title: Slippery ant-plants and skilful climbers: selection and protection of specific ant partners by epicuticular wax blooms in Macaranga (Euphorbiaceae).
abstract: In many ant-plant species of the genus Macaranga in South-East Asia, conspicuous 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 competitors. The epicuticular aggregates function as a physical barrier; no evidence 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 growth form of some glaucous Macaranga ant-plants enhances the influence of the wax barriers. The ant associates of glaucous and glossy Macaranga ant-plants (genera Crematogaster and Camponotus) differ strongly in 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 correspondence 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 epicuticular wax crystals are likely to have evolved in relation to insects.
authors.affiliation: Zoologie II, Universität Würzburg, Biozentrum, Am Hubland, D-97074 Würzburg, Germany, , , , , , DE.
authors.forename: Walter
authors.initials: W
authors.lastname: Federle
authors.affiliation: Zoologisches Institut, J.W. Goethe Universität, Siesmayerstr.70, D-60054 Frankfurt, Germany, , , , , , DE.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Maschwitz
authors.affiliation: Zoologie III, Universität Würzburg, Biozentrum, Am Hubland, D-97074 Würzburg, Germany, , , , , , DE.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Fiala
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany, , , , , , DE.
authors.forename: Markus
authors.initials: M
authors.lastname: Riederer
authors.affiliation: Zoologie II, Universität Würzburg, Biozentrum, Am Hubland, D-97074 Würzburg, Germany, , , , , , DE.
authors.forename: B
authors.initials: B
authors.lastname: Hölldobler
keywords: Adhesion; Epicuticular wax crystals; Glaucousness; Key words Ant-plant symbiosis; Macaranga