Ontogenic potentialities of the worker caste in two sympatric subterranean termites in France.

In termites, the capacity of workers to differentiate into neotenic reproductives is an important characteristic that deserves particular attention. To gain insight into the differentiation pathway, the potentialities of workers and the endocrinal changes during the formation of neotenics were compared in two sympatric termites, Reticulitermes flavipes and Reticulitermes grassei. After 1 year of development, 100% of R. flavipes worker groups produced neotenics against only 63% of R. grassei groups. The average production of female neotenics was significantly higher in R. flavipes worker groups compared with R. grassei groups and R. flavipes produced a greater proportion of female neotenics. Moreover, R. flavipes produced more offspring, not only because there were more females, but also because R. flavipes females were more productive. Moreover, the offspring produced by R. flavipes grew faster than the offspring of R. grassei. Both ecdysteroid and juvenile hormone (JH) titers varied significantly during the development of neotenics. The two species showed similar ecdysteroid titer variation patterns. However, the JH titer variation patterns strongly differed: in R. grassei, the concentration of JH increased in maturing neotenics then dropped in mature neotenics, whereas in R. flavipes, the level of JH was significantly higher than in R. grassei and remained constantly high in mature neotenics. Overall, these results suggest that these two species differ strongly in many life-history traits as well as in the physiological control of their caste differentiation system. Possible origins and mechanisms of such interspecific variations are discussed, as well as their evolutionary and ecological consequences.