UMR 5175, CEFE, CNRS - Université Montpellier - Université P. Valéry - EPHE, Montpellier, Cedex 5, France.
University Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Grenoble Institut National Polytechnique (INP), Mathématiques et Applications, Grenoble (TIMC-IMAG), Techniques de l'Ingénierie Médicale et de la Complexité - Informatique, F-38000, Grenoble, France.
Ecol Lett. 2019 Aug;22(8):1192-1202. doi: 10.1111/ele.13276. Epub 2019 May 17.
Negative frequency-dependent selection (NFDS) is an important mechanism for species coexistence and for the maintenance of genetic polymorphism. Long-term coexistence nevertheless requires NFDS interactions to be resilient to further evolution of the interacting species or genotypes. For closely related genotypes, NFDS interactions have been shown to be preserved through successive rounds of evolution in coexisting lineages. On the contrary, the evolution of NFDS interactions between distantly related species has received less attention. Here, we tracked the co-evolution of Escherichia coli and Citrobacter freundii that initially differ in their ecological characteristics. We showed that these two bacterial species engaged in an NFDS interaction particularly resilient to further evolution: despite a very strong asymmetric rate of adaptation, their coexistence was maintained owing to an NFDS pattern where fitness increases steeply as the frequency decreases towards zero. Using a model, we showed how and why such NFDS pattern can emerge. These findings provide a robust explanation for the long-term maintenance of species at very low frequencies.
负频率依赖性选择（NFDS）是物种共存和维持遗传多态性的重要机制。然而，长期共存需要 NFDS 相互作用能够抵御相互作用的物种或基因型的进一步进化。对于密切相关的基因型，已经表明 NFDS 相互作用通过共存谱系中的连续进化得以保留。相反，NFDS 相互作用在亲缘关系较远的物种之间的进化受到的关注较少。在这里，我们跟踪了大肠杆菌和弗氏柠檬酸杆菌的共同进化，它们最初在生态特征上有所不同。我们表明，这两种细菌之间存在一种特别能抵抗进一步进化的 NFDS 相互作用：尽管适应的不对称率非常强，但由于 NFDS 模式，它们的共存得以维持，在这种模式下，适应性随着频率向零的降低而急剧增加。我们使用模型展示了这种 NFDS 模式是如何以及为什么出现的。这些发现为长期维持非常低频率的物种提供了强有力的解释。
