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Dynamic networks composed of constituents that break and reform bonds reversibly are ubiquitous in nature owing to their modular architectures that enable functions like energy dissipation, self-healing, and even activity. While bond breaking depends only on the current configuration of attachment in these networks, reattachment depends also on the proximity of constituents. Therefore, dynamic networks composed of macroscale constituents (not benefited by the secondary interactions cohering analogous networks composed of molecular-scale constituents) must rely on primary bonds for cohesion and self-repair. Toward understanding how such macroscale networks might adaptively achieve this, we explore the uniaxial tensile response of 2D rafts composed of interlinked fire ants (S. invicta). Through experiments and discrete numerical modeling, we find that ant rafts adaptively stabilize their bonded ant-to-ant interactions in response to tensile strains, indicating catch bond dynamics. Consequently, low-strain rates that should theoretically induce creep mechanics of these rafts instead induce elastic-like response. Our results suggest that this force-stabilization delays dissolution of the rafts and improves toughness. Nevertheless, above 35 strain low cohesion and stress localization cause nucleation and growth of voids whose coalescence patterns result from force-stabilization. These voids mitigate structural repair until initial raft densities are restored and ants can reconnect across defects. However mechanical recovery of ant rafts during cyclic loading suggests that—even upon reinstatement of initial densities—ants exhibit slower repair kinetics if they were recently loaded at faster strain rates. These results exemplify fire ants’ status as active agents capable of memory-driven, stimuli-response for potential inspiration of adaptive structural materials.
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Metabolic scaling of fire ants ( Solenopsis invicta ) engaged in collective behaviors
ABSTRACT During flash floods, fire ants (Solenopsis invicta Buren) link their bodies together to build rafts to stay afloat, and towers to anchor onto floating vegetation. Can such challenging conditions facilitate synchronization and coordination, resulting in energy savings per capita? To understand how stress affects metabolic rate, we used constant-volume respirometry to measure the metabolism of fire ant workers. Group metabolic rates were measured in a series of conditions: at normal state, at three elevated temperatures, during rafting, and during tower-building. We hypothesized that the metabolic rate of ants at various temperatures would scale isometrically (proportionally with the group mass). Indeed, we found metabolic rates scaled isometrically under all temperature conditions, giving evidence that groups of ants differ from entire colonies, which scale allometrically. We then hypothesized that the metabolism of ants engaged in rafting and tower-building would scale allometrically. We found partial evidence for this hypothesis: ants rafting for short times had allometric metabolic rates, but this effect vanished after 30 min. Rafting for long times and tower-building both scaled isometrically. Tower-building consumed the same energy per capita as ants in their normal state. Rafting ants consumed almost 43% more energy than ants in their normal state, with smaller rafts consuming more energy per capita. Together, our results suggest that stressful conditions requiring coordination can influence metabolic demand. This article has an associated First Person interview with the first author of the paper.
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- Award ID(s):
- 1953451
- PAR ID:
- 10366675
- Publisher / Repository:
- The Company of Biologists
- Date Published:
- Journal Name:
- Biology Open
- Volume:
- 11
- Issue:
- 2
- ISSN:
- 2046-6390
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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