You can’t spell “group decision” without the “I”: how individuals determine colony level choices

All living things must be able to receive information from the environment and respond accordingly. This aspect of life is especially interesting in groups of living things that communicate with each other to most efficiently gather and respond to information. This applies to a vast range of systems like bacteria, cells in the body and the immune system, defense systems in plants (as described in a previous blog post) and groups of social animals that work together in a larger group.

Two turtle ant workers sharing information

Some major questions one can ask about these communicating systems are: how and what information do they get from the environment? How do they interpret that information? How do they communicate it to others? And how does it inform decision-making both at an individual and community level?

Our lab, in collaboration with Dr. Scott Powell’s lab at George Washington University, is trying to investigate how turtle ant behavior can help us answer some of these questions. The species of turtle ant we are studying is Cephalotes varians. Dr. Powell and his lab group collected our four queenright colonies (containing a reproducing queen) and five queenless fragment colonies from mangroves in the Florida Keys. There, they occupy hollowed out cavities in the branches made by beetle larvae. Each colony occupies many nests and competes with other animals in their environment for this valuable resource. Therefore it is extremely important to the colony to be able to efficiently search for and move into suitable nest cavities. Another feature of this species is that they employ ants of different physical and behavioral traits for this task, or castes: the workers and the soldiers. Powell and Dornhaus 2013 suggested that worker ants are the primary investigators of new nests, but that the soldiers may decide when to stay and more permanently occupy a nest based on their ability to defend it. Both soldiers and workers may then be employed in carrying brood (eggs, larvae and pupae) to the new nest. However, no studies of this species have explored how individual information gathering, decision making and communicating affects the group’s decision to occupy a nest. We hope to address this issue by marking individual ants and examining which individuals search for and assess different nests and how they and the colony make decisions about which nests to occupy.

Marking of individual ants with unique paint markings allows us to track their
movement and behavior patterns. Photos by Alexander Wild [1], [2].

We are also interested in how this information gathering and decision making is influenced by threat. If you need to make a decision in a hurry, you don’t spend as much time considering all the alternatives and may make a poorer decision. In the wild, these ants face competition from other animals that may take their nests from them, as well as potential degradation of currently occupied nests. In the lab, we can simulate these conditions by introducing a foreign ant species and by taking apart a nest they currently occupy. We can then observe how this influences individual exploration and a colony’s decision to occupy and defend a nest. 

Red ant from the BFS spreading her

scent around one of our fragment

colony’s nests and a turtle ant worker

investigating the nest entrance

However, before we can address these questions, there are several things we need to find out, and this is where our fragment colonies come in handy. We can use them as our guinea pigs in little pre-experiments, which will help us determine how to formulate the actual experiment for the queenright colonies. For example, we need to find an ant species to threaten our turtle ants so we can look at what they do under pressure. At first this may seem simple: just pick up an ant off the sidewalk. However, our ants are from Florida, and we are based in California. Thus we must find a close alternative to what they would see in the wild. The Robert J. Bernard Biological Field Station (BFS) has generously allowed us to search for ants there, and we will then drop these ants into our fragment colonies and see how the soldiers react. We have to test several different types of ants to get the right kind of reaction from them: we want the turtle ants to act defensively, by guarding their nests more, but not offensively, by attacking the foreign ant. Once we know what makes them feel threatened, we can design an experiment to figure out how individuals react under pressure and without it, and how that influences nest use.

Further Reading:

If you are interested in current research with this species, please check out our collaborator Dr. Scott Powell’s website.

Nest choice in other ant species that only choose one nest has been well documented. If you want to know more about those species:

• Pratt, S.C., Sumpter, D.J.T., Mallon, E.B., Franks, N.R. (2005) “An agent-based model of collective nest choice by the ant Temnothorax albipennis.” Animal Behaviour, 70(5): 1023-1036. (pdf from author)
• Mallon, E.B., Pratt, S.C., Franks, N.R. (2001) “Individual and collective decision-making during nest site selection by the ant Leptothorax albipennis” Behav. Ecol. Sociobiol. 50:352-359. (link to article on journal website)

For more information on other polydomous ants:

• Tofolo, V.C., Giannotti, E., Neves, E.F., Andrade, L.H.C., Lima, S.M., Súarez, Y.R., & Antonialli-Junior, W. F. (2014) “Polydomy in the ant Ectatomma opaciventre.” Journal of Insect Science, 14(21). (link to article on journal website)

Resource distribution and foraging behavior are also commonly studied subjects. For more on how polydomous ant species perform these other complex behaviors:

• Ellis, S., Franks, D.W., Robinson, E.J.H. (2014) “Resource redistribution in polydomous ant nest networks: local or global?” Behavioural Ecology, 25(5): 1183-1191. (link to article on journal website)
• Bucxkowski, G. (2012) “Colony spatial structure in polydomous ants: complimentary approaches reveal different patterns.” Insectes Sociaux, 59: 241-250. (pdf from author)

Media Credits:

[1] Alexander Wild: http://www.alexanderwild.com/Ants/Myrmecology-the-Study-of-Ants/Myrmecology/i-LwDcxvG/A

[2] Alexander Wild: http://www.alexanderwild.com/Ants/Myrmecology-the-Study-of-Ants/Myrmecology/i-DvwCKhV/A