The interplay of social structure, spatial spatial structure and disease transmission in ant societies

Abstract

Social living often comes at the cost of high epidemic risk. The risk of epidemics and the dy-
namics of disease transmission are shaped by social structure. In turn, spatial constraints
can determine social interactions, thereby also influencing disease transmission. Modifications
to social and spatial structure could, therefore, be a powerful strategy by which animal soci-
eties could mitigate epidemic risk. Here, I investigate this phenomenon in ant colonies. First,
I use automated tracking to show that colonies mount sanitary and transmission-inhibitory
social behaviours in the face of a dual-pathogen challenge: they compartmentalise their so-
cial networks, groom more, and pathogen-exposed ants avoid nest-mates exposed to a differ-
ent pathogen. Transmission analyses reveal that these modifications reduce the risk of both
pathogen-exposed and naive ants sustaining infections with both pathogens. Second, I combine
micro-CT scanning of nest development and spatial network analysis to show that ant groups
respond to pathogen threat by excavating nests with transmission-inhibitory properties: they
are more compartmentalised, less densely connected, contain fewer direct connections between
chambers, and have increased distances between entrances. Furthermore, I use agent-based
simulations to show that these modifications mitigate epidemic susceptibility. Finally, I exper-
imentally manipulate single sets of properties in the nest networks of tracked colonies to show
that the compartmentalisation and density of colony social networks are inherited from their
nest network. Additionally, spatial network manipulation can induce changes to colony mobility
patterns. Simulations of disease transmission show that spatial-induced changes to social net-
works and mobility are relevant for transmission dynamics. Overall, this thesis demonstrates
new ways in which ant colonies are able to use their social and spatial structure to reduce dis-
ease transmission, as components of their "social immunity", and that social structure, spatial
structure, and disease transmission are tightly interrelated in ant colonies, with relevance to a
diversity of social species.

Date of Award	18 Mar 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Nathalie I K A Stroeymeyt (Supervisor)