Data from: Patterns of local adaptation in space and time among soil bacteria

Our understanding of microbial biogeography has been governed by the dictum “Everything is everywhere, but the environment selects.” In other words, the distribution of microbes is thought to occur in a regime of extensive dispersal and strong selection, generating local adaptation. However, direct tests of these assumptions are rare. Here, we investigate the extent of local adaptation in space and time of a collection of soil-derived microbial isolates, most belonging to the genus Pseudomonas, across a growing season from a deciduous forest in western Quebec, Canada, using a reciprocal transplant design. Average performance of all clones varied substantially in both space and time, in line with the expectation of strong selection in both dimensions. The behavior of genotype-by-environment variance in fitness and its components, responsiveness and inconsistency, in space and through time suggests that the strength of divergent selection increases as sites become more distant from each other in both dimensions. However, divergent selection was not strong enough to maintain different specialized types across the environments studied, which suggests that Pseudomonas and their close relatives are not locally adapted to the prevailing conditions of growth.

我们对微生物生物地理学（microbial biogeography）的认知长期遵循"万物无处不在，环境择之"这一格言。换言之，学界普遍认为微生物的分布遵循广泛扩散与强力选择的模式，进而催生局部适应性（local adaptation）。然而，针对这些核心假设的直接验证研究却寥寥无几。本研究采用互惠移植实验设计（reciprocal transplant design），对加拿大魁北克西部一处落叶林整个生长季内采集的一批土壤来源微生物分离株（其中多数隶属于假单胞菌属（Pseudomonas））展开研究，旨在探究其在空间与时间维度上的局部适应性程度。所有克隆株的平均表现均在空间与时间维度上存在显著差异，契合了两个维度均存在强力选择的理论预期。对适合度（fitness）及其组分（响应性与不一致性）的基因型-环境互作方差（genotype-by-environment variance）在空间和时间维度上的变化分析表明，随着样地间空间距离增大，两个维度内的歧化选择（divergent selection）强度均会提升。但歧化选择的强度尚未达到能在所研究的环境中维持不同特化类群的水平，这说明假单胞菌属及其近缘类群并未对当地主流生长环境形成局部适应性。