| Diacamma ceylonense|
|At a Glance||• Gamergate|
Distribution based on Regional Taxon Lists
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In Diacamma, the future gamergate is very aggressive towards infertile workers during the first days of her adult life. Overt aggression disappears at about three weeks in D. ceylonense, when the future gamergate begins to lay male-destined eggs and is ready to mate. Over the same period, her Cuticular Hydrocarbons profile alters, changing from a chemical signature similar to that of a sterile worker towards that of a gamergate (Cuvillier-Hot et al. 2002). In nature, these behavioural and chemical changes coincide with a reduction in conflict within the nest: faced with a virgin future gamergate, infertile workers have an interest in producing male-destined eggs; however, once the gamergate produces female eggs, they have an interest in rearing her offspring. This is a clear demonstration of a shift from physical inhibition to chemical signalling.
In queenless ants, dominance interactions are highly directional, suggesting that olfactory recognition occurs. In Diacamma ceylonense, the cuticular hydrocarbons (C25–C35) of nestmate workers (same colony) vary in their proportions according to age and fertility. Newly eclosed adults (‘callows’) initially have the same cuticular profile, but with time this changes to that typical of foragers (Cuvillier-Hot et al. 2001). In contrast, workers that begin to produce eggs develop a different cuticular profile. Several substances (n-C29 and some methyl C25 and C27) discriminate these different social categories (callows, foragers and egg-layers). Inter-colony variation of the cuticular hydrocarbons was much lower than intra-colony variation. We also found qualitative differences between the sexes, with males having a clearly different profile with much more alkanes.
In several populations from south India, referred to as ‘nilgiri’, gamergates do not mutilate their nestmates but monopolize reproduction using dominance interactions . Various lines of evidence indicate that ‘nilgiri’ populations are closely related to the neighboring species D. ceylonense. To determine whether this important behavioural difference between ‘nilgiri’ and D. ceylonense is associated with significant genetic differentiation, Baudry et al. (2003) used microsatellite and mitochondrial markers to examine genetic variation within and between ‘nilgiri’ and D. ceylonense. Genetic differentiation between the two forms was very high, suggesting a lack of gene flow. There was an unexpected pattern of mitochondrial variation, because all ‘nilgiri’ populations showed identical or very closely related COII sequences except one population with a very different haplotype. This divergent haplotype is genetically much more distant from the other ‘nilgiri’ haplotypes than are D. ceylonense haplotypes. This pattern is not observed at the nuclear level, which suggests that introgression of mitochondrial DNA probably occurred in some ‘nilgiri’ populations.
Four larval instars were identified on the basis of cuticular processes – tubercles and spinules – which show discontinuous variation during growth and provide precise and reliable external morphological criteria for instar discrimination (Baratte et al. 2005).
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- ceylonense. Diacamma ceylonense Emery, 1897b: 159 (w.) SRI LANKA.
- Subspecies of rugosum: Forel, 1900d: 318; Forel, 1911d: 377; Emery, 1911d: 66; Chapman & Capco, 1951: 57.
- Status as species: Bingham, 1903: 79; Santschi, 1932b: 14; Bolton, 1995b: 169; Zettel, et al. 2016: 134 (redescription).
- Baratte, S., M. Cobb, J. Deutsch & C. Peeters 2005. Morphological variations in the pre-imaginal development of the ponerine ant Diacamma ceylonense. Acta Zoologica 86: 25-31. PDF
- Baudry, E., Peeters, C., Brazier, L., Veuille, M. & Doums, C. 2003. Shift in the behaviours regulating monogyny is associated with high genetic differentiation in the queenless ant Diacamma ceylonense. Insect. Soc. 50: 390-397.
- Bingham, C. T. 1903. The fauna of British India, including Ceylon and Burma. Hymenoptera, Vol. II. Ants and Cuckoo-wasps. London: Taylor and Francis, 506 pp. (page 79, Revived status as species)
- Cuvillier-Hot, V., Cobb, M., Malosse, C. & Peeters, C. 2001. Sex, age and ovarian activity affect cuticular hydrocarbons in Diacamma ceylonense, a queenless ant. J. Insect Physiol. 47: 485-493.
- Cuvillier-Hot, V., Gadagkar, R., Peeters, C. & M. Cobb, M. 2002. Regulation of reproduction in a queenless ant : aggression, pheromones and reduction in conflict. Proc. R. Soc. Lond. B 269: 1295-1300.
- Emery, C. 1897h. Revisione del genere Diacamma Mayr. Rend. Sess. R. Accad. Sci. Ist. Bologna (n.s.) 1: 147-167 (page 159, worker described)
- Emery, C. 1911e. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125 (page 66, Subspecies of rugosum)
- Forel, A. 1900f. Les Formicides de l'Empire des Indes et de Ceylan. Part VII. J. Bombay Nat. Hist. Soc. 13: 303-332 (page 318, Subspecies of rugosum)
- Santschi, F. 1932d. Résultats scientifiques du voyage aux Indes orientales néerlandaises de LL. AA. RR. le Prince et la Princesse Léopold de Belgique. Hymenoptera. Formicidae. Mém. Mus. R. Hist. Nat. Belg. 4: 11-29 (page 14, Revived status as species)
- Zettel, H., Pal, A. & Laciny, A. 2016. Taxonomic notes on the ant genus Diacamma Mayr, 1862, part 2. Zeitschrift der Arbeitsgemeinschaft Ősterreichischer Entomologen 68: 129-168.