Warsi Omar M, Dykhuizen Daniel E
Department of Ecology and Evolution Stony Brook University Stony Brook NY USA.
Department of Medical Biochemistry and Microbiology Uppsala University Uppsala Sweden.
Ecol Evol. 2017 Jun 8;7(14):5296-5309. doi: 10.1002/ece3.3096. eCollection 2017 Jul.
Interactions between different axes of an organism's niche determine the evolutionary trajectory of a population. An extreme case of these interactions is predicted from ecological theory in Liebig's law of the minimum. This law states that in environments where multiple nutrients are in relatively low concentrations, only one nutrient will affect the growth of the organism. This implies that the evolutionary response of the population would be dictated by the most growth-limiting nutrient. Alternatively, it is possible that an initial adaptation to the most limiting nutrient results in other nutrients present in low concentration affecting the evolutionary dynamics of the population. To test these hypotheses, we conducted twelve evolution experiments in chemostats using populations: four under nitrogen limitation, four under magnesium limitation, and four in which both nitrogen and magnesium are in low concentrations. In the last environment, only magnesium seems to limit growth (Low Nitrogen Magnesium Limited environment, LNML). We observe a decrease in nitrogen concentration in the LNML environment over the course of our evolution experiment indicating that nitrogen might become limiting in these environments. Genetic reconstruction results show that clones adapted to magnesium limitation have genes involved in nitrogen starvation, that is, (nitrogen starvation transcriptional regulator) and (transport protein) to be upregulated only in the LNML environment as compared to magnesium-limiting environments. Together, our results highlights that in low-nutrient environments, adaptation to the growth-limiting nutrient results in other nutrients at low concentrations to play a role in the evolutionary dynamics of the population.
生物体生态位不同轴之间的相互作用决定了种群的进化轨迹。这些相互作用的一个极端情况可从生态学理论中的利比希最小因子定律预测得出。该定律指出，在多种营养物质浓度相对较低的环境中，只有一种营养物质会影响生物体的生长。这意味着种群的进化反应将由最限制生长的营养物质决定。或者，有可能对最限制生长的营养物质的初始适应会导致低浓度存在的其他营养物质影响种群的进化动态。为了检验这些假设，我们使用种群在恒化器中进行了十二次进化实验：四次在氮限制条件下，四次在镁限制条件下，还有四次在氮和镁浓度都很低的环境中。在最后一种环境中，似乎只有镁限制生长（低氮镁限制环境，LNML）。在我们的进化实验过程中，我们观察到LNML环境中氮浓度降低，这表明在这些环境中氮可能会成为限制因素。基因重建结果表明，与镁限制环境相比，适应镁限制的克隆体中参与氮饥饿的基因，即（氮饥饿转录调节因子）和（转运蛋白）仅在LNML环境中上调。总之，我们的结果突出表明，在低营养环境中，对限制生长的营养物质的适应会导致低浓度的其他营养物质在种群的进化动态中发挥作用。
