Biology subjects

Kang, V.

Publications and source records attributed to Kang, V..

6 recordsLinked to original sources

bioRxiv2024

Behavioural biomechanics: leaf-cutter ant cutting behaviour depends on leaf edge geometry

Leaf-cutter ants cut fresh leaves to grow a symbiotic fungus as crop. During cutting, one mandible is typically anchored onto the leaf lamina while the other slices through it like a knife. When initiating cuts into the leaf edge, however, foragers sometimes deviate from this behaviour, and instead used their mandibles symmetrically, akin to scissors. In-vivo behavioural assays revealed that the preference for either of the two cutting strategies depended on leaf edge geometry, and differed between natural leaf margins that were straight or serrated with notch-like folds: leaf-cutter ants displayed a strong preference for scissor-cutting when leaf edges were straight or had wide notches. This preference, however, reversed in favour of knife-cutting when notches were narrow. To investigate whether this behavioural difference had a mechanical origin, we mimicked knife-cutting in ex-vivo cutting experiments: for wide notches, all but the sharpest mandibles failed to initiate cuts, or only did so at large forces, caused by substantial leaf buckling and bending. This increased force demand would substantially limit the ability of foragers to cut leaves, and so reduce the colonys access to food sources. Scissor-cutting may thus be an adaptation to the mechanical difficulties associated with bending and buckling of thin leaves.

animal behavior and cognition↗

bioRxiv2023

3D kinematics of leaf-cutter ant mandibles: not all dicondylic joints are simple hinges

Insects use their mandibles for a variety of tasks, including cutting and material transport, defence, building nests, caring for brood, and competing for mates. Despite this functional diversity, mandible motion is thought to be constrained to rotation about a single fixed axis in the majority of extant species. 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 3D using a multi-camera rig. Rigid body kinematic analyses revealed strong evidence that mandible movement occupies a kinematic space which requires more than one rotational degree of freedom: at large opening angles, mandible motion is dominated by yaw. But at small opening angles, mandibles 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 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.

evolutionary biology↗

bioRxiv2023

Biomechanics of cutting: sharpness, wear sensitivity, and the scaling of cutting forces in leaf-cutter ant mandibles

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 required 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 rationalise 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.

evolutionary biology↗

bioRxiv2021

How a sticky fluid facilitates prey retention in a carnivorous pitcher plant (Nepenthes rafflesiana)

Nepenthes pitcher plants live in nutrient-poor soils and produce large pitfall traps to obtain additional nutrients from animal prey. Previous research has shown that the digestive secretion in N. rafflesiana is a sticky viscoelastic fluid that is much more effective at retaining insects than water, even after significant dilution. Although the physical properties of the fluid are important for its retentive function, it is unclear how the fluid interacts with insect cuticle and how its sticky nature affects struggling insects. In this study, we investigated the mechanisms behind the efficient prey retention in N. rafflesiana pitcher fluid. By measuring the attractive forces exerted on insect body parts moving in and out of test fluids, we show that it costs insects significantly more energy to separate from pitcher fluid than from water. Moreover, both the maximum force and the energy required for retraction increase after the first contact with the pitcher fluid. We found that insects sink more easily into pitcher fluid than water and, accordingly, the surface tension of N. rafflesiana pitcher fluid was significantly lower than that of water (60.2 vs. 72.3 mN/m). By analysing the pitcher fluid dewetting behaviour, we demonstrate that it strongly resists dewetting from all surfaces tested, leaving behind residual films and filaments that can facilitate re-wetting. This inhibition of dewetting may be a further consequence of the fluids viscoelastic nature and likely represents a key mechanism underlying prey retention in Nepenthes pitcher plants.

plant biology↗

bioRxiv2020

Extreme suction attachment performance from specialised insects living in mountain streams (Diptera: Blephariceridae)

Suction is widely used by animals for strong controllable underwater adhesion but is less well understood than adhesion of terrestrial climbing animals. Here we investigate the attachment of an aquatic insect larva (Blephariceridae), which clings to rocks in torrential streams using the only known muscle-actuated suction organs in insects. We measured their attachment forces on well-defined rough substrates and found their adhesion was much less reduced by micro-roughness than terrestrial climbing insects. In vivo visualisation of the suction organs in contact with microstructured substrates revealed that they can mould around large asperities to form a seal. Moreover, we showed that spine-like microtrichia on the organ are stiff cuticular structures that only make tip contact on smooth and microstructured substrates. Our results highlight the performance and versatility of blepharicerid suction organs and introduce a new study system to explore biological suction.

ecology↗

bioRxiv2019

Sophisticated suction organs from insects living in raging torrents: Morphology and ultrastructure of the attachment devices of net-winged midge larvae (Diptera: Blephariceridae)

2.Suction organs provide powerful yet dynamic attachments for many aquatic animals, including octopus, squid, remora, and clingfish. While the functional morphology of suction organs from various cephalopods and fishes has been investigated in detail, there are only few studies on such attachment devices in insects. Here we characterise the morphology, ultrastructure, and in vivo movements of the suction attachment organs of net-winged midge larvae (genus Liponeura) - aquatic insects that live on rocks in rapid alpine waterways where flow rates can reach 3 m s-1 - using scanning electron microscopy, laser confocal scanning microscopy, and X-ray computed micro-tomography (micro-CT). We identified structural adaptations important for the function of the suction attachment organs from L. cinerascens and L. cordata. First, a dense array of spine-like microtrichia covering each suction disc comes into contact with the substrate upon attachment. Similar hairy structures have been found on the contact zones of suction organs from octopus, clingfish, and remora fish. These structures are thought to contribute to the seal and to provide increased shear force resistance in high-drag environments. Second, specialised rim microtrichia at the suction disc periphery form a continuous ring in close contact with a surface and may serve as a seal on a variety of surfaces. Third, a V-shaped cut on the suction disc (the V-notch) is actively peeled open via two cuticular apodemes inserting into its flanks. The apodemes are attached to dedicated V-notch opening muscles, thereby providing a unique detachment mechanism. The complex cuticular design of the suction organs, along with specialised muscles that attach to them, allows blepharicerid larvae to generate powerful attachments which can withstand strong hydrodynamic forces and quickly detach for locomotion. Our findings could be applied to bio-inspired attachment devices that perform well on a wide range of surfaces.

zoology↗