Data from: Niche differentiation in the dynamics of host-symbiont interactions: symbiont prevalence as a coexistence problem

Heritable symbioses can have important ecological effects and have triggered important evolutionary innovations. Current predictions for long-term symbiont prevalence are based on their fitness benefits and vertical transmission rates but ignore non-linear competitive feedbacks among symbiotic and symbiont-free hosts. We hypothesized that such feedbacks function as stabilizing mechanisms, promoting coexistence of host types and maintaining intermediate symbiont frequency at the population scale. Using a model grass / endophyte symbiosis, we manipulated competition within and between endophyte-symbiotic (E+) and endophyte-free (E-) hosts and fit competition models to experimental data. We show for the first time that symbiont-structured competition can generate stable coexistence of E+ and E- hosts, even under perfect vertical transmission. Niche differentiation was the key to coexistence, causing hosts of each type to limit themselves more strongly than each other. These results establish roles for non-linear competitive dynamics and niche differentiation in the ecology and evolution of heritable symbionts.

遗传共生（heritable symbioses）可产生重要的生态效应，并催生了关键的进化创新。当前针对共生体（symbiont）长期流行率的预测，均基于其适合度收益与垂直传播速率，却忽略了有共生体宿主与无共生体宿主之间的非线性竞争反馈。我们提出假设：这类反馈可作为稳定化机制，促进宿主类群共存，并在种群尺度维持中等水平的共生体频率。本研究以模式禾草-内生真菌（endophyte）共生体系为研究对象，操控了内生真菌共生（E+）与内生真菌无菌（E-）宿主内部及二者间的竞争，并将竞争模型拟合至实验数据。我们首次证实：即便在完全垂直传播的条件下，由共生体塑造的竞争格局也可促成E+与E-宿主的稳定共存。生态位分化是实现共存的关键，使得每一类宿主对同种个体的抑制作用强于对异种个体。本研究结果明确了非线性竞争动力学与生态位分化在遗传共生体的生态与进化过程中的重要作用。