Lignocellulose digestion by the higher Attine fungus-gardening ant symbiosis

Fungus gardening ants exhibit a unique interaction with specific fungi in an obligatory symbiosis; ants feed and prune their fungal symbiont in exchange for nourishment. While recent studies show that leaf-cutting (Atta and Acromyrmex) ants’ fungus is unable to digest cellulose, there has been little or no comparison to the other higher attine (family Myrmecinae) fungus gardening ants. Colonies of Trachymyrmex septentrionalis were fed either a diet of Texas Red Oak (Quercus buckleyi) catkins (staminate flowers) or tent caterpillar (Malacosoma americanum) frass to assess the ability of the symbiosis to digest plant-based carbohydrates. Fiber digestion techniques were used to evaluate the differences in lignocellulose and hemicellulose content of T. septentrionalis diets before and after assimilation in the fungus garden. The evidence supports the hypothesis that T. septentrionalis colonies are significant metabolizers of cellulose as levels of lignocellulose and hemicellulose were significantly lower in refuse piles than in the substrates the colonies were fed. Fungus gardens of T. septentrionalis extracted about 46% and 47% of the lignocellulose present in the catkins and frass, respectively, as well as 43% of the hemicellulose found in catkins and 67% of the hemicellulose that was found in frass.