MICHELANGELI, FABIAN A. L.H. Bailey Hortorium, Department of Plant Biology, Cornell University, Ithaca, NY 14853. - Ant-protection against herbivory and evolution of myrmecophytism in the genus Tococa (Melastomataceae).
Tococa is a neotropical genus of small trees and shrubs,
composed of about 45 species, 2/3 of which have simbiotic association
with ants. The ants inhabit domatia that developes at the base of the
leaf blade or the apex of the petiole. Natural history observations
and field experiments were carried out in order to study the
characteristics of this association. Ants from at least 7 different
genera from 3 different subfamilies were found inhabiting the domatia
of Tococa. Depending on their behavior, the inhabiting ants can
be characterized as timid or aggressive. The different types of
behavior are not associated with the host species, but with the
surrounding environment. Neither there are co-specific associations
between the ants and the different species of Tococa. Ant
exclusion experiments in ant-bearing Tococa demonstrated that
both timid and aggressive ants protect their host plants against
potential herbivores, by both warding off scouts of leaf-cutter ants
and removing the eggs of Lepidoptera and Coleoptera. The presence of
stem and petiole trichomes seems to be critical for the establishment
of ant colonies, since their removal often results in the ants
vacating their host plant. Employing a previously obtained phylogeny
of the genus Tococa, it was possible to determine that ant
domatia, and thus myrmecophytism, have evolved at least twice within
the genus. Secondary losses of domatia have also occurred. These
losses can be associated with the life history and habitat of the
species lacking domatia. The presence of stem pubescence has predated
the evolution of ant domatia in both instances within Tococa.
Key words: ant-plants, Character evolution, Melastomataceae, myrmecophytism, Tococa