Data from: Parasite genetic distance and local adaptation in coevolving bacteria-bacteriophage populations

Antagonistic coevolution between hosts and parasites can lead to local adaptation (LA), such that parasite fitness is greatest in sympatric hosts (or vice versa). The magnitude of LA typically increases with geographic distance, which is assumed to be because genetic (and hence phenotypic) distance increases with geographic distance. Here we explicitly test the relationships between parasite genetic and phenotypic distance and LA using isolates of coevolved viral parasites (lytic bacteriophage ϕ2) and the host bacterium Pseudomonas fluorescens SBW25. We find positive relationships between parasite genotype and infectivity phenotype, but the strength of the relationship was greater when infectivity was defined by the identity of hosts that could be infected rather than the actual number of hosts infected (host range), and when measurements were compared within rather than among populations. Crucially, we find a monotonic relationship between LA and genetic distance across phage isolates from different populations, although in contrast to many geographic studies, parasite LA decreased with genetic distance. These results can be explained by the fact that bacteria can rapidly adapt to phage infectivity mutations, but that evolved resistance has a degree of specificity to the local phage population. Our results show that antagonistic coevolution alone can result in predictable links between genetic distance and host-parasite local adaptation.宿主与寄生物间的拮抗共进化（antagonistic coevolution）可引发局部适应（local adaptation，LA），使得寄生物在同域宿主中的适合度达到最高（反之亦然）。局部适应的强度通常随地理距离增加而升高，这一现象被认为源于遗传（进而表型）距离随地理距离增大而增加。本研究针对共进化的病毒寄生物——裂解性噬菌体ϕ2（lytic bacteriophage ϕ2）及其宿主荧光假单胞菌（Pseudomonas fluorescens）SBW25的分离株，首次直接检验了寄生物遗传距离、表型距离与局部适应之间的关系。我们发现寄生物基因型与侵染表型间存在正相关关系，且当侵染性以可被侵染的宿主种类而非实际侵染宿主数量（即宿主范围）定义时，以及在种群内部而非种群间进行比较时，该关联的强度更高。至关重要的是，我们在来自不同种群的噬菌体分离株中观察到局部适应与遗传距离间存在单调关系，但与诸多地理相关研究形成反差的是，寄生物的局部适应程度随遗传距离增大而降低。上述结果可通过以下事实解释：细菌可快速适应噬菌体的侵染性突变，但演化出的抗性对当地噬菌体种群具有一定特异性。本研究结果表明，仅靠拮抗共进化即可在遗传距离与宿主-寄生物局部适应之间建立可预测的关联。