Transgressive gene expression disrupts the molting process in hybrids of two invasive termites

The Formosan subterranean termite (Coptotermes formosanus) and the Asian subterranean termite (Coptotermes gestroi) are among the most destructive termite pests in the world. Both species have spread to various regions worldwide with overlapping distributions in a few areas where they can potentially hybridize. Observations suggest that workers in hybrid colonies are slower to molt than those of the parental species, suggesting a disruption in the molting process as a form of hybrid incompatibility. Our goal was to identify misexpressed genes in hybrids during the molting process to help uncover the molecular mechanisms underlying molting disruption. We conducted RNA-seq and identified molting-related genes by performing a time course analysis on differentially expressed transcripts. We identified molting-related genes during each stage of the molting cycle (pre-, post- and inter-molt) in the parental species. We then compared expression levels of these genes in the hybrids to identify genes that were transgressively expressed (either over- or under-expressed) compared to the parental species. We identified several genes related to the molting cycle, muscle contraction, response to stress, and ecdysone metabolism that were under-expressed in hybrids relative to their parents. These differences may help explain the disruption of molting in hybrids and provide insights into the effects of hybridization on misexpression of genes during critical periods of growth and development. Moreover, identification of molting related genes in subterranean termites highlights the molecular pathways involved in the molting process in this group of insects with high developmental plasticity.