Spatial patterns in ant colonies

Abstract

The origins of large-scale spatial patterns in biology have been an important source of theoretical speculation since the pioneering work by Turing (1952) on the chemical basis of morphogenesis. Knowing how these patterns emerge and their functional role is important to our understanding of the evolution of biocomplexity and the role played by self organization. However, so far, conclusive evidence for local activation-long-range inhibition mechanisms in real biological systems has been elusive. Here a welldefined experimental and theoretical analysis of the pattern formation dynamics exhibited by clustering behavior in ant colonies is presented. These experiments and a simple mathematical model show that these colonies do indeed use this type of mechanism. All microscopic variables have been measured and provide the first evidence, to our knowledge, for this type of self-organized behavior in complex biological systems, supporting early conjectures about its role in the organization of insect societies.M any biological systems display large-scale features involving some characteristic scale that is much larger than the size of its individual components (1). These structures are observed in a broad range of systems and scales, from animal coats (2), shell patterns (3, 4), and neural structures (5) to the spatial distribution of individuals in ecosystems (6). In many cases, they reflect functionality and adaptation and in all of them, they provide clues for the underlying rules that generate them. In most cases, it is clear that the information available to individual units is gathered from a local neighborhood much smaller than the resulting structures, suggesting some type of amplification mechanism that relies on collective behavior.The first theoretical explanation of these types of structures was suggested in 1952 by Alan Turing (1,7,8). The basic mechanism at work involves local amplification of fluctuations (activation) and long-range inhibition and actually falls within a general class of mechanisms (9-12). These mechanisms have been identified in physical (13) and chemical (14) systems, in ecosystems (2, 6, 10, 15-18) and morphogenesis (2-5, 11, 19-26). In the slime mold (27, 28), the evidence is also strong. Critics have argued that a proof requires the identification and measurement of the microscopic mechanisms at work, and this is obviously a rather difficult task in biology.In this context, it was early suggested that social insects might actually use these types of mechanisms to build their nests (29,30) and produce a wide variety of spatiotemporal structures (31-34). Here we use social insects and their behavioral patterns of organization as our reference system. We follow a standard approach, using a well-defined and controlled experimental setup in which the whole set of parameters can be measured and therefore all of the microscopic rules can be identified. We show that the formation of cemeteries in ants (35-38) falls within the family of local activation-long range inhibition (LALI) processes...

Stigmergic construction and topochemical information shape ant nest architecture

“…S10) affects the spacing between pillars. In biological systems, processes based on a local-activation and long-range inhibition (41) provide a simple and efficient way to get such regular patterns, and the existence of these processes has been demonstrated to govern the spatial organization of corpse aggregates in the ant Messor sancta (28). In L. niger, pillar formation is based on a similar logic.…”

“…Theoretical models have been proposed to account for 3D nest construction in wasps and termites (17)(18)(19), indicating that stigmergic interactions can potentially explain the coordination of nest building in these animal groups. However, a detailed and experimentally founded understanding of the interactions between the animals and the structures that they are building is limited to the construction of simple 2D structures produced by ants and termites, either by digging the substrate (20)(21)(22)(23)(24)(25) or piling soil particles (26)(27)(28). In ants, 3D nest construction remains poorly documented and so far no study has attempted to connect a detailed quantitative description of individual building behavior with the growth dynamics and the resulting shape of nests.…”

Shape transition during nest digging in ants

“…In social insects, such transitions have been reported for trail foraging: Small ant colonies forage in a disorganized manner, with a transition to organized pheromone-based foraging in larger colonies (26)(27)(28). Other examples are reported for gregarious insects where the density of individuals controls the emergence of aggregation patterns (29)(30)(31) or for fish, where the number of individuals affects collective decision making (32). Such morphological transitions between two stages of growth have already been described in several chemical [electrochemical deposition (33), combustion (34) Concerning social animals, different examples reported in the literature strongly suggest that shape transitions are not restricted to the digging of social insects.…”

From behavioural analyses to models of collective motion in fish schools

“…The idea is to build a model incrementally from scratch, validating at each step the modelling choices through a specific experimental design. In the past, the very same methodological framework has been successfully applied to characterize and model individuals' interactions that govern collective behaviour in pre-social and social insects [97][98][99].…”