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.