Unraveling the molting associated genes in the subterranean termites, Coptotermes formosanus, Coptotermes gestroi, and their hybrids using RNA-seq analysis
The Formosan subterranean termite (Coptotermes formosanus) and the Asian subterranean termite (Coptotermes gestroi) are the most destructive termite pests in the world. Both species have spread to various regions worldwide with overlapping distributions in a few areas in which pre- and post-zygotic barriers against hybridization between the two species have been lifted. Although initial colony growth rates of hybrid colonies are similar to those of the parental species, colony growth appears to slow down in the hybrids after several years. Observations suggest that workers in hybrid colonies are slower to molt than those of the parental species, suggesting a disruption in this process. To understand the comprehensive gene expression profiles during the molting cycle of workers, differential gene expression profiles based on RNA-seq analysis were recorded for four mating combinations (2 conspecific workers and 2 heterospecific workers) at three different molting periods (pre-, post- and inter-molt). Many differentially expressed genes were identified between heterospecific and conspecific matings at each molting stage as well as within termite species among molting periods. We successfully  identified molting-related genes by characterizing gene expression profiles of the parental species during the molting cycle conducting a time course analysis of transcriptome data. We then compared expression levels of these molting-related genes in the hybrids to identify genes that were over or under expressed compared to the parental species. Genes related to the molting cycle, muscle contraction, response to stress, and ecdysone metabolism were found to be under-expressed in hybrids relative to their parents. These differences will help elucidate the stability and fitness of hybrids between these two Coptotermes species. Moreover, identification of molting related genes in subterranean termites highlights the molecular pathways involved in the molting process in termites. Overall design: RNA-seq profiling during the molting cycle of workers, differential gene expression profiles based on RNA-seq analysis were recorded for four mating combinations (2 conspecific workers and 2 heterospecific workers) at three different molting periods (pre-, post- and inter-molt)