Caste-specific expression of chemosensory genes in the Formosan subterranean termite

Subterranean termites live in underground colonies with a division of labor among castes (i.e., queens and kings, workers, and soldiers). The function of social colonies relies on sophisticated chemical communication. In termites, little is known about how the division of labor is regulated throught the chemosensory system. In this study, we characterized the morphological and molecular signatures of chemosensation in the dispersal alates in comparison with workers and soldiers in the Formosan subterranean termite, Coptotermes formosanus. We found that the composition of antennal sensilla diverges between reproductive and non-reproductive castes, but not between female and male alates or between worker and soldier castes. In addition, the antennal transcriptome analysis shows that there are more differently expressed genes between the reproductive and non-reproductive castes than that between workers and soldiers. Furthermore, we identified an ortholog encoding the odorant receptor co-receptor (Orco), and examined its temporal and spatial expression and variation in response to social conditions. The results show that Orco is expressed in all castes and developmental stages, including eggs, with an upregulation in the antennae of alates. The expression of Orco decreases in workers upon starvation for seven days, but it is not affected by the presence of soldiers or different group sizes. Our findings imply that the caste-specific differences in the chemosensory system may underlie the reproductive division of labor in termites, and further suggests a link between olfactory sensitivity and nutritional status.