Morphological and molecular characterization of the chemosensory system in a subterranean termite

Antennae are essential peripheral sensory organs for insects to adapt to the chemical environment. In social insects, colony function is maintained by a division of labor between the reproductive and non-reproductive castes, and chemosensation is critical for regulating their specialized social activities. Many social species in Hymenoptera (ants, bees, wasps) display caste-specific characteristics in antennal morphology, organization of sensilla, and chemosensory gene repertoire, reflecting their differential tasks. In termites, however, little is known how the division of labor is associated with the chemosensory system. In this study, we characterized the morphological and molecular signatures of chemosensation in the reproductive (dispersal alates) and non-reproductive (worker and soldier) castes of the Formosan subterranean termite, Coptotermes formosanus. Our results demonstrate that the quantitative 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, we identified putative chemosensory genes belonging to the families of odorant receptors, chemosensory proteins, and odorant binding proteins in each caste. The differential gene expression analysis shows that there are greater differences between the reproductive and non-reproductive castes than that between female and male alates or between worker and soldier castes. Our findings suggest that the caste-specific differences in chemosensory morphology and chemosensory gene profiles may underlie the reproductive division of labor in this termite.