The development of adultoid reproductives and brachypterous neotenic reproductives from the last instar nymphs in Reticulitermes labralis (Isoptera: Rhinotermitidae): a comparative study.

Secondary reproductives develop primarily from nymphs. However, they have been rarely studied; in particular, the development of adultoid reproductives (AR) with floppy wings is still unclear. In this study, the change in juvenile hormone (JH) levels, vitellogenin gene expression, and oogenesis during the development of AR and brachypterous neotenic reproductives (BN) from the last instar nymphs of Reticulitermes labralis are investigated and compared. The results showed that the AR derived from the last instar nymphs by molting, and they were more similar to neotenic reproductives in morphology. In addition, the paired AR were not able to survive in the absence of workers. In R. labralis, the process of the last instar nymphs developing into AR and BN took an increase in JH level as a starting point. The JH level of the last instar nymphs molting into BN was approximately 1.5-fold higher than that of the AR. Additionally, The JHIII level of BN peaked on day 5, and that of AR peaked on day 10, which induced the onset of vitellogenesis in BN and AR, respectively. After molting, the vitellogenin gene expression levels of both BN and AR initially increased and then declined, and the expression levels in the BN were significantly higher than those in the AR. In addition, the oocytes of BN matured earlier than those of the AR, and the number of eggs laid by the BN was higher than the number laid by the AR. Our results demonstrate that, in R. labralis, the last instar nymphs can develop into AR, which are significantly different from BN in their development.

Testicular development and modes of apoptosis during spermatogenesis in various castes of the termite Reticulitermes labralis (Isoptera:Rhinotermitidae).

The separation of reproductive and non-reproductive roles based on caste differentiation is the most prominent characteristic of termites. However, little is known about the mechanism of male reproductive division that underlies caste differentiation. In the present study, testicular development and stage-specific apoptotic patterns were investigated and compared during spermatogenesis in reproductives, workers and soldiers of the termite Reticulitermes labralis. The results showed that male workers were divided into two types, the workers with spermatozoa (WS) and the workers without spermatozoa (WN). Spermatogenesis in WN and soldiers arrested at the spermatocyte stage. Moreover, there were significant differences in testicular size and spermatogenesis among the various castes. The mode of apoptosis in late instar WS was similar to the reproductives, as demonstrated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) analysis. First, the majority of apoptotic cells were spermatogonia, and the spermatogonia of both late instar WS and reproductives exhibited lower apoptotic rates compared with late instar WN and soldiers. Second, the spermatocytes and spermatids showed very little apoptosis in the late instar WS and reproductives, and no TUNEL signal was detected in any of the examined spermatozoa. Our findings suggest that the male workers undergo a basal developmental schema comprising two undifferentiated larval instars, followed by a bifurcated development into either (i) the sexual lineage, in which the workers are able to provide normal spermatozoa to queens, or (ii) the neuter lineage, in which the male workers lose reproductive options. The level of testicular development may explain the significant discrepancies in reproductive capacity among the reproductives, workers and soldiers and reveal the reproductive division in male workers. These differences are controlled by apoptosis during early spermatogenesis.