Publications
43 results found
Labonte D, Bishop PJ, Dick TJM, et al., 2024, Dynamic similarity and the peculiar allometry of maximum running speed., Nat Commun, Vol: 15
Animal performance fundamentally influences behaviour, ecology, and evolution. It typically varies monotonously with size. A notable exception is maximum running speed; the fastest animals are of intermediate size. Here we show that this peculiar allometry results from the competition between two musculoskeletal constraints: the kinetic energy capacity, which dominates in small animals, and the work capacity, which reigns supreme in large animals. The ratio of both capacities defines the physiological similarity index Γ, a dimensionless number akin to the Reynolds number in fluid mechanics. The scaling of Γ indicates a transition from a dominance of muscle forces to a dominance of inertial forces as animals grow in size; its magnitude defines conditions of "dynamic similarity" that enable comparison and estimates of locomotor performance across extant and extinct animals; and the physical parameters that define it highlight opportunities for adaptations in musculoskeletal "design" that depart from the eternal null hypothesis of geometric similarity. The physiological similarity index challenges the Froude number as prevailing dynamic similarity condition, reveals that the differential growth of muscle and weight forces central to classic scaling theory is of secondary importance for the majority of terrestrial animals, and suggests avenues for comparative analyses of locomotor systems.
Püffel F, Walthaus OK, Kang V, et al., 2023, Biomechanics of cutting: sharpness, wear sensitivity and the scaling of cutting forces in leaf-cutter ant mandibles., Philos Trans R Soc Lond B Biol Sci, Vol: 378
Herbivores large and small need to mechanically process plant tissue. Their ability to do so is determined by two forces: the maximum force they can generate, and the minimum force required to fracture the plant tissue. The ratio of these forces determines the relative mechanical effort; how this ratio varies with animal size is challenging to predict. We measured the forces required to cut thin polymer sheets with mandibles from leaf-cutter ant workers which vary by more than one order of magnitude in body mass. Cutting forces were independent of mandible size, but differed by a factor of two between pristine and worn mandibles. Mandibular wear is thus likely a more important determinant of cutting force than mandible size. We rationalize this finding with a biomechanical analysis, which suggests that pristine mandibles are ideally 'sharp'-cutting forces are close to a theoretical minimum, which is independent of tool size and shape, and instead solely depends on the geometric and mechanical properties of the cut tissue. The increase of cutting force due to mandibular wear may be particularly problematic for small ants, which generate lower absolute bite forces, and thus require a larger fraction of their maximum bite force to cut the same plant. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.
Kang V, Püffel F, Labonte D, 2023, Three-dimensional kinematics of leaf-cutter ant mandibles: not all dicondylic joints are simple hinges., Philos Trans R Soc Lond B Biol Sci, Vol: 378
Insects use their mandibles for a variety of tasks, including food processing, material transport, nest building, brood care, and fighting. Despite this functional diversity, mandible motion is typically thought to be constrained to rotation about a single fixed axis. Here, we conduct a direct quantitative test of this 'hinge joint hypothesis' in a species that uses its mandibles for a wide range of tasks: Atta vollenweideri leaf-cutter ants. Mandible movements from live restrained ants were reconstructed in three dimensions using a multi-camera rig. Rigid body kinematic analyses revealed strong evidence that mandible movement occupies a kinematic space that requires more than one rotational degree of freedom: at large opening angles, mandible motion is dominated by yaw. But at small opening angles, mandibles both yaw and pitch. The combination of yaw and pitch allows mandibles to 'criss-cross': either mandible can be on top when mandibles are closed. We observed criss-crossing in freely cutting ants, suggesting that it is functionally important. Combined with recent reports on the diversity of joint articulations in other insects, our results show that insect mandible kinematics are more diverse than traditionally assumed, and thus worthy of further detailed investigation. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.
Plum F, Bulla R, Beck HK, et al., 2023, replicAnt: a pipeline for generating annotated images of animals in complex environments using Unreal Engine., Nat Commun, Vol: 14
Deep learning-based computer vision methods are transforming animal behavioural research. Transfer learning has enabled work in non-model species, but still requires hand-annotation of example footage, and is only performant in well-defined conditions. To help overcome these limitations, we developed replicAnt, a configurable pipeline implemented in Unreal Engine 5 and Python, designed to generate large and variable training datasets on consumer-grade hardware. replicAnt places 3D animal models into complex, procedurally generated environments, from which automatically annotated images can be exported. We demonstrate that synthetic data generated with replicAnt can significantly reduce the hand-annotation required to achieve benchmark performance in common applications such as animal detection, tracking, pose-estimation, and semantic segmentation. We also show that it increases the subject-specificity and domain-invariance of the trained networks, thereby conferring robustness. In some applications, replicAnt may even remove the need for hand-annotation altogether. It thus represents a significant step towards porting deep learning-based computer vision tools to the field.
Pueffel F, Meyer L, Imirzian N, et al., 2023, Developmental biomechanics and age polyethism in leaf-cutter ants (vol 290, 20230355, 2023), PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 290, ISSN: 0962-8452
Aibekova L, Keller RA, Katzke J, et al., 2023, Parallel and divergent morphological adaptations underlying the evolution of jumping ability in ants, Integrative Organismal Biology, Vol: 5, Pages: 1-20, ISSN: 2517-4843
Jumping is a rapid locomotory mode widespread in terrestrial organisms. However, it is a rare specialization in ants. Forward jumping has been reported within four distantly related ant genera: Gigantiops, Harpegnathos, Myrmecia, and Odontomachus. The temporal engagement of legs/body parts during jump, however, varies across these genera. It is unknown what morphological adaptations underlie such behaviors and whether jumping in ants is solely driven directly by muscle contraction or additionally relies on elastic recoil mechanism. We investigated the morphological adaptations for jumping behavior by comparing differences in the locomotory musculature between jumping and non-jumping relatives using X-ray micro-CT and 3D morphometrics. We found that the size-specific volumes of the trochanter depressor muscle (scm6) of the middle and hind legs are 3-5 times larger in jumping ants, and that one coxal remotor muscle (scm2) is reduced in volume in the middle and/or hind legs. Notably, the enlargement in the volume of other muscle groups is directly linked to the legs or body parts engaged during the jump. Furthermore, a direct comparison of the muscle architecture revealed two significant differences between jumping vs. non-jumping ants: First, the relative Physiological Cross-Sectional Area (PCSA) of the trochanter depressor muscles of all three legs were larger in jumping ants, except in the front legs of Odontomachus rixosus and Myrmecia nigrocincta; second, the relative muscle fiber length was shorter in jumping ants compared to non-jumping counterparts, except in the front legs of O. rixosus and M. nigrocincta. These results suggest that the difference in relative muscle volume in jumping ants is largely invested in the area (PCSA), and not in fiber length. There was no clear difference in the pennation angle between jumping and non-jumping ants. Additionally, we report that the hind leg length relative to body length was longer in jumping ants. Based on direct com
Püffel F, Roces F, Labonte D, 2023, Strong positive allometry of bite force in leaf-cutter ants increases the range of cuttable plant tissues, The Journal of Experimental Biology, Vol: 226, Pages: 1-14, ISSN: 0022-0949
Atta leaf-cutter ants are the prime herbivore in the Neotropics: differently sized foragers harvest plant material to grow a fungus as a crop. Efficient foraging involves complex interactions between worker size, task preferences and plant-fungus suitability; it is, however, ultimately constrained by the ability of differently sized workers to generate forces large enough to cut vegetation. In order to quantify this ability, we measured bite forces of Atta vollenweideri leaf-cutter ants spanning more than one order of magnitude in body mass. Maximum bite force scaled almost in direct proportion to mass; the largest workers generated peak bite forces 2.5 times higher than expected from isometry. This remarkable positive allometry can be explained via a biomechanical model that links bite forces with substantial size-specific changes in the morphology of the musculoskeletal bite apparatus. In addition to these morphological changes, we show that bite forces of smaller ants peak at larger mandibular opening angles, suggesting a size-dependent physiological adaptation, probably reflecting the need to cut leaves with a thickness that corresponds to a larger fraction of the maximum possible gape. Via direct comparison of maximum bite forces with leaf mechanical properties, we demonstrate (i) that bite forces in leaf-cutter ants need to be exceptionally large compared with body mass to enable them to cut leaves; and (ii), that the positive allometry enables colonies to forage on a wider range of plant species without the need for extreme investment in even larger workers. Our results thus provide strong quantitative arguments for the adaptive value of a positively allometric bite force.
Püffel F, Meyer L, Imirzian N, et al., 2023, Developmental biomechanics and age polyethism in leaf-cutter ants., Proceedings of the Royal Society B: Biological Sciences, Vol: 290, Pages: 1-11, ISSN: 0962-8452
Many social insects display age polyethism: young workers stay inside the nest, and only older workers forage. This behavioural transition is accompanied by genetic and physiological changes, but the mechanistic origin of it remains unclear. To investigate if the mechanical demands on the musculoskeletal system effectively prevent young workers from foraging, we studied the biomechanical development of the bite apparatus in Atta vollenweideri leaf-cutter ants. Fully matured foragers generated peak in vivo bite forces of around 100 mN, more than one order of magnitude in excess of those measured for freshly eclosed callows of the same size. This change in bite force was accompanied by a sixfold increase in the volume of the mandible closer muscle, and by a substantial increase of the flexural rigidity of the head capsule, driven by a significant increase in both average thickness and indentation modulus of the head capsule cuticle. Consequently, callows lack the muscle force capacity required for leaf-cutting, and their head capsule is so compliant that large muscle forces would be likely to cause damaging deformations. On the basis of these results, we speculate that continued biomechanical development post eclosion may be a key factor underlying age polyethism, wherever foraging is associated with substantial mechanical demands.
Labonte D, 2023, A theory of physiological similarity in muscle-driven motion., Proceedings of the National Academy of Sciences of USA, Vol: 120, Pages: 1-11, ISSN: 0027-8424
Muscle contraction is the primary source of all animal movement. I show that the maximum mechanical output of such contractions is determined by a characteristic dimensionless number, the "effective inertia," Γ, defined by a small set of mechanical, physiological, and anatomical properties of the interrogated musculoskeletal complex. Different musculoskeletal systems with equal Γ may be considered physiologically similar, in the sense that maximum performance involves equal fractions of the muscle's maximum strain rate, strain capacity, work, and power density. It can be demonstrated that there exists a unique, "optimal" musculoskeletal anatomy which enables a unit volume of muscle to deliver maximum work and power simultaneously, corresponding to Γ close to unity. External forces truncate the mechanical performance space accessible to muscle by introducing parasitic losses, and subtly alter how musculoskeletal anatomy modulates muscle performance, challenging canonical notions of skeletal force-velocity trade-offs. Γ varies systematically under isogeometric transformations of musculoskeletal systems, a result which provides fundamental insights into the key determinants of animal locomotor performance across scales.
Schultz JT, Labonte D, Clemente CJ, 2023, Multilevel dynamic adjustments of geckos (<i>Hemidactylus frenatus</i>) climbing vertically: head-up versus head-down, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 20, ISSN: 1742-5689
Greenway E, Beck HK, Labonte D, et al., 2023, <i>Testing the impact of autotomy on locomotion in the insect Leptoglossus phyllopus</i>, Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S125-S125, ISSN: 1540-7063
Walthaus OK, Kang V, Imirzian N, et al., 2023, <i>Mechanical efficiency of cutting inAtta cephalotes leafcutter ants</i>, Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S323-S323, ISSN: 1540-7063
Ahmed S, Kang V, Labonte D, et al., 2023, <i>Lattice structure of mandible closer muscles in leafcutter ants (Atta vollenweideri)</i>, Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S4-S5, ISSN: 1540-7063
Kaimaki D-M, Stoukidi MN, Andrew CN, et al., 2023, <i>In situ viscosity measurements of the stick insect pad secretion across temperatures and animal size</i>, Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S162-S162, ISSN: 1540-7063
Plum F, Labonte D, 2023, scAnt-an open-source platformfor the creation of 3D models of arthropods (and other small objects), Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S248-S248, ISSN: 1540-7063
Plum F, Bulla R, Imirzian N, et al., 2023, Synthetic datasets based on photogrammetry models power robust deep neural networks for behavioural analyses in social insects, Symposium on Best Practices for Bioinspired Design Education, Research and Product Development at the Virtual Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: S248-S249, ISSN: 1540-7063
Püffel F, Johnston R, Labonte D, 2023, A biomechanical model for the relation between bite force and mandibular opening angle in arthropods, Royal Society Open Science, Vol: 10, Pages: 1-23, ISSN: 2054-5703
Bite forces play a key role in animal ecology: they affect mating behaviour, fighting success, and the ability to feed. Although feeding habits of arthropods have a significant ecological and economical impact, we lack fundamental knowledge on how the morphology and physiology of their bite apparatus controls bite performance, and its variation with mandible gape. To address this gap, we derived a biomechanical model that characterizes the relationship between bite force and mandibular opening angle from first principles. We validate this model by comparing its geometric predictions with morphological measurements on the muscoloskeletal bite apparatus of Atta cephalotes leaf-cutter ants, using computed tomography (CT) scans obtained at different mandible opening angles. We then demonstrate its deductive and inductive utility with three examplary use cases: Firstly, we extract the physiological properties of the leaf-cutter ant mandible closer muscle from in vivo bite force measurements. Secondly, we show that leaf-cutter ants are specialized to generate extraordinarily large bite forces, equivalent to about 2600 times their body weight. Thirdly, we discuss the relative importance of morphology and physiology in determining the magnitude and variation of bite force. We hope that a more detailed quantitative understanding of the link between morphology, physiology, and bite performance will facilitate future comparative studies on the insect bite apparatus, and help to advance our knowledge of the behaviour, ecology and evolution of arthropods.
Labonte D, Holt NC, 2022, Elastic energy storage and the efficiency of movement, Current Biology, Vol: 32, Pages: R661-R666, ISSN: 0960-9822
Movement is an integral part of animal biology. It enables organisms to escape from danger, acquire food, and perform courtship displays. Changing the speed or vertical position of a body requires mechanical energy. This energy is typically provided by the biological motor, striated muscle. Striated muscle uses chemical (metabolic) energy to produce force, to move this force over a distance to do work, and to do this work within some time to generate power. The metabolic energy consumed in producing these mechanical outputs is a major component of an organism's energy budget, particularly during repetitive, cyclical movements. This energy could otherwise be used for maintenance, growth, and reproduction. Hence, fitness may be enhanced by improving locomotor efficiency - the ratio between work done and metabolic energy consumed. This may be achieved by reducing the need for muscle to do work, and by increasing the efficiency with which muscle does work.
Kaimaki D-M, Andrew CNS, Attipoe AEL, et al., 2022, The physical properties of the stick insect pad secretion are independent of body size, Journal of the Royal Society Interface, Vol: 19, ISSN: 1742-5662
Many insects use adhesive organs to climb. The ability to cling to surfaces is advantageous but is increasingly challenged as animals grow, due to the associated reduction in surface-to-volume ratio. Previous work has demonstrated that some climbing animals overcome this scaling problem by systematically altering the maximum force per area that their adhesive pads can sustain; their adhesive organs become more efficient as they grow, an observation which is also of substantial relevance for the design of bioinspired adhesives. What is the origin of this change in efficiency? In insects, adhesive contact is mediated by a thin film of a liquid, thought to increase adhesive performance via capillary and viscous forces. Here, we use interference reflection microscopy and dewetting experiments to measure the contact angle and dewetting speed of the secretion of pre-tarsal adhesive pads of Indian stick insects, varying in mass by over two orders of magnitude. Neither contact angle nor dewetting speed change significantly with body mass, suggesting that the key physical properties of the pad secretion-its surface tension and viscosity-are size-invariant. Thus, the observed change in pad efficiency is unlikely to arise from systematic changes of the physical properties of the pad secretion; the functional role of the secretion remains unclear.
Kaimaki D-M, Andrew CNS, Attipoe AEL, et al., 2022, The physical properties of the stick insect pad secretion are independent of body size
<jats:p>Many insects use adhesive organs to climb. The ability to cling to surfaces is advantageous but is increasingly challenged as animals grow, due to the associated reduction in surface-to-volume ratio. Previous work has demonstrated that some climbing animals overcome this scaling problem by systematically altering the maximum force per area their adhesive pads can sustain; their adhesive organs become more efficient as they grow, an observation which is also of substantial relevance for the design of bio-inspired adhesives. What is the origin of this change in efficiency? In insects, adhesive contact is mediated by a thin film of a liquid, thought to increase adhesive performance via capillary and viscous forces. Here, we use interference reflection microscopy and dewetting experiments to measure the contact angle and dewetting speed of the secretion of pre-tarsal adhesive pads of Indian stick insects, varying in mass by over two orders of magnitude. Neither contact angle nor dewetting speed change significantly with body mass, suggesting that the key physical properties of the pad secretion – its surface tension and viscosity – are size-invariant. Thus, the observed change in pad efficiency is unlikely to arise from systematic changes of the physical properties of the pad secretion; the functional role of the secretion remains unclear.</jats:p>
Puffel F, Pouget A, Liu X, et al., 2021, Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphic leaf-cutter ants, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 18, ISSN: 1742-5689
The extraordinary success of social insects is partially based on division oflabour, i.e. individuals exclusively or preferentially perform specific tasks.Task preference may correlate with morphological adaptations so implyingtask specialization, but the extent of such specialization can be difficult todetermine. Here, we demonstrate how the physical foundation of sometasks can be leveraged to quantitatively link morphology and performance.We study the allometry of bite force capacity inAtta vollenweiderileaf-cutterants, polymorphic insects in which the mechanical processing of plantmaterial is a key aspect of the behavioural portfolio. Through a morpho-metric analysis of tomographic scans, we show that the bite force capacityof the heaviest colony workers is twice as large as predicted by isometry.This disproportionate‘boost’is predominantly achieved through increasedinvestment in muscle volume; geometrical parameters such as mechanicaladvantage, fibre length or pennation angle are likely constrained by theneed to maintain a constant mandibular opening range. We analyse this pre-ference for an increase in size-specific muscle volume and the adaptations ininternal and external head anatomy required to accommodate it with simplegeometric and physical models, so providing a quantitative understandingof the functional anatomy of the musculoskeletal bite apparatus in insects
Nowlan N, Ahmed S, Kaimaki DM, et al., 2021, Prenatal muscle forces are necessary for vertebral segmentation and disc structure, but not for notochord involution in mice, European Cells and Materials, Vol: 41, Pages: 558-575, ISSN: 1473-2262
Embryonic muscle forces are necessary for normal vertebral development and spinal curvature, but their involvement in intervertebral disc (IVD) development remains unclear. The aim of the current study was to determine how muscle contractions affect (1) notochord involution and vertebral segmentation, and (2) IVD development including the mechanical properties and morphology, as well as collagen fibre alignment in the annulus fibrosus. Muscular dysgenesis (mdg) mice were harvested at three prenatal stages: at Theiler Stage (TS)22 when notochord involution starts, at TS24 when involution is complete, and at TS27 when the IVD is formed. Vertebral and IVD development were characterised using histology, immunofluorescence, and indentation testing. Our results revealed that notochord involution and vertebral segmentation occurred independently of muscle contractions between TS22 and TS24. However, in the absence of muscle contractions, we found vertebral fusion in the cervical region at TS27, along with (i) a displacement of the nucleus pulposus towards the dorsal side, (ii) a disruption of the structural arrangement of collagen in the annulus fibrosus, and (iii) an increase in viscous behaviour of the annulus fibrosus. These findings emphasise the important role of mechanical forces during IVD development, and demonstrate a critical role of muscle loading during development to enable proper annulus fibrosus formation. Our findings further suggest a need for mechanical loading in the creation of fibre-reinforced tissue engineering replacement IVDs as a therapy for IVD degeneration.
Plum F, Labonte D, 2021, scAnt-an open-source platform for the creation of 3D models of arthropods (and other small objects), PeerJ, Vol: 9, Pages: 1-29, ISSN: 2167-8359
We present scAnt, an open-source platform for the creation of digital 3D models of arthropods and small objects. scAnt consists of a scanner and a Graphical User Interface, and enables the automated generation of Extended Depth Of Field images from multiple perspectives. These images are then masked with a novel automatic routine which combines random forest-based edge-detection, adaptive thresholding and connected component labelling. The masked images can then be processed further with a photogrammetry software package of choice, including open-source options such as Meshroom, to create high-quality, textured 3D models. We demonstrate how these 3D models can be rigged to enable realistic digital specimen posing, and introduce a novel simple yet effective method to include semi-realistic representations of approximately planar and transparent structures such as wings. As a result of the exclusive reliance on generic hardware components, rapid prototyping and open-source software, scAnt costs only a fraction of available comparable systems. The resulting accessibility of scAnt will (i) drive the development of novel and powerful methods for machine learning-driven behavioural studies, leveraging synthetic data; (ii) increase accuracy in comparative morphometric studies as well as extend the available parameter space with area and volume measurements; (iii) inspire novel forms of outreach; and (iv) aid in the digitisation efforts currently underway in several major natural history collections.
Labonte D, Robinson A, Bauer U, et al., 2021, Disentangling the role of surface topography and intrinsic wettability in the prey capture mechanism of Nepenthes pitcher plants., Acta Biomaterialia, Vol: 119, Pages: 225-233, ISSN: 1742-7061
Nepenthes pitcher plants capture prey with leaves specialised as pitfall traps. Insects are trapped when they 'aquaplane' on the pitcher rim (peristome), a surface structured with macroscopic and microscopic radial ridges. What is the functional significance of this hierarchical surface topography? Here, we use insect pad friction measurements, photolithography, wetting experiments and physical modelling to demonstrate that the ridges enhance the trap's efficacy by satisfying two functional demands on prey capture: Macroscopic ridges restrict lateral but enhance radial spreading of water, thereby creating continuous slippery tracks which facilitate prey capture when little water is present. Microscopic ridges, in turn, ensure that the water film between insect pad and peristome remains stable, causing insects to aquaplane. In combination, the hierarchical ridge structure hence renders the peristome wettable, and water films continuous, so avoiding the need for a strongly hydrophilic surface chemistry, which would compromise resistance to desiccation and attract detrimental contamination.
Nakanishi K, Labonte D, Cebo T, et al., 2020, Mechanical properties of the hollow-wall graphene gyroid lattice, Acta Materialia, Vol: 201, Pages: 254-265, ISSN: 1359-6454
The macroscopic elastic modulus and yield strength of solid-wall nickel gyroids and hollow-wall graphene gyroids of cell size 60 nm are deduced from indentation tests on a thin coating of the gyroids, with suitable interpretation by finite element simulations. The solid-wall nickel gyroids are fabricated by the self-assembly of a triblock copolymer, followed by the chemical vapour deposition of a graphene film onto this catalytic template. The nano-indentation response of the gyroid-based coatings was measured using a Berkovich indenter. In order to interpret the indentation response, two sets of finite element simulations were performed: periodic cell calculations in order to deduce the effective macroscopic properties in terms of the relative density and cell wall properties of the lattice, and then indentation simulations of a continuum with the effective properties of the gyroid. Despite the knockdown in modulus and strength of the graphene gyroid lattice due to waviness of the layered cell walls, the structure remains remarkably strong due to nanoscale size effects.
Kaimaki DM, Attipoe AEL, Stoukidi MN, et al., 2020, Temperature-induced viscosity changes of the insect pad secretion, Annual Meeting of the Society-for-Integrative-and-Comparative-Biology (SICB), Publisher: OXFORD UNIV PRESS INC, Pages: E353-E353, ISSN: 1540-7063
Attipoe AEL, Kaimaki D-M, Labonte D, 2020, Surface tension of the insect pad secretion, Annual Meeting of the Society-for-Integrative-and-Comparative-Biology (SICB), Publisher: OXFORD UNIV PRESS INC, Pages: E276-E276, ISSN: 1540-7063
Labonte D, Struecker M-Y, Birn-Jeffery A, et al., 2019, Shear-sensitive adhesion enables size-independent adhesive performance in stick insects, Proceedings of the Royal Society B: Biological Sciences, Vol: 286, ISSN: 0962-8452
The ability to climb with adhesive pads conveys significant advantages, and is hence widespread in the animalkingdom. The physics of adhesion predict that attachment is more challenging for large animals, whereas detach-ment is harder for small animals, due to the difference in surface-to-volume ratios. Here, we use stick insects toshow that this problem is solved at both ends of the scale by linking adhesion to the applied shear force. Adhesiveforces of individual insect pads, measured with perpendicular pull-offs, increased approximately in proportion toa linear pad dimension across instars. In sharp contrast, whole-body force measurements suggested area-scalingof adhesion. This discrepancy is explained by the presence of shear forces during whole-body measurements, asconfirmed in experiments with pads sheared prior to detachment. When we applied shear forces proportional toeither pad area or body weight, pad adhesion also scaled approximately with area or mass, respectively, provid-ing a mechanism that can compensate for the size-related loss of adhesive performance predicted by isometry.We demonstrate that the adhesion-enhancing effect of shear forces is linked to pad sliding, which increased themaximum adhesive force per area sustainable by the pads. As shear forces in natural conditions are expectedto scale with mass, sliding is more frequent and extensive in large animals, thus ensuring that large animals canattach safely, while small animals can still detach their pads effortlessly. Our results therefore help to explain hownature’s climbers maintain a dynamic attachment performance across seven orders of magnitude in body weight.
Federle W, Labonte D, 2019, Dynamic biological adhesion: mechanisms for controlling attachment during locomotion, Philosophical Transactions B: Biological Sciences, Vol: 374, ISSN: 0962-8436
The rapid control of surface attachment is a key feature of natural adhesive systems used for locomotion, and a property highly desirable for man-made adhesives. Here, we describe the challenges of adhesion control and the timescales involved across diverse biological attachment systems and different adhesive mechanisms. The most widespread control principle for dynamic surface attachment in climbing animals is that adhesion is 'shearsensitive' (directional): pulling adhesive pads towards the body results in strong attachment, whereas pushing them away from it leads to easy detachment, providing a rapid mechanical `switch'. Shear-sensitivity is based on changes of contact area and adhesive strength, which in turn arise from non-adhesive default positions, the mechanics of peeling, pad sliding, and the targeted storage and controlled release of elastic strain energy. The control of adhesion via shear forces is deeply integrated with the climbing animals' anatomy and locomotion, and involves both active neuromuscular control, and rapid passive responses of sophisticated mechanical systems. The resulting dynamic adhesive systems are robust, reliable, versatile and nevertheless remarkably simple.
Pattrick JG, Labonte D, Federle W, 2018, Scaling of claw sharpness: mechanical constraints reduce attachment performance in larger insects, Journal of Experimental Biology, Vol: 221, ISSN: 0022-0949
Claws are the most widespread attachment devices in animals, but comparatively little is known about the mechanics of claw attachment. A key morphological parameter in determining attachment ability is claw sharpness; however, there is a conflict between sharpness and fracture resistance. Sharper claws can interlock on more surfaces but are more likely to break. Body size interacts with this conflict such that larger animals should have much blunter claws and consequently poorer attachment ability than smaller animals. This expected size-induced reduction in attachment performance has not previously been investigated, and it is unclear how animals deal with this effect, and whether it indeed exists. We explored the scaling of claw sharpness with body size using four insect species (Nauphoeta cinerea, Gromphadorhina portentosa, Atta cephalotes and Carausius morosus) each covering a large size range. The scaling of claw sharpness varied significantly between species, suggesting that they face different pressures regarding claw function. Attachment forces were measured for A. cephalotes and G. portentosa (which had different scaling of claw sharpness) on several rough surfaces using a centrifuge setup. As expected, attachment performance was poorer in larger animals. Firstly, larger animals were more likely to slip, although this effect depended on the scaling of claw sharpness. Secondly, when they gripped, they attached with smaller forces relative to their weight. This size-induced reduction in attachment performance has significant implications for the attachment ability of larger animals on rough surfaces.
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