Data from: Two different strategies of host manipulation allow parasites to persist in intermediate-definitive host systems

Trophically-transmitted parasites start their development in an intermediate host, before they finish the development in their definitive host when the definitive host preys on the intermediate host. In intermediate-definitive host systems, two strategies of host manipulation have been evolved: increasing the rate of transmission to the definitive host by increasing the chance that the definitive host will prey on the intermediate host, or increasing the lifespan of the parasite in the intermediate host by decreasing the predation chance when the intermediate host is not yet infectious. As the second strategy is less well studied than the first, it is unknown under what conditions each of these strategies are prevailed and evolved. We analysed the effect of both strategies on the presence of parasites in intermediate-definitive host systems with a structured population model. We show that the parasite can increase the parameter space where it can persist in the intermediate-definitive host system by using one of these two strategies of host manipulation. We found that when the intermediate host or the definitive host have life-history traits that allow the definitive host to reach large population densities, i.e. high reproduction rate of the intermediate host or high conversion efficiency of the definitive host (efficiency at which the uninfected definitive host converts caught intermediate hosts into offspring) respectively, evolving manipulation to decrease the predation chance of the intermediate host will be more beneficial than manipulation to increase the predation chance to enhance transmission. Furthermore, manipulation to decrease the predation chance of the intermediate host results in higher population densities of infected intermediate hosts than manipulation that increases the predation chance to enhance transmission. Our study shows that host manipulation in early stages of the parasite development to decrease predation might be a more frequently evolved way of host manipulation than is currently assumed.营养传播寄生虫（trophically-transmitted parasites）的发育起始于中间宿主（intermediate host），直至终宿主（definitive host）捕食中间宿主后，才在终宿主体内完成发育。在中间-终宿主系统中，寄生虫已演化出两类宿主操纵（host manipulation）策略：其一为通过提升终宿主捕食中间宿主的概率，加快向终宿主的传播速率；其二则是在中间宿主尚未具备感染性时，降低其被捕食的概率，以此延长寄生虫在中间宿主体内的存活时长。相较于第一类策略，第二类策略的研究关注度相对不足，目前学界仍不清楚在何种条件下这两类策略会占据演化优势并得以固定。我们借助结构化种群模型（structured population model），分析了这两类策略对中间-终宿主系统中寄生虫存续情况的影响。研究表明，寄生虫可通过采用上述任意一类宿主操纵策略，拓展其在该系统中得以存续的参数空间。我们发现，当中宿主或终宿主具备能让终宿主达到高种群密度的生活史特征（life-history traits）时——即中宿主具有高繁殖率，或终宿主具有高转化效率（conversion efficiency，即未感染的终宿主将捕获的中宿主转化为自身后代的效率）——选择操纵策略以降低中间宿主的被捕食概率，相比通过提升捕食概率来增强传播的策略，更具演化优势。此外，相较于通过提升捕食概率以强化传播的宿主操纵策略，降低中间宿主被捕食概率的操纵策略，会使受感染中间宿主的种群密度更高。本研究显示，在寄生虫发育早期阶段通过操纵宿主降低被捕食风险的策略，或许是比当前学界普遍认知中更为常见的宿主操纵演化路径。