Stepping patterns in ants. III.Influence of load (original) (raw)
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Stepping patterns in ants II. Influence of body morphology
Journal of Experimental Biology
The locomotory behaviour of 12 ant species belonging to four different genera (Formicinae: Cataglyphis, Formica, Lasius; Myrmicinae: Myrmica) was studied by filming individuals during walking on smoked-glass plates. Subsequent multivariate analyses of walking kinematics and footfall positions showed marked species-specific as well as size-dependent differences in the locomotory behaviour. The geometric properties of the footfall patterns resulting from the alternating tripod gait scale to leg dimensions in a geometric manner. At high speed, footprint distances between succeeding tripods exceed maximum leg extension, indicating that ants are 'trotting' from one tripod to the next one with intermittent aerial phases. In at least one species (Cataglyphis bombycina), there is evidence for quadrupedal locomotion at the highest speed. The functional relationship between stride length (s, the distance between successive footprints of the same foot) and speed (v) was best described by a curvilinear model, s=av b. Exponent b ranges from 0.3 to 0.6 and reveals differences between species. Within species, exponent b is constant, whereas factor a scales to leg length. Females and males show metachronal interleg coordination patterns rather than the alternating tripod coordination pattern seen in workers of the same species.
Stepping patterns in ants I. Influence of speed and curvature
Journal of Experimental Biology
The locomotory behaviour of workers of 12 ant species belonging to four different genera (Formicinae: Cataglyphis, Formica, Lasius; Myrmicinae: Myrmica) was studied by filming individuals walking on smoked-glass plates. Subsequent multivariate analyses of footfall positions and walking kinematics revealed a set of constant features characterizing ant locomotion. The alternating tripod gait prevails over a wide range of speeds. The temporal rigidity of tripod coordination is paralleled by spatially rigid footfall patterns. Tripod geometry is preserved irrespective of speed and curvature. When walking around curves, tripods are rotated relative to the walking trajectory. Whereas stride length on the inner side of the curve is shortened, that on the outer side is independent of curvature.
Journal of Comparative Physiology A: …, 2010
Grass-cutting ants (Atta vollenweideri) carry leaf fragments several times heavier and longer than the workers themselves over considerable distances back to their nest. Workers transport fragments in an upright, slightly backwards-tilted position. To investigate how they maintain stability and control the carried fragment’s position, we measured head and fragment positions from video recordings. Load-transporting ants often fell over, demonstrating the biomechanical difficulty of this behavior. Long fragments were carried at a significantly steeper angle than short fragments of the same mass. Workers did not hold fragments differently between the mandibles, but performed controlled up and down head movements at the neck joint. By attaching additional mass at the fragment’s tip to load-carrying ants, we demonstrated that they are able to adjust the fragment angle. When we forced ants to transport loads across inclines, workers walking uphill carried fragments at a significantly steeper angle, and downhill at a shallower angle than ants walking horizontally. However, we observed similar head movements in unladen workers, indicating a generalized reaction to slopes that may have other functions in addition to maintaining stability. Our results underline the importance of proximate, biomechanical factors for the understanding of the foraging process in leaf-cutting ants.
Insectes Sociaux, 2004
Locomotion velocity during foraging activities is determined by factors such as travel distance, habitat structure and load mass among others. However, few studies on foraging behavior have analyzed the influence of spatial heterogeneity and food transportation on the locomotion velocity of ants under natural conditions. In order to study the mentioned factors, we selected 20 nests of the ant Dorymyrmex goetschi (subfamily Dolichoderinae), in a lower Andes locality of central Chile. Half of the nests were offered a food patch located at 10 cm from the nest entrance, and at 20 cm for the other half. We measured the duration of trips between nest and food patch and vice versa, and the distances traveled. We also recorded spatial heterogeneity of the substratum and soil temperature. Temperature was used as a covariate in the statistical analysis. Travel speed was significantly slower when worker ants returned to the nest with a food load, compared to the velocity of foragers without load that traveled from the nest to the patch. When the food patch was located at greater distance, locomotion velocity was significantly faster. Spatial heterogeneity did not affect movement speed. The reduction in locomotion velocity in ants carrying a load of 5.6 mg represents an energetic cost of transportation equivalent to 79% of the costs involved in moving a body mass of 1.6 mg. Faster velocities at larger patch distances can be interpreted as a strategy to maintain an efficient resource exploitation, by way of decreasing the time exposed to higher predation risk.
Level locomotion in wood ants: evidence for grounded running
Journal of Experimental Biology, 2014
In order to better understand the strategies of locomotion in small insects, we have studied continuous level locomotion of the wood ant species Formica polyctena. We determined the three-dimensional centre of mass kinematics during the gait cycle and recorded the ground reaction forces of single legs utilizing a self-developed test site. Our findings show that the animals used the same gait dynamics across a wide speed range without dissolving the tripodal stride pattern. To achieve higher velocities the ants proportionally increased stride length and stepping frequency. The centre of mass energetics indicated a bouncing gait, in which horizontal kinetic and gravitational potential energy fluctuated in close phase. We determined a high degree of compliance especially in the front legs, as the effective leg length was nearly halved during the contact phase. This leads to only small vertical oscillations of the body, which are important in maintaining ground contact. Bouncing gaits w...
Physiological Entomology, 2011
The foraging behaviour of social insects is highly flexible because it depends on the interplay between individual and collective decisions. In ants that use foraging trails, high ant flow may entail traffic problems if different workers vary widely in their walking speed. Slow ants carrying extra-large loads in the leaf-cutting ant Atta cephalotes L. (Hymenoptera: Formicidae) are characterized as 'highly-laden' ants, and their effect on delaying other laden ants is analyzed. Highly-laden ants carry loads that are 100% larger and show a 50% greater load-carrying capacity (i.e. load size/body size) than 'ordinary-laden' ants. Field manipulations reveal that these slow ants carrying extra-large loads can reduce the walking speed of the laden ants behind them by up to 50%. Moreover, the percentage of highly-laden ants decreases at high ant flow. Because the delaying effect of highly-laden ants on nest-mates is enhanced at high traffic levels, these results suggest that load size might be adjusted to reduce the negative effect on the rate of foraging input to the colony. Several causes have been proposed to explain why leaf-cutting ants cut and carry leaf fragments of sizes below their individual capacities. The avoidance of delay in laden nest-mates is suggested as another novel factor related to traffic flow that also might affect load size selection The results of the presennt study illustrate how leaf-cutting ants are able to reduce their individual carrying performance to maximize the overall colony performance.
Dynamics and kinematics of ant locomotion: do wood ants climb on level surfaces?
The Journal of experimental biology, 2009
The biomechanics of running in small animals have remained poorly characterized because of the difficulty of recording three-dimensional ground reaction forces. Available techniques limit investigations to animals with a body mass above 1 g. Here we present, for the first time, single-leg ground reaction forces of ants (body mass 10 mg), measured with a custom-built miniature force plate. We investigated forces and high-speed kinematics for straight level runs (average speed: 8.4 cm s(-1)) of Formica polyctena workers. The major finding was that the time course of ground reaction forces strongly differed from previous observations of larger insects. Maximum vertical force was reached during the first third of the tripod contact phase. During this period the body was decelerated predominantly by the front legs. Subsequently, the front legs pulled and accelerated the body. This 'climbing' type of stride may be useful on the bumpy and unstable substrates that the animals face i...
Energetics of locomotion and load carriage in the nectar feeding ant, Camponotus rufipes
Physiological Entomology, 2005
To investigate if there is an energetic constraint influencing a nectar feeding ant's decision to come back to the nest with partial loads, the energetic costs of running and carrying a load in the ant Camponotus rufipes are measured. Metabolic rates of individuals are measured in a running tube respirometer while they are unladen and laden at 25 C. Workers voluntarily collect a load of 6 mL of a 30% sucrose solution (mass ¼ 6.8 mg), which results in an internal load of about 50% of the ant mass and is close to a full load for ants within this size range. The gross cost of unladen running is 264 J kg À1 m À1 , while that of laden running is 225 J kg À1 m À1 . The mass used to calculate the cost of laden running includes body mass of ant and load carried. Load carriage cost in C. rufipes foragers is calculated to be about 60% as much as body carriage per unit mass. Internal load carriage in C. rufipes is energetically cheaper compared with external carriage in other ant species. Such low carriage costs make it unlikely that the collection of partial crop loads in C. rufipes foragers is based on a minimization of foraging costs, as suggested for honeybees.
Propulsion in hexapod locomotion: How do desert ants traverse slopes?
Journal of Experimental Biology, 2017
The employment of an alternating tripod gait to traverse uneven terrains is a common characteristic shared among many hexapoda. Since this could be one specific cause for their ecological success, we examined the alternating tripod gait of the desert ant Cataglyphis fortis together with their ground reaction forces and weight-specific leg impulses for level locomotion and on moderate (±30°) and steep (±60°) slopes in order to understand mechanical functions of individual legs during inclined locomotion. Based on the experimental data, it was proposed that 1) the hind legs acted as the main brake (negative weight-specific impulse in the direction of progression) on both the moderate and steep downslopes while the front legs became the main motor (positive weight-specific impulse in the direction of progression) on the steep upslope. In both cases the primary motor or brake was found to be above the centre of mass. 2) Normalised double support durations were prolonged on steep slopes,...
Sequential load transport during foraging in Acromyrmex (Hymenoptera: Formicidae) leaf-cutting ants
The complex social organization of leaf cutter ants is closely linked with intricate patterns of division of labor in the worker force. For instance, foraging might involve division of labor between cutters and carriers, as well as task partitioning during leaf transport. However, little is known about division of labor during foraging in Acromyrmex, particularly under field conditions. The goal of the present study is to investigate the behavior of Acromyrmex leaf-cutting ants on trails of different lengths in order to elucidate the effect of foraging distance on the occurrence of transport chains under field and laboratory conditions, and to discuss the hypotheses to explain the occurrence of transport chains. In Acromyrmex crassispinus (FOREL, 1909) and Acromyrmex subterraneus subterraneus (FOREL, 1893), cutting and carrying of fragments were clearly separated activities performed by distinct worker groups differing in body size. In addition, the behavior of foragers of both species differed significantly according to variation in trail distances. On short trails (1 m), cutters frequently transported the fragments directly to the nest, whereas on long trails (more than 10 m), most cutters transferred the fragments to other workers. Transport chains happened more frequently when workers harvested plants far from the nest. These results demonstrate that Acromyrmex species display both division of labor between cutters and carriers, and task partitioning during leaf transport, with trail lengths showing marked effects on the likelihood of sequential transport. Furthermore, the results of this study provide support for the hypothesis that the be-havioral response of transferring fragments in Acromyrmex species would have been selected for because of its positive effect on the information flow between workers.