Fig 1.
Life history of R. speratus and RNA-seq samples.
Each colony of R. speratus produces innumerable alates in spring. After swarming, a pair of male and female alates establishes a new colony, and starts to produce offspring sexually as a primary king (PK) and a primary queen (PQ). As the PQ senesces, secondary queens (SQ) produced asexually by the PQ differentiate within the colony and supplement egg production, eventually replacing the PQ. For RNA sequencing (RNA-seq) analysis, we obtained alates from three swarming colonies, and the young PK and PQ were obtained from three incipient colonies artificially established by the same colonies. Mature PK, mature SQ, and both sexes of soldiers and workers were obtained from four large field colonies.
Fig 2.
(A) General structure of an insect sensillum (modified from [15]). In insects, odorants are detected by the dendrites of neuron that are housed within chemosensilla mainly on antennae and maxillary palps, and contact chemicals are detected mainly on labial palps and tarsi. The neurons are surrounded by accessory cells (To: tormogen, Th: thecogen, and Tr: trichogen cells). The dendrites of neurons are bathed in aqueous sensillar lymph that protects them from dehydration. After entering the sensillum through cuticular pores, the chemicals are transported by odorant-binding proteins (OBPs) or chemosensory proteins (CSPs) to reach the chemoreceptor on the membrane of dendrite as crossing the lymph. Each chemical binds to a corresponding chemoreceptor, thereby a chemical signal in the environment is converted into an electrical signal that can be interpreted by the insect nervous system. (B) Schematic diagrams of odorant receptor (OR), gustatory receptor (GR), and ionotropic receptor (IR) (modified from [16–18]). Insect ORs and GRs are seven-transmembrane domain proteins with a reversed membrane topology (intracellular N-terminus) compared to vertebrate ORs. The OR determining ligand specificity forms heteromers with a highly conserved odorant receptor co-receptor (ORCO) in insects. IRs have recently been discovered as another class of receptors involved in chemoreception in D. melanogaster. IR forms heteromers composed of the compound-specific receptor and the co-receptor.
Table 1.
Summary statistics of assembly.
Fig 3.
Differential expression of chemoreceptors among castes.
The heatmaps exhibit the differential expression of 22 OR, 7 GR, and 12 IR genes among termite castes. Relative expression level indicates the mean normalized Count per Million (CPM), ranging from red (scaled expression of 0) to white (scaled expression of 2.5). The tree at the left corresponds to hierarchical clustering of cluster-averaged expression. Numbers in parenthesis after caste names refer to the numbers of biological replication. Ten individuals were pooled for each sex of worker and soldier to obtain sufficient amount of RNA, while single individuals were used for RNA extraction of the other castes.
Fig 4.
Characteristic expression patterns of ligand-predicted chemoreceptors.
Comparison of the mean CPM of six receptor transcripts among castes and between the sexes (black: female, white: male) of each caste. Young reproductives refer to young PQs and PKs. Mature reproductives indicate mature secondary queens and mature PKs. Error bars denote standard errors. Results of statistical analyses for each gene expression are shown in the upper right side of each graph (n.s.: not significant, *: False Discovery Rate (FDR) < 0.05, **: FDR < 0.01, ***: FDR < 0.001).
Fig 5.
Differential expression of OBP and CSP among castes.
The heatmaps exhibit the differential expression of nine OBPs and three CSPs transcripts among termite castes. Abbreviations are referred to in Fig 3. Relative expression level indicates the mean CPM, ranging from red (scaled expression of 0) to white (scaled expression of 2). Tree at the left correspond to hierarchical clustering of cluster-averaged expression.