Data from: Tradeoffs, spatial heterogeneity, and the maintenance of microbial diversity

Specialization and concomitant tradeoffs are assumed to underlie the non-neutral coexistence of lineages. Tradeoffs across heterogeneous environments can promote diversity by preventing competitive exclusion. However, the importance of tradeoffs in maintaining diversity in natural microbial assemblages is unclear, as tradeoffs are frequently not detected in artificial evolution experiments. Stressful conditions associated with patches of heavy-metal enriched serpentine soils provide excellent opportunities for examining how heterogeneity may foster genetic diversity. Using a spatially-replicated design, we demonstrate that rhizobium bacteria symbiotic with legumes inhabiting contrasting serpentine and non-serpentine soils exhibit a tradeoff between a genotype’s nickel tolerance and its ability to replicate rapidly. Furthermore, we detected adaptive divergence in rhizobial assemblages across soil type heterogeneity at multiple sites, suggesting that this tradeoff may promote the coexistence of phenotypically distinct bacterial lineages. Tradeoffs and adaptive divergence may be important factors maintaining the tremendous diversity within natural assemblages of bacteria.

特化及其伴随的进化权衡(tradeoff)被认为是细菌谱系非中性共存的底层机制。异质环境中的进化权衡可通过抑制竞争性排斥来促进物种多样性。然而，进化权衡在维持自然微生物群落多样性中的作用尚未明确，因为在人工进化实验中往往难以检测到这类权衡。富含重金属的蛇纹岩土(serpentine soils)斑块所形成的胁迫环境，为探究环境异质性如何推动遗传多样性提供了绝佳的研究契机。本研究采用空间重复实验设计，证实了栖息于迥异的蛇纹岩土与非蛇纹岩土生境中的豆科植物共生根瘤菌(rhizobium)，其基因型的镍耐受性与快速繁殖能力之间存在显著的进化权衡。此外，我们在多个样点的土壤类型异质性梯度中检测到根瘤菌群落的适应性分化，这表明该进化权衡或可推动表型各异的细菌谱系实现非中性共存。进化权衡与适应性分化或为维持自然细菌群落极高多样性的关键驱动因素。