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，并催生了重要的进化创新。当前针对共生体长期流行率的预测，均以其适合度收益与垂直传播速率为依据，但却忽略了共生宿主与无共生宿主之间存在的非线性竞争反馈。我们据此提出假说：这类反馈可作为稳定化机制，促进不同宿主类型的共存，并在种群尺度上维持中等水平的共生体频率。本研究以禾本科植物-内生真菌（endophyte）共生体系为模型，操控了内生真菌共生宿主（E+）与无共生宿主（E-）内部及二者之间的竞争关系，并将竞争模型拟合至实验数据。我们首次证实，由共生体塑造的竞争可促使E+与E-宿主实现稳定共存，即便在完全垂直传播的条件下亦能成立。生态位分化是实现共存的核心机制，它使得各类宿主对同种个体的抑制作用显著强于对异种个体的抑制。本研究成果明确了非线性竞争动态与生态位分化在遗传共生体的生态与进化过程中的关键作用。