Contributions to the biology of the queenless ponerine ant Diacamma ceylonense Emery (Formicillae)

Abstract

All ants are generally classified as highly eusocial, However, there are some 100 species of ants belonging to the morphologically primitive subfamily Ponerinae, which lack a morphologically differentiated queen. One or a small number of mated workers (gamergates) function as queens, i.e. they produce male as well as female offspring. Such ant species are of great interest as they provide unique opportunities to understand the causes and consequences of queenlessness. This is the first report ofa long-term field study we have initiated on a large population of the queenless ponerine ant, Diacamma ceylonense Emery, on the campus of the Indian Institute of Science, Bangalore. Data are provided on the numbers of colonies present during a 213-week period, from which the probable time of colonisation of the site by D. ceylonense is suggested. Twenty-six entire colonies were excavated to study the adult and brood composition. While some colonies did not appear to have a gamergate at the time of excavation, others had only one gamergate per colony. Only the gamergate was mated and had well developed ovaries, while all the workers were unmated and had undeveloped ovaries. Excavated colonies had an average of 230 adult females, 2 males and 80 items of brood. The gamergates were indistinguishable from their workers in body size but there was significant variation in the size of workers between colonies. On an average, colonies employed 24% of their workers outside the nest for foraging and other duties. The relative constancy of this proportion permits estimation of total colony size by merely estimating the number of extranidal workers and thus without having to excavate the nests. In the five colonies studied, foragers spent an average of 9 to 23 days of their lives in performing foraging duties. Most foragers remained faithful to one or a narrow range of compass directions, although such directional preferences of all of them put together permitted colonies to exploit resources in all directions.