PREMISE The ecological outcomes of mutualism are well known to shift across abiotic or biotic environments, but few studies have addressed how different environments impact evolutionary responses, including the intensity of selection on and the expression of genetic variance in key mutualism-related traits. METHODS We planted 30 maternal lines of the legume Medicago lupulina in four field common gardens and compared our measures of selection on and genetic variance in nodulation, a key trait reflecting legume investment in the symbiosis, with those from a previous greenhouse experiment using the same 30 M. lupulina lines. RESULTS We found that both the mean and genetic variance for nodulation were much greater in the greenhouse than in the field and that the form of selection on nodulation significantly differed across environments. We also found significant genotype-by-environment (G × E) effects for fitness-related traits that were generated by differences in the rank order of plant lines among environments. CONCLUSIONS Overall, our results suggest that the expression of genotypic variation and selection on nodulation differ across environments. In the field, significant rank-order changes for plant fitness potentially help maintain genetic variation in natural populations, even in the face of directional or stabilizing selection.

中文翻译：

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环境变异影响豆科植物-根瘤菌共生的性状表达和选择

前提众所周知，共生的生态结果会在非生物或生物环境中转移，但很少有研究解决不同环境如何影响进化反应，包括选择的强度和关键共生相关性状的遗传变异的表达。方法 我们在四个田间普通花园中种植了 30 个豆科植物紫花苜蓿母系品系，并比较了我们对结瘤的选择和遗传变异的测量，结瘤是反映豆科植物在共生中投资的一个关键性状，与之前使用相同 30 M. lupulina 系。结果我们发现，温室中结瘤的均值和遗传方差都比田间大得多，而且结瘤的选择形式在不同环境中存在显着差异。我们还发现环境中植物品系的等级顺序差异产生的适应度相关性状的显着基因型-环境（G×E）效应。结论 总的来说，我们的结果表明基因型变异的表达和结瘤的选择因环境而异。在该领域，植物适应性的显着排序变化可能有助于维持自然种群的遗传变异，即使面对定向或稳定选择也是如此。