Poullain Virginie, Gandon Sylvain, Brockhurst Michael A, Buckling Angus, Hochberg Michael E
Institut des Sciences de l'Evolution (UM2-CNRS), Université Montpellier II, Place Eugène Bataillon, 34095, Montpellier, France.
Evolution. 2008 Jan;62(1):1-11. doi: 10.1111/j.1558-5646.2007.00260.x. Epub 2007 Nov 12.
The evolution of exploitative specificity can be influenced by environmental variability in space and time and the intensity of trade-offs. Coevolution, the process of reciprocal adaptation in two or more species, can produce variability in host exploitation and as such potentially drive patterns in host and parasite specificity. We employed the bacterium Pseudomonas fluorescens SBW25 and its DNA phage Phi2 to investigate the role of coevolution in the evolution of phage infectivity range and its relation with phage growth rate. At the phage population level, coevolution led to the evolution of broader infectivity range, but without an associated decrease in phage growth rate relative to the ancestor, whereas phage evolution in the absence of bacterial evolution led to an increased growth rate but no increase in infectivity range. In contrast, both selection regimes led to phage adaptation (in terms of growth rates) to their respective bacterial hosts. At the level of individual phage genotypes, coevolution resulted in within-population diversification in generalist and specialist infectivity range types. This pattern was consistent with a multilocus gene-for-gene interaction, further confirmed by an observed cost of broad infectivity range for individual phage. Moreover, coevolution led to the emergence of bacterial genotype by phage genotype interactions in the reduction of bacterial growth rate by phage. Our study demonstrates that the strong reciprocal selective pressures underlying the process of coevolution lead to the emergence and coexistence of different strategies within populations and to specialization between selective environments.
剥削特异性的进化可能受到时空环境变异性和权衡强度的影响。协同进化是两个或更多物种相互适应的过程，它会导致宿主利用方式的变异性，从而有可能推动宿主和寄生虫特异性的模式形成。我们利用荧光假单胞菌SBW25及其DNA噬菌体Phi2来研究协同进化在噬菌体感染范围进化中的作用及其与噬菌体生长速率的关系。在噬菌体种群水平上，协同进化导致感染范围变宽，但相对于祖先而言，噬菌体生长速率并未相应降低，而在没有细菌进化的情况下噬菌体进化则导致生长速率增加，但感染范围没有扩大。相比之下，两种选择机制都导致噬菌体（就生长速率而言）适应各自的细菌宿主。在单个噬菌体基因型水平上，协同进化导致种群内普遍型和特异型感染范围类型的多样化。这种模式与多位点基因对基因的相互作用一致，单个噬菌体感染范围变宽所带来的代价进一步证实了这一点。此外，协同进化导致了噬菌体基因型与细菌基因型之间的相互作用，从而使噬菌体降低细菌的生长速率。我们的研究表明，协同进化过程中强大的相互选择压力导致种群内不同策略的出现和共存，以及选择性环境之间的特化。
