SLIPPERY ANT-PLANTS AND SKILLFUL CLIMBERS - SELECTION AND PROTECTION OF SPECIFIC ANT PARTNERS BY EPICUTICULAR WAX BLOOMS IN MACARANGA (EUPHORBIACEAE)

In many ant-plant species of the genus Macaranga in South-East Asia, c onspicuous blooms of epicuticular wax crystals cover the stem surface. We found that many ant species were unable to walk on these surfaces. Only the specific ant partners of glaucous Macaranga host plants were capable of moving on the slippery stems without difficulty. Therefore , the epicuticular coatings of Macaranga myrmecophytes appear to have a selective function and protect the associated ants against competito rs. The epicuticular aggregates function as a physical barrier; no evi dence of chemical repellence was found, The extent to which ''foreign' ' ant species are excluded from a tree strongly depends on inclination , diameter and length of the glaucous stem sections. The particular gr owth form of some glaucous Macaranga ant-plants enhances the influence of the wax barriers. The ant associates of glaucous and glossy Macara nga ant-plants (genera Crematogaster and Camponotus) differ strongly i n their capacity to adhere to the glaucous stems. For this reason, the wax blooms in Macaranga can act as an ecological isolation mechanism for the sympiotic ants. Within the genus Macaranga, we find a high cor respondence between the occurrence of glaucousness and obligatory ant association (50% in ant-plants; 6.7% in non-myrmecophytes). The genus Macaranga thus represents one of the few cases known so far where epic uticular wax crystals are likely to have evolved in relation to insect s.