LIMITED AGGRESSIVENESS AMONG AFRICAN ARBOREAL ANTS (HYMENOPTERA, FORMICIDAE) SHARING THE SAME TERRITORIES - THE RESULT OF A CO-EVOLUTIONARYPROCESS

In order to understand how the arboreal ant mosaic functions, we hypot hesized that dominant, sub-dominant and non-dominant ant species shari ng the same trees have evolved behaviors permitting them to limit the cost of interactions during interspecific competition. We chose Oecoph ylla longinoda, the best known ''dominant'' species and two other Form icinae accepted on its territories: Polyrhachis laboriosa, a ''sub-dom inant'' species: and P. weissi, a ''non-dominant'' species. We experim ented in nature and on colonies reared on shrubs cultivated in planter s. During dyadic encounters, foragers of the three species generally i gnored each other. Aggressive interactions were rare and limited to in timidating postures such as opening the mandibles and raising the gast er. However, the need for protein leads arboreal ants sharing territor ies to prey robbing. The expected dominance hierarchy did not hold tru e at all levels as both O. longinoda and P. weissi rob prey from P. la boriosa. Also, foragers of P. weissi were able to follow the recruitme nt trails of P. laboriosa. As a result, predatory behavior is broken d own into two tasks in the latter species: workers carving the prey tha t tolerate the presence of interspecific intruders, and other workers acting as guards. P. laboriosa guards limit the activity of the compet itors thanks to allomones released during marking rounds, by drumming the gaster on the substrate, and through dissuasive postures such as o pening the mandibles, raising the gaster, bending the gaster and an '' outstretched posture'' described here for the first time. We concluded that a code containing chemical and behavioral information working at the interspecific level enables ants sharing territories in the arbor eal ant mosaic to defuse potentially volatile situations without the l oss of individuals. These behaviors can be compared to ''true'' ritual ized displays (i.e. intraspecific), and work here at the interspecific level, implying a co-evolutionary process as selective pressure.