Network structure and risk analysis in turtle ant nest choice
Joanna Chen Hsuan Chang, Joanna Chen Hsuan Chang , Matina Donaldson-Matasci
Department of Biology, Pomona College, Claremont, California; Department of Biology, Pomona College, Claremont, United States of America ; Department of Biology, Harvey Mudd College, Claremont, United States of America
Social insect colonies have individual members with specialized roles that interact and contribute to the fitness of the whole colony. This quality makes them useful for understanding and modeling decision-making strategies that involve gathering both individual and collective information. Here, we are interested in the nest choice of two turtle ant species, Cephalotes varians and Cephalotes texanus. Turtle ants are polydomous and live in arboreal networks, where limited nesting sites and the pathways between them may be frequently destroyed. Thus, turtle ant nest choice can lend insight into decision-making strategies across dynamic transport networks. We hypothesized that turtle ant colonies would minimize the risk of losing access to a nest and its resources by choosing nest networks that are more connected and compact. We presented colonies with opportunities to colonize two different nest networks: one that was more connected and compact and one that was less so. We filmed colony movement for 12 hours and inspected nest occupation for at least 3 days. Experiments were performed in the summer (n=6), then repeated in the fall (n=4) with an enlarged network containing more nests. The colonies in the summer moved a significant majority of their brood and workers into the more connected and compact nest network, but the colonies in the fall split their members across the two networks. Our analysis suggests this may be due to a seasonal difference in motivation and activity levels. In addition, the enlarged network configuration in the fall affected the ease of discovery of different parts of the network. This allowed us to analyze how the rate of discovery affects nest choice. Our results suggest that under some circumstances, turtle ants choose nests that are the most easily found, regardless of their arrangement within the network structure. Thus, the ants may often favor nest choice based on short-term accessibility rather than longer-term robustness to damage.