• The popular dual definition of lichen symbiosis is under question with recent findings of additional microbial partners living within the lichen body. Here we compare the distribution and co‐occurrence patterns of lichen photobiont and recently described secondary fungus (Cyphobasidiales yeast) to evaluate their dependency on lichen host fungus (mycobiont).
• We sequenced the nuclear internal transcribed spacer (ITS) strands for mycobiont, photobiont, and yeast from six widespread northern hemisphere epiphytic lichen species collected from 25 sites in Switzerland and Estonia. Interaction network analyses and multivariate analyses were conducted on operational taxonomic units based on ITS sequence data.
• Our study demonstrates the frequent presence of cystobasidiomycete yeasts in studied lichens and shows that they are much less mycobiont‐specific than the photobionts. Individuals of different lichen species growing on the same tree trunk consistently hosted the same or closely related mycobiont‐specific Trebouxia lineage over geographic distances while the cystobasidiomycete yeasts were unevenly distributed over the study area – contrasting communities were found between Estonia and Switzerland.
• These results contradict previous findings of high mycobiont species specificity of Cyphobasidiales yeast at large geographic scales. Our results suggest that the yeast might not be as intimately associated with the symbiosis as is the photobiont.

中文翻译：

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与常见附生地衣物种相关的光生物和酵母菌共生模式的对比

• 地衣共生的流行双重定义受到质疑，最近发现了生活在地衣体内的其他微生物伴侣。在这里，我们比较了地衣光生物体的分布和共生模式，并比较了最近描述的次生真菌（Cyphobasidiales酵母）来评估它们对地衣宿主真菌（真菌生物体）的依赖性。
• 我们对从瑞士和爱沙尼亚的25个站点收集的六个广泛的北半球附生地衣物种中的真菌生物素，光生物素和酵母的核内转录间隔区（ITS）链进行了测序。基于ITS序列数据，对操作分类单元进行了交互网络分析和多变量分析。
• 我们的研究表明，在已研究的地衣中经常存在囊藻类真菌酵母菌，并且表明它们与光生生物相比，其真菌生物素特异性要低得多。在同一棵树干上生长的不同地衣物种的个体在地理距离上始终具有相同或密切相关的特定于真菌的Trebouxia谱系，而在研究区域内膀胱孢子菌的酵母菌分布不均-爱沙尼亚和瑞士之间发现了相反的群落。
• 这些结果与以前在大型地理尺度上对拟除藻酵母菌的高分枝杆菌种特异性的发现相矛盾。我们的研究结果表明，酵母与共生关系可能不像光生物元那样紧密。