Abiotic heterogeneity drives parasite local adaptation in coevolving bacteria and phages

Spatial abiotic heterogenity can result in divergent selection, hence might increase the magnitude of host-parasite local adaptation (the mean difference in fitness of sympatric versus allopatric host-parasite combinations). We explicitly tested this hypothesis by measuring local adapation in experimentally coevolved populations of bacteria and viruses evolved in the same or different nutrient media. Consistent with previous work, we found that mean levels of evolved phage infectivity and bacteria resistance varied with nutrient concentration, with maximal levels at nutrient concentrations that supported the greatest densities of bacteria. Despite this variation in evolved mean infectivity and resistance between treatments, we found that parasite local adaptation was greatly increased when measured between populations evolved in different, compared to the same, media. This pattern is likely to have resulted from different media imposing divergent selection on bacterial hosts, and phages...

非生物空间异质性 (spatial abiotic heterogeneity) 可引发歧化选择 (divergent selection)，进而可能增大宿主-寄生虫局部适应性 (host-parasite local adaptation) 的幅度，该适应性即同域的（sympatric）与异域的（allopatric）宿主-寄生虫组合间适合度的平均差异。我们通过测定在相同或不同营养培养基中进化得到的细菌与噬菌体实验共进化种群的局部适应性，对该假说开展了明确检验。与既往研究结果一致，我们发现进化后噬菌体侵染性 (phage infectivity) 与细菌抗性 (bacteria resistance) 的平均水平随营养浓度发生变化，在可支撑细菌最高种群密度的营养浓度下达到最大值。尽管不同处理组间进化出的平均侵染性与抗性存在上述差异，但我们观察到，相较于同一培养基中进化出的种群，在不同培养基中进化出的种群间测定的寄生虫局部适应性显著提升。该模式大概率源于不同培养基对细菌宿主施加了歧化选择，而噬菌体……