Food bodies and their significance for obligate ant-association in the tree genus Macaranga (Euphorbiaceae)

Abstract

The production of extrafloral nectar and food bodies plays an important role in many tropical ant-plant mutualisms. In Malaysia, a close association exists between ants and some species of the pioneer tree genus Macaranga (Euphorbiaceae). Macaranga is a very diverse genus which exhibits all stages of interaction with ants, from facultative to obligatory associations. The ants nest inside the hollow internodes and feed mainly on food bodies provided by the plants. Food body production had previously been reported only in myrmecophytic Macaranga species, where it is usually concentrated on protected parts of the plants such as recurved stipules. We found that non-myrmecophytic Macaranga species also produce food bodies on leaves and stems, where they are collected by a variety of ants. Levels of food body production differ between facultatively and obligatorily ant-associated species but also among the various non-myrmecophytes. This may be related to the degree of interaction with ants. Food body production starts at a younger age in the myrmecophytic species than in the transitional or non-myrmeccophytic Macaranga. Although food bodies of the non-inhabited Macaranga species are collected by a variety of ants, there is no evidence of association with specific ant species. Our observations suggest that food bodies enhance the evolution of ant-plant interactions. Production of food bodies alone, however, does not appear to be the most important factor for the development of obligate myrmecophytism in Macaranga.