Data from: Can maternally inherited endosymbionts adapt to a novel host? Direct costs of Spiroplasma infection, but not vertical transmission efficiency, evolve rapidly after horizontal transfer into D. melanogaster

Maternally inherited symbionts are common in arthropods and many have important roles in host adaptation. The observation that specific symbiont lineages infect distantly related host species implies new interactions are commonly established by lateral transfer events. However, studies have shown that symbionts often perform poorly in novel hosts. We hypothesized selection on the symbiont may be sufficiently rapid that poor performance in a novel host environment is rapidly ameliorated, permitting symbiont maintenance. Here, we test this prediction for a Spiroplasma strain transinfected into the novel host Drosophila melanogaster. In the generations immediately following transinfection, the symbiont had low transmission efficiency to offspring and imposed severe fitness costs on its host. We observed that effects on host fitness evolved rapidly, being undetectable after 17 generations in the novel host, whereas vertical transmission efficiency was poorly responsive over this period. Our results suggest that long-term symbiosis may more readily be established in cases where symbionts perform poorly in just one aspect of symbiosis.母系遗传共生体广泛分布于节肢动物类群，且多数对宿主适应具有关键调控作用。特定共生体谱系可侵染远缘宿主物种这一观测结果，提示新的共生互作关系通常可通过水平转移事件得以建立。但已有研究证实，共生体在陌生宿主中往往表现不佳。我们据此提出假说：共生体所承受的选择压力足够迅速，使其在陌生宿主环境中的不良适配表现可被快速改善，从而保障共生体得以持续维持。本研究针对人工转染至新宿主黑腹果蝇（Drosophila melanogaster）的螺原体（Spiroplasma）菌株，对该假说进行了验证。在转染后的初始几代中，该共生体的子代传播效率低下，且对宿主造成了严重的适合度成本。研究发现，宿主适合度所受的负面影响快速演化，在新宿主中传代17代后便已无法检测到该影响；而同期的垂直传播效率则未出现显著改善。本研究结果表明，若共生体仅在共生互作的某单一维度表现不佳，则长期稳定的共生关系或许更易建立。