Diacamma ceylonense

Unlike what is known in other Diacamma species, one population of D. ceylonense in the Nilgiri Hills exhibits a mechanism of gamergate regulation that is not based on mutilation of the gemmae (Cournault & Peeters 2012).

Distribution based on Regional Taxon Lists
Oriental Region: India, Sri Lanka.

Biology
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 southern Karnataka, referred to as ‘nilgiri’, gamergates do not mutilate their nestmates but monopolize reproduction using dominance interactions (Cournault & Peeters 1992). 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.

Castes
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 ([[Media:Baratte ActaZool 2005 Diacamma ceylonense.pdf|Baratte et al. 2005]]).

Nomenclature

 *  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).

References based on Global Ant Biodiversity Informatics

 * Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
 * Dad J. M., S. A. Akbar, H. Bharti, and A. A. Wachkoo. 2019. Community structure and ant species diversity across select sites ofWestern Ghats, India. Acta Ecologica Sinica 39: 219–228.
 * Dias R. K. S. 2006. Current taxonomic status of ants (Hymenoptera: Formicidae) in Sri Lanka. The Fauna of Sri Lanka: 43-52. Bambaradeniya, C.N.B. (Editor), 2006. Fauna of Sri Lanka: Status of Taxonomy, Research and Conservation. The World Conservation Union, Colombo, Sri Lanka & Government of Sri Lanka. viii + 308pp.
 * Dias R. K. S. 2013. Diversity and importance of soil-dweeling ants. Proceedings of the National Symposium on Soil Biodiversity, chapt 4, pp 19-22.
 * Dias R. K. S., K. R. K. A. Kosgamage, and H. A. W. S. Peiris. 2012. The Taxonomy and Conservation Status of Ants (Order: Hymenoptera, Family: Formicidae) in Sri Lanka. In: The National Red List 2012 of Sri Lanka; Conservation Status of the Fauna and Flora. Weerakoon, D.K. & S. Wijesundara Eds., Ministry of Environment, Colombo, Sri Lanka. p11-19.
 * Dias R. K. S., and R. P. K. C. Rajapaksa. 2016. Geographic records of subfamilies, genera and species of ants (Hymenoptera: Formicidae) in the four climatic zones of Sri Lanka: a review. J. Sci. Univ. Kelaniya 11(2): 23-45.
 * Dias, R.K.S. 2006. Overview of ant research in Sri Lanka: 2000-2004. ANeT Newsletter 8:7-10
 * Emery C. 1911. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125.
 * Tiwari R. N. 1999. Taxonomic studies on ants of southern India (Insecta: Hymenoptera: Formicidae). Memoirs of the Zoological Survey of India 18(4): 1-96.
 * Tiwari, R.N. 1999. Taxonomic studies on ants of southern India (Insecta: Hymenoptera: Formicidae). Memoirs of the Zoological Survey of India 18(4):1-96
 * Varghese T. 2004. Taxonomic studies on ant genera of the Indian Institute of Science campus with notes on their nesting habits. Pp. 485-502 in : Rajmohana, K.; Sudheer, K.; Girish Kumar, P.; Santhosh, S. (eds.) 2004. Perspectives on biosystematics and biodiversity. Prof. T.C. Narendran commemoration volume. Kerala: Systematic Entomology Research Scholars Association, xxii + 666 pp.
 * Vedham K., P. Nair, T. Varghese, G. Royappa, M. Kolatkar, and R. Gadagkar. 2003. Contribution to the Biology of the queenless Ponerine ant, Diacamma ceylonense, Emery (Hymenopter, Formicidae). J.Bombay Nat. Hist. Soc. 100: 533-543