Characterization of the transcriptomes and cuticular protein gene expression of alate adult, brachypterous neotenic and adultoid reproductives of Reticulitermes labralis

The separation of primary reproductive and secondary reproductive roles based on the differentiation of alate adults and neotenic reproductives is the most prominent characteristic of termites. To clarify the mechanism underlying this differentiation, we sequenced the transcriptomes of alate adults (ARs), brachypterous neotenics (BNs) and adultoid reproductives (ANs) from the last instar nymphs of Reticulitermes labralis. A total of 404,152,188 clean sequencing reads was obtained and 61,953 unigenes were assembled. Of the 54 identified cuticular protein (CP) genes of the reproductives, 22 were classified into the CPR family and 7 were classified into the CPG family. qRT-PCR analyses of the 6 CP genes revealed that the CP genes involved in exocuticle sclerotization were highly expressed in the ARs and RR-1 involved in soft endocuticle was highly expressed in the ARs and ANs. These results suggest that the alate adults might increase cuticular component deposition to adapt to new or changing environments and that the development of reproductive individuals into primary or secondary reproductives is controlled by the expression of cuticular protein genes involved in the hardening of the exocuticle. In addition, the AN caste is a transitional type between the BN and AR castes in the process of evolution.