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Deutsche Forschungsgemeinschaft; Human Frontier Science Program and the National Research Foundation.

Biological tissues may exhibit graded heterogeneities in structure and mechanical properties that are crucial to their function. One biological structure that shows variation in both structure and function is the molluscan radula: the organ comprises a chitinous membrane with embedded teeth and serves to process and gather food. The tooth morphologies had been well studied in the last decades, but the mechanical properties of the teeth are not known for the vast majority of molluscs. This knowledge gap restricts our understanding of how the radula is able to act effectively on a target surface whilst simultaneously resisting structural failure. Here we employed nanoindentation technique to measure mechanical properties (hardness and Young's modulus) on distinct localities of individual radular teeth from 24 species of African paludomid gastropods. These species have distinct ecological niches as they forage on algae on different feeding substrates. A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. The presence or absence of large-scale gradients in these taenioglossan teeth could directly be linked with their specific function and in general with the species ecology, whereas the radular tooth morphologies do not always and fully reflect ecology. Statement of significance African Lake Tanganyika is well known for harbouring endemic and morphologically distinct genera. Its paludomid gastropods form a flock of high interest because of its diversity. As they show distinct radular tooth morphologies hypotheses about potential trophic specializations had always been at hand. Here we evaluated the mechanical properties Young’s modulus and hardness of 9027 individual teeth from 24 species along the tooth by nanoindentation and related them with the gastropods’ specific feeding substrate. We find that hard substrate feeders have teeth that are hard at the tips but much less stiff at the base and thus heterogeneous with respect to material properties, whereas soft substrate feeders have teeth that are flexible and homogenous with respect to material properties.

Animals can show bias in their use of laterally paired organs that do not have any conspicuous anatomical differentiation between the right and left organs. Like right handedness in humans, males of the giant earwig Labidura riparia (Labiduridae: Labidurinae) preferentially (~90%) use the right one of their laterally paired penises for copulation. To elucidate the evolutionary origin of this lateralization, patterns of penis use were examined for the related species of the genus Nala (Labiduridae: Nalinae). In multiple populations and broods of both Nala lividipes and Nala nepalensis, males that were ready to use the right or left penis were equally frequent, providing a striking contrast to Labidura. Surgical ablation of one of the two penises revealed that both penises are functionally competent in N. lividipes. Nevertheless, each male almost consistently used only one of the paired penises, either the right or the left one. Changes in penis use were estimated to occur only once per 64–143 days per male. The present study is the first report of individual-level lateralization for animal genitalia that do not show any conspicuous anatomical differentiation between the right and left organs. Possible advantages of lateralization are discussed in relationship to co-evolution of the genitalia between the sexes.

Dynamic signals are a widespread phenomenon in several taxa, usually associated with intraspecific communication. In contrast, dynamic iridescent signals are detectable only at specific angles of illumination; hence, the animal can hide the signal to avoid detection when necessary. This structural coloration is mostly dependent on the illumination, the contrast against the background and the vision of the receiver. Complex behavioural displays can be coupled with structural coloration to create dynamic visual signals that enhance these functions. Here, we address whether iridescence of the males of a damselfly that inhabits dark rainforests, Chalcopteryx scintillans, can be considered a dynamic visual signal. We analyse whether coloration is perceived by conspecifics, while reducing detectability to eavesdroppers against three types of backgrounds. Our results suggest that the visual background affects the detectability of male hindwings by different receivers, mostly predators and prey. We discuss whether these results and the angle dependence of colour could indicate a mechanism to avoid unwanted intraspecific interactions or even to lure both predators and prey. We conclude that the main functions of the dynamic iridescent signal are to communicate with conspecifics while hindering the signal for prey, adding evidence of the multifunctionality of structural coloration coupled with behavioural displays in animals.

The radula is the food gathering and processing structure and one important autapomorphy of the Mollusca. It is composed of a chitinous membrane with small, embedded teeth representing the interface between the organism and its ingesta. In the past, various approaches aimed at connecting the tooth shapes, which are highly distinct within single radulae due to their different functions. However, conclusions from the literature have been mainly drawn from microscopical analyses of mounted radulae, but the real interacting radular parts – even though the precise contact areas are essential for determining a tools functionality – and the 3D architecture of this complex feeding structure have not been previously determined. In the experimental approach presented here individuals of Vittina turrita (Neritidae, Gastropoda) were fed with algae paste attached to different sandpaper types. By comparison with radulae from a control group, sandpaper-induced tooth wear patterns were identified and both the area and volume loss were quantified. In addition to the exact contact area of each tooth, conclusions about the 3D position of teeth and the radular bending during feeding motion could be drawn. Furthermore, hypotheses about the specific functions of individual tooth types could be put forward. This kind of feeding experiments under controlled conditions is new for Mollusca and may provide a good basis for future studies on the radula functional morphology. It can be potentially applied to species with distinct tooth morphologies and ecological niches.

Dynamic switchable attachment/detachment behavior can be extensively observed in biological systems. Although wide interest has been focused on the fabrication of biomimetic synthetic switchable ad...

The insect leg is a multifunctional device, varying tremendously in form and function within Insecta: from a common walking leg, to burrowing, swimming or jumping devices, up to spinning apparatuses or tools for prey capturing. Raptorial forelegs, as predatory striking and grasping devices, represent a prominent example for convergent evolution within insects showing strong morphological and behavioural adaptations for a lifestyle as an ambush predator. However, apart from praying mantises (Mantodea)—the most prominent example of this lifestyle—the knowledge on morphology, anatomy, and the functionality of insect raptorial forelegs, in general, is scarce. Here, we show a detailed morphological description of raptorial forelegs of Mantispa styriaca (Neuroptera), including musculature and the material composition in their cuticle; further, we will discuss the mechanism of the predatory strike. We could confirm all 15 muscles previously described for mantis lacewings, regarding extrinsic and intrinsic musculature, expanding it for one important new muscle—M24c. Combining the information from all of our results, we were able to identify a possible catapult mechanism (latch-mediated spring actuation system) as a driving force of the predatory strike, never proposed for mantis lacewings before. Our results lead to a better understanding of the biomechanical aspects of the predatory strike in Mantispidae. This study further represents a starting point for a comprehensive biomechanical investigation of the convergently evolved raptorial forelegs in insects.

Power amplification with catapult-like structures in arthropods is well studied, including the jump mechanism of natural organisms and biomimetic applications in robotics. Most catapult jump mechanisms have been developed based on animals that use legs to jump. However, jumps of some arthropods that use body parts other than legs and that show outstanding performance have been less studied until now. Here, we experimentally studied the jumping behavior of the sandhopper Talitrus saltator to determine whether they jump through the catapult mechanism and identify its critical catapult structures. The results showed that the sandhopper jumps through a body-catapult mechanism (muscle-specific power output: 1.7–5.7 kW/kg, 3.4–11.4 times the power output limit of arthropod muscle). The arch-shaped structures at the fore margin of the five posterior segments can provide a large amount of strain energy storage and account for more than 80% of the total kinetic energy demand. In addition, we build a biomimetic bi-segment device whose extension movement is actuated by sandhopper-inspired spring units. The results indicate that a multi-segmented robotic configuration can achieve rapid jumps based on the same principles of the body-catapult mechanism of the sandhopper.

Animals that live in hot environments must deal with extreme temperatures and overcome the constraints imposed by overheating. Some species exhibit remarkable adaptations to control body temperature, usually in the form of structures that act as thermal windows to cool down the body by dissipating heat. Here, we describe the case of the dragonfly Zenithoptera lanei, which inhabits open areas in the Neotropical Savannah and the Amazon. Males have striking and unique adaptations on the wings, not known in any other insect. The wings are covered with wax nanocrystals that reflect ultraviolet light and infrared radiation. Furthermore, the wing membrane is permeated by an intricate system of tracheae, another unique trait in Insecta. We hypothesized that these adaptations might be important not only for intraspecific communication, but also for thermoregulation. We analysed male body and wing temperatures and compared them with another dragonfly with common translucent wings. The results suggest that the dorsal wing surface acts as a cooling system, whereas the ventral surface might serve to elevate body temperature. Therefore, we conclude that Z. lanei possesses adaptations that are unique in nature; a complex system of thermoregulation with the dual function of cooling down or elevating body temperature, depending on wing position.

The present ultrastructural investigation using scanning and transmission electron microscopy as well as light and fluorescence microscopy describes in detail the attachment devices and tarsal gland of the bug Coreus marginatus (L.) (Hemiptera: Coreidae). In particular, the fine structure of pulvilli reveals a ventral surface rich with pore channels, consistent with fluid emission, and a folded dorsal surface, which could be useful to enhance the pulvillus contact area during attachment to the substrate. The detailed description of the tarsal gland cells, whose structure is coherent with an active secretory function, allows us to consider the tarsal gland as the plausible candidate for the adhesive fluid production. Scolopidia strictly adhering to the gland cells are also described. On the basis of the fine structure of the tarsal gland, we hypothesise a fluid emission mechanism based on changes of the hydraulic pressure inside the gland, due to the unguitractor tendon movements. This mechanism could provide the fluid release based on compression of the pad and capillary suction, as demonstrated in other insects. The data here reported can contribute to understanding of insect adhesive fluid production, emission and control of its transport.

Background Postcopulatory mate choice occurs ubiquitously in the animal kingdom. However, it is usually a major challenge to visualise the process taking place in a body. This fact makes it difficult to understand the mechanisms of the process. By focusing on the shape of female sperm storage organs (spermathecae), we aimed to elucidate their functional morphology using six representative beetle species and to simulate sperm dynamics in artificial spermathecae with different structural features. Results Morphology and material gradients were studied using micro-computed tomography (μCT) and confocal laser scanning microscopy. This study shows a diversity of external and internal structures of the spermathecae among species. Despite the diversity, all species possess a common pumping region, which is composed of a sclerotised chamber, muscles and a resilin-enriched region. By focusing on the species Agelastica alni, whose spermatheca is relatively simple in shape with an internal protuberance, we simulated sperm dynamics by establishing a fabrication method to create enlarged, transparent, flexible and low-cost 3D models of biological structures based on μCT data. This experiment shows that the internal protuberance in the species functions as an efficient mixing device of stored sperm. Conclusions The observed spermathecal musculature implies that the sclerotised chamber of the spermatheca with muscles works as a pumping organ. Our fluid dynamics tests based on 3D printed spermathecae show that a tiny structural difference causes entirely different fluid dynamics in the spermatheca models. This result suggests that structural variations of the spermatheca strongly affect sperm dynamics. However, fluid dynamics tests still require essential measurements including sperm viscosity and the velocity of pumping cycles of the spermatheca.

While the morphology of the adhesive system of geckos has been investigated predominantly in a single species, the tokay Gekko gecko (Linnaeus, 1758), compared to that, there is still the need to examine those traits in a broad diversity of gecko species. Here we focus on the Asian representatives of eublepharid geckos, as a closely related group within Gekkota, and study the anatomy of micro-ornamentation as well as the morphology of bone structures of toes and tails in three species of Eublepharidae. Surface microstructures are described by using SEM microscopy. Osseous structures present in limbs and in the tail are compared by using 3D analysis based on micro-CT data. The presence of epidermal outgrowths associated with friction-enhancement in arboreal representatives of Eublepharidae and the lack of setae in ground-dwelling species is discussed. A clear allocation of the term ‘seta’ is provided. Apart from a comparative consideration of ecomorphological specialisations in limbs, adaptations to the lateral flexibility of the prehensile tail found in Aeluroscalabotes felinus (Gunther, 1864) are illustrated. Correlations between the life style of the species studied and the morphology of their osseous structures in limbs and tail are shown and their significance for locomotion is outlined.

Dung beetles can perform a number of versatile behaviours, including walking and dung ball rolling. While different walking and running gaits of dung beetles have been described in previous literature, little is known about their ball rolling gaits. From behavioural experiments and video recordings of the beetle Scarabaeus (Kheper) lamarcki, we analysed and identified four underlying rules for leg coordination during ball rolling. The rules describe the alternation of the front legs and protraction waves of the middle and hind legs. We found that while rolling a ball backwards, the front legs are decoupled or loosely coupled from the other legs, resulting in a non-standard gait, in contrast to previously described tripod and gallop walking gaits in dung beetles. This provides insight into the principles of leg coordination in dung beetle ball rolling behaviour and its underlying rules. The proposed rules can be used as a basis for further investigation into ball rolling behaviours on more complex terrain (e.g., uneven terrain and slopes). Additionally, the rules can also be used to guide the development of control mechanisms for bio-inspired ball rolling robots.

The contribution of water to gecko and gecko-inspired adhesion remains a debate. Here, by investigating the adhesion performances of gecko-inspired nanopillar arrays in humid environments, the func...

Flies of the genus Bradysia (Diptera, Sciaridae) are considered as major insect pests of greenhouse-grown horticultural crops. The ability of hooked trichomes of the French bean Phaseolus vulgaris to impale and entrap herbivorous insects thus resulting in insect reduced longevity, reproduction and larval mortality is well known. The present study investigates under laboratory conditions the ability of hooked trichomes of bean leaves to entrap fungus gnats Bradysia paupera, in order to estimate the reduction of their population. We characterized the entrapment mechanism of hooked trichomes towards B. paupera using cryo-scanning electron microscopy, and evaluated the silicon distribution in hooked trichomes with the energy dispersive X-ray microanalysis. We evaluated the trapping efficiency of hooked trichomes in fertilized and unfertilized bean plants towards B. paupera, in comparison with insects feeding on the plant leaf such as black bean aphid Aphis fabae and young stages of the southern green stinkbug Nezara viridula. For B. paupera, we recorded about 30% of entrapped insects in unfertilized plants. Considering the number of entrapped insects in relation to the leaf surface, the percentage of entrapped insect was higher in unfertilized than in fertilized plants having lower density of hooked trichomes. The presence of P. vulgaris plants in greenhouses could represent a useful method in integrated pest management to reduce Bradysia spp. population.

Insect wings have no flight muscles, except those situated in the thorax. However, they continuously respond to forces acting on them during flight. This ability is achieved by the specialised desi...

Simple Summary Flowering plants usually attract insect pollinators by offering them nectar, pollen or other energetically valuable sources. To deter ants, which are unreliable pollinators and can act as nectar thieves, plants have developed different systems either inside the flowers or associated with the stems. The latter one, called greasy pole syndrome, is based on the combined effect of several stem features hampering the access of ants to the apically located flowers. In this study, we examined the effects of different flower stem features in the round-leaved Alexanders Smyrnium rotundifolium on the visiting frequency of the generalist ant species, the black garden ant Lasius niger. We conducted the experiments with ants running on dry wooden sticks mimicking four different types of stems. To attract ants, we placed a sweet sugar syrup droplet on a stick tip. Ants visited different types of stem-mimicking sticks with significantly different frequencies. The highest number of insects were registered on untreated stick samples, whereas the lowest visiting frequency was observed on sticks bearing cuff-like structures (serving as macroscopic physical barriers) covered with a nano/microparticle film, which caused the slipperiness of the surface. Thus, by combining macroscopic obstacles and slippery surfaces, plants can protect their flowers from undesirable crawling visitors such as ants. Abstract In order to understand the effects of the morphology and surface texture of flower stems in Smyrnium rotundifolium on the visiting frequency of generalist ants, we conducted experiments with Lasius niger ants running on dry wooden sticks mimicking different types of stems: (1) intact (grooved) sticks; (2) sticks painted with slaked (hydrated) lime (calcium carbonate coverage) imitating plant epicuticular wax coverage; (3) intact sticks with smooth polyester plate-shaped cuffs imitating upper leaves; and (4) intact sticks bearing cuffs painted with slaked lime. Ants were attracted by the sweet sugar syrup droplets placed on a stick tip, and the number of ants visiting the drops was counted. Our data showed significant differences in the visiting frequencies between the different types of stem-mimicking samples. The number of recorded ants progressively decreased in the following order of samples: intact sticks—painted sticks—sticks with intact cuffs—sticks with painted cuffs. These results clearly demonstrated that micro/nanoscopic surface coverages and macroscopic physical barriers, especially if combined, have a negative impact on the attractiveness of stems to ants. This study provides further evidence for the hypothesis that having a diversity of plant stems in the field, generalist ants prefer substrates where their locomotion is less hindered by obstacles and/or surface slipperiness.

Sandy pitfall traps of antlions are elaborate constructions to capture prey. Antlions exploit the interactions between the particles in their habitat and build a stable trap. This trap is close to the unstable state; prey items will slide towards the centre—where the antlion ambushes—when entering the trap. This is efficient but requires permanent maintenance. According to the present knowledge, antlions throw sand, mainly to cause sandslides towards the centre of the pit. We hypothesized that: (i) sand-throwing causes sandslides towards the centre of the pit and (ii) sand-throwing constantly maintains the pitfall trap and thus keeps its efficiency high. Using laboratory experiments, as well as finite-element analysis, we tested these hypotheses. We show, experimentally and numerically, that sand that accumulates at the centre of the pit will be removed continuously by sand-throwing, this maintenance is leading to slope condition close to an unstable state. This keeps the slope angle steep and the efficiency of the trap constant. Furthermore, the resulting sandslides can relocate the trapped prey towards the centre of the pit. This study adds further insights from specific mechanical properties of a granular medium into the behavioural context of hunting antlion larvae.

The radula is the structure used for food processing in Mollusca. It can consist of a membrane with stiffer teeth, which is, together with alary processus, muscles and odontophoral cartilages, part of the buccal mass. In malacology, it is common practice to infer potential tooth functions from morphology. Thus, past approaches to explain functional principles are mainly hypothesis driven. Therefore, there is an urgent need for a workflow testing hypotheses on the function of teeth and buccal mass components and interaction of structures, which can contribute to understanding the structure as a whole. Here, in a non-conventional approach, we introduce a physical and dynamic radular model, based on morphological data ofSpekia zonata(Gastropoda, Paludomidae). Structures were documented, computer-modelled, three-dimensional-printed and assembled to gather a simplistic but realistic physical and dynamic radular model. Such a bioinspired design enabled studying of radular kinematics and interaction of parts when underlain supporting structures were manipulated in a similar manner as could result from muscle contractions. The presented work is a first step to provide a constructional manual, paving the way for even more realistic physical radular models, which could be used for understanding radular functional morphology and for the development of novel gripping devices.

The honey bee (Apis mellifera L.) tongue is a sophisticated and dexterous probing device that can bend and twist, adapting to various surfaces for liquid imbibition and/or gustatory sensing. The tongue exhibits remarkable extendibility, flexibility, and durability, which may be essentially ascribed to the internal elastic rod that supports the entire tongue. However, neither the material composition nor the structural features of the rod, especially a peculiar inner canal that facilitates feeding, have been studied in relation to their function. Herein, by combining a set of imaging techniques, including optical microscopy, high-speed videography, scanning electron microscopy, micro-computed tomography (micro-CT), and confocal laser scanning microscopy, we characterize the spatial morphology, surface wettability and material composition of honey bee tongue rods. By performing mechanical testing, including atomic force microscopy, fracture testing, and finite element analysis, we provide the first evidence that the internal canal of the rod may represent a specialized structure for water retention due to the specific chemistry of resilin, which is an elastomeric protein that dominates the entire rod and renders it highly elastic, compliant and robust. Numerical simulations also suggest that the opening of the canal may facilitate larger deformations in twisting, extending the flexibility of the rod. STATEMENT OF SIGNIFICANCE: The honey bee is one of the most important pollinators around the world and is capable of foraging a wide spectrum of liquid sources by dipping into them with a miniature hairy tongue. However, there are no direct muscles distributed inside the tongue, instead, there is a conspicuous elastic rod with a hollow core. The rod extends for its full length and, according to our study, structurally reinforces the entire tongue to achieve functional versatility, and suggests a water containing function of the rod canal for maintaining the elasticity of the protein (resilin) that constitutes the rod. Our results broaden understandings of the relationship among morphology, materials science, and function of a honey bee tongue.

Here, the ultrastructure and development of the white patches on thorax and head of Bactrocera oleae are analysed using scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. Based on these analyses and measurements of patch reflectance spectra, we infer that white patches are due to modified air sacs under transparent cuticle. These air sacs show internal arborisations with beads in an empty space, constituting a three-dimensional photonic solid responsible for light scattering. The white patches also show UV-induced blue autofluorescence due to the air sac resilin content. To the best of our knowledge, this research describes a specialized function for air sacs and the first observation of structural color produced by tracheal structures located under transparent cuticles in insects. Sexual dimorphism in the spectral emission also lays a structural basis for further investigations on the biological role of white patches in B. oleae., Manuela Rebora et al. use electron and fluorescence microscopy together with reflectance spectra to examine structural white patches present in the olive fruit fly, Bactrocera oleae. Their results suggest that white coloring is a result of transparent cuticle and modified air sacs within these patches, providing further insight into how structural white emerges in insects.

A protein-based lubricating substance is discovered in the femoro-tibial joint of the darkling beetleZophobas morio(Insecta). The substance extrudes to the contacting areas within the joint and appears in a form of filiform flows and short cylindrical fragments. The extruded lubricating substance effectively reduces the coefficient of sliding friction to the value of 0.13 in the tribosystemglass/lubricant/glass. This value is significantly lower than 0.35 in the control tribosystemglass/glassand comparable to the value of 0.14 for the tribosystemglass/dry PTFE(polytetrafluoroethylene or Teflon). The study shows for the first time that the friction-reducing mechanism found inZ. moriofemoro-tibial joints is based on the lubricant spreading over the contacting surfaces rolling or moving at low loads and deforming at higher loads, preventing direct contact of joint counterparts. BesidesZ. morio, the lubricant has been found in the leg joints of the Argentinian wood roachBlaptica dubia.

For flying insects, stability is essential to maintain the orientation and direction of motion in flight. Flight instability is caused by a variety of factors, such as intended abrupt flight manoeuvres and unwanted environmental disturbances. Although wings play a key role in insect flight stability, little is known about their oscillatory behaviour. Here we present the first systematic study of insect wing damping. We show that different wing regions have almost identical damping properties. The mean damping ratio of fresh wings is noticeably higher than that previously thought. Flight muscles and hemolymph have almost no ‘direct’ influence on the wing damping. In contrast, the involvement of the wing hinge can significantly increase damping. We also show that although desiccation reduces the wing damping ratio, rehydration leads to full recovery of damping properties after desiccation. Hence, we expect hemolymph to influence the wing damping indirectly, by continuously hydrating the wing system., Lietz, Rajabi and colleagues investigate the physiological and structural components of damping in insect wings. Notably, flight muscles and hemolyph appear to have no direct involvement in wing damping, compared to the function of the wing hinge.

Hair‐like structures of the shell in some terrestrial snails have been suggested to represent an adaptive advantage. One of the recently proposed explanations was the hypothesis that the possession of hairs facilitates the snails' adherence to the leaves of the plants during foraging, when humidity levels are high. In order to obtain some reliable data to test this contact mechanics hypothesis, the present paper deals with the frictional and adhesive properties of the smooth and hairy shells of two species of terrestrial mollusks, Trochulus hispidus and T. villosulus. Additionally, actively generated traction force of the snails was measured on different substrates. The conducted experiments revealed that in wet conditions the hairiness indeed increases friction and that adhesion through the water film is high enough to retain the weight of the snail. However, possession of long hairs decreases the adhesion, in comparison with the animals with short hairs. Our data suggest that hair‐like structures require more energy expenditure during locomotion and only provide the advantage of higher adhesion on wet substrates. Obtained maximal traction forces were about 30 times higher than friction forces of the shell surface dragged over the substrate. Neither wetting condition of the substrate nor surface roughness had considerable effect on the traction forces of snails. Therefore, the function of the hair‐like structures seems not to be related with snail locomotion and adhesion.

The outermost surface of insect cuticle is a high-performance interface that provides wear protection, hydration, camouflage and sensing. The complex and inhomogeneous structure of insect cuticle imposes stringent requirements on approaches to elucidate its molecular structure and surface chemistry. Therefore, a molecular understanding and possible mimicry of the surface of insect cuticle has been a challenge. Conventional optical and electron microscopies as well as biochemical techniques provide information about morphology and chemistry but lack surface specificity. We here show that a near edge X-ray absorption fine structure microscope at the National Synchrotron Light Source can probe the surface chemistry of the curved and inhomogeneous cuticle of the African flower scarab. The analysis shows the distribution of organic and inorganic surface species while also hinting at the presence of aragonite at the dorsal protrusion region of the Eudicella gralli head, in line with its biological function., Biology serves as inspiration in materials development; this requires improved understanding of the surface chemistry responsible for processes which are being mimicked. Here, the authors report on the use of near edge X-ray absorption fine structure (NEXAFS) imaging to analyze the surface chemistry of insect cuticle.

Fungi and arthropods represent some of the most diverse organisms on our planet, yet the ecological relationships between them remain largely unknown. In animals, fungal growth on body surfaces is often hazardous and is known to cause mortality. In contrast, here we report the presence of an apparently non-harmful mycobiome on the cuticle of whip spiders (Arachnida: Amblypygi). The associations are not species-specific and involve a diversity of fungal species, including cosmopolitan and local decomposers as well as entomopathogens. We discuss the ecology of the detected fungal species and hypothesize that the thick epicuticular secretion coat of whip spiders (the cerotegument) promotes fungal growth. It is possible that this relationship is beneficial towards the host if it leads to parasite control or chemical camouflage. Our findings, which are the first from this arthropod lineage, indicate that non-pathogenic interactions between arthropods and fungi may be much more widespread than predicted and call for more studies in this area.

This short communication reports on the warming ability of the damselfly Sympecma paedisca, which is known for its winter hibernation and tolerance to low temperatures. The data were collected usin...

Spiders attach silken threads to substrates by means of glue-coated nanofibers (piriform silk), spun into disc-like structures. The organization and ultrastructure of this nano-composite silk are largely unknown, despite their implications for the biomechanical function and material properties of thread anchorages. In this work, the ultrastructure of silken attachment discs was studied in representatives of four spider families with Transmission Electron Microscopy to facilitate a mechanistic understanding of piriform silk function across spiders. Based on previous findings from comparative studies of piriform silk gland morphology, we hypothesized that the fibre-glue proportion of piriform silk differs in different spiders, while the composition of fibre and glue fractions is consistent. Results confirmed large differences in the relative proportion of glue with low amounts in the orb weaver Nephila senegalensis (Araneidae) and the hunting spider Cupiennius salei (Ctenidae), larger amounts in the cobweb spider Parasteatoda tepidariorum (Theridiidae) and a complete reduction of the fibrous component in the haplogyne spider Pholcus phalangioides (Pholcidae). We rejected our hypothesis that glue ultrastructure is consistent. The glue is a colloid with polymeric and fluid fractions that strongly differ in proportions and assembly. We further confirmed that in all species studied both dragline and piriform silk fibres do not make contact with the environmental substrate. Instead, adhesion is established by a thin dense skin layer of the piriform glue. These results advance our understanding of piriform silk function and the interspecific variation of its properties, which is significant for spider biology, web function and the bioengineering of silk.

The aim of this study was to analyze the visiting frequency of generalist ants to plants with different surface textures of their stems. We performed an experiment in which Lasius niger ants were attracted by sweet drops to flower stems of five plant species bearing different surface structures: Alchemilla mollis (wax projections and long tread-shaped trichomes), Lilium lancifolium (without wax, with ribbon-shaped trichomes and cuticular folds), Salvia nemorosa (without wax, with trichomes of various lengths and cuticular folds), Tulipa gesneriana (wax projections, no trichomes), and Paeonia lactiflora (neither of above surface features). As control samples, dry, smooth bamboo sticks were placed in the vicinity of experimental plant stems. Using cryo scanning electron microscopy, the micromorphology of stem surfaces was examined. The present study demonstrates that, on the one hand, ants avoid climbing wax-covered stems, if trichomes are lacking. On the other hand, some trichome-bearing stems having specific trichome micromorphologies were also ignored by ants. The strongest attractiveness was revealed in glossy stems and stems covered with soft/floppy trichomes. This experiment supports the hypothesis that when exposed to a diversity of plant stems in the field, generalist ants choose substrates where their locomotion is less hampered by obstacles or slipperiness of surface. Presumably, additional locomotory efforts needed to master climbing on “greasy” or “spiny” stems lead to an increase of costs-to-benefits ratio. However, since every type of stem surface was visited at least once during the experiment, it does not automatically mean that ants are not capable of walking on such challenging surfaces.

Whiteflies attach their eggs to plants by implanting the egg pedicel into the epidermis of the underside of leaves. This pedicel works like a wall plug embedded in sealing cement, presenting a smart interconnection, which was exemplarily studied in Trialeurodes vaporariorum eggs on two stages of abaxial leaflets of four cut rose cultivars using a combination of microscopic and biomechanical techniques. The penetration force obtained by piercing single epidermal cells with an insect minuten pin did not significantly correlate with the force which was applied to pull off the greenhouse whitefly eggs from abaxial leaves. A maximum pull-off force of 5.4 mN was measured on young leaves of the rose cultivar ‘Schloss Ippenburg®’, corresponding to maximum 941 times the egg weight. Egg pull-off force significantly differed between cut rose cultivars and leaf ages. On greenhouse whitefly-susceptible cultivars ‘Poesie®’ and ‘Reggae®’, eggs detached, applying less force compared to that on resistant cultivars. Leaf structural features had no significant impact on greenhouse whitefly egg pull-off forces. A major effect of leaf turgor pressure and swelling of colleterial gland secretion (cement) surrounding the whitefly egg is assumed to facilitate the firm interconnection between egg and plant epidermis by a combination of form closure, friction locking, and adhesive bond forming a composite material in the contact region. This bond exhibits a maximum adhesive strength of 12.2 MPa, which is much higher than those in beetle and moth eggs glued to oviposition substrates.

Many plant diaspores dispersing by epizoochory bear special structures, such as burrs with hooks, which are responsible for the mechanical interlocking with animal fur or feathers. The numb...

The representatives of the damselfly family Pseudostigmatidae are known for their ability to catch small orb web spiders, or in some cases small kleptoparasitic spiders in the webs of other spiders. In this paper, I demonstrate that the nanoscopic crystalline wax coverage of wings in the pseudostigmatid damselfly Mecistogaster ornata is partially altered due to the presence of fluid-contaminated spots corresponding in their shapes and distribution to the typical beads-on-a-string (BOAS) geometry of sticky threads of orb web spiders. The spider fluid has the ability to wet superhydrophobic crystalline wax coverage. Also residues of the sticky threads were revealed in high quantities on the wing surface. The data suggest that the pseudostigmatid damselflies, due to their specific prey capturing method, have some costs and risks of being trapped by the sticky spider webs. However, high resolution SEM images revealed that the crystalline wax coverage of wings, in spite of its wettability by the spider glue, f...

The articulated appendages of arthropods are highly adaptable and potentially multifunctional, used for walking, swimming, feeding, prey capture, or other functions. Webspinners (Order Embioptera) are a paragon in this context. In contrast to other arthropods producing silk, they utilize their front feet for silk production. However, employing the same leg for alternative functions rather than for pure locomotion potentially imposes constraints and compromises. We here present morphological and experimental evidence for a "passive" pressure-induced silk spinning mechanism induced by external mechanical stimuli. Furthermore, we demonstrate that, as a consequence of the conflicting functions for their front feet, webspinners have evolved a unique style of walking that reduces the potentially problematic contact between silk ejectors and the substrate. Here we answer for the first time a long-term question within this enigmatic group of insects-how webspinners can use their front feet to spin their nanoscale silk. This knowledge may open the door for experimental studies on an artificial spinning process and for future utilization in applied fields of robotics or chemistry.

Insects devote a large amount of time to self-groom to remove foreign material, especially from their sensory appendages. Using various microscopy techniques and behavioural experiments on intact and ablated insects, the present study investigates the antennal grooming of the southern green stinkbug Nezara viridula, which represents a serious pest of different crops in most areas of the world. The antennal grooming behaviour encompasses an action of scraping involving the tibial comb complex (tibial comb + fossula) of both forelegs, generally followed by the tibial comb complex grooming of one leg using the tarsal hairy adhesive pad of the opposite leg (rubbing). From our observations, we can exclude a role in the antennal grooming of other structures such as the foretibial apparatus, while we show an involvement of this last structure in repositioning the stylets inside the labium. The external and internal morphology (cryo-scanning and transmission electron microscopy) and the evidence for the presence of large proportions of the elastic protein resilin (confocal laser scanning microscopy) in some parts of both the tibial comb complex and the foretibial apparatus are shown, and their functional roles are discussed. For the first time we demonstrated here the multipurpose role of the basitarsal hairy adhesive pad that is involved in both antennal grooming and adhesion to the substrate.

Elongated rostra (snouts) are remarkable features of many female weevils. The female of Curculio glandium uses the snout to excavate channels in acorns to oviposit. Considering the slenderness of the rostrum, the excavation of channels in solid substrates without buckling is a challenging task from both engineering and biological points of view. Here we aimed to examine the roles of the material properties and morphology of the rostrum in its buckling resistance. We employed microscopy techniques, non-destructive material characterisation and finite element (FE) modelling to shed more light on the excavation mechanics of the rostrum. We found that sexual dimorphisms are present not only in the length but also in the material, particularly the elastic modulus, and morphological features, particularly the curvature and thickness of the cuticular layers. Our FE modelling showed that those factors play essential roles to maximise the buckling resistance and minimise the bending resistance of the female rostrum. Considering that during excavation, the rostrum needs to be straightened without buckling, the functionality of the rostrum is likely to be a compromise between the flexibility and stiffness.

The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for food processing and gathering. For proper functioning, radular failures must be either avoided or reduced when interacting with the preferred food, as this might be of high significance for the individual fitness. Thus, the analysis of structural failure in radular teeth could be included in studies on trophic specializations. Here, we tested the failure of non-mineralized, chitinous radular teeth from taxa, belonging to an African paludomid species flock from Lake Tanganyika and surrounding river systems. These species are of high interest for evolutionary biologists since they represent a potential result of an adaptive radiation including trophic specialisations to distinct substrates, the food is attached to. In a biomechanical experiment a shear load was applied to tooth cusps with a force transducer connected to a motorized stage until structural failure occurred. Subsequently broken areas were measured and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist, could be documented. Wet teeth were able to resist higher forces, because of their increased flexibility and the flexibility of the embedding membrane, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure without the mineralisation with wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. Since the documented mechanical behaviour of radular teeth and the maximal forces, teeth resist, can directly be related to the gastropod ecological niche, both are here identified as an adaptation to preferred feeding substrates. Statement of significance The radula, a chitinous membrane with teeth, is the molluscan feeding structure. Here we add onto existing knowledge about the relationship between tooth's mechanical properties and species’ ecology by determining the tooth failure resistance. Six paludomid species (Gastropoda) of a prominent species flock from Lake Tanganyika, foraging on distinct feeding substrates, were tested. With a force transducer wet and dry teeth were broken, revealing the high influence of water content on mechanical behaviour and force resistance of teeth. Higher forces were needed to break wet radulae due to an increased flexibility of teeth and membrane, which resulted in an interlocking or twisting of teeth. Mechanical behaviour and force resistance were both identified as trophic adaptations to feeding substrate.

The forces exerted by the animal’s food processing structures can be important parameters when studying trophic specializations to specific food spectra. Even though molluscs represent the second largest animal phylum, exhibiting an incredible biodiversity accompanied by the establishment of distinct ecological niches including the foraging on a variety of ingesta types, only few studies focused on the biomechanical performance of their feeding organs. To lay a keystone for future research in this direction, we investigated the in vivo forces exerted by the molluscan food gathering and processing structure, the radula, for five stylommatophoran species (Gastropoda). The chosen species and individuals have a similar radular morphology and motion, but as they represent different body mass classes, we were enabled to relate the forces to body mass. Radular forces were measured along two axes using force transducers which allowed us to correlate forces with the distinct phases of radular motion. A radular force quotient, AFQ = mean Absolute Force/bodymass0.67, of 4.3 could be determined which can be used further for the prediction of forces generated in Gastropoda. Additionally, some specimens were dissected and the radular musculature mass as well as the radular mass and dimensions were documented. Our results depict the positive correlation between body mass, radular musculature mass, and exerted force. Additionally, it was clearly observed that the radular motion phases, exerting the highest forces during feeding, changed with regard to the ingesta size: all smaller gastropods rather approached the food by a horizontal, sawing-like radular motion leading to the consumption of rather small food particles, whereas larger gastropods rather pulled the ingesta in vertical direction by radula and jaw resulting in the tearing of larger pieces.

The radula, a chitinous membrane with embedded tooth rows, is the molluscan autapomorphy for feeding. The morphologies, arrangements and mechanical properties of teeth can vary between taxa, which is usually interpreted as adaptation to food. In previous studies, we proposed about trophic and other functional specialisations in taenioglossan radulae from species of African paludomid gastropods. These were based on the analysis of shape, material properties, force-resistance, and the mechanical behaviour of teeth, when interacting with an obstacle. The latter was previously simulated for one species (Spekia zonata) by the finite-element-analysis (FEA) and, for more species, observed in experiments. In the here presented work we test the previous hypotheses by applying the FEA on 3D modelled radulae, with incorporated material properties, from three additional paludomid species. These species forage either on algae attached to rocks (Lavigeria grandis), covering sand (Cleopatra johnstoni), or attached to plant surface and covering sand (Bridouxia grandidieriana). Since the analysed radulae vary greatly in their general size (e.g. width) and size of teeth between species, we additionally aimed at relating the simulated stress and strain distributions with the tooth sizes by altering the force/volume. For this purpose, we also included S. zonata again in the present study. Our FEA results show that smaller radulae are more affected by stress and strain than larger ones, when each tooth is loaded with the same force. However, the results are not fully in congruence with results from the previous breaking stress experiments, indicating that besides the parameter size, more mechanisms leading to reduced stress/strain must be present in radulae.

The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for mechanical food processing and gathering. For proper functioning, radular failures must be either avoided or reduced, as this might be of high significance for the individual fitness. The factors, leading to the structural failure of teeth, are related to trophic specializations of species. Here, the failure of non-mineralized, chitinous radular teeth from an African paludomid species flock, inhabiting Lake Tanganyika and surrounding river systems, were tested in a biomechanical experiment. These species are of high interest for evolutionary biologists, since they represent a potential result of an adaptive radiation. With a force transducer attached to a motorized stage, a shear load was applied to tooth cusps until structural failure occurred. Subsequently broken areas were measured, and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist to, could be documented. Wet teeth were able to resist to higher forces, because their flexibility was higher, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure, without the mineralisation by wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. As the documented mechanical behaviour of radular teeth is related to the gastropod ecological niche, it can thus be identified as an adaptation to preferred feeding substrates.

Young leaves of the common oak Quercus robur are susceptible to the powdery mildew fungus Erysiphe alphitoides that can induce necrosis on the leaf surface. It is known that the fungal mycelium changes the wettability of the leaf surface. The present study performed a series of measurements of contact angles of water, ethylene glycol and diiodomethane on the oak leaf surface. Based on the obtained contact angle data, we calculated surface free energy on the adaxial surface of fresh healthy leaves and compared it with that of leaves infected by the fungus. Both types of leaf surfaces were also studied using cryo scanning electron microscopy, to examine a correlation between healthy/infected leaf surface structure and measured contact angles and surface free energy values. Our microscopical and experimental data clearly demonstrate that the powdery mildew turns the oak leaf surface to the highly hydrophobic state. The fungal mycelium shows three-dimensional hierarchical structure consisting of microscopic hyphae having cylindrical cross section with conidiomata (the first hierarchical level) and nanoscopic papillae and scales on the hyphal surface (the second hierarchical level). Such hierarchy in combination with the hydrophobic nature of the surface substances of the fungus leads to the highly hydrophobic properties (and low surface free energy) of the infected surface of the leaf.

Animals that habitually cross the boundary between water and land face specific challenges with respect to locomotion, respiration, insulation, fouling and waterproofing. Many semi-aquatic invertebrates and plants have developed complex surface microstructures with water-repellent properties to overcome these problems, but equivalent adaptations of the skin have not been reported for vertebrates that encounter similar environmental challenges. Here, we document the first evidence of evolutionary convergence of hydrophobic structured skin in a group of semi-aquatic tetrapods. We show that the skin surface of semi-aquatic species of Anolis lizards is characterized by a more elaborate microstructural architecture (i.e. longer spines and spinules) and a lower wettability relative to closely related terrestrial species. In addition, phylogenetic comparative models reveal repeated independent evolution of enhanced skin hydrophobicity associated with the transition to a semi-aquatic lifestyle, providing evidence of adaptation. Our findings invite a new and exciting line of inquiry into the ecological significance, evolutionary origin and developmental basis of hydrophobic skin surfaces in semi-aquatic lizards, which is essential for understanding why and how the observed skin adaptations evolved in some and not other semi-aquatic tetrapod lineages., Summary: Multiple Anolis lineages independently evolved a similar skin surface microarchitecture with water-repellent properties as an adaptation to a semi-aquatic lifestyle.

Biological composites usually display graded heterogeneities in structure and mechanical properties, enabling proper functioning. The radula, one important molluscan autapomorphy and the organ for food processing, is well examined in the light of its morphology, but the mechanical properties that enable an efficient acting of the radular teeth on the ingesta with a simultaneous reduction of structural failure are not known for the vast majority of gastropods. In this case study, we employed nanoindentation technique, to measure mechanical properties (hardness and Young’s modulus) on three distinct localities of an individual radular tooth in taenioglossan radular teeth of African paludomid gastropods with distinct ecological niches (preferred feeding substrate). A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. We hypothesize, that large-scale gradients are not abundant in all biological materials and that the presence of functional gradients is rather directly linked with their specific function and in general with the species ecology.

Seed and fruit mucilage is composed of three types of polysaccharides—pectins, cellulose, and hemicelluloses—and demonstrates adhesive properties after hydration. One of the important functions of the mucilage is to enable seeds to attach to diverse natural surfaces. Due to its adhesive properties, which increase during dehydration, the diaspore can be anchored to the substrate (soil) or attached to an animal’s body and dispersed over varied distances. After complete desiccation, the mucilage envelope forms a thin transparent layer around the diaspore creating a strong bond to the substrate. In the present study, we examined the mucilaginous seeds of six different plant taxa (from genera Linum, Lepidium, Ocimum, Salvia and Plantago) and addressed two main questions: (1) How strong is the adhesive bond of the dried mucilage envelope? and (2) What are the differences in adhesion between different mucilage types? Generally, the dried mucilage envelope revealed strong adhesive properties. Some differences between mucilage types were observed, particularly in relation to adhesive force (Fad) whose maximal values varied from 0.58 to 6.22 N. The highest adhesion force was revealed in the cellulose mucilage of Ocimum basilicum. However, mucilage lacking cellulose fibrils, such as that of Plantago ovata, also demonstrated high values of adhesion force with a maximum close to 5.74 N. The adhesion strength, calculated as force per unit contact area (Fad/A0), was comparable between studied taxa. Obtained results demonstrated (1) that the strength of mucilage adhesive bonds strongly surpasses the requirements necessary for epizoochory and (2) that seed mucilage has a high potential as a nontoxic, natural substance that can be used in water-based glues.