Dynamics of locomotion in the seed harvesting antMessor barbarus:effect of individual body mass and transported load mass

Abstract

Ants are well-known for their amazing load carriage performances. Yet, the biomechanics of locomotion during load transport in these insects has so far been poorly investigated. Here, we present a study of the biomechanics of unloaded and loaded locomotion in the polymorphic seed-harvesting ant Messor barbarus (Linnaeus, 1767). This species is characterized by a strong intra-colonial size polymorphism with allometric relationships between the different body parts of the workers. In particular, big ants have much larger heads relative to their size than small ants. Their center of mass is thus shifted forward and even more so when they are carrying a load in their mandibles. We investigated the dynamics of the ant center of mass during unloaded and loaded locomotion. We found that during both unloaded and loaded locomotion, the kinetic energy and gravitational potential energy of the ant center of mass are in phase, which is in agreement with what has been described by other authors as a grounded-running gait. During unloaded locomotion, small and big ants do not display the same posture. However, they expend the same amount of mechanical energy to raise and accelerate their center of mass per unit of distance and per unit of body mass. While carrying a load, compared to the unloaded situation, ants seem to modify their locomotion gradually with increasing load mass. Therefore, loaded and unloaded locomotion do not involve discrete types of gait. Moreover, small ants carrying small loads expend less mechanical energy per unit of distance and per unit of body mass and their locomotion thus seem more mechanically efficient.

Universal features in panarthropod inter-limb coordination during forward walking

“…These 'rules' support early observations by Manton, whose extensive investigations into pa- Cupiennius salei (70) Locusta migratoria (51) Hypsibius exemplaris (47) Messor barbarus (45) inter-leg coordination across walking speeds wave tetrapod-like tripod Glomeris marginata (40) Cylindroiulus londinensis (41) Lithobus forficatus (40) Microchordeuma scutellare (41) Ophistreptus guineensis (41) Peripatus sedgwicki (38) Polymicrodon polydesmoides (41) Polyzonium germanicum (41) Scutigera coleoptrata (40) Tachypodoiulus niger (41) all Figure 4: Changes in inter-leg coordination with walking speed. Relationship between walking speed and measured phase offset in swing initiations between (a) ipsilateral and (b) contralateral leg pairs.…”

“…Furthermore, the relative weakness of coupling between contralateral leg pairs in comparison to ipsilateral leg pair coupling is consistent with the hypothesis that the underlying controller proposed based on Drosophila is shared across panarthropods. Contralateral phasing is quite variable across taxa, ranging from inphase in swimming Crustacea [80] to anti-phase in running insects [24,45] and arachnids [62,73]. However, ipsilateral phase relationships are consistent across nearly all characterized species (with few exceptions; see, e.g, [40,36]).…”

Universal Features in Panarthropod Inter-Limb Coordination during Forward Walking

“…Furthermore, the relative weakness of coupling between contralateral leg pairs in comparison with ipsilateral leg pair coupling is consistent with the hypothesis that the underlying controller proposed based on Drosophila is shared across panarthropods. Contralateral phasing is quite variable across taxa, ranging from in-phase in swimming Crustacea ( Zhang et al 2014 ) to anti-phase in running insects ( Full and Tu 1991 ; Merienne et al 2021 ) and arachnids ( Spagna et al 2011 ; Weihmann et al 2015 ). However, ipsilateral phase relationships are consistent across nearly all characterized species (with few exceptions; see, e.g., ( Manton 1952b ; Kuroda et al 2018 )).…”

Clearing the way to the external world: do ants make optimal decisions when removing obstacles from their subterranean galleries?

“…Note that these values of metabolic cost are probably somewhat underestimated since they are not based on the total mechanical work achieved by ants, which includes the mechanical cost of locomotion, i.e. the mechanical work required to accelerate the center of the mass of the ants [33] as well as the internal energy they use to accelerate their limbs during locomotion, but just on the mechanical work required to pull the obstacle. Nonetheless, the metabolic cost of locomotion is likely to represent only a small fraction of the cost of pulling the obstacle.…”