Evidence from the gut microbiota of swarming alates of a vertical transmission of the bacterial symbionts in Nasutitermes arborum (Termitidae, Nasutitermitinae).

Studies on termite symbiosis have revealed that significant symbiont lineages are maintained across generations. However, most studies have focused only on the worker caste. Little is known about the gut microbiota of reproductives, the most probable vectors for transmitting these lineages to offspring. Using 16S rRNA gene-based Illumina MiSeq sequencing, we compared the gut microbiota of swarming alates of the higher termite Nasutitermes arborum with those of their nestmates from the parental colony. The OTU-based alpha diversity indices showed that the gut microbiota of the alates was at least as diverse as those of non-reproductive adults. It was largely dominated by Spirochaetes mostly of the Treponema I cluster (63.1% of reads), the same dominant taxa found in soldiers and workers of this species and in workers of closely related Nasutitermes species. The termite-specific lineages also included other representative taxa such as several clusters of Bacteroidetes and Fibrobacteres-TG3 group. The microbiota of alates was dominated by a core set of host-specific lineages (87% of reads, 77.6% of OTUs), which were always present across all castes/stages. This first comprehensive survey of the microbiota of the founding reproductives of these xylophagous higher termites shows that the bulk of the host endogenous symbionts, mostly taxa that cannot thrive outside the gut, are brought from the parent colony. The royal pair therefore seems to be a key player in the transmission of symbionts across generations and thereby in host-symbiont codiversification. The high proportion of fiber-degrading lineages in their gut suggests a wood-rich diet unlike the larval stages.