Table_1_Can Differences in Symbiont Transmission Mode Explain the Abundance and Distribution of Fungus-Growing Termites in West Africa?.docx

Fungus-growing termites (Isoptera: Macrotermitinae) dominate African savannah ecosystems where they play important roles in ecosystem functioning. Their ecological dominance in these ecosystems has been attributed to living in an ectosymbiosis with fungi of the genus Termitomyces (Lyophyllaceae). Evolutionary theory predicts that the transmission mode of a symbiont determines cooperation and conflict between host and symbiont with vertical transmission (co-transmission of host and symbiont offspring to the next generation) leading to less conflict than horizontal transmission (symbionts are acquired by the host from the environment). Thus, one can hypothesize associations with vertical transmission to be ecological more successful than those with horizontal transmission. We tested this by analyzing whether there is an association between transmission mode and fungus-growing termite species abundance and distribution in West-African savannah and forest ecosystems. We used data from a total of 78 study sites comprising protected National Parks as well as anthropogenically disturbed ecosystems, covering Benin, Côte d'Ivoire, and Togo. Our results showed that, in contrast to expectation, species with horizontal symbiont transmission were more common. We encountered more often species with horizontal than vertical transmission. This result might be due to the fact that only five out of the 25 identified fungus-growing termite species had vertical transmission. Yet, species with horizontal transmission also had higher relative abundances within study sites than those with vertical transmission. Thus, transmission mode is unlikely to explain abundance differences between fungus-growing termite species.

培菌白蚁（Isoptera: Macrotermitinae，等翅目大白蚁亚科）是非洲稀树草原生态系统的优势类群，在生态系统功能维持中发挥关键作用。这类白蚁在该类生态系统中的生态主导地位，源于其与白蚁伞属（Termitomyces，白蘑科Lyophyllaceae）真菌形成的外共生（ectosymbiosis）关系。进化理论预测，共生体的传播模式决定宿主与共生体之间的合作与冲突：垂直传播（vertical transmission，即宿主与共生体的后代共同传递至下一代）相较于水平传播（horizontal transmission，即宿主从环境中获取共生体），引发的冲突更少。据此可提出假说：采用垂直传播模式的共生关系，其生态适应性优于水平传播的共生关系。本研究通过分析西非稀树草原与森林生态系统中，传播模式与培菌白蚁物种丰度、分布的相关性，对该假说进行了验证。我们共收集了78个研究样地的数据，样地覆盖贝宁、科特迪瓦、多哥境内的国家公园（National Parks）及受人为活动干扰的生态系统。研究结果与预期不符：采用水平传播共生方式的物种更为常见，我们观测到的水平传播物种数量显著多于垂直传播物种。这一结果可能源于：在已鉴定的25种培菌白蚁中，仅5种采用垂直传播模式。此外，在各研究样地内，水平传播物种的相对丰度也高于垂直传播物种。因此，传播模式无法解释培菌白蚁物种间的丰度差异。