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.

针对捕食压力的常见进化响应，是提升繁殖投入，最终形成快速型生活史。理论与比较研究均表明，短寿命生物对寄生虫的防御投入低于长寿命生物（即生活史速率假说）。结合这些进化理论的核心论点，可推导出一项尚未被验证的具体预测：在同一物种种群内，遭遇更高捕食压力的种群，其对寄生虫的防御投入更低。
特立尼达孔雀鱼（*Poecilia reticulata*）为验证该预测提供了绝佳研究模型：相较于河流上游种群，河流下游的孔雀鱼种群面临更高的捕食压力，因此演化出更快的生活史。
一项大规模野外调查的数据显示，感染三代虫属（*Gyrodactylus*）寄生虫的个体，其身体状况（通过标度质量指数量化）低于未感染个体，但该现象仅存在于下游种群中。尽管本研究提供的证据为相关性数据，但结果表明上游种群的孔雀鱼相较于下游种群，其感染后的适合度代价更低，即耐受性更强。
因此本研究数据与寄生虫防御分配的生活史速率假说一致，并暗示生活史性状可介导捕食者对猎物寄生虫的间接调控效应。