Environmentally acquired microbial symbionts could contribute to host adaptation to local conditions like vertically transmitted symbionts do. This scenario necessitates symbionts to have different effects in different environments. We investigated this idea in Drosophila melanogaster, a species which communities of bacterial symbionts vary greatly among environments. We isolated four bacterial strains isolated from the feces of a D. melanogaster laboratory strain and tested their effects in two conditions: the ancestral environment (i.e. the laboratory medium) and a new environment (i.e. fresh fruit with live yeast). All bacterial effects on larval and adult traits differed among environments, ranging from very beneficial to marginally deleterious. The joint analysis of larval development speed and adult size further shows bacteria affected developmental plasticity more than resource acquisition. This effect was largely driven by the contrasted effects of the bacteria in each environment. Our study illustrates that understanding D. melanogaster symbiotic interactions in the wild will necessitate working in ecologically realistic conditions. Besides, context-dependent effects of symbionts, and their influence on host developmental plasticity, shed light on how environmentally acquired symbionts may contribute to host evolution.

中文翻译：

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果蝇-细菌共生的环境特异性影响宿主发育可塑性

环境获得的微生物共生体可能有助于宿主适应当地条件，就像垂直传播的共生体一样。这种情况需要共生体在不同的环境中产生不同的影响。我们在 Drosophila melanogaster 中研究了这个想法，Drosophila melanogaster 是一种细菌共生体群落在环境中差异很大的物种。我们从黑腹果蝇实验室菌株的粪便中分离出四种细菌菌株，并在两种条件下测试了它们的效果：祖先环境（即实验室培养基）和新环境（即带有活酵母的新鲜水果）。所有细菌对幼虫和成虫性状的影响因环境而异，从非常有益到轻微有害。幼虫发育速度和成虫大小的联合分析进一步表明，细菌对发育可塑性的影响大于资源获取。这种效果很大程度上是由细菌在每种环境中的对比效果驱动的。我们的研究表明，了解野生黑腹果蝇的共生相互作用将需要在生态现实条件下工作。此外，共生体的环境依赖性影响及其对宿主发育可塑性的影响，揭示了环境获得的共生体如何促进宿主进化。野生黑腹果蝇共生相互作用将需要在生态现实条件下工作。此外，共生体的环境依赖性影响及其对宿主发育可塑性的影响，揭示了环境获得的共生体如何促进宿主进化。野生黑腹果蝇共生相互作用将需要在生态现实条件下工作。此外，共生体的环境依赖性影响及其对宿主发育可塑性的影响，揭示了环境获得的共生体如何促进宿主进化。