Nitrogen recycling through proctodeal trophallaxis in the Japanese damp-wood termite Hodotermopsis japonica (Isoptera, Termopsidae)

Summary:

Trophallaxis is one of a variety of nutritional tactics that enable termites to conserve and recycle nitrogenous compounds. In this study, we designed three experiments to reveal the function and importance of proctodeal trophallaxis in the Japanese damp-wood termite Hodotermopsis japonica. First, our observations showed that younger instars and soldiers tended to behave as recipients of proctodeal fluid, while older instars acted mainly as donors. Secondly, nitrogen-deficient groups of termite individuals were introduced to groups of nourished individuals; results indicate that the frequency of proctodeal trophallaxis was significantly higher than in control groups. Additionally, the nitrogen content in the proctodeal fluid of nitrogen-deficient individuals increased after trophallactic interactions with well-nourished individuals. Finally, we set up three groups reared with different concentrations of nitrogenous compounds (amino acids) in their diet, to investigate the correlation between the frequency of trophallactic behavior and the protein concentration of proctodeal fluid. As expected, proctodeal fluid of low protein content was frequently exchanged among individuals in nitrogen-poor conditions, while high-protein proctodeal fluid was transferred less frequently under nitrogen-rich conditions. These results suggest that termites have plasticity of trophallactic behavior in response to their nutritional conditions, and trophallaxis contributes to the nutritional homeostasis of colonies.