Vision is one of the most important senses used by animals and contributes to fundamental behaviors, including foraging, navigation, and mate detection and selection.1 Although much is known about how eye position and orientation correlate to ecology in the context of binocularity,2 animals with multipartite visual systems (more than two eyes) remain comparatively neglected. Spiders are highly successful predators that occupy a range of ecological niches and usually possess eight eyes. Here, we use three-dimensional geometric morphometrics and evolutionary modeling to test whether eye positions, orientations, and interocular angles correlate with hunting strategies in 52 species across the spider phylogeny. We demonstrate that eye configurations diversified from an ancestral medial cluster, as seen in modern trapdoor spiders, to a halo-like configuration in orb-weavers, and to the frontal clustering of eyes in several members of derived spider lineages. We show that visual hunters have the highest disparity and evolutionary rates in the configuration of their eyes but display a distinct morphological signature with multiple eye pairs concentrated at the front of the carapace. Moreover, we quantify the extent to which eye configuration is modular and show that the position and orientation of the eye pairs evolve semi-independently of each other. Our findings demonstrate that modularity in the spider visual system facilitates not only the specialization of individual eyes but also the whole architecture of the visual system, in line with different hunting strategies, body plans, and ecological niches.

Innovative filtration systems are essential to enhance air quality or improve aerosol sampling for analysis, while addressing challenges such as high energy consumption, clogging and inefficiencies in capturing a wide range of particle diameters. Bio-inspiration provides novel design strategies by translating natural particle separation mechanisms (PSMs) into more efficient, adaptive and sustainable filtration technologies. This review systematically identifies six organismic groups as biological models that use distinct particle capture mechanisms to retain airborne particles for nutrition, reproduction and protection. Filtration-based PSMs in air, such as insect spiracles, hornet silk caps and spider webs, employ dead-end filtration with varying mesh structures to either purify air or capture prey. Non-filtration PSMs, including nasal cavities and wind pollination, rely on passive aerodynamic mechanisms such as impaction, interception and settling for particle retention. Flow regime control is crucial for non-filtration PSMs, where structures like nasal turbinates and pine cone surfaces optimize local airflows. Adhesive mechanisms, found in spider webs and nasal mucus, improve particle attachment. By mapping these principles to aerosol filtration challenges—such as particle adhesion, flow optimization and efficient removal of submicrometre particles—this review identifies promising pathways for bio-inspired aerosol filters in environmental monitoring, industrial hygiene and public health.

The function of biomineralization in plants has been widely discussed. Herbivore defense is generally considered an one important function. This has been demonstrated for, e.g., needle‐shaped raphides in combination with toxic contents, widely found in families such as Araceae. For calcium oxalate (CaOx) crystals and druses (crystal aggregates), which are abundant in leaves of many eudicotyledons, herbivore deterrence has been suggested in the literature, but there is little direct evidence. We used light microscopy and micro‐computer‐tomography to illustrate the biominerals in several temperate shrubs and trees and followed their path upon consumption by caterpillars. We show that a range of different caterpillars consume leaves full of crystals and druses without any apparent harm and that the CaOx druses pass through the animals virtually unchanged. Our observations document the ineffectiveness of CaOx for herbivore deterrence. At least specialized insects are capable of overcoming these obstacles.

Campaniform sensilla (CS) are mechanosensors embedded in the cuticle of insects. They are often found at locations near the joints of leg segments. On legs, CS are generally considered to respond directionally to cuticle bending during legged locomotion. It is currently unclear how CS locations affect strain levels at the CS, but this information is crucial for understanding how CS respond to stimuli. Here we present a parametric finite element model of the femoral CS field for Drosophila hind legs with 12 general and seven CS-specific parameters each. This model allows testing how changes in CS location, orientation and material property affect strain levels at each CS. We used experimentally acquired kinematic data and computed ground reaction forces to simulate in vivo-like forward stepping. The displacements found in this study at the physiological CS field location near the trochanter-femur joint are smaller than those necessary for conformation changes of ion channels involved in signal elicitation. Also, variation of material properties of the CS had little influence on displacement magnitudes at the CS cap where the sensory neuron attaches. Thus, our results indicate that ground reaction forces alone are unlikely to serve CS field activation during forward walking.

Although species evolve in response to many intrinsic and extrinsic factors, frequently one factor has a dominating influence on a given organ system. In this context, mouthpart shape and function are thought to correlate strongly with dietary niche and this was advocated for decades, e.g., for insects. Orthoptera (grasshoppers, crickets, and allies) are a prominent case in this respect because mandible shape has been even used to predict feeding preferences. Here, we analyzed mandible shape, force transmission efficiency, and their potential correlation with dietary categories in a phylogenetic framework for 153 extant Orthoptera. The mechanical advantage profile was used as a descriptor of gnathal edge shape and bite force transmission efficiency in order to understand how mandible shape is linked to biting efficiency and diet, and how these traits are influenced by phylogeny and allometry. Results show that mandible shape, in fact, is a poor predictor of feeding ecology and phylogenetic history has a strong influence on gnathal edge shape. Being ancestrally phytophagous, Orthoptera evolved in an environment with food sources being always abundant so that selective pressures leading to more specialized mouthpart shapes and force transmission efficiencies were low.

Walking is the most common form of how animals move on land. The model organism Drosophila melanogaster has become increasingly popular for studying how the nervous system controls behavior in general and walking in particular. Despite recent advances in tracking and modeling leg movements of walking Drosophila in 3D, there are still gaps in knowledge about the biomechanics of leg joints due to the tiny size of fruit flies. For instance, the natural alignment of joint rotational axes was largely neglected in previous kinematic analyses. In this study, we therefore present a detailed kinematic leg model in which not only the segment lengths but also the main rotational axes of the joints were derived from anatomical landmarks, namely, the joint condyles. Our model with natural oblique joint axes is able to adapt to the 3D leg postures of straight and forward walking fruit flies with high accuracy. When we compared our model to an orthogonalized version, we observed that our model showed a smaller error as well as differences in the used range of motion (ROM), highlighting the advantages of modeling natural rotational axes alignment for the study of joint kinematics. We further found that the kinematic profiles of front, middle, and hind legs differed in the number of required degrees of freedom as well as their contributions to stepping, time courses of joint angles, and ROM. Our findings provide deeper insights into the joint kinematics of walking in Drosophila, and, additionally, will help to develop dynamical, musculoskeletal, and neuromechanical simulations.

Bilateral symmetry is widespread across animals, yet, among bilaterians, many cases of conspicuous asymmetries evolved. This means that bilaterally homologous structures on the left and right sides display divergent phenotypes. The evolution of such divergent phenotypes between otherwise similarly shaped structures can be thought to be favored by modularity, but this has rarely been studied in the context of left-right differences. Here, we provide an empirical example, using geometric morphometrics to assess patterns of asymmetry and covariation between landmark partitions in a grasshopper with conspicuously asymmetric mandibles. Our morphometric data confirm the presence of strictly directional conspicuous asymmetry in the mandibles and surrounding structures. Covariance patterns and tests hint at a strong integration between mandibles despite their divergent morphologies, and variational modularity with the head capsule. While mandibles have been selected to achieve a key-and-lock morphology by having interlocking shapes, the developmental modularity required to achieve this seems to be overwritten by developmental and/or functional integration, allowing the precise matching required for feeding. The consequent conflicting covariation patterns are reminiscent of the palimpsest model. Finally, the degree of directional asymmetry appears to be under selection, although we find no relationship between bite force and mandible shape or asymmetry.

Microplastics (MPs) are released into the environment through human activities and are transported by rivers from land to sea. Biofilms, which are ubiquitous in aquatic ecosystems such as rivers, may play an essential role in the fate of MPs and their ingestion by biofilm protists. To assess this, biofilms were naturally grown on clay tiles in the River Rhine, Germany, and analysed in a combined field and laboratory study. Compared to the ambient river water, biofilms grown for 6, 12, and 18 months in the River Rhine contained up to 10 times more MPs. Between 70% and 78% of all MPs were smaller than 50 μm. In laboratory experiments, clay tiles covered with 1-month-old naturally grown biofilm retained 6-12 times more MPs than clay tiles without biofilm coverage. Furthermore, the ingestion of MPs of 6 and 10 μm by the ciliate Stentor coeruleus was confirmed, and a positive correlation between ingestion rates and ambient MP concentrations was found. The results are relevant for particle transport models in riverine systems, risk assessment of MPs regarding their distribution and fate in the aquatic environment, and the effects of MPs on micro- and macroorganisms.

Bite force is a decisive performance trait in animals because it plays a role for numerous life history components such as food consumption, inter- and intraspecific interactions, and reproductive success. Bite force has been studied across a wide range of vertebrate species, but only for 32 species of insects, the most speciose animal lineage. Here we present the insect bite force database with bite force measurements for 654 insect species covering 476 genera, 111 families, and 13 orders with body lengths ranging from 3.76 to 180.12 mm. In total we recorded 1906 bite force series from 1290 specimens, and, in addition, present basal head, body, and wing metrics. As such, the database will facilitate a wide range of studies on the characteristics, predictors, and macroevolution of bite force in the largest clade of the animal kingdom and may serve as a basis to further our understanding of macroevolutionary processes in relation to bite force across all biting metazoans.

Performance traits such as bite forces are crucial to fitness and relate to the niche and adaptation of species. However, for many insects it is not possible to directly measure bite forces because they are too small. Biomechanical models of bite forces are therefore relevant to test hypotheses of adaptation in insects and other small organisms. Although such models are based on classical mechanics, combining forces, material properties and laws of levers, it is currently unknown how various models relate to bite forces measured in vivo. One critical component of these models is the physiological cross-sectional area (PCSA) of muscles, which relates to the maximum amount of force they can produce. Here, using the grasshopper Schistocerca gregaria, we compare various ways to obtain PCSA values and use in vivo measurements of bite forces to validate the biomechanical models. We show that most approaches used to derive PCSA (dissection, 3D muscle convex hull volume, muscle attachment area) are consistent with the expected relationships between PCSA and bite force, as well as with the muscle stress values known for insects. The only exception to this are PCSA values estimated by direct 3D muscle volume computation, which could be explained by noisy variation produced by shrinkage. This method therefore produces PCSA values which are uncorrelated to in vivo bite forces. Furthermore, despite the fact that all other methods do not significantly differ from expectations, their derived PCSA values vary widely, suggesting a lack of comparability between studies relying on different methods.

Although organ systems evolve in response to many intrinsic and extrinsic factors, frequently one factor has a dominating influence. For example, mouthpart shape and mechanics are thought to correlate strongly with aspects of the diet. Within insects, this paradigm of a shape-diet connection is advocated for decades but the relationship has so far never been quantified and is mostly based on qualitative observations. Orthoptera (grasshoppers, crickets, and allies) are a prominent case, for which mandible shape and dietary preference are thought to correlate strongly and even lead to predictions of feeding preferences. Here, we analysed mandible shape, biting efficiency, and their potential correlation with dietary categories in a phylogenetic framework for a broad sampling of several hundred extant Orthoptera covering nearly all families. The mandibular mechanical advantage was used as a descriptor of gnathal edge shape and bite force transmission efficiency. We aimed to understand how mandible shape is linked to biting efficiency and diet, and how these traits are influenced by phylogeny and allometry. The investigation reveals that feeding ecology is not the unequivocal predictor of mandible shape that it was assumed to be. There is a strong phylogenetic signal suggesting that phylogenetic history does have a much more prevalent influence on gnathal edge shape and distal mechanical advantage, than, e.g., feeding guilds or the efficiency of the force transmission to the food. Being ancestrally phytophagous, Orthoptera evolved in an environment with abundant food sources so that selective pressures leading to more specialized mouthpart shapes and force transmission efficiencies were low.

IntroductionFilter-feeding fish separate food particles from the surrounding water by cross-flow filtration in which a suspension flows parallel to a porous filter medium, thereby transporting particles along the surface.MethodsHere, we investigate cross-flow filtration in five ram-feeding fish species from two groups, Scombridae (Scomber scombrus and Rastrelliger kanagurta) and Clupeidae (Clupea harengus, Sardina pilchardus, and Engraulis encrasicolus). Using a combination of morphometrics, micro-CT scanning, video analysis, and water tunnel experiments, we give a detailed description of the gill arch system, calculate filtration parameters, observe particle movement, and identify morphological traits that induce cross-flow filtration.ResultsOur findings suggest that these ram-feeding fish species use a combination of cross-flow and dead-end filtration as the underlying filtration principle. Specifically, the particles are transported along the surface of gill rakers and denticles towards the esophagus where they accumulate before being periodically swallowed. We infer three distinct morphotypes characterized by variations in geometry, mesh size, and surface structures, which indicate variations of the general mechanism.DiscussionThe description presented in this study contributes to the development of models for investigating the influence of morphological variation on fluid flow and particle retention in filter-feeding fish and on their ecology and biomimetic application.

Suspension feeders (SFs) evolved a high diversity of mechanisms, sometimes with remarkably convergent morphologies, to retain plankton, detritus and man-made particles with particle sizes ranging from less than 1 µm to several centimetres. Based on an extensive literature review, also including the physical and technical principles of solid–liquid separation, we developed a set of 18 ecological and technical parameters to review 35 taxa of suspension-feeding Metazoa covering the diversity of morphological and functional principles. This includes passive SFs, such as gorgonians or crinoids that use the ambient flow to encounter particles, and sponges, bivalves or baleen whales, which actively create a feeding current. Separation media can be flat or funnel-shaped, built externally such as the filter houses in larvaceans, or internally, like the pleated gills in bivalves. Most SFs feed in the intermediate flow region of Reynolds number 1–50 and have cleaning mechanisms that allow for continuous feeding. Comparison of structure–function patterns in SFs to current filtration technologies highlights potential solutions to common technical design challenges, such as mucus nets which increase particle adhesion in ascidians, vanes which reduce pressure losses in whale sharks and changing mesh sizes in the flamingo beak which allow quick adaptation to particle sizes.

Animal closing forces such as bite and pinch forces may determine access to food and mates and are therefore important performance metrics related to fitness. Previous measurement setups to obtain in vivo closing force data were often custom‐made for each study, hampering comparisons among different studies. Additionally, most setups were limited in the size range of taxa they can measure, especially towards smaller species. We introduce forceX , a closing force measurement setup that allows the measurement of a large range of taxa with a great size variety, and forceR , an accompanying software package to analyse the data. forceX is mostly based on off‐the‐shelf components and 3D‐printed or metal‐turned parts. Gape distance can be modified during measurements, and replaceable tip elements of varying thickness allow a minimal gape distance of ~0.3 mm. Thus, forceX allows closing force measurements of smaller species, while still being able to measure medium‐sized animals as well. Animals are not harmed during the measurements, and the whole setup can be assembled within minutes, is battery‐powered, light‐weight and transportable. The forceX system is able to accurately (linear regression of measured forces vs. control forces: p < 0.001; R 2 > 0.999; n = 1,609) and reproducibly (mean of absolute relative errors = 0.93%; SD = 1.42%; n = 1,609) measure forces across three orders of magnitude (0.01–10 N). Importantly, whole force curves, instead of just maximum force values are stored, and forceR allows extracting individual peak shapes from these curves to facilitate the statistical analysis of both maximum force values and peak curve shapes. forceX and forceR facilitate rapid and minimally invasive in vivo measurements and analyses of closing forces in animals across a wider range of taxa than previously possible, including, for example, many small species of the megadiverse insects. The system allows studying the characteristics, predictors, and evolution of both maximum closing forces and force curve shapes.

We report fluid feeding with a sucking pump in the arthropod class Diplopoda, using a combination of synchrotron tomography, histology, electron microscopy, and three-dimensional reconstructions. Within the head of nine species of the enigmatic Colobognatha, we found a pumping chamber, which acts as positive displacement pump and is notably similar to that of insects, showing even fine structural convergences. The sucking pump of these millipedes works together with protractible mouthparts and externally secreted saliva for the acquisition of liquid food. Fluid feeding is one of the great evolutionary innovations of terrestrial arthropods, and our study suggests that it evolved with similar biomechanical solutions convergent across all major arthropod taxa. While fluid-feeding insects are megadiverse today, it remains unclear why other lineages, such as Colobognatha, are comparably species poor.

Insect load sensors, called campaniform sensilla (CS), measure strain changes within the cuticle of appendages. This mechanotransduction provides the neuromuscular system with feedback for posture and locomotion. Owing to their diverse morphology and arrangement, CS can encode different strain directions. We used nano-computed tomography and finite-element analysis to investigate how different CS morphologies within one location-the femoral CS field of the leg in the fruit fly Drosophila-interact under load. By investigating the influence of CS substructures' material properties during simulated limb displacement with naturalistic forces, we could show that CS substructures (i.e. socket and collar) influence strain distribution throughout the whole CS field. Altered socket and collar elastic moduli resulted in 5% relative differences in displacement, and the artificial removal of all sockets caused differences greater than 20% in cap displacement. Apparently, CS sockets support the distribution of distal strain to more proximal CS, while collars alter CS displacement more locally. Harder sockets can increase or decrease CS displacement depending on sensor location. Furthermore, high-resolution imaging revealed that sockets are interconnected in subcuticular rows. In summary, the sensitivity of individual CS is dependent on the configuration of other CS and their substructures.

(Synchrotron-) µCT scans of the heads of 144 earwig (Hexapoda: Polyneoptera: Dermaptera) and 75 stonefly (Hexapoda: Polyneoptera: Plecoptera) species. When using these scans, please cite the following publication: Rühr, P.T., van de Kamp, T., Faragó, T., Hammel, J., Wilde, F., Edel, C., Frenzel, M., Borisova, E., Baumbach, T., Blanke, A. (2021): Juvenile ecology drives adult morphology in two insect orders. Proceedings of the Royal Society B 288: 20210616. https://doi.org/10.1098/rspb.2021.0616 For scan details, please refer to the file "_Ruehr_et_al_2021_scan_details.csv" and the original article.