Collective decision‐making, caste roles and sequential transport during colony emigration in the small carpenter ant, Camponotus yamaokai

Abstract

AbstractEffective coordination of group actions underlies the success of group‐living organisms. Making decisions collectively is a crucial step in executing behaviours affecting the whole group. In social insects, decision‐making is typically achieved in a self‐organised manner and incorporates a quorum process, which can improve decision accuracy and be tailored to different conditions. Studies of the nest‐selection process in different social insect species have revealed remarkable consistency in the mode of decision‐making despite marked differences in life history and colony size. However, an often‐overlooked aspect of this decision process is how it might be influenced by diversity in behavioural propensity among colony members. Higher diversity can improve collective processes, but could also represent a cost if certain classes of individual do not contribute to the cooperative activity. Many ant species exhibit caste polymorphism, with different worker castes specialised to different functions. These castes could thus enhance or erode the collective decision process depending on whether they contribute to this process or not. In this study, we explore the process of colony emigration and nest‐site choice in the small carpenter ant Camponotus yamaokai, a species with two distinct worker castes. We show that this species is likely to use a quorum decision process facilitated by navigation with chemical trails. Both major and minor castes contributed to the collective decision and emigration process. However, although major workers comprised 24% of the colony on average, they were 5.5 times less likely than expected to be involved in assessing new nests and 4.6 times less likely than expected to contribute to brood transport. This may represent a previously unrecognised cost to the colony in the emigration process. In addition, we document the first observations of sequential brood transfer during emigration behaviour and speculate upon the function of this behaviour.