Jones Jacob R, Steenrod Camille L, Marino John A
Biology Department, Bradley University, Peoria, IL, USA.
Department of Geography, University of Maryland, College Park, MD, USA.
Curr Zool. 2019 Dec;65(6):657-664. doi: 10.1093/cz/zoz004. Epub 2019 Feb 8.
Spatial distributions of animals can affect interactions with their natural enemies, such as parasites, and thus have important implications for host-parasite dynamics. While spatial variation in infection risk has been explored in many systems at the landscape scale, less attention has been paid to spatial structure at smaller scales. Here, we explore a hypothesized relationship between a common spatial variable, vertical position, and risk of parasite infection in a model aquatic system, larval frogs () and trematode (Digenea) parasites. Vertical position is relevant to this system given evidence that the densities of snail first intermediate hosts, tadpole second intermediate hosts, and trematode infective stages can vary with depth. To test the effects of depth on infection risk of larval frogs by trematodes, we performed two enclosure experiments, one in the laboratory and one in the field, in which larval frogs in cages just below the water surface or near the bottom of the water column were exposed to parasites. Compared with near-surface cages, mean infection load (number of cysts) in tadpoles in near-bottom cages was 83% higher after 48-h exposures in the laboratory and 730% higher after 10-day exposures in the field. Our findings thus indicate that infection risk depends on depth, which may have adaptive significance, as tadpoles have previously been shown to change vertical position in response to parasite presence. These results motivate future work examining vertical variation in infection risk and may have broader implications for host-parasite dynamics and evolution of host and parasite behavior.
动物的空间分布会影响它们与寄生虫等天敌的相互作用，因此对宿主 - 寄生虫动态具有重要意义。虽然在许多系统中已经在景观尺度上探讨了感染风险的空间变化，但在较小尺度上对空间结构的关注较少。在这里，我们在一个模型水生系统（幼蛙（ ）和吸虫（复殖目）寄生虫）中探索了一个常见空间变量——垂直位置与寄生虫感染风险之间的假设关系。鉴于有证据表明蜗牛第一中间宿主、蝌蚪第二中间宿主和吸虫感染阶段的密度会随深度变化，垂直位置与该系统相关。为了测试深度对幼蛙被吸虫感染风险的影响，我们进行了两个围隔实验，一个在实验室，一个在野外，将水面以下或水柱底部附近笼子里的幼蛙暴露于寄生虫中。与近水面笼子相比，在实验室中暴露48小时后，近底部笼子里蝌蚪的平均感染负荷（囊肿数量）高出83%，在野外暴露10天后高出730%。因此，我们的研究结果表明感染风险取决于深度，这可能具有适应性意义，因为之前已经证明蝌蚪会根据寄生虫的存在改变垂直位置。这些结果推动了未来研究感染风险垂直变化的工作，并且可能对宿主 - 寄生虫动态以及宿主和寄生虫行为的进化具有更广泛的意义。
