How does starvation affect spatial organization within nests in Lasius niger?

Abstract

Spatial distribution of ant workers within the nest is a key element of the colony social organization contributing to the efficiency of task performance and division of labour. Spatial distribution must be efficiently organized when ants are highly starved and have to get food rapidly. By studying ants’ behaviour within the nest during the beginning of food recruitment, this study demonstrates how the spatial organization is affected by starvation and improves the efficiency and the speed of recruitment as well as the allocation of food. (1) In starved nests, nestmates left the deep part of the nest and crowded near the nest entrance. This modification of the spatial distribution is a local phenomenon concerning only the individuals situated in the first chamber near the nest entrance. These starved individuals have a higher probability of leaving the nest after a contact with recruiters than nestmates situated deeper in the nest. This strongly suggests that nestmates situated near the nest entrance have a low response threshold to the signals emitted by recruiters. Their higher responsiveness speeds up their exit to the foraging area and hence may increase the efficiency of highly starved colonies in exploiting new food opportunities. (2) In starved nests, the trajectory covered by recruiters between contacts with nestmates was nearly twice as small. For recruiters, this represented a gain of time in the allocation of food. As the recruitment process follows snowball dynamics, this gain of time by starved recruiters might also speed up the exploitation of food. This study evidences how the spatial distribution of individuals as a function of their motivational state might have a regulatory function in the recruitment process, which should be generic for many social species.