Coevolution’s conflicting role in the establishment of beneficial associations

Reciprocal adaptation between hosts and symbionts can drive the maintenance of symbioses, resulting in coevolution and beneficial genotypic interactions. Consequently, hosts may experience decreased fitness when paired with non-sympatric partners compared to sympatric symbionts. However, coevolution does not preclude conflict—host and symbiont can act to advance their own fitness interests, which do not necessarily align with those of their partner. Despite coevolution’s importance in extant symbioses, we know little about its role in shaping the origin of symbioses. Here, we tested the role of coevolution in establishing a novel association by experimentally (co)evolving a host with a protective bacterium under environmental stress. While evolution in the presence of non-evolving bacteria facilitated host adaptation, co-passaged hosts did not exhibit greater adaptation rates than hosts paired with non-evolving bacteria. Furthermore, co-passaged hosts exhibited greater fecundity when pa...

宿主（host）与共生体（symbiont）之间的互惠适应可驱动共生关系的维持，进而催生协同进化（coevolution）与有益的基因型互作。相较于搭配同域（sympatric）共生体，宿主与非同域（non-sympatric）伙伴配对时，其适合度（fitness）可能出现下降。然而协同进化并不排除演化冲突的存在——宿主与共生体各自会为提升自身适合度利益而行动，而这些利益未必与对方的利益相一致。尽管协同进化在现存共生体系（extant symbioses）中至关重要，但我们对其在共生关系起源塑造过程中所扮演的角色仍知之甚少。本研究通过在环境胁迫（environmental stress）条件下，对宿主与保护性细菌开展实验性（共）演化，以此检验协同进化在建立新型共生关系中的作用。尽管与未演化细菌共培养可促进宿主适应，但共传代（co-passaged）宿主的适应速率并未显著高于与未演化细菌配对的宿主。此外，共传代宿主在与……配对时展现出更高的繁殖力（fecundity）。