Pathogenic fungus causes density‐ and trait‐mediated trophic cascades in an aquatic community
Pathogenic fungus causes density‐ and trait‐mediated trophic cascades in an aquatic community
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DOI：
10.1002/ecs2.4043
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发表时间：
2022-04
期刊：
影响因子：
2.7
通讯作者：
Carmen C. Harjoe;J. Buck;Jason Rohr;Claire E. Roberts;D. Olson;A. Blaustein
中科院分区：
文献类型：
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作者：
Carmen C. Harjoe;J. Buck;Jason Rohr;Claire E. Roberts;D. Olson;A. Blaustein
病原体可以通过对群落造成直接和间接的影响来改变物种组成和生态系统功能。菊科真菌巴氏杆菌(Batrachochytrium Dendrobatidis，以下简称Bd)是一种与世界范围内两栖动物数量减少有关的病原体，其游动孢子可被滤食性浮游动物吞噬，并可损害受感染的两栖类幼虫的口器。因此，我们推测这种病原体会影响浮游动物的丰度以及两栖类幼虫的生存和取食能力。反过来，这可能会影响浮游动物和蝌蚪的藻类食物资源，其中可能包括浮游植物和附生植物。我们通过控制室外中胚层中西方蟾蜍(Anaxyus Boreas)幼虫和Bd的存在，并量化两栖动物、浮游动物、浮游植物和附生植物的密度来检验这些假设。BD感染降低了两栖类幼虫的密度，但这只对附生生物有微弱的好处(一种密度中介的间接影响)。在控制幼虫密度后，有Bd暴露幼虫的围生生物量显著高于有幼虫但没有Bd的围生生物量，这与感染诱导的口器损伤降低幼虫对附着藻类的摄食率(一种性状介导的间接效应)一致。事实上，Bd对附生植物生物量的估计性状中介效应大于密度中介效应。然而，我们没有发现证据表明Bd暴露引发了向滤食性浮游植物的转变。Bd的存在与桡足类丰度的增加有关，这与浮游动物消耗壶类游动孢子的情况一致。这些结果表明，Bd有可能引起特征和密度中介的间接影响，从而改变淡水生态系统的群落组成，甚至可能改变初级生产力。
Pathogens can alter species composition and ecosystem function by causing direct and indirect effects on communities. Zoospores of the chytrid fungusBatrachochytrium dendrobatidis(hereafter, Bd), a pathogen implicated in worldwide amphibian declines, can be consumed by filter‐feeding zooplankton and can damage mouthparts of infected amphibian larvae. Consequently, we hypothesized that this pathogen would affect the abundance of zooplankton and survival and feeding abilities of larval amphibian hosts. In turn, this could affect the algal food resources of zooplankton and tadpoles, which can include phytoplankton and periphyton. We tested these hypotheses by manipulating the presence of western toad (Anaxyrus boreas) larvae and Bd in outdoor mesocosms and quantifying the densities of amphibians, zooplankton, phytoplankton, and periphyton. Bd infections reduced amphibian larval densities, but this only weakly benefitted periphyton (a density‐mediated indirect effect). After controlling for larval densities, mesocosms with Bd‐exposed larvae had significantly more periphyton biomass than mesocosms with larvae but no Bd, consistent with infection‐induced mouthpart damage reducing larval feeding rates on attached algae (a trait‐mediated indirect effect). In fact, the estimated trait‐mediated effect of Bd on periphyton biomass was larger than the density‐mediated effect. However, we did not find evidence that Bd exposure triggered a switch to filter‐feeding phytoplankton. The presence of Bd was associated with increased copepod abundance, consistent with zooplankton consuming chytrid zoospores. These results suggest that Bd has the potential to cause both trait‐ and density‐mediated indirect effects that can alter community composition and perhaps the primary productivity of freshwater ecosystems.