Following approximately 200 generations of experimental evolution, we screened 720 evolved clones for changes in their pyoverdine production levels. We found no evidence for the re-evolution of full cooperation, even in environments with increased spatial structure, and reduced costs of public good production - two conditions that have previously been shown to maintain cooperation. In contrast, we observed selection for complete abolishment of pyoverdine production. The patterns of complete trait degradation were likely driven by \"cheating on cheats\" in unstructured, iron-limited environments where pyoverdine is important for growth, and selection against a maladaptive trait in iron-rich environments where pyoverdine is superfluous.
Our study shows that the path to re-evolve public-goods cooperation can be constrained. While a limitation of the number of mutational targets potentially leading to reversion might be one reason for the observed pattern, an alternative explanation is that the selective conditions required for revertants to spread from rarity are much more stringent than those needed to maintain cooperation.
经过大约200代的实验进化,我们筛选了720个进化克隆的pyoverdine生产水平的变化。我们没有发现全面合作重新演变的证据,即使在空间结构增加的环境中,并降低了公共物品生产的成本-这两个条件以前已被证明可以保持合作。相比之下,我们观察到选择完全废除pyoverdine生产。完全性状退化的模式可能是由非结构化的“作弊作弊”驱动的,铁限制的环境,其中pyoverdine是重要的生长,以及在富铁环境中选择一种适应不良的性状,其中pyoverdine是多余的。
我们的研究表明,重新发展公共产品合作的路径可能会受到限制。虽然可能导致逆转的突变靶标数量的限制可能是观察到的模式的一个原因,另一种解释是,回复体从稀有性传播所需的选择条件比保持合作所需的条件严格得多。