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谱系（bacterial lineages）。白蚁肠道特有的细菌存在两类传播途径：一是从亲代蚁群向子代蚁群的垂直传播，二是有时发生在不同白蚁物种蚁群间的水平传播。目前，这两类传播途径在塑造白蚁肠道微生物群（gut microbiota）方面的相对重要性仍未明确。本研究依托从197头白蚁以及1头隐尾蠊属（Cryptocercus）蜚蠊的肠道宏基因组（gut metagenomes）中获取的细菌标记基因，证实白蚁肠道特有的细菌主要通过垂直途径传播。本研究共鉴定出18个肠道细菌谱系，它们与白蚁在数千万年的演化历程中呈现共系统发育（cophylogenetic）模式。对16个细菌谱系估算得到的水平传播速率，与15个线粒体基因的估算速率区间重合，这表明水平传播较为罕见，垂直传播是这些细菌谱系的主导传播途径。其中部分共生关联的历史可追溯至1.5亿多年前，其演化时长较哺乳动物宿主与其肠道细菌的共系统发育模式高出一个数量级。本研究结果显示，自白蚁首次被记录于地质历史中以来，其便与其肠道细菌持续发生共物种形成（cospeciation）过程。