Form and function of anguilliform swimming.

Anguilliform swimmers are long and narrow animals that propel themselves by undulating their bodies. Observations in nature and recent investigations suggest that anguilliform swimming is highly efficient. However, understanding the underlying reasons for the efficiency of this type of locomotion requires interdisciplinary studies spanning from biology to hydrodynamics. Regrettably, these different fields are rarely discussed together, which hinders our ability to understand the repeated evolution of this swimming mode in vertebrates. This review compiles the current knowledge of the anatomical features that drive anguilliform swimming, compares the resulting kinematics across a wide range of anguilliform swimmers, and describes the resulting hydrodynamic interactions using data from both in vivo experiments and computational studies.

Effect of the ischial support on muscle force estimation during transfemoral walking.

BACKGROUND: Transmission of loads between the prosthetic socket and the residual limb is critical for the comfort and walking ability of people with transfemoral amputation. This transmission is mainly determined by the socket tightening, muscle forces, and socket ischial support. However, numerical investigations of the amputated gait, using modeling approaches such as MusculoSkeletal (MSK) modeling, ignore the weight-bearing role of the ischial support. This simplification may lead to errors in the muscle force estimation. OBJECTIVE: This study aims to propose a MSK model of the amputated gait that accounts for the interaction between the body and the ischial support for the estimation of the muscle forces of 13 subjects with unilateral transfemoral amputation. METHODS: Contrary to previous studies on the amputated gait which ignored the interaction with the ischial support, here, the contact on the ischial support was included in the external loads acting on the pelvis in a MSK model of the amputated gait. RESULTS: Including the ischial support induced an increase in the activity of the main abductor muscles, while adductor muscles' activity was reduced. These results suggest that neglecting the interaction with the ischial support leads to erroneous muscle force distribution considering the gait of people with transfemoral amputation. Although subjects with various bone geometries, particularly femur lengths, were included in the study, similar results were obtained for all subjects. CONCLUSIONS: Eventually, the estimation of muscle forces from MSK models could be used in combination with finite element models to provide quantitative data for the design of prosthetic sockets.

Reduce, Replace, Refine: Determining A Posteriori Reference Intervals for Biochemistry in Hermann's Tortoise (Testudo hermanni).

Biochemical and hematological analyses are important for the assessment of animal health. However, for most wild species their use is hindered by the scarcity of reliable reference intervals. Indeed, collecting body fluids (e.g., blood, urine) in free-ranging animals is often technically challenging. Further, sampling many individuals would be essential to consider major sources of variations, such as species, populations, sex, age, and seasons. One alternative, according to the reduction, refinement, and replacement framework, is to establish reference intervals a posteriori using literature survey and unpublished data. We produced reference intervals for free-ranging Hermann's tortoises (Testudo hermanni), using analyses performed on blood samples collected in previous studies and conservation programs conducted in the field between 2010 and 2016 in southern France (n=195 individuals). Thirteen parameters were analyzed: packed-cell volume, blood concentrations of corticosterone, testosterone, glycemia, cholesterol, triglyceride, urea, uric acid, calcium, sodium, potassium, asparagine aminotransferase (AST), and alanine aminotransferases (ALT). Reference intervals for subgroups defined by sex and season were relevant for corticosterone, triglyceride, and calcium (sex) and cholesterol (season). Comparing our results with those obtained in captive individuals in Germany, except for urea and AST levels the intervals from both free-ranging versus captive tortoises were similar, suggesting that reference intervals established from captive individuals may be suitable for free-ranging populations in this species.

Gait-Oriented Post-Stroke Rehabilitation Tasks Online Trajectory Generation for 1-DOF Hip Lower-Limb Exoskeleton.

In the field of gait rehabilitation lower limb exoskeletons have received a lot of interest. An increasing number of them are revised to be adapted for post-stroke rehabilitation. These exoskeletons mostly work in complement of conventional physiotherapy in the subacute phase to practice gait training. For this gait training the reference trajectory generation is one of the main issues. This is why it usually consists in reproducing some averaged healthy patient's gait pattern. This paper's purpose is to display the online trajectory generation (OTG) algorithm developed to provide reference trajectories applied to gait-oriented tasks designed based on conventional physiotherapy. This OTG algorithm is made to reproduce trajectories similar to the ones a therapist would follow during the same tasks. In addition, experiments are presented in this paper to compare the trajectories generated with the OTG algorithm for two rehabilitation tasks with the trajectories followed by a therapist in the same conditions. During these experiments the OTG is implemented in a runtime system with a 500µs cycle time on a bench able to emulate late and early patients' interaction. These experiments results assess that the OTG can work at a 500µs cycle time to reproduce a similar trajectory as the one followed by the therapist during the two rehabilitation tasks implemented.

Spot the odd one out: do snake pictures capture macaques' attention more than other predators?

Detecting and identifying predators quickly is key to survival. According to the Snake Detection Theory (SDT), snakes have been a substantive threat to primates for millions of years, so that dedicated visual skills were tuned to detect snakes in early primates. Past experiments confronted the SDT by measuring how fast primate subjects detected snake pictures among non-dangerous distractors (e.g., flowers), but did not include pictures of primates' other predators, such as carnivorans, raptors, and crocodilians. Here, we examined the detection abilities of N = 19 Tonkean macaques (Macaca tonkeana) and N = 6 rhesus macaques (Macaca mulatta) to spot different predators. By implementing an oddity task protocol, we recorded success rates and reaction times to locate a deviant picture among four pictures over more than 400,000 test trials. Pictures depicted a predator, a non-predator animal, or a simple geometric shape. The first task consisted of detecting a deviant picture among identical distractor pictures (discrimination) and the second task was designed to evaluate detection abilities of a deviant picture among different distractor pictures (categorization). The macaques detected pictures of geometric shapes better and faster than pictures of animals, and were better and faster at discriminating than categorizing. The macaques did not detect snakes better or faster than other animal categories. Overall, these results suggest that pictures of snakes do not capture visual attention more than other predators, questioning previous findings in favor of the SDT.

Seasonal variations of testis anatomy and of G-coupled oestrogen receptor 1 expression in Gerbillus gerbillus.

The gerbil, Gerbillus gerbillus, a nocturnal desert rodent of northern Africa, exhibits a seasonal reproductive cycle with marked anatomical and behavioural shifts between breeding season and resting season. The aim of this study is to investigate key elements involved in these seasonal changes, specifically in males: the histology of the testis as well as the expression of the G-protein-coupled oestrogen receptor 1 (GPER1) in the testis. During the breeding season, the seminiferous tubules were full of spermatozoa, and their epithelium contained germinal cells embedded in Sertoli cells. Amidst tubules, well-developed Leydig cells were observed around blood vessels, with peritubular myoid cells providing structural and dynamic support to the tubules. GPER1 was largely expressed throughout the testis. Notably, Leydig cells, spermatogonia and spermatocytes showed strong immunohistochemical signals. Sertoli cells, spermatozoa and peritubular myoid cells were moderately stained. During the resting season, spermatogenesis was blocked at the spermatocyte stage, spermatids and spermatozoa were absent and the interstitial space was reduced. The weight of the testis decreased significantly. At this stage, GPER1 was found in Leydig cells, spermatocytes and peritubular myoid cells. Sertoli cells and spermatogonia were not marked. Overall, the testis of the gerbil, Gerbillus gerbillus, has undergone noticeable histological, cellular and weight changes between seasons. In addition, the seasonal expression pattern of GPER1, with pronounced differences between resting season and breeding season, indicates that this receptor is involved in the regulation of the reproductive cycle.

Measuring the 3D wake of swimming snakes (Natrix tessellata) using volumetric particle image velocimetry.

We describe a method for measuring the 3D vortical structures produced by an anguilliform swimmer using volumetric velocimetry. The wake of freely swimming dice snakes (Natrix tessellata) was quantified, revealing the creation of multiple vortices along the body of the snake due to its undulation. The 3D structure of the vortices generally consisted of paired vortex tubes, some of which were linked together to form a hairpin structure. The observations match predictions from computational fluid dynamic studies of other anguilliform swimmers. Quantitative measurements allowed us to study vortex circulation and size, and global kinetic energy of the flow, which varied with swimming speed, vortex topology and individual characteristics. Our findings provide a baseline for comparing wake structures of snakes with different morphologies and ecologies and investigating the energetic efficiency of anguilliform swimming.

Continuum Robots: From Conventional to Customized Performance Indicators.

Continuum robots have often been compared with rigid-link designs through conventional performance metrics (e.g., precision and Jacobian-based indicators). However, these metrics were developed to suit rigid-link robots and are tuned to capture specific facets of performance, in which continuum robots do not excel. Furthermore, conventional metrics either fail to capture the key advantages of continuum designs, such as their capability to operate in complex environments thanks to their slender shape and flexibility, or see them as detrimental (e.g., compliance). Previous work has rarely addressed this issue, and never in a systematic way. Therefore, this paper discusses the facets of a continuum robot performance that cannot be characterized by existing indicator and aims at defining a tailored framework of geometrical specifications and kinetostatic indicators. The proposed framework combines the geometric requirements dictated by the target environment and a methodology to obtain bioinspired reference metrics from a biological equivalent of the continuum robot (e.g., a snake, a tentacle, or a trunk). A numerical example is then reported for a swimming snake robot use case.

Evolutionary convergence of muscle architecture in relation to locomotor ecology in snakes.

The epaxial muscles in snakes are responsible for locomotion and as such can be expected to show adaptations in species living in different environments. Here, we tested whether the structural units that comprise the superficial epaxial muscles (semispinalis-spinalis, SSP; longissimus dorsi, LD; iliocostalis, IC) were different in animals occupying similar habitats. To do so, we analyzed and compared the muscle architecture (mass, fiber length, and physiological cross-sectional area) of the superficial epaxial muscle segments in snakes that differ in their habitat use (e.g., arboreal, terrestrial, and aquatic). Our results showed that arboreal species have on average longer muscles and tendons spanning more segments likely important during gap bridging. Moreover, aquatic snakes show relatively heavier semispinalis-spinalis muscles with a greater cross-sectional area. The longissimus dorsi muscles also showed a greater cross-sectional area compared with terrestrial and especially arboreal snakes. Whereas the more strongly developed muscles in aquatic snakes are likely associated with the dense and viscous environment through which they move, the lighter muscles in arboreal snakes may provide an advantage when climbing. Future studies comparing other ecologies (e.g., burrowing snakes) and additional muscle units (e.g., multifidus; hypaxial muscles) are needed to better understand the structural features driving variation in locomotor performance and efficiency in snakes.

Three-dimensional reconstruction of the hand from biplanar X-rays: Assessment of accuracy and reliability.

BACKGROUND: Functional disorders of the hand are generally investigated first using conventional radiographic imaging. However, X-rays (two-dimensional (2D)) provide limited information and the information may be reduced by overlapping bones and projection bias. This work presents a three-dimensional (3D) hand reconstruction method from biplanar X-rays. METHOD: This approach consists of the deformation of a generic hand model on biplanar X-rays by manual and automatic processes. The reference examination being the manual CT segmentation, the precision of the method was evaluated by a comparison between the reconstructions from biplanar X-rays and the corresponding reconstructions from the CT scan (0.3mm section thickness). To assess the reproducibility of the method, 6 healthy hands (6 subjects, 3 left, 3 men) were considered. Two operators repeated each reconstruction from biplanar X-rays three times to study inter- and intra-operator variability. Three anatomical parameters that could be calculated automatically from the reconstructions were considered from the bone surfaces: the length of the scaphoid, the depth of the distal end of the radius and the height of the trapezius. RESULTS: Double the root mean square error (2 Root Mean Square, 2RMS) at the point/area difference between biplanar X-rays and computed tomography reconstructions ranged from 0.46mm for the distal phalanges to 1.55mm for the bones of the distal carpals. The inter-intra-observer variability showed precision with a 95% confidence interval of less than 1.32mm for the anatomical parameters, and 2.12mm for the bone centroids. DISCUSSION: The current method allows to obtain an accurate 3D reconstruction of the hand and wrist compared to the traditional segmented CT scan. By improving the automation of the method, objective information about the position of the bones in space could be obtained quickly. The value of this method lies in the early diagnosis of certain ligament pathologies (carpal instability) and it also has implications for surgical planning and personalized finite element modeling. LEVEL OF PROOF: Basic sciences.

A Biomimetic Method to Replicate the Natural Fluid Movements of Swimming Snakes to Design Aquatic Robots.

Replicating animal movements with robots provides powerful research tools because key parameters can be manipulated at will. Facing the lack of standard methods and the high complexity of biological systems, an incremental bioinspired approach is required. We followed this method to design a snake robot capable of reproducing the natural swimming gait of snakes, i.e., the lateral undulations of the whole body. Our goal was to shift away from the classical broken line design of poly-articulated snake robots to mimic the far more complex fluid movements of snakes. First, we examined the musculoskeletal systems of different snake species to extract key information, such as the flexibility or stiffness of the body. Second, we gathered the swimming kinematics of living snakes. Third, we developed a toolbox to implement the data that are relevant to technical solutions. We eventually built a prototype of an artificial body (not yet fitted with motors) that successfully reproduced the natural fluid lateral undulations of snakes when they swim. This basis is an essential step for designing realistic autonomous snake robots.

Finite element analysis of the stump-ischial containment socket interaction: a technical note.

The role of the above-knee socket is to ensure the load transfer via the coupling of residual limb-prosthesis with minimal discomfort and without damaging the soft tissues. Modelling is a potential tool to predict socket fit prior to manufacture. However, state-of-the-art models only include the femur in soft tissues submitted to static loads neglecting the contribution of the hip joint. The hip joint is particularly challenging to model because it requires to compute the forces of muscles inserting on the residual limb. This work proposes a modelling of the hip joint including the estimation of muscular forces using a combined MusculoSKeletal (MSK)/Finite Element (FE) framework. An experimental-numerical approach was conducted on one femoral amputee subject. This allowed to i) model the hip joint and personalise muscular forces, ii) study the impact of the ischial support, and iii) evaluate the interface pressure. A reduction of the gluteus medius force from the MSK modelling was noticed when considering the ischial support. Interface pressure, predicted between 63 to 71 kPa, agreed with experimental literature data. The contribution of the hip joint is a key element of the modelling approach for the prediction of the socket interface pressure with the residual limb soft tissues.

Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity.

Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.

Proteomic insight into the venom composition of the largest European rear-fanged snake, Malpolon monspessulanus monspessulanus.

Snake envenomations constitute a worldwide neglected tropical disease, with the vast majority of lethal bites inflicted by front-fanged snakes from the viperid and elapid groups. Rear-fanged snakes (colubrids) were often considered harmless and as a result, are much less studied, but several documented deaths have suggested potent venom in this group as well. The largest European snake (Malpolon monspessulanus monspessulanus), known as the "Montpellier snake", is such a rear-fanged snake that belongs to the Lamprophiidae family. Its venom remains largely unknown but cases of envenomation with neurological symptoms have been reported. Here, we provide the first insights into the composition of its venom using mass spectrometry methods. First, liquid chromatography coupled mass spectrometry analysis of the manually collected venom samples reveals a complex profile, with the majority of masses encompassing the range 500-3000 Da, 4000-8000 Da, and 10 000-30 000 Da. Next, shotgun proteomics allowed the identification of a total of 42 different known families of proteins, including snake venom metalloproteinases, peptidase M1, and cysteine-rich secretory proteins, as the most prominent. Interestingly, three-finger toxins were not detected, suggesting that neurotoxicity may occur via other, yet to be determined, toxin types. Overall, our results provide the basis for a better understanding of the effects of a peculiar snake venom on human symptomatology, but also on the main prey consumed by this species.

Distribution of joint work during walking on slopes among persons with transfemoral amputation.

Persons with above-knee amputation have increased energy consumption and greater difficulty in negotiating uphill and downhill slopes. Walking on slopes requires an adaptation of the positive and negative work performed by the joints of the lower limb to propel the center of mass. Modern prosthetic feet and knees can only partially adapt to changes in inclination, and the redistribution of joint work among persons with above-knee amputation is not described in the literature. Level, upslope and downslope walking (at 5% and 12% inclinations) were investigated for twelve subjects with transfemoral amputation fitted with an Energy Storing And Return foot (ESAR) and a Microprocessor controlled Prosthetic Knee (MPK) versus a control group of seventeen asymptomatic subjects. Lower limb joint and individual limb power and work were compared between prosthetic, contralateral and control limbs. The prosthesis dissipates less energy than the joints of the lower limb of the control group when descending the slope, but the demand on the contralateral limb is limited by a lower speed and step length. The huge deficit of positive work produced by the prosthetic ankle cannot be compensated by the residual hip during level and slope ascent which transfers the demand for energy production to the contralateral limb up to 40% on a 12% slope. This study highlights that prosthetic devices (ESAR foot and MPK) for persons with above-knee amputation present some limitations during slope walking that cannot be compensated by the residual hip and increase the work performed by the contralateral limb.

Development and evaluation of a new methodology for Soft Tissue Artifact compensation in the lower limb.

Skin Marker (SM) based motion capture is the most widespread technique used for motion analysis. Yet, the accuracy is often hindered by Soft Tissue Artifact (STA). This is a major issue in clinical gait analysis where kinematic results are used for decision-making. It also has a considerable influence on the results of rigid body and Finite Element (FE) musculoskeletal models that rely on SM-based kinematics to estimate muscle, contact and ligament forces. Current techniques devised to compensate for STA, in particular multi-body optimization methods, often consider simplified joint models. Although joint personalization with anatomical constraints has improved kinematic estimation, these models yet don't represent a fully reliable solution to the STA problem, thus allowing us to envisage an alternative approach. In this perspective, we propose to develop a conceptual FE-based model of the lower limb for STA compensation and evaluate it for 66 healthy subjects under level walking motor task. Both hip and knee joint kinematics were analyzed, considering both rotational and translational joint motion. Results showed that STA caused underestimation of the hip joint kinematics (up to 2.2°) for all rotational DoF, and overestimation of knee joint kinematics (up to 12°) except in flexion/extension. Joint kinematics, in particular the knee joint, appeared to be sensitive to soft tissue stiffness parameters (rotational and translational mean difference up to 1.5° and 3.4 mm). Analysis of the results using alternative joint representations highlighted the versatility of the proposed modeling approach. This work paves the way for using personalized models to compensate for STA in healthy subjects and different activities.

Experimental characterization of the moment-angle curve during level and slope locomotion of transtibial amputee: Which parameters can be extracted to quantify the adaptations of microprocessor prosthetic ankle?

In case of transtibial amputation, the deficit resulting from the loss of the lower limb can be partly compensated with a prosthetic foot and adapted rehabilitation. New prosthetic feet have been developed for transtibial amputees to mimic ankle adaptability to varying terrain. Among them, Microprocessor Prosthetic Ankles (MPA) have a microprocessor to control an electric or a hydraulic actuator to adapt ankle kinematics in stairs and slopes. The objective is to investigate parameters extracted from the moment-angle curve (MAC) and use them to compare 3 MPA during level and slope locomotion against energy storing and return (ESR) foot. Five persons with lower limb transtibial amputation successively fitted with 3 MPA (Propriofoot™, Elan™, Meridium™) compared to their ESR foot. The participants had 2 weeks of adaptation before data acquisition and then a 3 week wash-out period. Range of motion, equilibrium point, hysteresis, late stance energy released, and quasi-stiffness were computed on level ground and 12% slope (upward and downward) thanks to the MAC at the ankle. The study shows the relevance of MAC parameters to evaluate the behavior of MPA. In particular, compared to ESR, all MPA tested in the present study demonstrated a better angle adaptation between walking conditions but a decrease of available energy for the propulsion. Among MPA, main results were: (i) for the Propriofoot™: an adaptation of the ankle angle without modification of the pattern of the MAC (ii) for the Elan™: a limited adaptation of the range of motion but a modification of the energy released (iii) for the Meridium™, the highest adaptation of the range of motion but the lowest available energy of propulsion. One of the main findings of the research is to show and quantify the relationship between range of motion and energy available when using different prosthetic feet in different walking conditions.

Androgen and estrogen receptors immunolocalization in the sand rat (Psammomys Obesus) cauda epididymis.

Both androgens and estrogens play key, albeit incompletely described, roles in the functioning of the epididymis. Because this tightly-coiled tubular structure is compartmented, precise mapping of the distribution of sex steroid's receptors is important. Such receptors have been located in the first segments (caput, corpus), but the last part (cauda) remains poorly explored. We used immunochemistry to localize androgen (AR) and estrogen (ESR1 and ESR2) receptors in the cauda in the fat sand rat (Psammomys obesus). We compared results obtained during the breeding versus resting seasons. We also used individuals castrated, or castrated then treated with testosterone, or subjected to the ligation of their efferent ducts. During the breeding season, in principal cells, we found strong staining both for AR and ESR1 in the apical cytoplasm, and strong staining for ESR2 in the nucleus. During the resting season, principal cells were positive for AR and ESR1, but negative for ESR2. In castrated animals, staining was null for ESR2 and AR, and weak for ESR1. In castrated then treated animals, immuno-expression was restored but only for AR and ESR1. Following efferent duct ligation, AR reactivity decreased while ESR1 and ESR2 provided strong staining. Broadly similar, but not fully identical patterns were observed in basal cells. They were positive for ESR2 and AR during the breeding season, but not for ESR1. During the resting season, staining was modest for ESR1 and AR and negative for ESR2. In all experimentally treated animals, we observed weak staining for AR and ESR1, and a lack of signal for ESR2. Overall, this study provides strong evidence that androgens and estrogens are involved in the seasonal regulation of the whole epididymis in the fat sand rat, with marked differences between caput and cauda (the corpus is highly reduced in rodent).

Plasticity matches phenotype to local conditions despite genetic homogeneity across 13 snake populations.

In a widespread species, a matching of phenotypic traits to local environmental optima is generally attributed to site-specific adaptation. However, the same matching can occur via adaptive plasticity, without requiring genetic differences among populations. Adult sea kraits (Laticauda saintgironsi) are highly philopatric to small islands, but the entire population within the Neo-Caledonian Lagoon is genetically homogeneous because females migrate to the mainland to lay their eggs at communal sites; recruits disperse before settling, mixing up alleles. Consequently, any matching between local environments (e.g. prey sizes) and snake phenotypes (e.g. body sizes and relative jaw sizes (RJSs)) must be achieved via phenotypic plasticity rather than spatial heterogeneity in gene frequencies. We sampled 13 snake colonies spread along an approximately 200 km northwest-southeast gradient (n > 4500 individuals) to measure two morphological features that affect maximum ingestible prey size in gape-limited predators: body size and RJS. As proxies of habitat quality (HQ), we used protection status, fishing pressure and lagoon characteristics (lagoon width and distance of islands to the barrier reef). In both sexes, spatial variation in body sizes and RJSs was linked to HQ; albeit in different ways, consistent with sex-based divergences in foraging ecology. Strong spatial divergence in morphology among snake colonies, despite genetic homogeneity, supports the idea that phenotypic plasticity can facilitate speciation by creating multiple phenotypically distinct subpopulations shaped by their environment.