Data from: Pace of life, predators and parasites: predator-induced life history evolution in Trinidadian guppies predicts decrease in parasite tolerance

A common evolutionary response to predation pressure is increased investment in reproduction, ultimately resulting in a fast life history. Theory and comparative studies suggest that short-lived organisms invest less in defence against parasites than those that are longer lived (the pace of life hypothesis). Combining these tenets of evolutionary theory leads to the specific, untested prediction that within species, populations experiencing higher predation pressure invest less in defence against parasites. The Trinidadian guppy, Poecilia reticulata, presents an excellent opportunity to test this prediction: guppy populations in lower courses of rivers experience higher predation pressure, and as a consequence have evolved faster life histories, than those in upper courses. Data from a large-scale field survey showed that fish infected with Gyrodactylus parasites were of a lower body condition (quantified using the scaled mass index) than uninfected fish, but only in lower course populations. Although the evidence we present is correlational, it suggests that upper course guppies sustain lower fitness costs of infection, i.e. are more tolerant, than lower course guppies. The data are therefore consistent with the pace of life hypothesis of parasite defence allocation, and suggest that life-history traits mediate the indirect effect of predators on the parasites of their prey.

面对捕食压力，生物常见的演化应对策略为提升繁殖投入，最终形成快速生活史（fast life history）。演化理论与比较研究表明，短命生物相较于长命生物，在寄生虫防御上的投入更少，这一结论即生活节奏假说（pace of life hypothesis）。整合上述演化理论原则，可推导出一个尚未经检验的具体预测：在同一物种内，面临更高捕食压力的种群，其寄生虫防御投入更低。特立尼达孔雀鱼（Poecilia reticulata）为验证该预测提供了绝佳实验模型：相较于河流上游的种群，下游孔雀鱼种群面临的捕食压力更高，因此演化出了更快的生活史。大规模野外调查数据显示，感染三代虫（Gyrodactylus）的个体，其身体状况（通过尺度质量指数（scaled mass index）量化）较未感染个体更差，但该现象仅存在于下游种群中。尽管本研究提供的证据仅为相关性证据，但结果表明，上游种群的孔雀鱼相较于下游种群，感染寄生虫后的适合度成本更低，即对寄生虫的耐受性更强。因此，本研究数据与寄生虫防御分配的生活节奏假说一致，同时表明生活史特征可介导捕食者对猎物寄生虫的间接影响。