Role of quorum in decision making regarding a new dwelling in an Indian ant

Suresh, Sachin (2019) Role of quorum in decision making regarding a new dwelling in an Indian ant. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Social insects dominate most of the terrestrial biomass on the planet. Eusocial insects have one of the most complex forms of communication and social organization among insects. Eusocial insects include ants and various species of wasps, honey bees and termites. Eusocial insects share the following characteristic features: adults live in groups, cooperative care of broods, reproductive division of labor, and overlap of generations. Collective decision making is one of the crucial properties that distinguishes social insects from solitary insects. The social insect colony integrates individual opinions to reach a consensus decision regarding the best solution among several alternatives. Consensus decision making offers advantages such as maintenance of group cohesion, enhancement of decision accuracy compared with lone individuals and improvement in decision speed. Quorum-based decision making depends on the number of individuals that are present at a resource which changes the behavioral features of the colony. Diacamma indicum is a primitively eusocial queenless ponerine ant. There is only a single reproductive individual present in each colony which is known as gamergate. The ant colony relocates to the new nest by tandem running. A leader ant leads a follower ant to the new nest keeping physical contact with antennae during tandem runs. Extensive studies on ant species like Temnothorax albipennis on quorum-based collective decision making were previously done. In the current work, we started investigating whether a quorum has a significant impact on the relocation dynamics as well as the choice of nest site selection in Diacamma indicum (n = 17) in lab condition. We performed three categories of experiments (control, treatment, and positive control) to investigate the effect of quorum on colony dynamics. We found out that the colonies relocated to the new nest irrespective of the presence or absence of the quorum. This allowed us to conclude that a quorum is not obligatory for the colony to relocate to a new nest. However, It is found that the absence of a quorum delays the relocation process significantly. In the next step, we analyzed the impact of quorum on the nest choice selection in ants. Colonies (n = 12) did not have a particular preference for either of the target nests in the experiments, where the quorum was undisturbed in the target nests. However, 10 out of 12 colonies moved from the nest where the quorum was removed to the other nest, where the quorum was undisturbed. Based on our findings in the current study, we conclude that the relocation of an ant colony to a new nest occurs irrespective of the presence or absence of a quorum. It is the relocation time that is significantly impacted by the absence of a quorum. Absence of quorum also affects the choice of nest site selection in this species. This is the first study to examine the influence of quorum in Diacamma indicum. These experiments will facilitate new facets of the behavioral organization in this species.

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