DAVIES, STUART J.1, SHAWN K.Y. LUM2*, RAYMUND CHAN3, and LUAN KENG WANG4. 1Harvard University Herbaria, Dept of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA; 2Natural Sciences Academic Group, National Institute of Education, Singapore; 3Jepson Herbarium and Dept of Integrative Biology, University of California, Berkeley, CA; 4Burke Museum, Dept of Zoology, University of Washington, Seattle, WA. - Evolution of myrmecophytism in west Malesian species of Macaranga (Euphorbiaceae).
Plants inhabited by ants (myrmecophytes) have evolved in a diversity
of tropical plant lineages. The Paleotropical tree genus
Macaranga (Euphorbiaceae) includes ~300 species. Twenty-six
west Malesian species of Macaranga are myrmecophytic, and they
vary in their morphological specializations for ant association. In
order to ascertain the origins and diversification of myrmecophytism
in Macaranga, phylogenetic analyses of selected Malesian
species were conducted using morphological and nrITS DNA characters,
followed by the mapping of ant-plant associations and allied traits
onto the resulting phylogenetic trees. Combined analysis of
morphological and ITS data resulted in a well-supported hypothesis of
relationships. Mapping 'myrmecophytism' on all most parsimonious trees
resulting from the combined analysis indicated that myrmecophytism
evolved independently in Macaranga between two and four times
and was lost between one and three times (five changes). Mapping
morphological traits on the phylogeny suggested that myrmecophytism
was not homologous among lineages, and that each independent origin
involved a suite of different specializations for the ant-plant
association. A number of different morphological, ecological and
biogeographic factors appear to have facilitated and constrained this
radiation of ant-plants.
Key words: Macaranga, myrmecophytism, west Malesia