Data from: Host infection history modifies co-infection success of multiple parasite genotypes

1. Co-infections by multiple parasite genotypes are common and have important implications for host-parasite ecology and evolution through within-host interactions. Typically, these infections take place sequentially and therefore, the outcome of co-infection may be shaped by host immune responses triggered by previous infections. For example, in vertebrates specific immune responses play a central role in protection against disease over the course of life, but co-infection research has mostly focused on previously uninfected individuals. 2. Here, we investigated whether sequential exposure and activation of host resistance in rainbow trout Oncorhynchus mykiss affects infection success and interactions between co-infecting parasite genotypes of the trematode eye-fluke Diplostomum pseudospathaceum. 3. In accordance with earlier results, we show that a simultaneous attack of two parasite genotypes facilitates parasite establishment in previously uninfected hosts. However, we find for the first time that this facilitation in co-infection is lost in hosts with prior infection. 4. We conclude that vertebrate host infection history can affect the direction of within-host parasite interactions. Our results may have significant implications for the evolution of co-infections and parasite transmission strategies.

1. 多种寄生虫基因型的混合感染极为常见，且通过宿主内相互作用对宿主-寄生虫生态学与演化过程产生重要影响。通常这类感染多按序发生，因此混合感染的结局可能受先前感染触发的宿主免疫应答所调控。例如，在脊椎动物中，特异性免疫应答在终生抵御病害的过程中发挥核心作用，但现有混合感染研究大多聚焦于未曾感染过的个体。
2. 本研究以虹鳟（Oncorhynchus mykiss）为实验对象，探究宿主抗性的序贯暴露与激活，是否会影响共感染的眼吸虫（Diplostomum pseudospathaceum）各基因型的感染成功率及其相互作用。
3. 与既往研究结果一致，本研究证实两种寄生虫基因型的同时侵袭可促进未感染宿主的寄生虫定植。但本研究首次发现，在曾发生过感染的宿主中，这种混合感染的促进效应会消失。
4. 本研究得出结论：脊椎动物宿主的感染史可调控宿主内寄生虫相互作用的方向。本研究结果或对混合感染的演化以及寄生虫的传播策略研究产生重要意义。