Domatia as most important adaptations in the evolution of myrmecophytes in the paleotropical tree genusMacaranga (Euphorbiaceae)

The paleotropical tree genusMacaranga (Euphorbiaceae) comprises all stages of interaction with ants, from facultative associations to obligate myrmecophytes. In SE.-Asia food availability does not seem to be the limiting factor for the development of a close relationship since all species provide food for ants in form of extrafloral nectar and/or food bodies. Only myrmecophyticMacaranga species offer nesting space for ants (domatia) inside internodes which become hollow due to degeneration of the pith. Non-myrmecophytic species have a solid stem with a compact and wet pith and many resin ducts. The stem interior of some transitional species remains solid, but the soft pith can be excavated. The role of different ant-attracting attributes for the development of obligate ant-plant interactions is discussed. In the genusMacaranga, the provision of nesting space seems to be the most important factor for the evolution of obligate myrmecophytism.