Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS Biol. 2019 Jan 25;17(1):e3000121. doi: 10.1371/journal.pbio.3000121. eCollection 2019 Jan.
Maximum growth rate per individual (r) and carrying capacity (K) are key life-history traits that together characterize the density-dependent population growth and therefore are crucial parameters of many ecological and evolutionary theories such as r/K selection. Although r and K are generally thought to correlate inversely, both r/K tradeoffs and trade-ups have been observed. Nonetheless, neither the conditions under which each of these relationships occur nor the causes of these relationships are fully understood. Here, we address these questions using yeast as a model system. We estimated r and K using the growth curves of over 7,000 yeast recombinants in nine environments and found that the r-K correlation among genotypes changes from 0.53 to -0.52 with the rise of environment quality, measured by the mean r of all genotypes in the environment. We respectively mapped quantitative trait loci (QTLs) for r and K in each environment. Many QTLs simultaneously influence r and K, but the directions of their effects are environment dependent such that QTLs tend to show concordant effects on the two traits in poor environments but antagonistic effects in rich environments. We propose that these contrasting trends are generated by the relative impacts of two factors-the tradeoff between the speed and efficiency of ATP production and the energetic cost of cell maintenance relative to reproduction-and demonstrate an agreement between model predictions and empirical observations. These results reveal and explain the complex environment dependency of the r-K relationship, which bears on many ecological and evolutionary phenomena and has biomedical implications.
个体最大增长率(r)和承载能力(K)是关键的生活史特征，它们共同描述了密度依赖的种群增长，因此是许多生态和进化理论的关键参数，如 r/K 选择。尽管 r 和 K 通常被认为是负相关的，但 r/K 权衡和 r/K 提升都有被观察到。尽管如此，这两种关系发生的条件以及这些关系的原因还没有被完全理解。在这里，我们使用酵母作为模型系统来解决这些问题。我们使用 9 种环境中超过 7000 个酵母重组体的生长曲线来估计 r 和 K，发现基因型之间的 r-K 相关性从 0.53 变化到-0.52，随着环境质量的提高，以环境中所有基因型的平均 r 来衡量。我们分别在每种环境中绘制了 r 和 K 的数量性状基因座(QTL)。许多 QTL 同时影响 r 和 K，但它们的影响方向是环境依赖的，即 QTL 往往在恶劣环境中对这两个性状表现出一致的影响，而在富裕环境中表现出拮抗的影响。我们提出，这些相反的趋势是由两个因素的相对影响产生的，即 ATP 产生的速度和效率与细胞维持相对于繁殖的能量成本之间的权衡，以及模型预测和经验观察之间的一致性。这些结果揭示并解释了 r-K 关系的复杂环境依赖性，这与许多生态和进化现象有关，并且具有医学意义。
