Caste-specific N and C isotope ratios in fungus-growing termites with special reference to uric acid preservation and their nutritional interpretation

1. Nitrogen and carbon isotope ratios and uric acid concentrations in fungus-growing termites (Isoptera: Termitidae: Macrotermitinae), sampled in Cameroon and Thailand, were determined in order to compare castes that are known to differ in behaviour and feeding habits. 2. Nitrogen isotope ratios (δ15N) were either not significantly changed or lower in workers compared with the diet (the fungus combs), whereas carbon isotope ratios (δ13C) were higher in worker termites than in the fungus combs. 3. In old workers, δ15N values were unexpectedly low and correlated negatively with whole-body uric acid concentrations. This indicates that older workers retain uric acid, which has a low δ15N value, to conserve nitrogen within the colony and, furthermore, that older colony members may ultimately be consumed by younger conspecifics.