The overwintering honey bee: Effect of age and climate on the hindgut microbiome- WW/CW samples

Managed honey bee colonies are overwintered in a variety of climates. Successfully overwintered colonies are paramount to spring agricultural pollination demands, which provide nutrients for early-year colony growth. High rates of winter colony loss have prompted investigations into overwintering climate, including indoor climate controlled overwintering. Core to overall colony health, the gut microbiome has largely been ignored in this context. While the gut microbiomes of short-lived workers and long-lived queens have been investigated, that of intermediate-lived, overwintering (diutinus) workers is relatively unknown. We sequenced the hindgut microbiota of overwintering workers from both a warm southern climate and controlled indoor cold climate. A cohort of known chronological age was sampled congruently for comparison. Chronological age was associated with significantly decreased bacterial and fungal load, but the relative structure of the core hindgut microbiome did not change with age. In both climates, the hindgut microbiome was generally stable overwinter. However, collective microbiome changes in the southern climate suggest compromised host physiology. Fungal abundance increased by two orders of magnitude in southern climate hindguts and was positively correlated with non-core, likely opportunistic bacteria. Our results contribute to understanding overwintering honey bee biology and microbial ecology and provide insight into overwintering strategies.

人工饲养的蜜蜂蜂群需在多样气候条件下完成越冬。成功越冬的蜂群是保障春季农业授粉需求的核心前提，而授粉活动可为蜂群年度早期生长提供养分。
蜂群越冬高损失率推动了学界针对越冬气候的相关研究，其中涵盖室内温控越冬模式。作为蜂群整体健康的核心要素，肠道微生物组（gut microbiome）在该研究方向中长期被忽视。尽管学界已对短命工蜂与长寿命蜂王的肠道微生物组展开探究，但中等寿命的越冬（diutinus）工蜂的肠道微生物组仍鲜有研究。
本研究对来自温暖南方气候与室内低温控气候的越冬工蜂的后肠道微生物群（hindgut microbiota）进行了测序，并同步采集了已知日龄的工蜂队列样本作为对照。
分析结果显示，工蜂日龄与细菌、真菌载量的显著降低呈显著相关，但核心后肠道微生物群的相对组成结构并未随日龄发生变化。
在两种气候环境下，工蜂的后肠道微生物群在越冬周期内整体保持稳定。然而，南方气候组的微生物群落整体变化提示宿主生理机能受损：该组工蜂后肠道的真菌丰度提升了两个数量级，且真菌丰度与非核心、大概率为机会性的细菌呈正相关。
本研究结果有助于加深对蜜蜂越冬生物学与微生物生态学的理解，并为优化越冬策略提供参考。