Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability

It Pays to Be Bumpy: Drag Reducing Armor in the Pacific Spiny Lumpsucker, Eumicrotremus orbis

Armor is a multipurpose set of structures that has evolved independently at least 30 times in fishes. In addition to providing protection, armor can manipulate flow, increase camouflage, and be sexually dimorphic. There are potential tradeoffs in armor function: increased impact resistance may come at the cost of maneuvering ability; and ornate armor may offer visual or protective advantages, but could incur excess drag. Pacific spiny lumpsuckers (Eumicrotremus orbis) are covered in rows of odontic, cone-shaped armor whorls, protecting the fish from wave driven impacts and the threat of predation. We are interested in measuring the effects of lumpsucker armor on the hydrodynamic forces on the fish. Bigger lumpsuckers have larger and more complex armor, which may incur a greater hydrodynamic cost. In addition to their protective armor, lumpsuckers have evolved a ventral adhesive disc, allowing them to remain stationary in their environment. We hypothesize a tradeoff between the armor and adhesion: little fish prioritize suction, while big fish prioritize protection. Using micro-CT, we compared armor volume to disc area over lumpsucker development and built 3D models to measure changes in drag over ontogeny. We found that drag and drag coefficients decrease with greater armor coverage and vary consistently with orientation. Adhesive disc area is isometric but safety factor increases with size, allowing larger fish to remain attached in higher flows than smaller fish.

Central Pattern Generator (CPG)-Based Locomotion Control and Hydrodynamic Experiments of Synergistical Interaction between Pectoral Fins and Caudal Fin for Boxfish-like Robot

Locomotion control of synergistical interaction between fins has been one of the key problems in the field of robotic fish research owing to its contribution to improving and enhancing swimming performance. In this paper, the coordinated locomotion control of the boxfish-like robot with pectoral and caudal fins is studied, and the effects of different control parameters on the propulsion performance are quantitatively analyzed by using hydrodynamic experiments. First, an untethered boxfish-like robot with two pectoral fins and one caudal fin was designed. Second, a central pattern generator (CPG)-based controller is used to coordinate the motions of the pectoral and caudal fins to realize the bionic locomotion of the boxfish-like robot. Finally, extensive hydrodynamic experiments are conducted to explore the effects of different CPG parameters on the propulsion performance under the synergistic interaction of pectoral and caudal fins. Results show that the amplitude and frequency significantly affect the propulsion performance, and the propulsion ability is the best when the frequency is 1 Hz. Different phase lags and offset angles between twisting and flapping of the pectoral fin can generate positive and reverse forces, which realize the forward, backward, and pitching swimming by adjusting these parameters. This paper reveals for the first time the effects of different CPG parameters on the propulsion performance in the case of the synergistic interaction between the pectoral fins and the caudal fin using hydrodynamic experimental methods, which sheds light on the optimization of the design and control parameters of the robotic fish.

Biomimethics: a critical perspective on the ethical implications of biomimetics in technological innovation

Biomimetics, bioinspiration, biomimicry, and related nature-inspired activities-collectively known as biom*-are witnessing an unprecedented surge in popularity, as they offer unparalleled opportunities for technological advancement, innovation, and sustainable development. The growing prevalence of biom*, however, has sparked moral debates regarding their approaches, emphasizing the need for universally applicable ethical guidelines that can effectively guide practitioners in their work. In this perspective, we outline some of the moral, ethical, and legal challenges associated with biom*, particularly the scientific discipline of biomimetics, focusing on various issues surrounding our motivations for pursuing these approaches, the valuation of nature within them, and regulations in the commercialization of biological knowledge. By highlighting the challenges inherent in biom*, this perspective aims to empower practitioners in the field to make informed decisions and take purposeful action. Specific recommendations are provided to guide them in choosing the right course of action for the right reasons.

Community-scale relationships between body shape and trophic ecology in tropical demersal marine fish of northeast Brazil

Functional morphology investigates the relationships between morphological characters and external factors, such as environmental, physical and ecological features. Here, we evaluate the functional relationships between body shape and trophic ecology of a tropical demersal marine fish community using geometric morphometrics techniques and modelling, hypothesizing that shape variables could partially explain fish trophic level. Fish were collected over the continental shelf of northeast Brazil (4-9°S). Analysed fish were distributed into 14 orders, 34 families and 72 species. Each individual was photographed in lateral view, and 18 landmarks were distributed along the body. A principal component analysis (PCA) applied on morphometric indices revealed that fish body elongation and fin base shape were the main axes of variation explaining the morphology. Low trophic levels (herbivore and omnivore) are characterized by deep bodies and longer dorsal and anal fin bases, while predators present elongated bodies and narrow fin bases. Fin position (dorsal and anal fins) on the fish body is another important factor contributing to (i) body stability at high velocity (top predators) or (ii) manoeuvrability (low trophic levels). Using multiple linear regression, we verified that 46% of trophic level variability could be explained by morphometric variables, with trophic level increasing with body elongation and size. Interestingly, intermediate trophic categories (e.g., low predators) presented morphological divergence for a given trophic level. Our results, which can likely be expanded to other tropical and nontropical systems, show that morphometric approaches can provide important insights into fish functional characteristics, especially in trophic ecology.

Bio-Model Selection, Processing and Results for Bio-Inspired Truck Streamlining

We introduce a method for the selection and processing of a biological model to derive an outline that provides morphometric information for a novel aerodynamic truck design. Because of the dynamic similarities, our new truck design will be inspired by biological shapes with a known high level of streamlining and low drag for operation near the seabed, i.e., the head of a trout, but other model organisms will also be used later. Demersal fish are chosen because they live near the bottom of rivers or the sea. Complementary to many biomimetic studies so far, we plan to concentrate on reshaping the outline of the fish's head and extend it to a 3D design for the tractor that, at the same time, fits within EU regulations and maintains the truck's normal use and stability. We intend to explore this biological model selection and formulization involving the following elements: (i) the reason for selecting fish as a biological model for a streamlined truck design; (ii) The choice of a fish model via a functional similarity method; (iii) biological shape formulization based on the morphometric information of models in (ii) outline pick-up, a reshaping step and a subsequent design process; (iv) modify the biomimetic designs and test utilizing CFD; (v) further discussion, outputs and results from the bio-inspired design process.

Biological Concepts as a Source of Inspiration for Efficiency, Consistency, and Sufficiency

Sustainable development is a global challenge addressed by the 2030 Agenda with internationally adopted goals. The consideration of the three major sustainability strategies of efficiency, consistency, and sufficiency can guide us toward more sustainable policy approaches, product manufacturing, service offers, and consumption lifestyles. We select the growth form “liana”, which has evolved several times independently, to identify traits of lianas and general biological concepts derived therefrom. Even though sustainability is an anthropocentric approach and does not exist in biology, we can attribute biological concepts to sustainability strategies. The biological concepts of lightweight construction, modularity, function-related tissue formation, and trade-off can be attributed to efficiency; the concepts of zero waste, best fit, and damage repair to consistency; and the change of growth form and the concept of less is more and good enough to sufficiency. We discuss the analogies between parasitic architecture and the “structural parasitism” of lianas on host trees and between polymers with switchable autonomous properties and ontogenetic changes in the lianescent growth form. Efficiency can be analyzed quantitatively and consistency qualitatively, whereas sufficiency, as an aspect of human consumption patterns, cannot be mathematically measured. Biological concepts can thus serve as a source of inspiration for improving sustainability in the technosphere.

Paleomimetics: A Conceptual Framework for a Biomimetic Design Inspired by Fossils and Evolutionary Processes

In biomimetic design, functional systems, principles, and processes observed in nature are used for the development of innovative technical systems. The research on functional features is often carried out without giving importance to the generative mechanism behind them: evolution. To deeply understand and evaluate the meaning of functional morphologies, integrative structures, and processes, it is imperative to not only describe, analyse, and test their behaviour, but also to understand the evolutionary history, constraints, and interactions that led to these features. The discipline of palaeontology and its approach can considerably improve the efficiency of biomimetic transfer by analogy of function; additionally, this discipline, as well as biology, can contribute to the development of new shapes, textures, structures, and functional models for productive and generative processes useful in the improvement of designs. Based on the available literature, the present review aims to exhibit the potential contribution that palaeontology can offer to biomimetic processes, integrating specific methodologies and knowledge in a typical biomimetic design approach, as well as laying the foundation for a biomimetic design inspired by extinct species and evolutionary processes: Paleomimetics. A state of the art, definition, method, and tools are provided, and fossil entities are presented as potential role models for technical transfer solutions.

Keels of boxfish carapaces strongly improve stabilization against roll

Boxfish (Ostraciidae) have peculiar body shapes, with conspicuous keels formed by their bony carapaces. Previous studies have proposed various hydrodynamic roles for these keels, including reducing drag during swimming, contributing to passive stabilization of the swimming course, or providing resistance against roll rotations. Here, we tested these hypotheses using computational fluid dynamics simulations of five species of Ostraciidae with a range of carapace shapes. The hydrodynamic performance of the original carapace surface models, obtained from laser scanning of museum specimens, was compared with models where the keels had been digitally reduced. The original carapaces showed no reduced drag or increased passive stability against pitch and yaw compared to the reduced-keel carapaces. However, consistently for all studied species, a strong increase in roll drag and roll-added mass was observed for the original carapaces compared to the reduced-keel carapaces, despite the relatively small differences in keel height. In particular, the damping of roll movement by resistive drag torques increased considerably by the presence of keels. Our results suggest that the shape of the boxfish carapace is important in enabling the observed roll-free forward swimming of boxfish and may facilitate the control of manoeuvres.

How much biology is in the product? Role and relevance of biological evolution and function for bio-inspired design

Bio-inspired design (BID) means the concept of transferring functional principles from biology to technology. The core idea driving BID-related work is that evolution has shaped functional attributes, which are termed “adaptations” in biology, to a high functional performance by relentless selective pressure. For current methods and tools, such as data bases, it is implicitly supposed that the considered biological models are adaptations and their functions already clarified. Often, however, the identification of adaptations and their functional features is a difficult task which is not yet accomplished for numerous biological structures, as happens to be the case also for various organismic features from which successful BID developments were derived. This appears to question the relevance of the much stressed importance of evolution for BID. While it is obviously possible to derive an attractive technical principle from an observed biological effect without knowing its original functionality, this kind of BID (“analog BID”) has no further ties to biology. In contrast, a BID based on an adaptation and its function (“homolog BID”) is deeply embedded in biology. It is suggested that a serious and honest clarification of the functional background of a biological structure is an essential first step in devising a BID project, to recognize possible problems and pitfalls as well as to evaluate the need for further biological analysis.

Changes in rays' swimming stability due to the phase difference between left and right pectoral fin movements

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins. However, few studies on the swimming of rays have mentioned left and right pectoral fin movements. Moreover, the effects of movements of the left and right pectoral fins on swimming have not been clarified. This paper describes a computational study of phase differences of pectoral fin movements in the swimming of rays with the validity of fluid analysis methods. The movement and shape of the ray were made based on previous biological research and pictures. An overset grid was used to reproduce the ray’s complex motions. The analysis was performed under four phase difference conditions: 0 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T$$\end{document}T (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T$$\end{document}T is the period), 0.25 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T$$\end{document}T, 0.5 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T$$\end{document}T, and 0.75 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T$$\end{document}T. The results show that a phase difference between the left and right pectoral fin movements affects swimming stability and maneuverability but not propulsive efficiency. We suggest that the phase difference in pectoral fin movements is essential for the swimming of rays, and rays adjust the phase difference between the movement of the left and right pectoral fins to suit their purpose.

Predator Environment Does Not Predict Life History in the Morphologically Constrained Fish Alfaro cultratus (Cyprinodontiformes: Poeciliidae)

Predation is known to have a significant effect on life history diversification in a variety of species. However, physical constraints of body shape and size can sometimes limit life history divergence. We test this idea in the Costa Rican livebearing fishAlfaro cultratus. Individuals in this species have a narrow body and keeled ventral surface, and females do not develop a distended abdomen when pregnant like other livebearing fishes. Here, we describe the life history ofA. cultratusfrom 20 different populations across both high-predation and low-predation environments. We found significantly lower reproductive allotment in females from high-predation environments than in females from low-predation environments, but no significant difference in female or male size at maturity, number of offspring produced by females, or size of offspring. We found thatA. cultratusexhibit isometric patterns of allocation for clutch dry mass in relation to female dry mass in high-predation and low-predation environments. Our results suggest that body shape constraints in this species limit the life history divergence we typically see between populations from high-predation and low-predation environments in other species.

Thriving artificial underwater drag-reduction materials inspired from aquatic animals: progresses and challenges

In the past decades, drag-reduction surfaces have attracted more and more attention due to their potentiality and wide applications in various fields such as traffic, energy transportation, agriculture, textile industry, and military. However, there are still some drag-reduction materials that need to be deeply explored. Fortunately, natural creatures always have the best properties after long-term evolution; aquatic organisms have diversified surface microstructures and drag-reducing materials, which provide design templates for the development of thriving artificial underwater drag-reduction materials. Aquatic animals are tamed by the current while fighting against the water, and thus have excellent drag reduction that is unparalleled in water. Inspired by biological principles, using aquatic animals as a bionic object to develop and reduce frictional resistance in fluids has attracted more attention in the past few years. More and more aquatic animals bring new inspiration for drag-reduction surfaces and a tremendous amount of research effort has been put into the study of surface drag-reduction, with an aim to seek the surface structure with the best drag-reduction effect and explore the drag-reduction mechanism. This present paper reviews the research on drag-reduction surfaces inspired by aquatic animals, including sharks, dolphins, and other aquatic animals. Aquatic animals as bionic objects are described in detail, with a discussion on the drag-reduction mechanism and drag-reduction effect to understand the development of underwater drag-reduction fully. In bionic manufacturing, the effective combination of various preparation methods is summarized. Moreover, bionic surfaces are briefly explained in terms of traffic, energy sources, sports, and agriculture. In the end, both existing problems in bionic research and future research prospects are proposed. This paper may provide a better and more comprehensive understanding of the current research status of aquatic animals-inspired drag reduction.

Bionic Drag Reduction for Box Girders Based on Ostracion cubicus

With the development trend of large-scale and flexible structures in engineering, the research on drag reduction of structures becomes more urgent. This paper presents a drag reduction design method for box girders based on the bionic method. Through the analysis of the Ostracion cubicus body shape, three features of the “fish mouth”, which were helpful for drag reduction were extracted. Then the bionic design model with the height of the box girder (D) as the design variable was obtained. By attaching lightweight materials to the windward side, the bionic shape of the structure can be realized without changing the loading characteristics of the original structure. Taking a box girder (rectangular cylinder, side ratio B/D = 0.6) as a prototype, the flow around two structures (rectangular cylinder and bionic attachment cylinder) was numerically simulated. The results show that the drag coefficient of the bionic attachment structure is reduced by 66.5%. The reduction of wind-load means that this method can save energy consumption of the equipment. Meanwhile, the aerodynamic parameter oscillation of the structure is weakened, which represents that the bionic attachment structure can effectively reduce the wind-induced vibration on the structure and improve the stability of the structure in the wind field.

Aracaniform Swimming: A Proposed New Category of Swimming Mode in Bony Fishes (Teleostei: Tetraodontiformes: Aracanidae)

The deepwater boxfishes of the family Aracanidae are the phylogenetic sister group of the shallow-water, generally more tropical boxfishes of the family Ostraciidae. Both families are among the most derived groups of teleosts. All members of both families have armored bodies, the forward 70% of which are enclosed in rigid bony boxes (carapaces). There is substantial intragroup variation in both groups in body shapes, sizes, and ornamentation of the carapaces. Swimming-related morphology, swimming mode, biomechanics, kinematics, and hydrodynamics have been studied in detail in multiple species of the ostraciids. Ostraciids are all relatively high-performance median and paired fin swimmers. They are highly maneuverable. They swim rectilinearly with substantial dynamic stability and efficiency. Aracanids have not been previously studied in these respects. This article describes swimming-related aspects of morphology, swimming modes, biomechanics, and kinematics in two south Australian species (striped cowfish and ornate cowfish) that are possibly representative of the entire group. These species differ morphologically in many respects, both from each other and from ostraciids. There are differences in numbers, sizes, and placements of keels on carapaces. The most important differences from ostraciids are openings in the posterior edges of the carapaces behind the dorsal and anal fins. The bases of those fins in ostraciids are enclosed in bone. The openings in aracanids free the fins and tail to move. As a result, aracanids are body and caudal fin swimmers. Their overall swimming performances are less stable, efficient, and effective. We propose establishing a new category of swimming mode for bony fishes called "aracaniform swimming."

Modulating yaw with an unstable rigid body and a course-stabilizing or steering caudal fin in the yellow boxfish (Ostracion cubicus)

Despite that boxfishes have a rigid carapace that restricts body undulation, they are highly manoeuvrable and manage to swim with remarkably dynamic stability. Recent research has indicated that the rigid body shape of boxfishes shows an inherently unstable response in its rotations caused by course-disturbing flows. Hence, any net stabilizing effect should come from the fishes' fins. The aim of the current study was to determine the effect of the surface area and orientation of the caudal fin on the yaw torque exerted on the yellow boxfish, Ostracion cubicus, a square cross-sectional shaped species of boxfish. Yaw torques quantified in a flow tank using a physical model with an attachable closed or open caudal fin at different body and tail angles and at different water flow speeds showed that the caudal fin is crucial for controlling yaw. These flow tank results were confirmed by computational fluid dynamics simulations. The caudal fin acts as both a course-stabilizer and rudder for the naturally unstable rigid body with regard to yaw. Boxfishes seem to use the interaction of the unstable body and active changes in the shape and orientation of the caudal fin to modulate manoeuvrability and stability.

Coasting in live-bearing fish: the drag penalty of being pregnant

Swimming performance of pregnant live-bearing fish is presumably constrained by the additional drag associated with the reproductive burden. Yet, it is still unclear how and to what extent the reproductive investment affects body drag of the females. We examined the effect of different levels of reproductive investment on body drag. The biggest measured increase in body volume due to pregnancy was about 43%, linked to a wetted area increase of about 16% and 69% for the frontal area. We printed three-dimensional models of live-bearing fish in a straight body posture representing different reproductive allocation (RA) levels. We measured the drag and visualized the flow around these models in a flow tunnel at different speeds. Drag grew in a power fashion with speed and exponentially with the increase of RA, thus drag penalty for becoming thicker was relatively low for low speeds compared to high ones. We show that the drag increase with increasing RA was most probably due to bigger regions of flow separation behind the enlarged belly. We suggest that the rising drag penalty with an increasing RA, possibly together with pregnancy-related negative effects on muscle- and abdominal bending performance, will reduce the maximum swimming speed.

Control surfaces of aquatic vertebrates: active and passive design and function

Aquatic vertebrates display a variety of control surfaces that are used for propulsion, stabilization, trim and maneuvering. Control surfaces include paired and median fins in fishes, and flippers and flukes in secondarily aquatic tetrapods. These structures initially evolved from embryonic fin folds in fishes and have been modified into complex control surfaces in derived aquatic tetrapods. Control surfaces function both actively and passively to produce torque about the center of mass by the generation of either lift or drag, or both, and thus produce vector forces to effect rectilinear locomotion, trim control and maneuvers. In addition to fins and flippers, there are other structures that act as control surfaces and enhance functionality. The entire body can act as a control surface and generate lift for stability in destabilizing flow regimes. Furthermore, control surfaces can undergo active shape change to enhance their performance, and a number of features act as secondary control structures: leading edge tubercles, wing-like canards, multiple fins in series, finlets, keels and trailing edge structures. These modifications to control surface design can alter flow to increase lift, reduce drag and enhance thrust in the case of propulsive fin-based systems in fishes and marine mammals, and are particularly interesting subjects for future research and application to engineered systems. Here, we review how modifications to control surfaces can alter flow and increase hydrodynamic performance.

Recent Progress in Biomimetic Additive Manufacturing Technology: From Materials to Functional Structures

Nature has developed high-performance materials and structures over millions of years of evolution and provides valuable sources of inspiration for the design of next-generation structural materials, given the variety of excellent mechanical, hydrodynamic, optical, and electrical properties. Biomimicry, by learning from nature's concepts and design principles, is driving a paradigm shift in modern materials science and technology. However, the complicated structural architectures in nature far exceed the capability of traditional design and fabrication technologies, which hinders the progress of biomimetic study and its usage in engineering systems. Additive manufacturing (three-dimensional (3D) printing) has created new opportunities for manipulating and mimicking the intrinsically multiscale, multimaterial, and multifunctional structures in nature. Here, an overview of recent developments in 3D printing of biomimetic reinforced mechanics, shape changing, and hydrodynamic structures, as well as optical and electrical devices is provided. The inspirations are from various creatures such as nacre, lobster claw, pine cone, flowers, octopus, butterfly wing, fly eye, etc., and various 3D-printing technologies are discussed. Future opportunities for the development of biomimetic 3D-printing technology to fabricate next-generation functional materials and structures in mechanical, electrical, optical, and biomedical engineering are also outlined.

On the diverse roles of fluid dynamic drag in animal swimming and flying

Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid-structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers.

The comparative hydrodynamics of rapid rotation by predatory appendages

Countless aquatic animals rotate appendages through the water, yet fluid forces are typically modeled with translational motion. To elucidate the hydrodynamics of rotation, we analyzed the raptorial appendages of mantis shrimp (Stomatopoda) using a combination of flume experiments, mathematical modeling and phylogenetic comparative analyses. We found that computationally efficient blade-element models offered an accurate first-order approximation of drag, when compared with a more elaborate computational fluid-dynamic model. Taking advantage of this efficiency, we compared the hydrodynamics of the raptorial appendage in different species, including a newly measured spearing species, Coronis scolopendra The ultrafast appendages of a smasher species (Odontodactylus scyllarus) were an order of magnitude smaller, yet experienced values of drag-induced torque similar to those of a spearing species (Lysiosquillina maculata). The dactyl, a stabbing segment that can be opened at the distal end of the appendage, generated substantial additional drag in the smasher, but not in the spearer, which uses the segment to capture evasive prey. Phylogenetic comparative analyses revealed that larger mantis shrimp species strike more slowly, regardless of whether they smash or spear their prey. In summary, drag was minimally affected by shape, whereas size, speed and dactyl orientation dominated and differentiated the hydrodynamic forces across species and sizes. This study demonstrates the utility of simple mathematical modeling for comparative analyses and illustrates the multi-faceted consequences of drag during the evolutionary diversification of rotating appendages.

Bio-Inspired Functional Surfaces Based on Laser-Induced Periodic Surface Structures

Nature developed numerous solutions to solve various technical problems related to material surfaces by combining the physico-chemical properties of a material with periodically aligned micro/nanostructures in a sophisticated manner. The utilization of ultra-short pulsed lasers allows mimicking numerous of these features by generating laser-induced periodic surface structures (LIPSS). In this review paper, we describe the physical background of LIPSS generation as well as the physical principles of surface related phenomena like wettability, reflectivity, and friction. Then we introduce several biological examples including e.g., lotus leafs, springtails, dessert beetles, moth eyes, butterfly wings, weevils, sharks, pangolins, and snakes to illustrate how nature solves technical problems, and we give a comprehensive overview of recent achievements related to the utilization of LIPSS to generate superhydrophobic, anti-reflective, colored, and drag resistant surfaces. Finally, we conclude with some future developments and perspectives related to forthcoming applications of LIPSS-based surfaces.

Cost of flight and the evolution of stag beetle weaponry

Male stag beetles have evolved extremely large mandibles in a wide range of extraordinary shapes. These mandibles function as weaponry in pugnacious fights for females. The robust mandibles of Cyclommatus metallifer are as long as their own body and their enlarged head houses massive, hypertrophied musculature. Owing to this disproportional weaponry, trade-offs exist with terrestrial locomotion: running is unstable and approximately 40% more costly. Therefore, flying is most probably essential to cover larger distances towards females and nesting sites. We hypothesized that weight, size and shape of the weaponry will affect flight performance. Our computational fluid dynamics simulations of steady-state models (without membrane wings) reveal that male stag beetles must deliver 26% more mechanical work to fly with their heavy weaponry. This extra work is almost entirely required to carry the additional weight of the massive armature. The size and shape of the mandibles have only negligible influence on flight performance (less than 0.1%). This indicates that the evolution of stag beetle weaponry is constrained by its excessive weight, not by the size or shape of the mandibles and head as such. This most probably paved the way for the wide diversity of extraordinary mandible morphologies that characterize the stag beetle family.

The armored carapace of the boxfish

The boxfish (Lactoria cornuta) has a carapace consisting of dermal scutes with a highly mineralized surface plate and a compliant collagen base. This carapace must provide effective protection against predators as it comes at the high cost of reduced mobility and speed. The mineralized hydroxyapatite plates, predominantly hexagonal in shape, are reinforced with raised struts that extend from the center toward the edges of each scute. Below the mineralized plates are non-mineralized collagen fibers arranged in through-the-thickness layers of ladder-like formations. At the interfaces between scutes, the mineralized plates form suture-like teeth structures below which the collagen fibers bridge the gap between neighboring scutes. These sutures are unlike most others as they have no bridging Sharpey's fibers and appear to add little mechanical strength to the overall carapace. It is proposed that the sutured interface either allows for accommodation of the changing pressures of the boxfish's ocean habitat or growth, which occurs without molting or shedding. In both tension and punch testing the mineralized sutures remain relatively intact while most failures occur within the collagen fibers, allowing for the individual scutes to maintain their integrity. This complex structure allows for elevated strength of the carapace through an increase in the stressed area when attacked by predators in both penetrating and crushing modes.

Stability versus Maneuvering: Challenges for Stability during Swimming by Fishes

Fishes are well known for their remarkable maneuverability and agility. Less visible is the continuous control of stability essential for the exploitation of the full range of aquatic resources. Perturbations to posture and trajectory arise from hydrostatic and hydrodynamic forces centered in a fish (intrinsic) and from the environment (extrinsic). Hydrostatic instabilities arise from vertical and horizontal separation of the centers of mass (CM) and of buoyancy, thereby creating perturbations in roll, yaw, and pitch, with largely neglected implications for behavioral ecology. Among various forms of hydrodynamic stability, the need for stability in the face of recoil forces from propulsors is close to universal. Destabilizing torques in body-caudal fin swimming is created by inertial and viscous forces through a propulsor beat. The recoil component is reduced, damped, and corrected in various ways, including kinematics, shape of the body and fins, and deployment of the fins. We postulate that control of the angle of orientation, θ, of the trailing edge is especially important in the evolution and lifestyles of fishes, but studies are few. Control of stability and maneuvering are reflected in accelerations around the CM. Accelerations for such motions may give insight into time-behavior patterns in the wild but cannot be used to determine the expenditure of energy by free-swimming fishes.