Data from: Spatial heterogeneity lowers rather than increases host-parasite specialization

Abiotic environmental heterogeneity can promote the evolution of diverse resource specialists, which in turn may increase the degree of host-parasite specialization. We coevolved Pseudomonas fluorescens and lytic phage ϕ2 in spatially structured populations, each consisting of two interconnected subpopulations evolving in the same or different nutrient media (homogeneous and heterogeneous environments, respectively). Counter to the normal expectation, host-parasite specialization was significantly lower in heterogeneous compared with homogeneous environments. This result could not be explained by dispersal homogenizing populations, as this would have resulted in the heterogeneous treatments having levels of specialization equal to or greater than that of the homogeneous environments. We argue that selection for costly generalists is greatest when the coevolving species are exposed to diverse environmental conditions and that this can provide an explanation for our results. A simple coevolutionary model of this process suggests that this can be a general mechanism by which environmental heterogeneity can reduce rather than increase host-parasite specialization.

非生物环境异质性可促进多样资源特化类群的演化，进而可能提升宿主-寄生虫的特化水平。我们在空间结构化种群中开展了荧光假单胞菌（Pseudomonas fluorescens）与裂解性噬菌体ϕ2的共演化实验：该种群包含两个相互连通的亚种群，分别在相同（同质环境）或不同（异质环境）营养培养基中演化。与学界常规预期相悖，异质环境中的宿主-寄生虫特化程度显著低于同质环境。该结果无法通过“扩散导致种群同质化”这一机制解释——若该机制成立，异质处理组的特化水平应等于或高于同质处理组。我们提出，当共演化物种处于多样环境条件下时，对需付出适应代价的泛化型类群的选择压力最强，这一机制可解释本实验的观测结果。针对该过程构建的简单共演化模型表明，环境异质性可通过这一通用机制降低而非提升宿主-寄生虫的特化程度。