Abstract：
The evolution of animals and their gut symbionts is a complex phenomenon, obscured by lability and diversity. In social organisms, transmission of symbionts among relatives may yield systems with more stable associations. Here, we study the history of a social insect symbiosis involving cephalotine ants and their extracellular gut bacteria, which come predominantly from host-specialized lineages. We perform multi-locus phylogenetics for symbionts from nine bacterial orders, and map prior amplicon sequence data to lineage-assigned symbiont genomes, studying distributions of rigorously defined symbionts across 20 host species. Based on monophyly and additional hypothesis testing, we estimate that these specialized gut bacteria belong to 18 distinct lineages, of which 15 have been successfully isolated and cultured. Several symbiont lineages showed evidence for domestication events that occurred later in cephalotine evolutionary history, and only one lineage was ubiquitously detected in all 20 host species and 48 colonies sampled with amplicon 16S rRNA sequencing. We found evidence for phylogenetically constrained distributions in four symbionts, suggesting historical or genetic impacts on community composition. Two lineages showed evidence for frequent intra-lineage co-infections, highlighting the potential for niche divergence after initial domestication. Nearly all symbionts showed evidence for occasional host switching, but four may, more often, co-diversify with their hosts. Through our further assessment of symbiont localization and genomic functional profiles, we demonstrate distinct niches for symbionts with shared evolutionary histories, prompting further questions on the forces underlying the evolution of hosts and their gut microbiomes.
摘要：
动物及其肠道共生体的进化是一个复杂的现象,被脆弱和多样性所掩盖。在社会有机体中，亲属之间共生体的传播可能会产生具有更稳定关联的系统。这里,我们研究了涉及头孢蚂蚁及其细胞外肠道细菌的社会昆虫共生的历史，主要来自宿主专门的血统。我们对9个细菌顺序的共生体进行多基因座系统发育，并将先前的扩增子序列数据映射到谱系分配的共生体基因组，研究20种宿主物种中严格定义的共生体的分布。基于单生和附加假设检验，我们估计这些专门的肠道细菌属于18个不同的谱系，其中15个已成功分离培养。几个共生体谱系显示了在头孢菌素进化史后期发生的驯化事件的证据，在所有20种宿主物种和48个菌落中，仅普遍检测到一个谱系，并通过扩增子16SrRNA测序进行采样。我们发现了四个共生体中系统发育受限分布的证据，表明历史或遗传对群落组成的影响。两个谱系显示了频繁的谱系内共感染的证据，突出初始驯化后生态位发散的潜力。几乎所有共生体都显示出偶尔发生宿主交换的证据，但是5月4日，更多的时候,与他们的主人共同多样化。通过我们对共生体定位和基因组功能谱的进一步评估，我们展示了具有共同进化史的共生体的独特生态位，对宿主及其肠道微生物组进化的潜在力量提出了进一步的质疑。
