Differential role of symbiotic fungi in lignin degradation and food provision for fungus-growing termites (Macrotermitinae: Isoptera)

1. To investigate whether the role of symbiotic fungi in lignin degradation and food provision differs among fungus-growing termites (four species of Macrotermes, three species of Odontotermes, Hypotermes makhamensis, Ancistrotermes pakistanicus and Pseudacanthotermes militaris), the chemical composition of fungus combs of different ages and the chitinolytic activity in the gut of termites were analysed. In addition, the carbon stable isotope ratios (δ¹³C) in old combs, worker termite tissues and fungal nodules (aggregated conidia) were compared. 2. In Macrotermes spp., the carbohydrate: lignin ratio of the combs increased with increased comb age, but it decreased or remained the same in Odontotermes spp., H. makhamensis, A. pakistanicus and P. militaris. In contrast, the chitin:carbohydrate ratio and ash content increased more over time in the combs of Odontotermes spp., H. makhamensis, A. pakistanicus and P. militaris than in the combs of Macrotermes spp. 3. Chitinolytic activity in the gut of workers was higher in O. takensis, H. makhamensis and A. pakistanicus than in M. annandalei. 4. In all species examined, the δ¹³C value increased in the sequence: old combs < termites < fungal nodules. Based on a two-source model of δ¹³C, the contribution of fungi to termite nutrition was considered higher in Odontotermes spp., H. makhamensis, A. pakistanicus and P. militaris than in Macrotermes spp. 5. These results suggest that symbiotic fungi play different roles among fungus-growing termites. In Macrotermes spp., the main role of symbiotic fungi is to degrade lignin, so that the termites can utilize cellulose more efficiently, whereas in Odontotermes spp., H. makhamensis, A. pakistanicus and P. militaris, it is to serve as a food source.