Studying Reproductive Conflict and its Effect on Collective Decision Making in the Context of Relocation in an Indian Ant

Rajagopal, Supraja (2019) Studying Reproductive Conflict and its Effect on Collective Decision Making in the Context of Relocation in an Indian Ant. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The presence of a sterile worker caste in social insect colonies gives rise to a perplexing question in evolutionary biology- why would some individuals give up personal reproduction and raise another individual’s offspring? Inclusive fitness theory and haplo-diploid sex determination in social insects provides an explanation for the evolution and persistence of a sterile worker caste. The same theory also predicts the existence of potential conflict in insect societies, as all individuals are not genetically identical and may have divergent genetic interests. Workers have to choose between actions that favour either direct fitness, like egg-laying, or inclusive fitness, like raising the queen’s offspring. The reproductive division of labour in the colony is maintained by the presence of the queen, via behaviours like dominance interactions or policing, or chemically through pheromones that modulate worker reproduction. The loss of the reproductive individual in social insect colonies can lead to social reorganization, due to the workers fighting over male egg production. The reproductive individual in the colony is important for the maintenance of reproductive division of labour and the reduction of within colony aggression. The loss of key individuals in a group can have drastic effects in colony function. Social reorganization and worker egg laying can affect the ability of the colony to perform other collective tasks. Here, we study the effect of reproductive conflict over male egg production among the workers on collective decision making in the context of relocation. We study this by characterizing the aggression profile of the colony on removal of the gamergate (orphaning), and confirming if the conflict is over male egg production by performing dissections (N = 10 colonies). We then force a colony with reproductive conflict to relocate in the presence of four target nests, one optimal and the others are sub-optimal, to examine how the relocation process and decision making in the context of relocation is affected by the presence of conflict (Control: N = 12 colonies, Orphan: N = 14 colonies). We finally observe if a colony with reproductive conflict will reunify with the gamergate (worker with a queen-like role) if given a choice (N = 10 colonies). Reunifying with the gamergate reduces the direct reproduction of the workers, thus this experiment gives the colonies a choice between direct fitness (not reunifying) and inclusive fitness (reunification). We found that removal of the gamergate causes aggression among the workers. We found a significant increase in the number of acts of aggression and the proportion of individuals involved in aggressive interactions from immediately on orphaning to when an increase aggression levels was observed. We also observed ovarian development in the workers of a colony without the gamergate. We further saw that reproductive conflict had an effect on the organization of the relocation task. Interestingly, there was no effect on the task dynamics or decision making. Hence, we conclude that the relocation process and decision making in the context of relocation was robust. In our next set of experiments, we saw that when given the option to reunify with the gamergate, orphan colonies always chose to do so.

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