X. laevis exhibited intraguild predation by consuming Daphnia, which also prey upon Bd zoospores. The results suggest that X laevis is not a large reservoir for Bd and its larval stage may offer some reduction of Bd transmission through direct predation.
两栖动物物种正由于感染真菌病原体——蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）而面临种群数量下降的问题。非洲爪蟾（Xenopus laevis）是Bd的无症状携带者，这种病原体通过全球贸易扩散，并在几大洲建立了入侵种群。然而，此前的研究尚未探究这种两栖动物的两个生活阶段与Bd之间的关系。虽然变态后的个体可能充当病原体储存库，将感染传播给易感物种，但滤食性幼虫可能会摄食水柱中的游动性Bd游动孢子，从而有可能降低病原体数量，进而减少感染的可能性。我们通过评估变态后个体野外种群中的Bd流行率和感染强度，并开展实验室实验以确定非洲爪蟾幼虫是否会捕食Bd游动孢子，来探究这些相反的过程。水蚤（大型溞，Daphnia magna）被纳入Bd摄食试验，以比较摄食率，并探究非洲爪蟾幼虫与大型溞之间是否可能发生集团内捕食，这可能会干扰大型溞对Bd游动孢子的控制。对南加州三个非洲爪蟾种群进行的野外调查中，检测了70只变态后的个体是否感染Bd，结果发现感染率为10%。所有受感染个体的感染负荷都非常低（所有Bd负荷均低于5个游动孢子当量）。实验室实验发现，非洲爪蟾幼虫会摄食Bd游动孢子，因此可能会降低Bd数量以及两栖动物之间的传播。然而，变态期和幼年非洲爪蟾会通过捕食大型溞表现出集团内捕食行为，而大型溞也会捕食Bd游动孢子。结果表明，非洲爪蟾不是Bd的大型储存库，其幼虫阶段可能会通过直接捕食在一定程度上减少Bd传播。
