Characterisation of Recruitment During Relocation in an Indian Ant

Karunakaran, Anoop (2019) Characterisation of Recruitment During Relocation in an Indian Ant. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Relocation in ants is unique in the animal kingdom in that they not only have to relocate adults but also the immobile brood. Many ant species rely upon chemical trail mediated relocation, other species carry adults and brood to the new site with the help of a few workers, while yet other species rely upon a primitive recruitment behaviour known as tandem running, or a combination of these methods. Tandem running involves a few leaders leading the rest of the colony to the new site, usually one at a time. This study examines the various facets of relocation dynamics of a primitively eusocial Indian ant, Diacamma indicum. These ants inhabit subterranean nests that house all of the brood and most of the adults in the colony. Earlier studies reveal that colonies evacuate to one or more temporary nests in the face of a disturbance rendering the old nest inhospitable. D. indicum is the only known ant species that uses tandem running for relocation of all adult females in the colony, hence it would be particularly interesting to characterise the process of recruitment in this species. By examining 9500 uniquely marked ants over 10000 minutes of active transportation in the course of 92 colony relocations, we address different questions. This thesis starts with analysis of the recruitment through tandem running in the natural habitat and continues to address how individual ants and their colonies choose and relocate to target nests in an environment that offers temporal and spatial choices using lab based experiments. Relocation was found to be very efficient with more than 75% of the colony members successfully transported at velocities of about 3 body-lengths per second. Terrain heterogeneity showed a significant effect on transport efficiency causing a 20% reduction in the speed of transporting ants. These ants also showed remarkable flexibility in their decision making process. When faced with changes in the target nest quality mid-relocation, they reversed their path and relocated to an optimal nest without a single erroneous transport, thus bypassing the need for a new relocation and saving time and energy associated with the same. These findings pave the way for the latter part of the thesis which delves into evaluation of the decision making process under lucid as well as subtle choices. Further we examine how individual leaders in the relocation process shape colony level decisions. In the course of this study not only do we get a good idea of how an essential task in the life of these ants is conducted, but we also get to appreciate how well this organism has adopted to its environment.

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