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，生物体常见的演化响应是提升繁殖投入，最终形成快速生活史（fast life history）。理论研究与比较分析均表明，短寿命生物体对寄生虫的防御投入低于长寿命生物体，即生活史速率假说（pace of life hypothesis）。结合演化理论的这些核心论点，可以推导出一个尚未被验证的具体预测：在同一物种内，承受更高捕食压力的种群，其寄生虫防御投入更低。特立尼达孔雀花鳉（Poecilia reticulata）为验证这一预测提供了绝佳的研究体系：河流下游种群的捕食压力高于上游种群，因此前者演化出了更快的生活史。大规模野外调查数据显示，感染三代虫属（Gyrodactylus）寄生虫的个体，其身体状况（通过标度质量指数量化）较未感染个体更差，但这一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花鳉感染后的适合度代价更低，即相较于下游种群，上游个体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史速率假说一致，并表明生活史性状介导了捕食者对猎物寄生虫的间接影响。