1. Deneubourg, J. L., Goss, S., Franks, N. 6. Goss, S., Aron, S., Deneubourg, J. L., 10. M6glich, M., Maschwitz, U., HOlldo- R., Pasteels, J. M.: J. . Behav. 2, Pasteels, J. M.: Naturwissenschaften bier, B. : Science 186, 1046 (1974) 719 (1989) 76, 579 (1989) "11. HOlldobler, B., Wilson, E. O.: The 2. Deneubourg, J. L., Aron, S., Goss, S., 7. Beckers, R., Deneubourg, J. L., Goss, . Belknap Press of Harvard Univ. Pasteels, J. M. : ibid. 3, 159 (1990) S. : J. Theor. Biol. (in press) Press 1990 3. Franks, N. R., Gomez, N., Goss, S., 8. Deneubourg, J. L., Goss, S., Sandini, 12. Beckers, J. L., Goss, S., Deneubourg, J. Deneubourg, J. L.: ibid. 4, 583 (1991) G., Beckers, R., in: Self organization, L., Pasteels, J. M.: Psyche 96, 239 4. Camazine, S.: Behav. Ecol. Sociobiol. emerging properties and learning, p 267 (1989) 28, 61 (1991) (A. Babloyantz, ed.). NATO ASI series 13. Pasteels, J. M., Goss, S., Deneubourg, 5. Seeley, T. D., Camazine, S., Sneyd, J.: B, Physics 260 (1991) J. L. : Experientia Suppl. 54, 155 (1987) ibid. 28, 277 (1991) 9. HOlldobler, B.: Adv. Stud. Behav. 8, 75 (1978)

Naturwissenschaften 79, 572- 573 (1992) © Springer-Verlag 1992 "gemmae" are normally recessed into a distinct cavity, although they can be bitten off during dominance interac- Alternative Dominance Mechanisms Regulating tions. In D. australe, the gemmae are Monogyny in the Queenless filled with glandular cells which are connected to minute pores opening to C. Peeters the outside [3]. Queens (which constitute a mor- Laboratoire d'Ethologie, CNRS URA 667, Universit6 Paris Nord, F-93430 Villetaneuse and Zoologie II, Biozentrum der Universit~it, phologically specialized caste in ants) W-8700 Wtirzburg, FRG do not exist in Diacamma, and instead members of the worker caste are able to J. Billen mate and reproduce ("" [4]). In D. australe and D. rugosum, ZoOlogisch Instituut, Katholieke Universiteit Leuven, B-3000 Leuven there is only one in each B. H611dobler colony, and other workers are inhibited from laying eggs. The gamergate is the Zoologie II, Biozentrum der Universit~t, W-8700 Wtirzburg, FRG only individual which keeps the gemmae - new workers which emerge Compared to other ants, the genus Dia- workers eclose with a single pair of tiny in her presence are soon mutilated [5, camma (subfamily ) is mor- bladder-like appendages attached later- 6]. Workers without gemmae have phologically extraordinary, because all ally on the thorax ([1, 2], Fig. 1). These never been found to be inseminated, which suggests that the gemmae are es- sential to mate. Their exocrine secre- tions may function as sexual attrac- tants. Furthermore, mutilation of the gemmae has a dramatic effect on indi- vidual behavior, which soon changes from aggressive to timid. Although mu- tilation of the gemmae is an essential component of reproductive dominance in D. australe and D. rugosum, we re- port here that it does not occur in an In- dian species of Diacamma. We collected ten colonies of D. vagans from Masunigodi, Tamil Nadu, south- ern India. We immediately noticed that all the workers retain the gemmae in this species (except for sporadic indi- viduals in some colonies). A his- tological investigation revealed that a gemma of D. vagans contains much fewer glandular cells (about 50) than in D. australe (about 500); the external Fig. 1. Scanning electron micrograph of a gemma in D. vagans. Arrow indicates the narrow morphology (Fig. 1) is similar, al- stalk which is attached to the thorax. Note the long sensory hairs on the gemma's upper though there are fewer pores. Dissec- surface tion of a sample of 390 workers from 572 Naturwissenschaften79 (1992) © Springer-Verlag 1992 five colonies, together with experi- gosum (Peeters, unpublished), and in- and D. rugosum is exceptional, since mental fission of colonies, indicated stead a sex attractant emanating from both sexual attractiveness and that there is only one gamergate per the gemmae may be more important. dominance status are controlled solely colony. The other workers, only a few The different patterns of aggression by the mutilation of the gemmae. of which were mutilated, all had empty documented in the orphaned colonies spermathecae, and exhibited unde- of D. vagans seem to correspond to This study was supported by the veloped ovaries in the presence of a various stages involved in the establish- Deutsche Forschungsgemeinschaft gamergate. ment of a stable . (Leibniz Prize to B. HNldobler). We We studied four large colony fragments Over time, the interactions between a thank T. Musthak Ali (Department of without a gamergate [7]; these groups dominant worker and her subordinates Entomology, University of Agri- consisted of 50-250 workers marked become less physical, and this is asso- cultural Sciences, Bangalore) for help with individual color codes. In two ciated with the cessation of ovarian ac- in excavating the colonies; O. Dtil3- orphaned groups, frequent aggressive tivity in the latter. Eventually, the top- mann (Warzburg) for some of the be- interactions occurred among a propor- ranked worker may exhibit sexual call- havioral observations and dissections; tion of the workers. Various indi- ing, and we presume that she will mate K. Fiedler and J. Heinze (Warzburg) viduals were repeatedly bitten and and become the gamergate when for- for comments on this manuscript. jerked, or were held captive for long eign males visit the nest. When the do- periods of time. Examination of the minant worker was removed from a pattern of aggressive interactions in- colony in which no aggression was oc- dicated that one worker was clearly do- curring, after 1 day violent fighting minant in each group. Subordinate started among a small number of work- workers who were aggressive towards ers. each other behaved timidly when at- The gemmae of Diacamma workers are tacked by the top-ranked worker. unique structures among . The Many workers laid eggs, but these were sensory of the hairs on their often cannibalized by the dominant in- upper surface (Fig. 1), and the branch- dividual. In contrast, her eggs were ing pattern of their afferent axons in Received August 17, 1992 never eaten. When dissected, many the central nervous system [9], suggest workers involved in dominance interac- homology with the first pair of wings tions had active ovaries (no workers found in ant queens. However, the were inseminated). glandular cells present inside have 1. Tulloch, G. S.: Ann. Entomol. Soc. In another two orphaned groups, com- evolved de novo, but it is not clear Am. 27, 273 (1934) paratively little aggression was ob- whether they have a pheromonal func- 2. Bitsch, J., Peeters, C.: Bull. Soc. en- served. A dominant worker was also rec- tion in all species. Furthermore, in D. tomol. France 96, 213 (1991) ognized, who frequently patrolled vagans, there is no association between 3. Peeters, C., Billen, J.: Experientia 47, through the nest, with body held up the presence or absence of the gemmae, 229 (1991); BiUen, J., Peeters, C. : Belg. high ("strutting"). She directed an- and the level of aggressiveness. In the J. Zool. 121, 203 (1991) tennal boxing or mandible threats to- absence of phylogenetic data on the re- 4. Peeters, C.: Biol. J. Linn. Soc. 44, 141 (1991) wards nest mates, who often avoided lationships within the genus Dia- 5. Fukumoto, Y. Abe, T., Taki, A. : Phys- her. Eggs were not laid by other work- camma, it is not yet possible to de- iol. Ecol. Japan 26, 55 (1989) ers, and dissections confirmed that only termine whether the noninvolvement of 6. Peeters, C., Higashi, S.: Naturwissen- the dominant worker had active the gemmae in reproductive control is schaften 76, 177 (1989) ovaries. The latter was distinguished by the ancestral condition, or a secondary 7. Peeters, C., Diil3mann, O., H011dobler, another behavior - she frequently modification. B., Musthak All, T., Billen, J. : in prep. rubbed both hind legs against her pos- The occurrence within the genus Dia- 8. HSlldobler, B., Haskins, C.: Science terior abdominal tergites, both inside camma of two different mechanisms 195, 793 (1977) and outside the observation nest. Since regulating the incidence of mating is of 9. Gronenberg, W., Peeters, C., in: Proc. a pygidial gland occurs in this region, great evolutionary interest. The 20th G~ttingen Neurobiol. Conference, p. 127 (N. Eisner, D. Richter, eds.). this conspicuous behavior may repre- dominance interactions in D. vagans Stuttgart: Thieme 1992 sent sexual calling. In RhytMoponera are similar to those observed in other 10. Ito, F., Higashi, S.: Naturwissen- metallica, the pygidial gland has been queenless ponerines, where they also schaften 78, 80 (1991) shown to be involved in mate attraction function to regulate egg laying, and 11. Peeters, C., in: Queen number and so- [8]. This form of sexual calling was ultimately insemination [10, 11]. In ciality in (L. Keller, ed.). Oxford never observed in D. australe or D. ru- contrast, the situation in D. australe Univ. Press 1993

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