To reunite or not to: Study on artificially fragmented Diacamma indicum colonies

Sahu, Prateek Kumar (2018) To reunite or not to: Study on artificially fragmented Diacamma indicum colonies. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Social insects are among the most dominant and abundant of all organisms on earth. They include termites, ants and various species of wasps and bees. The nests of the social insects provide shelter, protection of brood and adults from predators. Nests also help in rearing of juveniles, storage of food and thermoregulation. It is understood that social insects have achieved ecological dominance due to cooperative brood care, overlapping of generations, division of labor and colony cohesion. Colony cohesion and cooperation are essential for colonies in efficient food acquisition, building nests, rearing of juveniles, survival in adverse conditions, group defence and protection from predation. However, colony cohesion is disrupted when they become exposed to physical disturbance or due to destruction of their nest. Colony cohesion is also interrupted in the species that reproduce by means of budding. Diacamma indicum is a primitively eusocial queenless ant. There is one reproductive individual present in each colony known as gamergate. The ant colony relocate to new nest by tandem running. A leader ant leads a follower ant to the new nest keeping antennae contact during tandem runs. In a previous study, it has been shown that Diacamma indicum colonies split into multiple temporary fragments before reuniting to a single site during the relocation in the natural habitat of these ants. In the current work we started by asking the question do D.indicum colonies relocate to a new nest even if they are living in a similar quality undisturbed nest (n=12) in lab conditions. Colonies did not relocate to the new nest nor did they fragment to occupy both nests, allowing us to conclude that D.indicum colonies do not relocate whenever a new nest becomes available or in the absence of any disturbance to their nest. Thus, this are not a nomadic species as the costs of relocation is presumably non-zero and is avoided as long as their old nest is habitable. In the next step we examined if fragmented colonies reunite. For this we used 17 colonies as replicate. Colonies were fragmented randomly into three fragments (60%,30% and 10% of their colony size). The three nest sites along with an empty nest of comparable quality was placed in the experimental arena corner randomly. We found that statistical significant number of colonies (15/17) reunited at one nest and this nest was the one that contained the gamergate (13/15). This naturally led us to ask what happens if we setup a trade-off between nest quality and presence of gamergate. In the next set of experiments (n=9), the quality of gamergate occupied nest site was degraded. We found that quality is important for final reunified nest. Colonies reunited at a good quality nest even though the gamergate was not present in it and in 7 out of 8 cases and the gamergate was transported into the final nest site. There are costs involved in the relocation the process. When the colonies were given new nest of similar quality they did not relocate. On the basis of our findings in the current study we conclude that tandem running is optimised for quality of the nest and gamergate but not to reduce work load as colonies did not always reunify at nest with majority of workers when the physical parameters of the nest sites are equal. The gamergate plays an important role in reunification and she is not disturbed and workers are transported to the location she occupies. This possibly ensures minimum exposure of the gamergate to potentially harmful environment and other risks during reunification. The reunification dynamics were analysed using behavioral and network analysis. The behavioral analysis was done by following a total of 4384 uniquely labelled ants for around 8028 min across 38 colonies in the laboratory. This is the first study to examine the reunification dynamics for in an ant that uses only tandem running as the mode of transportation during the relocation in the world. This is a small step towards understanding how the little brains inside of these ants function to bring about colony reunification and how they decide their new nest’s address.

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