Supplementary tables from Evidence of cospeciation between termites and their gut bacteria on a geological time scale

Termites host diverse communities of gut microbes, including many bacterial lineages only found in this habitat. The bacteria endemic to termite guts are transmitted via two routes: a vertical route from parent colonies to daughter colonies and a horizontal route between colonies sometimes belonging to different termite species. The relative importance of both transmission routes in shaping the gut microbiota of termites remains unknown. Using bacterial marker genes derived from the gut metagenomes of 197 termites and one <i>Cryptocercus</i> cockroach, we show that bacteria endemic to termite guts are mostly transferred vertically. We identified 18 lineages of gut bacteria showing cophylogenetic patterns with termites over tens of millions of years. Horizontal transfer rates estimated for 16 bacterial lineages were within the range of those estimated for 15 mitochondrial genes, suggesting that horizontal transfers are uncommon and vertical transfers are the dominant transmission route in these lineages. Some of these associations probably date back more than 150 million years and are an order of magnitude older than the cophylogenetic patterns between mammalian hosts and their gut bacteria. Our results suggest that termites have cospeciated with their gut bacteria since first appearing in the geological record.

白蚁宿主拥有多样的肠道微生物群落，其中包含诸多仅在此类生境中被发现的细菌类群。特生于白蚁肠道的细菌通过两种途径传播：一是从亲代蚁群到子代蚁群的垂直传播途径，二是不同蚁群（有时属于不同白蚁物种）之间的水平传播途径。目前尚不明确这两种传播途径在塑造白蚁肠道微生物群过程中的相对重要性。本研究基于197头白蚁与1头隐尾蠊（Cryptocercus）的肠道宏基因组获取细菌标记基因，分析显示特生于白蚁肠道的细菌大多通过垂直途径传播。我们鉴定出18个肠道细菌类群，这些类群与白蚁之间存在长达数千万年的共系统发育（cophylogenetic）模式。对16个细菌类群估算的水平传播速率，处于15个线粒体基因估算的速率范围之内，这表明水平传播较为罕见，垂直传播是这些类群的主要传播途径。其中部分共生关系的历史可追溯至1.5亿年以上，比哺乳动物宿主与其肠道细菌之间的共系统发育模式古老一个数量级。本研究结果表明，自白蚁首次出现在地质记录中以来，它们便与其肠道细菌发生了协同物种形成（cospeciation）。