Division of labour promotes the spread of information in colony emigrations by the ant Temnothorax rugatulus

Abstract

The fitness of group-living animals often depends on how well members share information needed for collective decision-making. Theoretical studies have shown that collective choices can emerge in a homogeneous group of individuals following identical rules, but real animals show much evidence for heterogeneity in the degree and nature of their contribution to group decisions. In social insects, for example, the transmission and processing of information is influenced by a well-organized division of labour. Studies that accurately quantify how this behavioural heterogeneity affects the spread of information among group members are still lacking. In this paper, we look at nest choices during colony emigrations of the ant Temnothorax rugatulus and quantify the degree of behavioural heterogeneity of workers. Using clustering methods and network analysis, we identify and characterize four behavioural castes of workers-primary, secondary, passive and wandering-covering distinct roles in the spread of information during an emigration. This detailed characterization of the contribution of each worker can improve models of collective decision-making in this species and promises a deeper understanding of behavioural variation at the colony level.

Keywords: Temnothorax rugatulus; collective decision making; colony emigration; division of labour; information spread; network analysis.

Figure 1.

Illustration of the results of the clustering at the higher level of the hierarchy. Distribution of behavioural features of workers clustered in the groups active and inactive ants (the average visit duration is reported in hours). (Online version in colour.)

Figure 2.

Illustration of the results of the clustering at the lower level of the hierarchy. (a) Results of the two-level clustering of all ants for colony 6 as a circle plot. (b) Results for active workers clustered in the groups primary and secondary ants. (c) Results for the inactive workers clustered in the groups passive and wandering ants. The average visit duration and the total visit duration before transport are reported in hours; the average transport duration is reported in minutes. (Online version in colour.)

Figure 3.

Illustration of recruitment networks and their outdegree distribution. (a) Recruitment network for colony 6, emigration 1. (b) Recruitment network for colony 208, emigration 2. Solid arrows represent tandem runs (both direct and reverse), dotted arrows represent transport events. (c) Outdegree distribution for primary and secondary ants for all colonies. (Online version in colour.)

Figure 4.

Illustration of aggregate recruitment networks for colony 6. (a) Aggregate recruitment network of all emigrations for colony 6. (b) The core of the network in panel (a). Solid arrows represent tandem runs (both direct and reverse), dotted arrows represent transport events. Isolated nodes are not shown. (c) Illustration of the relations between the role covered by each ant as defined from the clustering analysis and their location in the aggregate network (i.e. core or periphery). (Online version in colour.)