Excavated substrate modulates growth instability during nest building in ants

Abstract

In social insects, the nests of the same species can show a large difference in size and shape. Despite these large variations, the nests share the same substructures, some appearing during nest growth. In ants, the interplay between nest size and digging activity leads to two successive morphological transitions from circular to branched shapes (budding along the perimeter of the circular cavity and tunnelling of the galleries). Like several other self-organized collective behaviours, this phenomenon, as well as the entire nest-digging process, is thought to be modulated by environmental properties. The present study investigates the effect of excavated substrate on the nest morphogenesis and the morphological transitions by using two materials with different cohesions. Here, we show that the two morphological transitions occur more frequently with a cohesive substrate than with a granular one: 96 per cent of cohesive experiments showed both transitions, whereas only 50 per cent did in granular experiments. We found that transitions and excavation cessation follow area -response thresholds: the shape transitions take place and the digging activity stops when the dug area reaches the corresponding threshold values. The shape transition thresholds are lower with the cohesive substrate and that of stopping digging is independent of nest shape and material. According to simulations, the experimental frequencies of transitions found their origin in the competition between transitions and activity cessation and in the difference between the transition threshold values of each substrate. Our results demonstrate how the substrate properties modulate the collective response and lead to various patterns. Considering the non-specific mechanisms at work, such effects of substrate coarseness have their counterparts in various collective behaviours, generating alternative patterns to colonize and exploit the environment.

Morphogenesis of an extended phenotype: four-dimensional ant nest architecture

“…Previous studies of excavation dynamics, involving indirect measures of three-dimensional nest growth [20] or two-dimensional scenarios, identified logistic dynamics with an initial exponential growth phase followed by a plateau [22][23][24][25]. Such studies suggested that excavation could be mediated by recruitment with ants being stimulated to excavate by pheromones, carbon dioxide concentrations or physical contacts among ants [20,22,23,41].…”

Effects of worker size on the dynamics of fire ant tunnel construction

“…Environmental factors such as soil granularity and cohesiveness influence the morphology and orientation of tunnels [23,24,29] while the excavation dynamics (digging rate, network growth rate) are a function of group size [25,30] and worker age [11].…”

The determination of nest depth in founding queens of leaf-cutting ants (Atta vollenweideri): idiothetic and temporal control

“…Physical features of the soil (i.e. moisture, composition or sediment boundaries) are known to influence the digging behavior of ant workers, and thus the shape of the excavated structures (Espinoza and Santamarina, 2010;Minter et al, 2011;Toffin et al, 2010). However, it appears unlikely that queens may respond to environmental soil conditions while digging across the soil profile, and switch to chamber digging once a physical discontinuity, or a specific temperature, moisture or soil composition, is encountered.…”