Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
Carl Woese Institute for Genomic Biology, University of Illinois at Champaign-Urbana, Urbana, IL, 61801, USA.
Am J Bot. 2020 Feb;107(2):195-208. doi: 10.1002/ajb2.1432. Epub 2020 Feb 16.
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.
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.
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.
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.
互利共生的生态结果众所周知会随着非生物或生物环境的变化而变化，但很少有研究探讨不同环境如何影响进化反应，包括对关键互利共生相关特征的选择强度和遗传方差的表达。
我们在四个野外公共花园中种植了 30 条豆科植物 Lupinus lupulina 的母系，并将我们对结瘤的选择强度和遗传方差的测量结果与之前使用相同的 30 条 M. lupulina 系进行的温室实验进行了比较，结瘤是反映豆科植物在共生中投资的关键特征。
我们发现，结瘤的平均值和遗传方差在温室中都远远大于在野外，而且结瘤的选择形式在不同的环境中也有显著差异。我们还发现与适应度相关的性状存在显著的基因型与环境（G × E）互作效应，这些效应是由植物系在环境之间的等级顺序差异产生的。
总的来说，我们的研究结果表明，遗传方差的表达和对结瘤的选择在不同的环境中存在差异。在野外，植物适应度的显著等级变化可能有助于维持自然种群中的遗传变异，即使面临定向或稳定选择。
