Host–microbe interactions underlie the development and fitness of many macroorganisms, including bees. Whereas many social bees benefit from vertically transmitted gut bacteria, current data suggests that solitary bees, which comprise the vast majority of species diversity within bees, lack a highly specialized gut microbiome. Here we examine the composition and abundance of bacteria and fungi throughout the complete life cycle of the ground-nesting solitary bee Anthophora bomboides standfordiana. In contrast to expectations, immature bee stages maintain a distinct core microbiome consisting of Actinobacterial genera (Streptomyces, Nocardiodes) and the fungus Moniliella spathulata. Dormant (diapausing) larval bees hosted the most abundant and distinctive bacteria and fungi, attaining 33 and 52 times their initial copy number, respectively. We tested two adaptive hypotheses regarding microbial functions for diapausing bees. First, using isolated bacteria and fungi, we found that Streptomyces from brood cells inhibited the growth of multiple pathogenic filamentous fungi, suggesting a role in pathogen protection during overwintering, when bees face high pathogen pressure. Second, sugar alcohol composition changed in tandem with major changes in fungal abundance, suggesting links with bee cold tolerance or overwintering biology. We find that A. bomboides hosts a conserved core microbiome that may provide key fitness advantages through larval development and diapause, which raises the question of how this microbiome is maintained and faithfully transmitted between generations. Our results suggest that focus on microbiomes of mature or active insect developmental stages may overlook stage-specific symbionts and microbial fitness contributions during host dormancy.

中文翻译：

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共生细菌和真菌在滞育期间增殖，可能会提高独居蜜蜂的越冬生存率


宿主与微生物的相互作用是许多宏观生物（包括蜜蜂）发育和适应的基础。尽管许多群居蜜蜂受益于垂直传播的肠道细菌，但目前的数据表明，构成蜜蜂物种多样性绝大多数的独居蜜蜂缺乏高度专业化的肠道微生物组。在这里，我们研究了地面筑巢独居蜜蜂 Anthophora boboidesstandfordiana 整个生命周期中细菌和真菌的组成和丰度。与预期相反，未成熟的蜜蜂阶段维持着独特的核心微生物组，由放线菌属（链霉菌属、诺卡氏菌属）和念珠菌属真菌组成。休眠（滞育）幼虫蜂拥有最丰富、最独特的细菌和真菌，分别达到其初始拷贝数的 33 倍和 52 倍。我们测试了关于滞育蜜蜂微生物功能的两个适应性假设。首先，利用分离的细菌和真菌，我们发现来自巢细胞的链霉菌抑制了多种致病丝状真菌的生长，这表明当蜜蜂面临高病原体压力时，它们在越冬期间具有病原体保护作用。其次，糖醇成分随着真菌丰度的重大变化而变化，这表明与蜜蜂的耐寒性或越冬生物学有关。我们发现，A. boboides 拥有保守的核心微生物组，可能通过幼虫发育和滞育提供关键的适应性优势，这就提出了如何维持该微生物组并在代际间忠实传播的问题。我们的结果表明，关注成熟或活跃的昆虫发育阶段的微生物组可能会忽视宿主休眠期间特定阶段的共生体和微生物适应性的贡献。