The damping properties of the foam-filled shaft of primary feathers of the pigeon Columba livia

The avian feather combines mechanical properties of robustness and flexibility while maintaining a low weight. Under periodic and random dynamic loading, the feathers sustain bending forces and vibrations during flight. Excessive vibrations can increase noise, energy consumption, and negatively impact flight stability. However, damping can alter the system response, and result in increased stability and reduced noise. Although the structure of feathers has already been studied, little is known about their damping properties. In particular, the link between the structure of shafts and their damping is unknown. This study aims at understanding the structure-damping relationship of the shafts. For this purpose, laser Doppler vibrometry (LDV) was used to measure the damping properties of the feather shaft in three segments selected from the base, middle, and tip. A combination of scanning electron microscopy (SEM) and micro-computed tomography (µCT) was used to investigate the gradient microstructure of the shaft. The results showed the presence of two fundamental vibration modes, when mechanically excited in the horizontal and vertical directions. It was also found that the base and middle parts of the shaft have higher damping ratios than the tip, which could be attributed to their larger foam cells, higher foam/cortex ratio, and higher percentage of foam. This study provides the first indication of graded damping properties in feathers.

The role of mucilage envelope in the endozoochory of selected plant taxa

Myxodiaspory (formation of mucilage envelope around seeds and fruits) is a common adaptation to dry habitats known in many families of Angiosperms. The mucilage envelope of some seeds seems to be also a unique morphological adaptation which protects myxospermatic diaspores while passing through the bird’s digestive system. To evaluate the protective potential of mucilage, we fed the diaspores of seven plant species (representing three different mucilage types and three species of non-mucilaginous plants) to pigeons, Columba livia domestica. Twenty-four hours later, we collected the droppings of pigeons and examined a total of 18,900 non-destroyed diaspores to check for mucilage presence and germination ability. Out of all the examined diaspores, 4.5% were mucilaginous seeds. Among them, the highest number (12.2–13.5%) of viable diaspores belonged to the hemicellulosic type of mucilage (from Plantago species). Only 3.7% of germinating diaspores with pectic mucilage (Linum usitatissimum) were collected, and no seeds representing cellulosic mucilage (e.g., Ocimum basilicum). For non-mucilaginous plants, we collected only a few individual seeds (0.1% out of 8100 seeds used). We noted that the mucilaginous seeds found in the droppings were able to germinate; however, the germination ability was generally smaller in comparison to the control (i.e., not digested) seeds. Our results revealed that the presence of mucilage envelope has an impact on diaspore dispersal and survivability. With our experiments, we demonstrated for the first time that the mucilage envelope, especially of the non-cellulosic type, supports endozoochory. We also showed that non-mucilaginous seeds can be occasionally dispersed via endozoochory and are able to germinate. The results of our studies can explain the ways of plants distribution at a small, local scale as well as in long-distance dispersal, e.g., between islands or even continents.

Comparison of tarsal attachment in two closely related leaf beetle species

Green dock beetles Gastrophysa viridula and Colorado potato beetles Leptinotarsa decemlineata having distinctly different body mass and gait habits were compared with respect to their tarsal morphology and attachment ability. The focus laid on shapes and dimensions of tenent setae related to the peeling line, i.e., the sum of widths of all thin-film elements participating in contact. High-speed rotation of the two leaf beetle species attached to the horizontal and vertical sides of a Plexiglass drum resulted in higher attachment forces of the heavier beetle species that has a larger number of tarsal setae and a larger peeling line length. However, normalizing the measured forces with the corresponding peeling line lengths led to a reversed relationship. This allowed us to assume that the design of adhesive setae in different leaf beetle species matches the requirements imposed by their habitats. In accordance with the theory of thin film peeling, tangential forces were found to be higher than normal forces. The attachment system of females was found to exhibit stronger functional efficiency, which can be correlated to the morphology of their setae.

Biological adhesion in seagrasses: The role of substrate roughness in Posidonia oceanica (L.) Delile seedling anchorage via adhesive root hairs

Seagrasses are marine flowering plants that developed several adaptive traits for living in submerged waters. Among this group, Posidonia oceanica (L.) Delile is the dominant species of the Mediterranean Sea, forming persistent meadows that provide valuable ecosystem services to human communities. P. oceanica seedlings can anchor to rocky substrates through adhesive root hairs. Here we investigate, for the first time, the bioadhesion process in seagrasses. Seedlings were grown on substrates provided with different roughness in order to identify mechanisms involved in the adhesion process. Root anchorage strength was measured through a peel test and hair morphology at different micro-roughness was analysed by electron and fluorescence microscopy. Maximum anchorage strength was recorded at roughness levels between 3 and 26 μm, while on finer (0.3) and coarser (52, 162 μm) roughness attachment was weaker. No attachment was obtained on smooth surfaces. Accordingly, root hair tip morphology strongly responded to the substrate. Morphological adaptation of the root hairs to surface topography and mechanical interlocking into the micro-roughness of the substrate appear the main mechanisms responsible for bioadhesion in the system under study. Substrate roughness at the scale of microns and tens of microns is pivotal for P. oceanica seedling attachment to take place. These findings contribute to identification of features of optimal microsite for P. oceanica seedling settlement and to the development of novel approaches to seagrass restoration that take advantage of species' key life history traits.

Persistence of plastic debris and its colonization by bacterial communities after two decades on the abyssal seafloor

The fate of plastic debris entering the oceans is largely unconstrained. Currently, intensified research is devoted to the abiotic and microbial degradation of plastic floating near the ocean surface for an extended period of time. In contrast, the impacts of environmental conditions in the deep sea on polymer properties and rigidity are virtually unknown. Here, we present unique results of plastic items identified to have been introduced into deep-sea sediments at a water depth of 4150 m in the eastern equatorial Pacific Ocean more than two decades ago. The results, including optical, spectroscopic, physical and microbial analyses, clearly demonstrate that the bulk polymer materials show no apparent sign of physical or chemical degradation. Solely the polymer surface layers showed reduced hydrophobicity, presumably caused by microbial colonization. The bacterial community present on the plastic items differed significantly (p < 0.1%) from those of the adjacent natural environment by a dominant presence of groups requiring steep redox gradients (Mesorhizobium, Sulfurimonas) and a remarkable decrease in diversity. The establishment of chemical gradients across the polymer surfaces presumably caused these conditions. Our findings suggest that plastic is stable over extended times under deep-sea conditions and that prolonged deposition of polymer items at the seafloor may induce local oxygen depletion at the sediment-water interface.

Material stiffness variation in mosquito antennae

The antennae of mosquitoes are model systems for acoustic sensation, in that they obey general principles for sound detection, using both active feedback mechanisms and passive structural adaptations. However, the biomechanical aspect of the antennal structure is much less understood than the mechano-electrical transduction. Using confocal laser scanning microscopy, we measured the fluorescent properties of the antennae of two species of mosquito—Toxorhynchites brevipalpis and Anopheles arabiensis—and, noting that fluorescence is correlated with material stiffness, we found that the structure of the antenna is not a simple beam of homogeneous material, but is in fact a rather more complex structure with spatially distributed discrete changes in material properties. These present as bands or rings of different material in each subunit of the antenna, which repeat along its length. While these structures may simply be required for structural robustness of the antennae, we found that in FEM simulation, these banded structures can strongly affect the resonant frequencies of cantilever-beam systems, and therefore taken together our results suggest that modulating the material properties along the length of the antenna could constitute an additional mechanism for resonant tuning in these species.

Numerical simulation of the pattern formation of the springtail cuticle nanostructures

Springtails (Collembola) are known to exhibit complex hierarchical nanostructures of their exoskeleton surface that repels water and other fluids with remarkable efficiency. These nanostructures were previously widely studied due to their structure, chemistry and fluid-repelling properties. These ultrastructural and chemical studies revealed the involvement of different components in different parts of the nanopattern, but the overall process of self-assembly into the complex rather regular structures observed remains unclear. Here, we model this process from a theoretical point of view partially using solutions related to the so-called Tammes problem. By using densities of three different reacting substances, we obtained a typical morphology that is highly similar to the ones observed on the cuticle of some springtail species. These results are important not only for our understanding of the formation of hierarchical nanoscale structures in nature, but also for the fabrication of novel surface coatings.

A simple, high-resolution, non-destructive method for determining the spatial gradient of the elastic modulus of insect cuticle

Nature has evolved structures with high load-carrying capacity and long-term durability. The principles underlying the functionality of such structures, if studied systematically, can inspire the design of more efficient engineering systems. An important step in this process is to characterize the material properties of the structure under investigation. However, direct mechanical measurements on small complex-shaped biological samples involve numerous technical challenges. To overcome these challenges, we developed a method for estimation of the elastic modulus of insect cuticle, the second most abundant biological composite in nature, through simple light microscopy. In brief, we established a quantitative link between the autofluorescence of different constituent materials of insect cuticle, and the resulting mechanical properties. This approach was verified using data on cuticular structures of three different insect species. The method presented in this study allows three-dimensional visualisation of the elastic modulus, which is impossible with any other available technique. This is especially important for precise finite-element modelling of cuticle, which is known to have spatially graded properties. Considering the simplicity, ease of implementation and high-resolution of the results, our method is a crucial step towards a better understanding of material-function relationships in insect cuticle, and can potentially be adapted for other graded biological materials.

Functional morphology of the sting in two digger wasps (Hymenoptera: Crabronidae) with different types of prey transport

Digger wasps of the family Crabronidae (Insecta: Hymenoptera) are generally known to use their sting to paralyze or kill a prey. However, only a few species of digger wasps transport their prey to the nest impaled on the sting. How sting morphology correlates with this peculiar type of prey carriage is still unclear. We examined the sting morphology of two phylogenetically closely-related species of digger wasps of similar size, which hunt for similar preys but use different types of prey transportation. Data from light microscopy (LM), scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were analyzed to find possible correlations between shape, material composition, and function of the stings. The similarity of the material composition in the stings of the two species suggests that the material of stings does not play a dominant role in their functional differences. On the contrary, differences in the curvature and surface sculpture of sting elements likely result in different stress distributions under mechanical loading.

Stiffness gradients facilitate ovipositor bending and spatial probing control in a parasitic wasp

Many parasitic wasps use slender and steerable ovipositors to lay eggs in hosts hidden in substrates, but it is currently unknown how steering is achieved. The ovipositors generally consist of three longitudinally connected elements, one dorsal and two ventral valves that can slide along each other. For the parasitic wasp Diachasmimorpha longicaudata, it has been shown that protraction of the ventral valves causes incurving of the ventral valves towards the dorsal one, which results in a change in probing direction. We hypothesise that this shape change is due to differences in bending stiffness along the ovipositor. Alignment of the stiff tip of the dorsal valve with a more flexible ventral S-shaped region situated just behind the tip straightens this S-bend and results in upwards rotation of the ventral tip. We show that the S-shaped region of the ventral valves has a low bending stiffness because it contains soft materials such as resilin. In contrast, the large cross-sectional area of the dorsal valve tip area probably results in a high bending stiffness. Elsewhere, the dorsal valve is less stiff than the ventral valves. Our results support the hypothesis that the interaction between the stiff dorsal valve portion and the more flexible S-shaped region co-determine the configurational tip changes required for steering the ovipositor in any desired direction along curved paths in the substrate. This provides novel insights in the understanding of steering mechanisms of the hymenopteran ovipositor, and for the application in man-made probes.

"Cylindrical worlds" in biology: Does the aggregation strategy give a selective advantage?

Tree trunks and other cylindrical objects, where aggregated insects live, represent a very specific world for predator-prey interactions, which must differ from the situation on a 2D plane. In the present paper, in order to gain a better understanding of the specificity of predator-prey interaction in a cylindrical space, we applied a theoretical approach. Here we introduce a numerical model that allows us to test the effect of different interaction properties between predator and aggregated prey on the plane (2D) and on a cylinder (3D), taking into consideration different abilities of predators to visually detect the prey in these two types of space. The main aim was to test these interactions in an environment, which more realistically reproduces the conditions where aggregated insects usually live. We showed that the aggregation in conjunction with a specific environment may bring additional advantages for the prey. When one prey subgroup aggregates on the other side of the tree trunk and becomes invisible behind the horizon of events for the predator, the subgroup will survive with an extremely high probability. After all, the predator moving along one side of the tree will finally loose the major group completely.

Both stiff and compliant: morphological and biomechanical adaptations of stick insect antennae for tactile exploration

Active tactile exploration behaviour is constrained to a large extent by the morphological and biomechanical properties of the animal's somatosensory system. In the model organism Carausius morosus, the main tactile sensory organs are long, thin, seemingly delicate, but very robust antennae. Previous studies have shown that these antennae are compliant under contact, yet stiff enough to maintain a straight shape during active exploration. Overcritical damping of the flagellum, on the other hand, allows for a rapid return to the straight shape after release of contact. Which roles do the morphological and biomechanical adaptations of the flagellum play in determining these special mechanical properties? To investigate this question, we used a combination of biomechanical experiments and numerical modelling. A set of four finite-element (FE) model variants was derived to investigate the effect of the distinct geometrical and material properties of the flagellum on its static (bending) and dynamic (damping) characteristics. The results of our numerical simulations show that the tapered shape of the flagellum had the strongest influence on its static biomechanical behaviour. The annulated structure and thickness gradient affected the deformability of the flagellum to a lesser degree. The inner endocuticle layer of the flagellum was confirmed to be essential for explaining the strongly damped return behaviour of the antenna. By highlighting the significance of two out of the four main structural features of the insect flagellum, our study provides a basis for mechanical design of biomimetic touch sensors tuned to become maximally flexible while quickly resuming a straight shape after contact.

Micro-morphological adaptations of the wing nodus to flight behaviour in four dragonfly species from the family Libellulidae (Odonata: Anisoptera)

Adult dragonflies can be divided into two major groups, perchers and fliers, exhibiting notably different flight behaviour. Previous studies have yielded conflicting results regarding the link between the wing macro-morphology and flight style in these two groups. In this study, we present the first systematic investigation of the micro-morphological differences of wings of percher and flier dragonflies in four closely related species from the family Libellulidae. Our results suggest that the shape and material composition of wing microstructural components and, in particular, the nodus are adapted to facilitate the specific wing functioning in fliers and perchers. The findings further indicate a decreasing trend in the area proportion of the soft resilin-dominated cuticle in the nodus in the series of species from typical perchers to typical fliers. Such a reduction in the resilin proportion in the nodus of fliers is associated with an increase in the wing aspect ratio. The knot-shaped protrusion at the nodus of perchers, which becomes notably smaller in that of strong fliers, is likely to act as a mechanical stopper, avoiding large wing displacements. This study aims to develop a novel framework for future research on the relationship between wing morphology and flight behaviour in dragonflies.

Stiffness distribution in insect cuticle: a continuous or a discontinuous profile?

Insect cuticle is a biological composite with a high degree of complexity in terms of both architecture and material composition. Given the complex morphology of many insect body parts, finite-element (FE) models play an important role in the analysis and interpretation of biomechanical measurements, taken by either macroscopic or nanoscopic techniques. Many previous studies show that the interpretation of nanoindentation measurements of this layered composite material is very challenging. To develop accurate FE models, it is of particular interest to understand more about the variations in the stiffness through the thickness of the cuticle. Considering the difficulties of making direct measurements, in this study, we use the FE method to analyse previously published data and address this issue numerically. For this purpose, sets of continuous or discontinuous stiffness profiles through the thickness of the cuticle were mathematically described. The obtained profiles were assigned to models developed based on the cuticle of three insect species with different geometries and layer configurations. The models were then used to simulate the mechanical behaviour of insect cuticles subjected to nanoindentation experiments. Our results show that FE models with discontinuous exponential stiffness gradients along their thickness were able to predict the stress and deformation states in insect cuticle very well. Our results further suggest that, for more accurate measurements and interpretation of nanoindentation test data, the ratio of the indentation depth to cuticle thickness should be limited to 7% rather than the traditional '10% rule'. The results of this study thus might be useful to provide a deeper insight into the biomechanical consequences of the distinct material distribution in insect cuticle and also to form a basis for more realistic modelling of this complex natural composite.

The eversible tentacle organs of Polyommatus caterpillars (Lepidoptera, Lycaenidae): Morphology, fine structure, sensory supply and functional aspects

In their late (3rd and 4th) larval stages, caterpillars of the myrmecophilous lycaenid (Lepidoptera) species Polyommatus coridon and Polyommatus icarus, possess on their 8th abdominal segment two eversible so called tentacle organs (TOs). Previous histological and behavioural results have proposed that the TOs may release a volatile substance that elicits "excited runs" in attendant ants. In our study we investigated for the first time the temporal in- and eversion pattern of TOs. Using nerve tracing, Micro-CT, light- and electron microscopy techniques we studied (i) the histology of the 8th abdominal segment, (ii) the fine structure of the cuticular and cellular apparatus of the TOs, (iii) the attachment sites of the retractor muscle of each TO and (iv) the fine structure of the long slender tentacle hairs which are exposed to the outside, when the TOs are everted and fold back into the TO-sac during inversion. Our data show that the tentacle hairs are typical insect mechanoreceptors, each innervated by a small bipolar sensory cell with a tubular body in the tip of the outer dendritic segment. The latter is enclosed by a cuticular sheath previously called the "internal cuticular duct" and misinterpreted in earlier studies as the space, where the tentacle hairs actively secrete fluids. However, we found no glandular structures nearby or in the wall of the TO-sac. Also we did not reveal any conspicuous signs of secretory activity in one of the enveloping cells belonging to a tentacle hair. Although highly unusual features for an insect mechanoreceptor are: (a) the hair-shaft lumen of tentacle hairs contains flocculent material as well small vesicles and (b) the thin cuticular wall of the hair-shaft and its spines possess few tiny pores. Our data do not support the assumption of previous studies that volatile substances are released via the tentacle organs during their interactions with ants which in turn are supposed to cause excited runs in ants.

Simple contact mechanics model of the vertebrate cartilage

We study a simple contact mechanics model of the vertebrate cartilage, which includes (bulk) osmotic effects. The surface roughness power spectrum of a pig cartilage is obtained from the measured surface topography. Using the Reynolds equations with fluid flow factors, calculated using the Persson contact mechanics theory and the Bruggeman effective medium theory, we show how the area of contact and the average interfacial separation change with time. We found that in most cases the contact area percolates, resulting in islands of confined fluid which carry most of the external load. Most importantly, we find that the pressure in the area of real contact is nearly independent of the external load, and well below 1 MPa. This allows the surfaces in the area of "real contact", to be separated (at nanometer range separation distance) by osmotic repulsion, resulting in a very small (breakloose) friction force observed even after a long time of stationary contact.

Resilin microjoints: a smart design strategy to avoid failure in dragonfly wings

Dragonflies are fast and manoeuvrable fliers and this ability is reflected in their unique wing morphology. Due to the specific lightweight structure, with the crossing veins joined by rubber-like resilin patches, wings possess strong deformability but can resist high forces and large deformations during aerial collisions. The computational results demonstrate the strong influence of resilin-containing vein joints on the stress distribution within the wing. The presence of flexible resilin in the contact region of the veins prevents excessive bending of the cross veins and significantly reduces the stress concentration in the joint.

Basal Complex and Basal Venation of Odonata Wings: Structural Diversity and Potential Role in the Wing Deformation

Dragonflies and damselflies, belonging to the order Odonata, are known to be excellent fliers with versatile flight capabilities. The ability to fly over a wide range of speeds, high manoeuvrability and great agility are a few characteristics of their flight. The architecture of the wings and their structural elements have been found to play a major role in this regard. However, the precise influence of individual wing components on the flight performance of these insects remains unknown. The design of the wing basis (so called basal complex) and the venation of this part are responsible for particular deformability and specific shape of the wing blade. However, the wing bases are rather different in representatives of different odonate groups. This presumably reflects the dimensions of the wings on one hand, and different flight characteristics on the other hand. In this article, we develop the first three-dimensional (3D) finite element (FE) models of the proximal part of the wings of typical representatives of five dragonflies and damselflies families. Using a combination of the basic material properties of insect cuticle, a linear elastic material model and a nonlinear geometric analysis, we simulate the mechanical behaviour of the wing bases. The results reveal that although both the basal venation and the basal complex influence the structural stiffness of the wings, it is only the latter which significantly affects their deformation patterns. The use of numerical simulations enabled us to address the role of various wing components such as the arculus, discoidal cell and triangle on the camber formation in flight. Our study further provides a detailed representation of the stress concentration in the models. The numerical analysis presented in this study is not only of importance for understanding structure-function relationship of insect wings, but also might help to improve the design of the wings for biomimetic micro-air vehicles (MAVs).

Vertically aligned multi walled carbon nanotubes prevent biofilm formation of medically relevant bacteria

A significant part of human infections is frequently associated with the establishment of biofilms by (opportunistic) pathogens. Due to the increasing number of untreatable biofilms, there is a rising need to develop novel and effective strategies to prevent biofilm formation on surfaces in medical as well as in technical areas. Bacterial initial attachment and adhesion to surfaces followed by biofilm formation is highly influenced by the physical properties of the surfaces. Consequently, changing these properties or applying different nanostructures is an attractive approach to prevent biofilm formation. Here we report on the effect(s) of surface grown and anchored vertically aligned multi walled carbon nanotubes (MWCNT), which have been made wettable by immersion through a graded ethanol series, on biofilm formation of Klebsiella oxytoca, Pseudomonas aeruginosa, and Staphylococcus epidermidis. We evaluated the biofilm formation under continuous flow conditions by confocal laser scanning microscopy and scanning electron microscopy, and demonstrated significant inhibition of biofilm formation of all the different pathogens by MWCNT of different lengths. Furthermore, the anti-adhesive effects of the MWCNT increased with their overall length. The application potential of our findings on surface grown and anchored vertically aligned MWCNT may represent a suitable contact mechanics based approach to prevent biofilm formation on medical devices or technical sensors operating in fluid environments.

Effects of multiple vein microjoints on the mechanical behaviour of dragonfly wings: numerical modelling

Dragonfly wings are known as biological composites with high morphological complexity. They mainly consist of a network of rigid veins and flexible membranes, and enable insects to perform various flight manoeuvres. Although several studies have been done on the aerodynamic performance of Odonata wings and the mechanisms involved in their deformations, little is known about the influence of vein joints on the passive deformability of the wings in flight. In this article, we present the first three-dimensional finite-element models of five different vein joint combinations observed in Odonata wings. The results from the analysis of the models subjected to uniform pressures on their dorsal and ventral surfaces indicate the influence of spike-associated vein joints on the dorsoventral asymmetry of wing deformation. Our study also supports the idea that a single vein joint may result in different angular deformations when it is surrounded by different joint types. The developed numerical models also enabled us to simulate the camber formation and stress distribution in the models. The computational data further provide deeper insights into the functional role of resilin patches and spikes in vein joint structures. This study might help to more realistically model the complex structure of insect wings in order to design more efficient bioinspired micro-air vehicles in future.

Effect of microstructure on the mechanical and damping behaviour of dragonfly wing veins

Insect wing veins are biological composites of chitin and protein arranged in a complex lamellar configuration. Although these hierarchical structures are found in many 'venous wings' of insects, very little is known about their physical and mechanical characteristics. For the first time, we carried out a systematic comparative study to gain a better understanding of the influence of microstructure on the mechanical characteristics and damping behaviour of the veins. Morphological data have been used to develop a series of three-dimensional numerical models with different material properties and geometries. Finite-element analysis has been employed to simulate the mechanical response of the models under different loading conditions. The modelling strategy used in this study enabled us to determine the effects selectively induced by resilin, friction between layers, shape of the cross section, material composition and layered structure on the stiffness and damping characteristics of wing veins. Numerical simulations suggest that although the presence of the resilin-dominated endocuticle layer results in a much higher flexibility of wing veins, the dumbbell-shaped cross section increases their bending rigidity. Our study further shows that the rubber-like cuticle, friction between layers and material gradient-based design contribute to the higher damping capacity of veins. The results of this study can serve as a reference for the design of novel bioinspired composite structures.

A comparative study of the effects of vein-joints on the mechanical behaviour of insect wings: I. Single joints

The flight performance of insects is strongly affected by the deformation of the wing during a stroke cycle. Many insects therefore use both active and passive mechanisms to control the deformation of their wings in flight. Several studies have focused on the wing kinematics, and plenty is known about the mechanism of their passive deformability. However, given the small size of the vein-joints, accurate direct mechanical experiments are almost impossible to perform. We therefore developed numerical models to perform a comparative and comprehensive investigation of the mechanical behaviour of the vein-joints under external loading conditions. The results illustrate the effect of the geometry and the presence of the rubberlike protein resilin on the flexibility of the joints. Our simulations further show the contribution of the spikes to the anisotropic flexural stiffness in the dorsal and ventral directions. In addition, our results show that the cross veins, only in one joint type, help to transfer the stress to the thicker longitudinal veins. The deformation pattern and the stress distribution in each vein-joint are discussed in detail. This study provides a strong background for further realistic modelling of the dragonfly wing deformation.

Diversity of functional microornamentation in slithering geckos Lialis (Pygopodidae)

The skin of geckos is covered with countless microscopic protuberances (spines). This surface structure causes low wettability to water. During evolution, representatives of the recent gekkotan clade Pygopodidae started slithering on the ground. This manner of locomotion affected limb reduction resulting in a snake-like body. Regarding abrasion and frictional properties, a surface covered with gekkotan spines is a topography that hampers the snake-like locomotion mode. Using scanning electron microscopy, we investigated the shed skins of two pygopodid lizards, Lialis jicari (Papua snake lizard) and Lialis burtonis (Burton's legless lizard), in order to show epidermal adaptations to limbless locomotion. Our data showed that Pygopodidae differ from their relatives not only anatomically, but also in their epidermal microstructure. Scales of L. jicari have five different structural patterns on various body regions. Ventral scales have nanoridges, similar to those found on the ventralia of snakes. Surfaces of scales covering the jaw bones, have flattened spine-like microstructures that might be an adaptation to reduce abrasion. Dorsal scales have oblong microscopic bulges covered with nanoridges. Spines cover the undersides and the interstices of scales over the entire body of both species and in L. jicari also the top of dorsal head scales. Our measurements of surface wettability (surface free energy) show superhydrophobic properties of the spiny surfaces in comparison with the other microstructural patterns of other body parts.

Detailed three-dimensional visualization of resilin in the exoskeleton of arthropods using confocal laser scanning microscopy

Resilin is a rubber-like protein found in the exoskeleton of arthropods. It often contributes large proportions to the material of certain structures in movement systems. Accordingly, the knowledge of the presence and distribution of resilin is essential for the understanding of the functional morphology of these systems. Because of its specific autofluorescence, resilin can be effectively visualized using fluorescence microscopy. However, the respective excitation maximum is in the UV range, which is not covered by the lasers available in most of the modern commercial confocal laser scanning microscopes. The goal of this study was to test the potential of confocal laser scanning microscopy (CLSM) in combination with a 405 nm laser to visualize and analyse the presence and distribution of resilin in arthropod exoskeletons. The results clearly show that all resilin-dominated structures, which were visualized successfully using wide-field fluorescence microscopy (WFM) and a 'classical' UV excitation, could also be visualized efficiently with the proposed CLSM method. Furthermore, with the application of additional laser lines CLSM turned out to be very appropriate for studying differences in the material composition within arthropod exoskeletons in great detail. As CLSM has several advantages over WFM with respect to detailed morphological imaging, the application of the proposed CLSM method may reveal new information about the micromorphology and material composition of resilin-dominated exoskeleton structures leading to new insights into the functional morphology and biomechanics of arthropods.

Slippery pores: anti-adhesive effect of nanoporous substrates on the beetle attachment system

Traction experiments with adult seven-spotted ladybird beetles Coccinella septempunctata (L.) were carried out to study the influence of surface structure on insect attachment. Force measurements were performed with tethered walking insects, both males and females, on five different substrates: (i) smooth glass plate, (ii) smooth solid Al(2)O(3) (sapphire) disc, and (iii-v) porous Al(2)O(3) discs (anodisc membranes) with the same pore diameter but different porosity. The traction force of beetles ranged from 0.16 to 16.59 mN in males and from 0.32 to 8.99 mN in females. In both sexes, the highest force values were obtained on smooth solid surfaces, where males showed higher forces than females. On all three porous substrates, forces were significantly reduced in both males and females, and the only difference within these surfaces was obtained between membranes with the highest and lowest porosity. Males produced essentially lower forces than females on porous samples. The reduction in insect attachment on anodisc membranes may be explained by (i) possible absorption of the secretion fluid from insect adhesive pads by porous media and/or (ii) the effect of surface roughness. Differences in attachment between males and females were probably caused by the sexual dimorphism in the terminal structure of adhesive setae.

Underwater attachment in current: the role of setose attachment structures on the gills of the mayfly larvae Epeorus assimilis (Ephemeroptera, Heptageniidae)

Setose pads of aquatic Epeorus assimilis larvae are specialised structures located ventrally on the part of the gill lamella contacting the substrate and were suggested to have an attachment function in strong currents. In order to test the role of these setose pads in underwater attachment for the first time, we measured friction (shear) forces generated by the gill lamellae on solid substrates. Moreover, the influence of a different kind of surface roughness on attachment was investigated. Scanning electron microscopy showed that four different seta types can be found on the pads. Our results revealed that the pads significantly contributed to friction force generated on smooth and on some rough substrates but not on certain surfaces of intermediate roughness. The contribution of pads to the friction coefficient in experiments was lower than expected under natural conditions, which may be caused by a smaller contact area between the pads and the substrate (changes in material properties, lack of the active control of body positioning of the larva). The friction coefficient of the gill lamellae with the substrate depended on the surface roughness of the substrate and on the pulling direction. These results suggest that interlocking between structures of the insect cuticle and substrate irregularities, as well as molecular adhesion, contribute to friction.

Surface structure and frictional properties of the skin of the Amazon tree boa Corallus hortulanus (Squamata, Boidae)

The legless locomotion of snakes requires specific adaptations of their ventral scales to maintain friction force in different directions. The skin microornamentation of the snake Corallus hortulanus was studied by means of scanning electron microscopy and the friction properties of the skin were tested on substrates of different roughness. Skin samples from various parts of the body (dorsal, lateral, ventral) were compared. Dorsal and lateral scales showed similar, net-like microornamentation and similar friction coefficients. Average friction coefficients for dorsal and lateral scales on the epoxy resin surfaces were 0.331 and 0.323, respectively. In contrast, ventral scales possess ridges running parallel to the longitudinal body axis. They demonstrated a significantly lower friction coefficient compared to both dorsal and lateral scales (0.191 on average). In addition, ventral scales showed frictional anisotropy comparing longitudinal and perpendicular direction of the ridges. This study clearly demonstrates that different skin microstructure is responsible for different frictional properties in different body regions.

Terminal contact elements of insect attachment devices studied by transmission X-ray microscopy

For the first time, the terminal elements (spatulae) of setal (hairy)attachment devices of the beetle Gastrophysa viridula (Coleoptera,Chrysomelidae) and the fly Lucilia caesar (Diptera, Calliphoridae)were studied using transmission X-ray microscopy (TXM) with a lateral resolution of about 30 nm. Since images are taken under ambient conditions, we demonstrate here that this method can be applied to study the contact behaviour of biological systems, including animal tenent setae, in a fresh state. We observed that the attached spatulae show a viscoelastic behavior increasing the contact area and providing improved adaptability to the local topography of the surface. The technique can be extended to TXM tomography,which would provide three-dimensional information and a deeper insight into the details of insect attachment structures.

Sexual dimorphism in the attachment ability of the Colorado potato beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) to rough substrates

Many representatives of the beetle family Chrysomelidae exhibit a distinctive sexual dimorphism in the structure of adhesive tarsal setae. The present study demonstrates the influence of surface roughness on the friction force of Leptinotarsa decemlineata males and females. The maximum friction force of individual beetles was measured on epoxy resin surfaces (smooth and with asperities ranging from 0.3 to 12.0 microm) using a centrifugal force tester. On the smooth surface, no considerable differences between males and females were found, whereas on rough surfaces, females attached significantly (up to two times) stronger than males. Clawless beetles generated lower forces than intact ones, but demonstrated similar differences between males and females. The results indicate that the female adhesive system has its main functional trait in a stronger specialisation to rough plant surfaces whereas the adhesive system of males possess a certain trade-off between attachment to rough plant surfaces during locomotion on vegetation and to the smooth surface of the female elytra, while mating.

Physicochemical properties of functional surfaces in pitchers of the carnivorous plant Nepenthes alata Blanco (Nepenthaceae)

Pitchers of the carnivorous plant Nepenthes alata are highly specialized organs adapted to attract, capture, and digest animals, mostly insects. They consist of several well distinguishable zones, differing in macro-morphology, surface microstructure, and functions. Since physicochemical properties of these surfaces may influence insect adhesion, we measured contact angles of non-polar (diiodomethane) and polar liquids (water and ethylene glycol) and estimated the free surface energy of 1) the lid, 2) the peristome, 3) the waxy surface of the slippery zone, and 4) the glandular surface of the digestive zone in N. alata pitchers. As a control, the external surface of the pitcher, as well as abaxial and adaxial surfaces of the leaf blade, was measured. Both leaf surfaces, both lid surfaces, and the external pitcher surface showed similar contact angles and had rather high values of surface free energy with relatively high dispersion component. These surfaces are considered to support strong adhesion forces based on the capillary interaction, and by this, to promote successful attachment of insects. The waxy surface is almost unwettable, has extremely low surface energy, and therefore, must essentially decrease insect adhesion. Both the peristome and glandular surfaces are wetted readily with both non-polar and polar liquids and have very high surface energy with a predominating polar component. These properties result in the preclusion of insect adhesion due to the hydrophilic lubricating film covering the surfaces. The obtained results support field observations and laboratory experiments of previous authors that demonstrated the possible role of different pitcher surfaces in insect trapping and retention.

[Novel miniature-like m42 mutant of Drosophila virilis. Unusual microstructure of wing fibres]

Distinctive defects of cuticular wing vein microstructure in Drosophila virilis miniature-like m42 allele and the possible role of m42 locus in cytoskeleton reorganization during of wing morphogenesis are discussed.

Frictional properties of contacting surfaces in the hemelytra-hindwing locking mechanism in the bug Coreus marginatus (Heteroptera, Coreidae)

The structure and function of the hemelytra-to-hindwing locking mechanism of the bug Coreus marginatus were analysed. The system consists of a cuticular protrusion in the ventral side of the hemelytra, which locks the subcostal border of the hindwing in flight. The speed and distance slid by both surfaces against one another during flight were assessed using a combination of high-speed video recordings and a 2D geometrical model. The friction coefficient between sliding surfaces was assessed using a micromanipulator, coupled with force transducers. This was done under three experimental conditions: freshly dissected, air dried and rehydrated ethanol preserved samples. The results showed a high speed of sliding, approximately 0.18 m s(-1), with a relatively low friction coefficient (0.2 micro). There was no evident difference in the friction measured under the various treatments, with the exception of the rehydrated condition, which was lower. The surface morphology of the wing locking mechanism, namely outgrowths of one part having rounded edges, and completely flat surface on the counterpart, effectively aids in the reduction of friction at the microscopic level. The structure is effective even dry, and after being preserved in ethanol, suggesting that no cuticle secreted lubrication substance is responsible for its effectiveness. The ultrastructure presumably confers mechanical stability to the system under the high load it is subjected to in flight.

Attachment forces of the hemelytra-locking mechanisms in aquatic bugs (Heteroptera: Belostomatidae)

Combined hemelytra-locking system of Heteroptera, consisting of several locking mechanisms, aids the mechanical stabilisation of the body at rest, resists external loads, and keeps air stored with the option to easily unlock hemelytra prior to flight. The resistance to unlocking of the hemelytron was measured (in mN) with the aid of a load cell force transducer combined with a three-axial micromanipulator. It is shown that macro- and microstructural features of several submechanisms are responsible for their directionality. The highest resistance to unlocking was measured in lateral and dorsal directions. Summarised force of separately measured submechanisms was considerably lower than the force measured in the combined mechanism. Each submechanism is optimised for achieving high resistance to the hemelytron uncoupling in particular direction(s) and to be easily unlocked in another direction. It was demonstrated in the high-speed videorecordings that hemelytra uncoupling is promoted by their short anterior displacement.

Probabilistic fasteners with parabolic elements: biological system, artificial model and theoretical considerations

Probabilistic fasteners are attachment devices composed of two surfaces covered with cuticular micro-outgrowths. Friction-based fasteners demonstrate high frictional forces when the surfaces come into contact. Attachment in this case is based on the use of the surface profile and mechanical properties of materials, and is fast, precise and reversible. The best-studied examples composed of parabolic elements are the wing-locking mechanism in beetles and the head arrester in dragonflies. This study combines experimental data of force measurements, obtained in an artificial model system, and theoretical considerations based on the simple model of behaviour of probabilistic fasteners with parabolic elements. Elements of the geometry in both cases correspond to the biological prototypes. Force measurements on the artificial system show that the attachment force is strongly dependent on the load force. At small loads, the increase of attachment is very slow, whereas rapid increase of attachment was detected at higher loads. At very high loads, a saturation of the attachment force was revealed. A simple explanation of the attachment principle is that with an increasing load elements of both surfaces slide into gaps of the corresponding part. This results in an increase of lateral loading forces acting on elements. High lateral forces lead to an increase of friction between single sliding elements. An analytical model which describes behaviour of the probabilistic fasteners with parabolic elements is proposed.

Evolution of locomotory attachment pads of hexapods

This study shows that, in their evolution, hexapods have convergently developed two distinctly different mechanisms to attach themselves to a variety of substrates during locomotion. The first mechanism is provided by hairy surfaces and the second one by smooth flexible pads. The main similarity of both mechanisms is that the structured pad surface or particular properties of pad materials guarantee a maximum real contact with diverse substrata, regardless of their microsculpture. Ten characters of the two alternative designs were coded and analyzed together with a data matrix containing 105 additional morphological characters of different stages and body parts. The analysis demonstrates that similar structures (arolium, euplantulae, hairy tarsomeres) have evolved independently in several hexapod lineages. The evolution of flight and the associated necessity of being able to cling to vegetation or other substrates are suggested to be major triggers for the evolution of attachment structures.

[Myrmecochorous syndrome]

Myrmecochorous plants have a set of morphological, anatomical, biochemical and phenological features connected to ant dispersal. This complex of plant adaptations is called myrmecochorous syndrome. Present review is based on literature data and original field and laboratory experiments of the authors. The diversity of plant adaptations and its role for ant attraction are analysed. The main feature of myrmecochorous syndrome is elaiosome (a fat body) connected with diaspore. Elaisomes differ by shape, colours, size, anatomy and origin. Different parts of ovule, pericarp or even flower may serve as an initial tissue for elaiosome origin. Fats of elaiosome have a particular complex of fat acids, mainly 1,2-diolein, that attract ant workers. Seed setting periods, synchronizing with maximum ant activity, strictly determined size of diaspores also help in ant attraction. If a plant is not obligate myrmecochore and has some additional mechanism for diaspore dispersal, some characters of myrmecochorous syndrome may be absent or less expressed.

[Effect of parameters of myrmecochorous syndrome on rates of removal of Corydalis cava and Pulmonaria obscura by Formica polyctena ants]

Complex of adaptations of myrmecochorous plants to the ant dispersal composes so called myrmecochorous syndrome. To study the effect of some morphological and anatomical adaptations on diaspore attractiveness for ants, the field experiments with diaspores and their extracts were carried out. It was shown that chemical cues attracting ants are located in different parts of diaspores: in elaiosome only (C. cava) or in elaiosome, coverage of external layer of the fruit and in the fruit collar (P. obscura). Anatomy of adaptive structure of diaspores is also discussed together with the results of field experiments.

Microsculpture of the wing surface in Odonata: evidence for cuticular wax covering

The insect wing membrane is usually covered by scales, hairs, and acanthae, which serve diverse functions, such as species-specific coloration pattern, decrease of wind resistance during flight or decrease of wing wettability. Representatives of Palaeoptera (Odonata and Ephemeroptera) have no hairy structures on the wing membrane, but both its sides are fine-sculptured. In this study, the nature of the wing covering was studied using acoustic microscopy, scanning- and transmission electron microscopy followed by a variety of chemical treatments. It was shown that wing microsculptures are not cuticular outgrowths, but a wax covering, which is similar to pruinosity, which has been previously described in several odonate taxa. Data from scanning acoustic microscopy revealed that scratches on the wax covering have material density different from the surrounding material. Various functions of the wax covering are discussed.

The elytra-to-body binding mechanism of the flightless rainforest species Tabarus montanus Kaszab (Coleoptera: Tenebrionidea)

The elytra-to-body binding mechanism of the flightless rainforest species Tabarus montanus Kaszab (Coleoptera: Tenebrionidea) is described. Previously, studies on this complex character system in tenebrionids have focused mostly on either fully-winged or flightless, desert-dwelling species with a hermetically sealed subelytral cavity. Data presented here show that the rainforest species Ta. montanus has permanently joined interlocking macrostructures between the two elytra along the midline and between the elytral epipleuron and the sides of the body. These are very similar adaptations to ones found in flightless desert tenebrionids. Frictional patches of microtrichia, previously reported in all wing-folding beetle suborders including flightless taxa, are completely absent in Ta. montanus. This constitutes the first report of the complete loss of frictional microtrichia patches in a beetle with fully-developed elytra. Sensory organs (hair sensilla), usually involved in the correct positioning of the elytra over the beetles' body at rest are also absent in Ta. montanus. The significance of these results relating to the evolution of the tenebrionid subelytral cavity is discussed.

Porous channels in the cuticle of the head-arrester system in dragon/damselflies (Insecta:Odonata)

The ultrastructure of the porous channels (PC) of the postcervical sclerite (SPC), which provides additional head fixation to the neck in adult odonates, was studied using TEM and high resolution SEM microscopy. Single chitin-protein microfibrils, about 0.14 micron thick, are arranged into channels with cylinder-like shapes. The axial rod of the chitin fiber (0.04 micron thick) is located in the center of the cylinder. The orientation of the axial rods was three-dimensionally demonstrated after dissolving the protein cover with NaOH. The PCs are arranged vertically to the surface and pass from the epidermal cells through all the cuticular layers to the surface of the cuticle. In the exo- and endocuticle, the PCs are usually oval in cross-section and about 0.3 micron thick. In the endocuticle, the cross-sectional area of the PCs varies widely, from 0.01-0.15 micron2. The shape of the PC is determined by the macromolecular organization of the chitin-protein microfibrils: the long axis of the channel is orientated parallel to the axis of the preferred orientation of the cuticular microfibrils. The microfibrils tend to follow the line of the channel very closely. In fractures orientated perpendicular to the surface, the PC resembles a ribbon-like construction, which was clearly demonstrated by casts. The strongly parallel orientation of PCs in the deep layers of the cuticle changes within the microtrichia (MT), and they begin to be curved. Numerous PCs pass through the microtrichium, and most of them end on its side wall. PCs usually contain channel filaments about 0.09 micron thick. Usually, a single channel contained one filament, but channels located in the deep layers of the endocuticle have from one to five single filaments. The filaments were observed in the intact cuticle and in the cuticle enzymatically treated with chitinase, while in the cuticle treated with NaOH filaments were absent. The porous channel system of the odonate arrester is interpreted as a device transporting adhesive excretions from the epidermal cells to the cuticular surface.

Central projections of ovipositor sense organs in the damselfly, Sympecma annulata (Zygoptera, Lestidae)

Central projections of sensilla on different parts of the endophytic ovipositor of the lestid damselfly Sympecma annulata are traced. Sensilla include apical hairs of the stylus (STh), hair rows on the ventral part of the valvula (Vh), and distal campaniform sensilla of upper (ULc) and lower (LLc) ovipositor leaves. Backfilling of afferent fibers, using anterograde cobalt fills, reveals the presence of contralaterally projecting fibers for all organs. The main fiber bundle of the LLc enters the terminal ganglion laterally via the genital nerve, but the fibers from ULc enter via the posterior nerve. Main fiber bundles of both leaves end in a lateral part of the ganglion called the lateral neuromere; they demonstrate that sensory information from the two leaves has the same target area. It is hypothesized that the independent pathways of nerves from upper and lower ovipositor leaves (ULc and LLc) may indicate the phylogenetic origin of these appendages from different abdominal segments-the lower leaf from the 8th and upper from 9th. The convergence of afferent fibers from the sensilla of the different ovipositor parts (median, anterior, and lateral processes) in common ganglionic centers may provide the anatomical basis to account for coordination of the movements of different ovipositor parts during oviposition. © 1994 Wiley-Liss, Inc.