Diacamma indicum

This species is native to the Indian subcontinent and has been introduced into southern Japan.

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Distribution
Terayama et al. (2014) name the single species known from Japan as D. indicum. This is consistent with the molecular data of Viginier et al. (2004) that suggest a human-mediated introduction from India to the Ryukyu islands, Japan.

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

Biology
Kolay and Sumana (2015) - Diacamma indicum is a primitively eusocial ponerine ant reported from the eastern and southern parts of India and Sri Lanka. Their colony size is small and varies from 20–300 monomorphic adults with a single reproductive individual. The colony size remains largely constant throughout the year and there is no drastic reduction in brood content during monsoon. Colonies of D. indicum had been reported to inhabit simple ground nests consisting of a single chamber which is connected to the exterior by a tunnel.

Investigations of their nesting behavior, especially regarding their potential adaptations to seasonal flooding, is reported in this study. Monsoons, presenting a seasonal rather than persistent flooding risk, are dealt with by occupying shallow nests and modifying the entrance with decorations and soil mounds. When nests are inundated they are evacuated and the ants occupy shelters at higher elevations. Nests were less likely to be found in the ground during monsoon season (25.6% of nests subterranean). Nests instead were found in tree trunks (25.6%), hollows of bamboo stems (18.6%), cracks in brick piles (18.6%), fallen logs (4.7%) and other opportunistic nesting sites (7%). Beyond the monsoon season, a majority of nests are subterranean (70.3% nests pre-monsoon and 82.8% post-monsoon).

Viginier et al. (2004) - D. indicum differs from previously studied Diacamma species in various ecological characteristics that are expected to result in higher dispersal rates and/or colonization abilities:

1) Even though Diacamma ants typically nest underground in open areas, D. indicum is more opportunistic with regard to its nesting preferences. We observed typical underground nests, but also nests under stones, in abandoned rice paddies, in fissures of walls in an ancient fort and even in tree branches. Related to this opportunistic nesting habit, the nests of D. indicum are generally shallow, with little signs of construction. 2) Colonies of D. indicum are small (88 ± 62 workers, N = 11) and are prone to emigrate. Nest relocation can be triggered by slight physical disturbance of the nests, whereas in the other Diacamma species from the south of India, workers retreat to the deeper chambers when the nest is disturbed. 3) D. indicum has a larger distribution area relative to other species. Indeed, D. indicum has been found in a large part of southern India and in Sri Lanka, as well as in the north (near Calcutta), whereas the other Diacamma species from the south of India appear geographically restricted to small and nonoverlapping areas. In contrast, D. indicum can be sympatric with other Diacamma species.

Diacamma indicum exhibits various life history traits (see above) suggesting higher dispersal abilities than the other Diacamma species. Only 4 of 11 microsatellites were polymorphic and only 1 had more than 4 alleles over 166 individuals originating from 7 populations from the south of India (Viginier et al. 2004). Only one mitochondrial DNA (mtDNA) haplotype was detected throughout India (including one population in the north) and Sri Lanka. Such a level of polymorphism is exceedingly low compared with other Diacamma species having much smaller ranges in the south of India. Such species exhibited strong genetic differentiation between populations separated by more than a few kilometres. We also analysed the genetic differentiation between the Indian populations and two populations from the Japanese island of Okinawa, which are morphologically similar (e.g. male genitalia, W.L. Brown unpublished monograph) and apparently belong to the same species. The genetic differentiation was high for both markers, suggesting an absence of ongoing gene flow between these populations.

Nomenclature

 *  indicum. Diacamma rugosum var. indica Santschi, 1920g: 179 (w.) INDIA. [First available use of Diacamma rugosum r. vagans var. indicum Forel, 1903d: 400; unavailable name.] Junior synonym of vagans: Mukerjee & Ribeiro, 1925: 205. Revived from synonymy and raised to species: Doums, 1999: 1958.