Using Pose Estimation and 3D Rendered Models to Study Leg-Mediated Self-righting by Lanternflies.

The ability to upright quickly and efficiently when overturned on the ground (terrestrial self-righting) is crucial for living organisms and robots. Previous studies have mapped the diverse behaviors used by various animals to self-right on different substrates, and proposed physical models to explain how body morphology can favor specific self-righting methods. However, to our knowledge, no studies have quantified and modeled all of an animal's limb motions during these complicated behaviors. Here, we studied terrestrial self-righting by immature invasive spotted lanternflies (Lycorma delicatula), an insect species that must frequently recover from being overturned after jumping and falling in its native habitat. These nymphs self-righted successfully in 92-100% of trials on three substrates with different friction and roughness, with no significant difference in the time or number of attempts required. They accomplished this using three stereotypic sequences of movements. To understand these motions, we combined 3D poses tracked on multi-view high-speed video with articulated 3D models created using photogrammetry and Blender rendering software. The results were used to calculate the mechanical properties (e.g., potential and kinetic energy, angular speed, stability margin, torque, force, etc.) of these insects during righting trials. We used an inverted physical pendulum model (a "template") to estimate the kinetic energy available in comparison to the increase in potential energy required to flip over. While these insects began righting using primarily quasistatic motions, they also used dynamic leg motions to achieve final tip-over. However, this template did not describe important features of the insect's center of mass trajectory and rotational dynamics, necessitating the use of an "anchor" model comprising the 3D rendered body model and six articulated two-segment legs to model the body's internal degrees of freedom and capture the role of the legs' contribution to inertial reorientation. This anchor elucidated the sequence of highly coordinated leg movements these insects used for propulsion, adhesion, and inertial reorientation during righting, and how they frequently pivot about a body contact point on the ground to flip upright. In the most frequently used method, diagonal rotation, these motions allowed nymphs to spin their bodies to upright with lower force with a greater stability margin compared to the other less frequently used methods. We provide a concise overview of necessary background on 3D orientation and rotational dynamics, and the resources required to apply these low-cost modeling methods to other problems in biomechanics.

Putting a new spin on insect jumping performance using 3D modeling and computer simulations of spotted lanternfly nymphs.

How animals jump and land on diverse surfaces is ecologically important and relevant to bioinspired robotics. Here, we describe the jumping biomechanics of the planthopper Lycorma delicatula (spotted lanternfly), an invasive insect in the USA that jumps frequently for dispersal, locomotion and predator evasion. High-speed video was used to analyze jumping by spotted lanternfly nymphs from take-off to impact on compliant surfaces. These insects used rapid hindleg extensions to achieve high take-off speeds (2.7-3.4 m s-1) and accelerations (800-1000 m s-2), with mid-air trajectories consistent with ballistic motion without drag forces or steering. Despite rotating rapidly (5-45 Hz) about time-varying axes of rotation, they landed successfully in 58.9% of trials. They also attained the most successful impact orientation significantly more often than predicted by chance, consistent with their using attitude control. Notably, these insects were able to land successfully when impacting surfaces at all angles, pointing to the importance of collisional recovery behaviors. To further understand their rotational dynamics, we created realistic 3D rendered models of spotted lanternflies and used them to compute their mechanical properties during jumping. Computer simulations based on these models and drag torques estimated from fits to tracked data successfully predicted several features of the measured rotational kinematics. This analysis showed that the rotational inertia of spotted lanternfly nymphs is predominantly due to their legs, enabling them to use posture changes as well as drag torque to control their angular velocity, and hence their orientation, thereby facilitating predominately successful landings when jumping.

Sizing up spotted lanternfly nymphs for instar determination and growth allometry.

A major ongoing research effort seeks to understand the behavior, ecology and control of the spotted lanternfly (SLF) (Lycorma delicatula), a highly invasive pest in the U.S. and South Korea. These insects undergo four nymphal stages (instars) before reaching adulthood, and appear to shift host plant preferences, feeding, dispersal and survival patterns, anti-predator behaviors, and response to traps and chemical controls with each stage. However, categorizing SLF life stage is challenging for the first three instars, which have the same coloration and shape. Here we present a dataset of body mass and length for SLF nymphs throughout two growing seasons and compare our results with previously-published ranges of instar body lengths. An analysis using two clustering methods revealed that 1st-3rd instar body mass and length fell into distinct clusters consistently between years, supporting using these metrics to stage nymphs during a single growing season. The length ranges for 2nd-4th instars agreed between years in our study, but differed from those reported by earlier studies for diverse locations, indicating that it is important to obtain these metrics relevant to a study's region for most accurate staging. We also used these data to explore the scaling of SLF instar bodies during growth. SLF nymph body mass scaled with body length varied between isometry (constant shape) and growing somewhat faster than predicted by isometry in the two years studied. Using previously published data, we also found that SLF nymph adhesive footpad area varies in direct proportion to weight, suggesting that footpad adhesion is independent of nymphal stage, while their tarsal claws display positive allometry and hence disproportionately increasing grasp (mechanical adhesion). By contrast, mouthpart dimensions are weakly correlated with body length, consistent with predictions that these features should reflect preferred host plant characteristics rather than body size. We recommend future studies use the body mass vs length growth curve as a fitness benchmark to study how SLF instar development depends on factors such as hatch date, host plant, temperature, and geographic location, to further understanding of life history patterns that help prevent further spread of this invasive insect.

Effect of two parallel intruders on total work during granular penetrations.

The intrusion of single passive intruders into granular particles has been studied in detail. However, the intrusion force produced by multiple intruders separated at a distance from one another, and hence the effect of their presence in close proximity to one another, is less explored. Here, we used numerical simulations and laboratory experiments to study the force response of two parallel rods intruding vertically into granular media while varying the gap spacing between them. We also explored the effect of variations in friction, intruder size, and particle size on the force response. The total work (W) of the two rods over the depth of intrusion was measured, and the instantaneous velocities of particles over the duration of intrusion were calculated by simulations. We found that the total work done by the intruders changes with distance between them. We observed a peak in W at a gap spacing of ∼3 particle diameters, which was up to 25% greater than W at large separation (>11 particle diameters), beyond which the total work plateaued. This peak was likely due to reduced particle flow between intruders as we found a larger number of strong forces-identified as force chains-in the particle domain at gaps surrounding the peak force. Although higher friction caused greater force generation during intrusion, the gap spacing between the intruders at which the peak total work was generated remained unchanged. Larger intruder sizes resulted in greater total work with the peak in W occurring at slightly larger intruder separations. Taken together, our results show that peak total work done by two parallel intruders remained within a narrow range, remaining robust to most other tested parameters.

Early amphibians evolved distinct vertebrae for habitat invasions.

Living tetrapods owe their existence to a critical moment 360-340 million years ago when their ancestors walked on land. Vertebrae are central to locomotion, yet systematic testing of correlations between vertebral form and terrestriality and subsequent reinvasions of aquatic habitats is lacking, obscuring our understanding of movement capabilities in early tetrapods. Here, we quantified vertebral shape across a diverse group of Paleozoic amphibians (Temnospondyli) encompassing different habitats and nearly the full range of early tetrapod vertebral shapes. We demonstrate that temnospondyls were likely ancestrally terrestrial and had several early reinvasions of aquatic habitats. We find a greater diversity in temnospondyl vertebrae than previously known. We also overturn long-held hypotheses centered on weight-bearing, showing that neural arch features, including muscle attachment, were plastic across the water-land divide and do not provide a clear signal of habitat preferences. In contrast, intercentra traits were critical, with temnospondyls repeatedly converging on distinct forms in terrestrial and aquatic taxa, with little overlap between. Through our geometric morphometric study, we have been able to document associations between vertebral shape and environmental preferences in Paleozoic tetrapods and to reveal morphological constraints imposed by vertebrae to locomotion, independent of ancestry.

Autotomy-induced effects on the locomotor performance of the ghost crab Ocypode quadrata.

The voluntary amputation of an appendage, or autotomy, is an effective defensive mechanism that allows an animal to escape aggressive interactions. However, animals may suffer long-term costs that can reduce their overall fitness. Atlantic ghost crabs (Ocypode quadrata) are one of the fastest terrestrial invertebrates, and regularly lose one or more limbs in response to an antagonist encounter. When running laterally at fast speeds, they adopt a quadrupedal gait using their first and second pairs of legs while raising their fourth, and sometimes the third, pair of legs off the ground. This suggests that some limbs may be more important for achieving maximal locomotor performance than others. The goal of this study was to determine whether the loss of certain limbs would affect running performance more than others, and what compensatory strategies were used. Crabs were assigned to four different paired limb removal treatments or the control group and run on an enclosed trackway in their natural habitat. Ghost crabs were found to adjust stride kinematics in response to limb loss. Loss of the second or third limb pairs caused a reduction in running speed by about 25%, suggesting that the remaining intact limbs were unable to compensate for the loss of either limb, either due to a lack of propulsive forces produced by these limbs or issues stemming from re-coupling limb arrangements. Loss of any of the other limbs had no detectable effect on running speed. We conclude that compensatory ability varies depending on the limb that is lost.

Benefits and limitations of three-dimensional printing technology for ecological research.

BACKGROUND: Ecological research often involves sampling and manipulating non-model organisms that reside in heterogeneous environments. As such, ecologists often adapt techniques and ideas from industry and other scientific fields to design and build equipment, tools, and experimental contraptions custom-made for the ecological systems under study. Three-dimensional (3D) printing provides a way to rapidly produce identical and novel objects that could be used in ecological studies, yet ecologists have been slow to adopt this new technology. Here, we provide ecologists with an introduction to 3D printing. RESULTS: First, we give an overview of the ecological research areas in which 3D printing is predicted to be the most impactful and review current studies that have already used 3D printed objects. We then outline a methodological workflow for integrating 3D printing into an ecological research program and give a detailed example of a successful implementation of our 3D printing workflow for 3D printed models of the brown anole, Anolis sagrei, for a field predation study. After testing two print media in the field, we show that the models printed from the less expensive and more sustainable material (blend of 70% plastic and 30% recycled wood fiber) were just as durable and had equal predator attack rates as the more expensive material (100% virgin plastic). CONCLUSIONS: Overall, 3D printing can provide time and cost savings to ecologists, and with recent advances in less toxic, biodegradable, and recyclable print materials, ecologists can choose to minimize social and environmental impacts associated with 3D printing. The main hurdles for implementing 3D printing-availability of resources like printers, scanners, and software, as well as reaching proficiency in using 3D image software-may be easier to overcome at institutions with digital imaging centers run by knowledgeable staff. As with any new technology, the benefits of 3D printing are specific to a particular project, and ecologists must consider the investments of developing usable 3D materials for research versus other methods of generating those materials.

Limping following limb loss increases locomotor stability.

Although many arthropods have the ability to voluntarily lose limbs, how these animals rapidly adapt to such an extreme perturbation remains poorly understood. It is thought that moving with certain gaits can enable efficient, stable locomotion; however, switching gaits requires complex information flow between and coordination of an animal's limbs. We show here that upon losing two legs, spiders can switch to a novel, more statically stable gait, or use temporal adjustments without a gait change. The resulting gaits have higher overall static stability than the gaits that would be imposed by limb loss. By decreasing the time spent in a low-stability configuration - effectively 'limping' over less-stable phases of the stride - spiders increased the overall stability of the less statically stable gait with no observable reduction in speed, as compared with the intact condition. Our results shed light on how voluntary limb loss could have persisted evolutionarily among many animals, and provide bioinspired solutions for robots when they break or lose limbs.

Vertebrate land invasions-past, present, and future: an introduction to the symposium.

The transition from aquatic to terrestrial habitats was a seminal event in vertebrate evolution because it precipitated a sudden radiation of species as new land animals diversified in response to novel physical and biological conditions. However, the first stages of this environmental transition presented numerous challenges to ancestrally aquatic organisms, and necessitated changes in the morphological and physiological mechanisms that underlie most life processes, among them movement, feeding, respiration, and reproduction. How did solutions to these functional challenges evolve? One approach to this question is to examine modern vertebrate species that face analogous demands; just as the first tetrapods lived at the margins of bodies of water and likely moved between water and land regularly, many extant fishes and amphibians use their body systems in both aquatic and terrestrial habitats on a daily basis. Thus, studies of amphibious vertebrates elucidate the functional demands of two very different habitats and clarify our understanding of the initial evolutionary challenges of moving onto land. A complementary approach is to use studies of the fossil record and comparative development to gain new perspectives on form and function of modern amphibious and non-amphibious vertebrate taxa. Based on the synthetic approaches presented in the symposium, it is clear that our understanding of aquatic-to-terrestrial transitions is greatly improved by the reciprocal integration of paleontological and neontological perspectives. In addition, common themes and new insights that emerged from this symposium point to the value of innovative approaches, new model species, and cutting-edge research techniques to elucidate the functional challenges and evolutionary changes associated with vertebrates' invasion of the land.

Thrash, flip, or jump: the behavioral and functional continuum of terrestrial locomotion in teleost fishes.

Moving on land versus in water imposes dramatically different requirements on the musculoskeletal system. Although many limbed vertebrates, such as salamanders and prehistoric tetrapodomorphs, have an axial system specialized for aquatic locomotion and an appendicular system adapted for terrestrial locomotion, diverse extant teleosts use the axial musculoskeletal system (body plus caudal fin) to move in these two physically disparate environments. In fact, teleost fishes living at the water's edge demonstrate diversity in natural history that is reflected in a variety of terrestrial behaviors: (1) species that have only incidental contact with land (such as largemouth bass, Micropterus) will repeatedly thrash, which can roll an individual downhill, but cannot produce effective overland movements, (2) species that have occasional contact with land (like Gambusia, the mosquitofish, which evade predators by stranding themselves) will produce directed terrestrial movement via a tail-flip jump, and (3) species that spend more than half of their lives on land (like the mudskipper, Periopthalmus) will produce a prone-jump, a behavior that allows the fish to anticipate where it will land at the end of the flight phase. Both tail-flip and prone jumps are characterized by a two-phase movement consisting of body flexion followed by extension-a movement pattern that is markedly similar to the aquatic fast-start. Convergence in kinematic pattern between effective terrestrial behaviors and aquatic fast starts suggests that jumps are an exaptation of a neuromuscular system that powers unsteady escape behaviors in the water. Despite such evidence that terrestrial behaviors evolved from an ancestral behavior that is ubiquitous among teleosts, some teleosts are unable to move effectively on land-possibly due to morphological trade-offs, wherein specialization for one environment comes at a cost to performance in the other. Indeed, upon emergence onto land, gravity places an increased mechanical load on the body, which may limit the maximum size of fish that can produce terrestrial locomotion via jumping. In addition, effective terrestrial locomotor performance may require a restructuring of the musculoskeletal system that directly conflicts with the low-drag, fusiform body shape that enhances steady swimming performance. Such biomechanical trade-offs may constrain which teleost species are able to make the evolutionary transition to life on land. Here, we synthesize the current knowledge of intermittent terrestrial locomotion in teleosts and demonstrate that extant fishes represent an important model system for elucidating fundamental evolutionary mechanisms and defining the physiological constraints that must be overcome to permit life in both the aquatic and terrestrial realms.

Multi-functional foot use during running in the zebra-tailed lizard (Callisaurus draconoides).

A diversity of animals that run on solid, level, flat, non-slip surfaces appear to bounce on their legs; elastic elements in the limbs can store and return energy during each step. The mechanics and energetics of running in natural terrain, particularly on surfaces that can yield and flow under stress, is less understood. The zebra-tailed lizard (Callisaurus draconoides), a small desert generalist with a large, elongate, tendinous hind foot, runs rapidly across a variety of natural substrates. We use high-speed video to obtain detailed three-dimensional running kinematics on solid and granular surfaces to reveal how leg, foot and substrate mechanics contribute to its high locomotor performance. Running at ~10 body lengths s(-1) (~1 m s(-1)), the center of mass oscillates like a spring-mass system on both substrates, with only 15% reduction in stride length on the granular surface. On the solid surface, a strut-spring model of the hind limb reveals that the hind foot saves ~40% of the mechanical work needed per step, significant for the lizard's small size. On the granular surface, a penetration force model and hypothesized subsurface foot rotation indicates that the hind foot paddles through fluidized granular medium, and that the energy lost per step during irreversible deformation of the substrate does not differ from the reduction in the mechanical energy of the center of mass. The upper hind leg muscles must perform three times as much mechanical work on the granular surface as on the solid surface to compensate for the greater energy lost within the foot and to the substrate.

Running on water: Three-dimensional force generation by basilisk lizards.

Water provides a unique challenge for legged locomotion because it readily yields to any applied force. Previous studies have shown that static stability during locomotion is possible only when the center of mass remains within a theoretical region of stability. Running across a highly yielding surface could move the center of mass beyond the edges of the region of stability, potentially leading to tripping or falling. Yet basilisk lizards are proficient water runners, regularly dashing across bodies of water to evade predators. We present here direct measurements of time-averaged force produced by juvenile plumed basilisk lizards (Basiliscus plumifrons) while running across water. By using digital particle image velocimetry to visualize fluid flow induced by foot movement, we show that sufficient support force is generated for a lizard to run across water and that novel strategies are also required to run across a highly yielding surface. Juvenile basilisk lizards produce greatest support and propulsive forces during the first half of the step, when the foot moves primarily vertically downwards into the water; they also produce large transverse reaction forces that change from medial (79% body weight) to lateral (37% body weight) throughout the step. These forces may act to dynamically stabilize the lizards during water running. Our results give insight into the mechanics of how basilisk lizards run across water and, on a broader scale, provide a conceptual basis for how locomotor surface properties can challenge established rules for the mechanics of legged locomotion.

Three-dimensional hindlimb kinematics of water running in the plumed basilisk lizard (Basiliscus plumifrons).

Much of what is known about tetrapod locomotion is based upon movement over solid surfaces. Yet in the wild, animals are forced to move over substrates with widely varying properties. Basilisk lizards are unique in their ability to run across water from the time they hatch to adulthood. Previous studies have developed mechanical models or presented theoretical analyses of running across water, but no detailed kinematic descriptions of limb motion are currently available. The present study reports the first three-dimensional kinematic descriptions of plumed basilisk lizards (Basiliscus plumifrons) running across water, from hatchling (2.8 g) to adult (78 g) size range. Basilisks ran on a 4.6 m-long water track and were filmed with two synchronized high-speed cameras at 250 frames s(-1) and 1/1250 s shutter speed. All coordinates were transformed into three dimensions using direct linear transformation. Seventy-six kinematic variables and six morphological variables were measured or calculated to describe the motion of the hindlimb, but only 32 variables most relevant to kinematic motion are presented here. Kinematic variation among individuals was primarily related to size differences rather than sprint speed. Although basilisk lizards applied some of the same strategies to increase running velocity across water as other tetrapods do on land, their overall kinematics differ dramatically. The feet exhibit much greater medio-lateral excursions while running through water than do those of other lizards while running on land. Also, whereas the hindlimb kinematics of other lizards on land are typically symmetrical (i.e. limb excursions anterior to the hip are of similar magnitude to the limb excursions aft of the hip), basilisks running through water exhibit much greater excursions aft than they do anterior to the hip. Finally, ankle and knee flexion in early stance is a defining feature of a tetrapod step during terrestrial locomotion; yet this characteristic is missing in aquatic basilisk running. This may indicate that the basilisk limb acts primarily as a force producer - as opposed to a spring element - when locomoting on a highly damping surface such as water.