Data from: Specific adaptation to strong competitors can offset the negative effects of population size reductions

Competition plays a crucial role in determining adaptation of species, yet we know little as to how adaptation is affected by the strength of competition. On the one hand, strong competition typically results in population size reductions, which can hamper adaptation due to a shortage of beneficial mutations; on the other hand, specificity of adaptation to competitors may offset the negative evolutionary consequences of such population size effects. Here, we investigate how competition strength affects population fitness in the bacterium Pseudomonas fluorescens. Our results demonstrate that strong competition constrains adaptation of focal populations, which can be partially explained by population size reductions. However, fitness assays also reveal specific adaptation of focal populations to particular competitors varying in competitive ability. Additionally, this specific adaptation can offset the negative effects of competitor-mediated population size reductions under strong competition. Our study therefore highlights the importance of opposing effects of strong competition on species adaptation, which may lead to different outcomes of colonization under intense and relaxed competitive environments in the context of population dispersal.

竞争在决定物种适应性的过程中扮演着关键角色，但目前我们对竞争强度如何影响物种适应性仍知之甚少。一方面，强竞争通常会导致种群规模缩减，而有益突变的匮乏会进一步阻碍适应性进化；另一方面，针对特定竞争者的适应性特异性，或许能够抵消这类种群规模效应所带来的负面进化后果。本研究以荧光假单胞菌（Pseudomonas fluorescens）为实验材料，探究竞争强度如何影响种群适合度。研究结果显示，强竞争会限制目标种群的适应性，这一现象可部分通过种群规模缩减得到解释。不过适合度测定实验还发现，目标种群会对竞争能力存在差异的特定竞争者产生特异性适应。此外，这种特异性适应能够抵消强竞争环境下，由竞争者介导的种群规模缩减所带来的负面影响。因此，本研究强调了强竞争对物种适应性的双向作用，这可能会导致在种群扩散的背景下，高强度与低强度竞争环境中的物种定殖结果存在差异。