Protective function of the plant-ant Cladomyrma maschwitzi to its host, Crypteronia griffithii, and the dissolution of the mutualism (Hymenoptera: Formicidae)

The hypothesis that the ant Cladomyrma maschwitzi (Formicinae), obligately associated with the tree Crypteronia griffithii(Crypteroniaceae), protects its host plant against herbivory was investigated in an dipterocarp lowland forest in West Malaysia. Censuses of ant activity revealed that the presence of ants is strongly concentrated on immature leaves. Bait experiments showed that the ants regularly attack caterpillars and remove insect eggs from the plant surface. Immature leaves of twigs with ants experimentally removed suffered significantly greater damage levels compared to immature leaves of control twigs (ants maintained). In contrast, the strongly coriaceous mature leaves of both experimental and control twigs did not suffer any damage during the study period. The results suggest this association to be mutualistic, While the mature leaves of the host plant are protected by toughness, immature leaves are protected by the ants, thus acting as biotic defence-agents. The association appears to be restricted to juvenile trees. Examination of both herbarium specimens and adult trees in the field indicate that C. griffithii is not inhabited any more as a mature, flowering tree. The possible implications for the ant/plant association are discussed.