Parallel evolution of termite-egg mimicry by sclerotium-forming fungi in distant termite groups

Abstract

Among the great diversity of insect–fungus associations, fungal mimicry of termite eggs is a particularly fascinating consequence of evolution. Along with their eggs, Reticulitermes termites often harbour sclerotia of the fungus Fibularhizoctonia sp., called ‘termite balls’, giving the fungus competitor-free habitat within termite nests. The fungus has evolved sophisticated morphological and chemical camouflage to mimic termite eggs. To date, this striking insect–fungus association has been found in eight temperate termite species, but is restricted to the lower termite genera Reticulitermes and Coptotermes. Here, we report the discovery of a novel type of termite ball (‘Z-type’) in the subtropical termite, Nasutitermes takasagoensis. Phylogenetic analysis indicated that the Z-type termite ball is an undescribed Trechisporoid fungus, Trechispora sp., that is phylogenetically distant from Fibularhizoctonia, indicating two independent origins of termite-egg mimicry in sclerotium-forming fungi. Egg protection bioassays using dummy eggs revealed that Reticulitermes speratus and N. takasagoensis differ in egg-size preference. A comparative study of termite ball size and egg-size preference of host termites showed that both fungi evolved a termite ball size that optimized the acceptance of termite balls as a unit investment. Termite-egg mimicry by these fungi offers a model case of parallel evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 531–537.