Doctor of Entomology (PENTM)
The Formosan subterranean termite, Coptotermes formosanus, is a eusocial insect species. Its members live in colonies consisting of reproductive (queen and king) and non-reproductive individuals (workers and soldiers). Olfaction is an essential sense for the social life of many insects. However, in termites, little is known about how olfactory cues are perceived in the peripheral sensory system (antennae) and processed in the central nervous system (brain) to elicit different behavioral responses across castes. In this study, we investigated the olfactory system in all castes (soldiers, workers, and reproductive alates), from the antennal and brain morphology to the antennal gene expression.
The morphological analysis revealed nine types of antennal sensilla present in all castes, of which about 90% are chemosensilla. The quantitative composition of antennal sensilla differs between alates and non-reproductives (workers and soldiers). Structural differences in the brain were also found among castes. While alates have larger brains and antennal lobes than the non-reproductive castes, the numbers of glomeruli in the antennal lobes are similar between alates and workers, with soldiers possessing the fewest glomeruli. The morphological characteristics are associated with developmental differences and behavioral repertoires among castes.
At the molecular level, more than 100 putative chemosensory genes were identified from the antennal transcriptomes of all castes. The differential gene expression analysis revealed greater differences between reproductive and non-reproductive castes than that between workers and soldiers. The odorant receptor co-receptor (orco) is a fundamental protein for the function of olfaction. The orco gene is mainly expressed in the antennae, with higher expression levels in alates than workers and soldiers. In addition, orco is expressed in eggs and all postembryonic developmental stages, suggesting a possible function in olfactory neurogenesis during early development. The expression of orco is downregulated after seven days of starvation in workers, which may contribute to the nutrition-dependent olfactory plasticity.
Overall, this research provided a comprehensive analysis of the olfactory system across castes at the morphological and molecular levels, which is fundamental to understanding the caste-based division of labor in termites. The results will facilitate future investigations of chemosensory mechanisms underlying the regulation social behavior.
Castillo, Paula, "Morphological and Molecular Characterization of the Olfactory System in the Formosan Subterranean Termite" (2023). LSU Doctoral Dissertations. 6234.
Available for download on Wednesday, July 10, 2024