Reduced chitinase activities in ant plants of the genus Macaranga

Many plant species have evolved mutualistic associations with ants, protect ing their host against detrimental influences such as herbivorous insects. Letourneau (1998) reported in the case of Piper that ants defend their plan ts principally against stem-boring insects and also reduce fungal infection s on inflorescences. Macaranga plants that were experimentally deprived of their symbiotic Crematogaster ants suffered heavily from shoot borers and p athogenic fungi (Heil 1998). Here we report that ants seem to reduce fungal infections actively in the obligate myrmecophyte Macaranga triloba (Euphor biaceae), while ant-free plants can be easily infected. We also found extre mely low chitinase activity in Macaranga plants. The plants' own biochemica l defense seems to be reduced, and low chitinase activity perhaps may repre sent a predisposition for the evolution of myrmecophytism. These plants are therefore highly dependent on their ante, which obviously function not onl y as an antiherbivore defense but also as an effective agent against fungal pathogens.