Data from: Selection mosaics differentiate Rhizobium-host plant interactions across different nitrogen environments

The nature and direction of coevolutionary interactions between species is expected to differentiate among distinct environments. Consequently, locally coevolved symbiotic traits would be well matched in similar environments, but mismatched elsewhere. In a classic mutualistic trade-off, rhizobia provide nitrogen (N) to legume host plants in return for photosynthates. Despite earlier predictions, there is little evidence so far that spatial differences in soil N content mediate the coevolutionary outcome of the legume–Rhizobium mutualism. To test the existence of such selection mosaics, different genotypes of Vicia cracca and Rhizobium leguminosarum originating from spatially and environmentally highly differentiated sites were cross inoculated across different soil N regimes. In accordance with theoretical predictions, we found highly significant effects of genotype by genotype by environment (G×G×E) interactions, on both nodulation and plant growth, even when R. leguminosarum genotypes showed high genetic similarity. Our results show that the trajectory of the coevolutionary interactions between rhizobia and legumes is differentiated across different environments, and that selection mosaics may play an important role in shaping differences in the genetic composition of rhizobial populations.

物种间协同进化互作（coevolutionary interactions）的本质与方向，预计会随不同环境发生分化。据此，本地协同进化形成的共生性状在相似环境中匹配度极高，但在其他环境中则会出现错配。在经典的互利共生权衡关系中，根瘤菌（Rhizobium）会为豆科宿主植物提供氮素（N），以换取光合产物。尽管已有前期相关预测，但目前几乎没有证据表明，土壤氮含量的空间差异会介导豆科-根瘤菌共生体系的协同进化结果。为验证此类选择镶嵌（selection mosaics）是否存在，研究人员对取自空间与环境差异极大的生境的广布野豌豆（Vicia cracca）和豌豆根瘤菌（Rhizobium leguminosarum）的不同基因型，开展了不同土壤氮水平下的交叉接种实验。与理论预测一致，研究人员发现，即便豌豆根瘤菌基因型间遗传相似性较高，基因型×基因型×环境（G×G×E）互作仍对结瘤与植株生长产生了极显著影响。本研究结果表明，根瘤菌与豆科植物间协同进化互作的动态轨迹会随环境不同而产生分化，且选择镶嵌或许在塑造根瘤菌种群的遗传组成差异方面发挥着重要作用。