Influence of monsoon on nesting behaviour: a study on an Indian ant, Diacamma indicum

Bhattacharyya, Kushankur (2023) Influence of monsoon on nesting behaviour: a study on an Indian ant, Diacamma indicum. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD dissertation of Kushankur Bhattacharyya (13IP020)) 13IP020.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

Nest is a very important physical space serving several functions such as protection from environmental adversities and predators, a secure location for rearing broods, storing food and other resources, luring partners during mating time to mentions a few. Social insect nests are considered as wonders of animal architecture and ants are no exceptions. Ants, living in subterranean nests face different threats related to monsoon in the tropics and to combat those challenges, they make floatable rafts, build mounds and wall-paper their chambers. In this thesis, I have explored several facets of nesting biology of an Indian ant Diacamma indicum (subfamily Ponerinae) which are known to live in subterranean nests and have small number of adults (range 12-261) in the colony. The species is found in India, Bangladesh, Srilanka and probably in Japan. Characterisation of nest entrance, subterranean nest architecture and correlation of colony size with nest volume was done from 107 natural nests. Nest entrance and its vicinity is heterogeneous and changes across seasons. Nests are relatively simple with a single entrance and a single chamber joined by an entrance tunnel and after the chamber another secondary tunnel extending further downwards. The overall nest architecture remained comparable across seasons. Nest mound was characterised and its response to various degrees of damage was checked on 57 natural nest mounds. Mounds could effectively reduce water seepage inside the nest by raising the height of nest entrance and narrowing down the nest entrance. Mounds were recovered upon damage even in the absence of rain. Mound building was triggered in lab by nest inundation on 26 colonies. I also checked if nest mounds influenced nest choice of previously inundated colonies. Colonies built mounds even without nest inundation, but inundated nests made significantly more modifications to their mounds quantitatively. Inundated colonies preferred nests with mounds over a good quality nest without mound. I also investigated if nest architectural features influenced colonies’ nest choice while relocating on a total of 52 colonies. Entrance tunnel length and diameter and presence of secondary tunnel did not influence the nest choice. Relatively larger chambers were preferred by larger colonies when the choices were equidistant. If the good quality nest was placed far away, the larger colonies also chose the nearby nests with small chamber. Together these results suggest that, nest architectural features were not particularly important to relocating colonies. Extranidal behaviours of 8 colonies was observed for a span of 96 hours to check if different individuals performing different tasks form separate clusters and specifically the tandem leaders. I observed 24 different extranidal behaviours. I found no such clusters regarding tasks performed and even tandem leaders did not form a separate cluster. 55 different colonies were put to three different monsoon related challenges, i) relocation while it’s raining, ii) relocation from flooded nest, and iii) relocation through waterlogged terrain. Colonies were able to relocate successfully. Water seeping inside the nest chamber made colonies to relocate, and the decision to relocate was made significantly quicker. Colonies took longer to relocate through waterlogged terrains. Number of failed tandem runs, interruptions and switchovers increased significantly and speed was reduced. The thesis elucidated the various behavioural modifications of tropical ponerine D. indicum ant from the perspective of an environmental factor monsoon, which will contribute to the literature about these superorganisms and create scope for further experiments.

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