Abraham HEFETZ and Christine ERRARD
Department of Zoology, Tel Aviv University, Ramat Aviv, 69978 Israel and Laboratoire
d'Ethologie Experimentale et Comparee, Universite Paris Nord, CNRS 667, 93430,
Villetaneuse, France.
Ants reared in mixed species group (Manica rubida co-nesting with Formica selysi) exchange constantly recognition cues among them, resulting in a unifomm group odor that is composed of substances produced by both species. To unravel whether the postpharyngeal glands is a source of recognition cues we tested the reaction of M. rubida to their nestmates that was treated with glandular secretion from varoius sources.
Behavioral tests comprised of two consecutive encounters between five ants and their color marked nestmate. The first encounter was performed with an untreated ant constituting a control, whereas in the second encounter the marked ant was treated with postpharyngeal gland exudate. Scoring was done using an aggression index obtained by direct observation, and an agitation index deduced from a frame by frame analysis of videotapes of the various tests. Tests were conducted with M. rubida that originated from homospecific colonies or from mixed species group. The PPG source was either from M. rubida or from F. selysi. as appropriate.
In the tests using ants from homospecific colonies, when the glandular secretion originated from an alien M. rubida ant, the ants became very agitated and were aggressive towards their nestmate. In contrast to the application of exudates originating from a nestmate, that left the ants generally calm, although their rates of selfgrooming increased. Augmented aggression was also observed when the secretion applied was from F. selysi. Having established that the glandular secretion is a source of recognition cues, we repeated these experiments using M. rubida that were reared in mixed species group. In general, the reaction of these ants was much milder and was graded dependeing on the source of the secretion. The highest aggression appeared towards ants applied with exudates of F. selysi from homospecific colonies. At the other exterme, the reaction towards the ants applied with secretion belonging to F. selysi nestmates was not significantly different from the control.
These results demonstrate that workers M. rubida that are reared in mixed species group and are exposed to a heterospecific colony odor become more tolerant to ants bearing a similar bouquet. Nevertheless the odor of nestmates or alien ants reared in similar mixed species groups seems to be the most familiar.