Intimate associations between different species drive community composition across ecosystems. Understanding the ecological and evolutionary drivers of these symbiotic associations is challenging because their structure eventually determines stability and resilience of the entire species network. Here, we compiled a detailed database on naturally occurring ant–symbiont networks in Europe to identify factors that affect symbiont network topology. These networks host an unrivalled diversity of macrosymbiotic associations, spanning the entire mutualism–antagonism continuum, including: (i) myrmecophiles – commensalistic and parasitic arthropods; (ii) trophobionts – mutualistic aphids, scale insects, planthoppers and caterpillars; (iii) social parasites – parasitic ant species; (iv) parasitic helminths; and (v) parasitic fungi. We dissected network topology to investigate what determines host specificity, symbiont species richness, and the capacity of different symbiont types to switch hosts. We found 722 macrosymbionts (multicellular symbionts) associated with European ants. Symbiont type explained host specificity and the average relatedness of the host species. Social parasites were associated with few hosts that were phylogenetically highly related, whereas the other symbiont types interacted with a larger number of hosts across a wider taxonomic distribution. The hosts of trophobionts were the least phylogenetically related across all symbiont types. Colony size, host range and habitat type predicted total symbiont richness: ant hosts with larger colony size, a larger distribution range or with a wider habitat range contained more symbiont species. However, we found that different sets of host factors affected diversity in the different types of symbionts. Ecological factors, such as colony size, host range and niche width predominantly determined myrmecophile species richness, whereas host phylogeny was the most important predictor of mutualistic trophobiont, social parasite and parasitic helminth species richness. Lastly, we found that hosts with a common biogeographic history support a more similar community of symbionts. Phylogenetically related hosts also shared more trophobionts, social parasites and helminths, but not myrmecophiles. Taken together, these results suggest that ecological and evolutionary processes structure host specificity and symbiont richness in large‐scale ant–symbiont networks, but these drivers may shift in importance depending on the type of symbiosis. Our findings highlight the potential of well‐characterized bipartite networks composed of different types of symbioses to identify candidate processes driving community composition.

中文翻译：

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整个欧洲蚂蚁共生网络的拓扑结构和驱动因素

不同物种之间的密切联系推动了整个生态系统的群落组成。了解这些共生关联的生态和进化驱动因素具有挑战性，因为它们的结构最终决定了整个物种网络的稳定性和恢复力。在这里，我们编译了一个关于欧洲自然发生的蚂蚁共生网络的详细数据库，以确定影响共生网络拓扑的因素。这些网络承载着无与伦比的大共生关联多样性，跨越整个共生-对抗连续体，包括：(ii) 滋养生物——共生蚜虫、介壳虫、飞虱和毛虫；(iii) 社会寄生虫——寄生蚂蚁物种；(iv) 寄生蠕虫；(v) 寄生真菌。我们剖析了网络拓扑，以研究是什么决定了宿主特异性、共生体物种丰富度以及不同共生体类型切换宿主的能力。我们发现了 722 个与欧洲蚂蚁相关的宏共生体（多细胞共生体）。共生体类型解释了宿主特异性和宿主物种的平均相关性。社会寄生虫与少数在系统发育上高度相关的宿主相关，而其他共生体类型与更广泛的分类分布中的大量宿主相互作用。滋养生物的宿主在所有共生生物类型中的系统发育相关性最低。菌落大小、宿主范围和栖息地类型预测了总共生体丰富度：具有较大菌落大小、较大分布范围或具有更广泛栖息地范围的蚂蚁宿主包含更多的共生体物种。然而，我们发现不同的宿主因素会影响不同类型共生体的多样性。生态因素，如菌落大小、寄主范围和生态位宽度主要决定了食蚁兽物种丰富度，而寄主系统发育是共生滋养生物、社会寄生虫和寄生蠕虫物种丰富度的最重要预测因子。最后，我们发现具有共同生物地理历史的宿主支持更相似的共生体社区。系统发育相关的宿主也共享更多的滋养生物、社会寄生虫和蠕虫，但不是myrmecophiles。综上所述，这些结果表明，生态和进化过程构成了大规模蚂蚁共生网络中宿主的特异性和共生体丰富度，但这些驱动因素的重要性可能会根据共生的类型而发生变化。