France

Animal-legged locomotion is the result of tight interaction of biomechanics and neural control. Special focus has been set on multi-articulate coupling mechanisms; muscle-tendon networks that act simultaneously at multiple joints. Multi-articulate mechanisms are associated with joint movement coordination, reduction of forces and metabolic cost of transport, and even power amplification. Yet most multi-articulate configurations remain without sufficient functional explanation. In this presentation I will describe our latest projects in human- and bird-like locomotion, where we develop mechanical models (legged robots) featuring complex multi-articulate mechanisms. Our robots allow us to test the interaction of a complex leg design, with integrated neuromuscular-inspired control, and while locomotion in the physical world. Robots allow collecting rich biomechanical data from within: we measure joint angles, forces and torques, and electrical power consumption of motors. Already with simple control (feedforward) and a high degree of under-actuation (spring-tendon based function), we observe the emergence of natural-looking gaits. Specifically, our bird-inspired robot demonstrates a self-engaging and disengaging parallel leg elasticity that is switched through foot-ground contact. This is the first available proof where mechanical coupling between joint kinematics and function replaces neural coupling, to a large amount. We show that complex leg trajectories and leg function (stance leg, swing leg, and transitions) are established almost entirely through multi-articulate mechanical coupling, and with base-line control that mimics muscles isometric mode. We also show that our leg mechanism is theoretically scalable to dynamic loads and sizes of the largest animals ever roaming this world.

SEB Conference 2022

Mechanical joint coupling in an avian inspired legged robot

technical paper

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2022 found over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France.

We all assume that physiological plasticity is advantageous because it allows organisms to respond to diverse or changing conditions. However, can being too plastic actually be detrimental? Malagasy common tenrecs, Tenrec ecaudatus, have many plesiomorphic traits and may represent an ancestral placental mammal. The physiology of these tenrecs is extraordinary. Tenrec body temperature (Tb) may approximate ambient temperature to as low as 12°C even when tenrecs are fully active. Conversely, tenrecs can hibernate with Tb of 28°C. During the active season, resting oxygen consumption may vary 25-fold with little or no change in Tb. We found that tenrecs essentially place homeostatic processes like kidney function on hold when metabolism is low much like a hibernator. In contrast to Boreoeutherian hibernators like ground squirrels, tenrecs are surprisingly intolerant of extremes in ambient temperature (&lt;8 or &gt;34°C). While plasticity may confer numerous energetic advantages in consistently moderate environments, environmental extremes may have limited the success and distribution of plastic basal mammals.

Physiological plasticity and the evolution of environmental tolerance in the common tenrec.

Thermal acclimation of some temperate fish species can stimulate changes in the physiological capacity of the heart. This is due to modifications to the active and passive properties of the myocardium. These modifications include changes in the Ca2+ sensitivity of the contractile element and to the amount and composition of myocardial collagen. Interestingly, this response is sex specific. Using cultured cardiac fibroblasts, from male and female trout, we have been working to determine how a change in physiological temperature leads to a change in deposited collagen. This work has integrated experiments examining the effect of biomechanical stretch, TGF-B, testosterone, angiotensin II, and microRNAs on the cell signalling pathways that regulate collagen deposition and turnover. We propose that increased biomechanical stimulation of the heart, caused by an increase in vascular resistance and blood viscosity, triggered by a decrease in physiological temperature, activates mitogen-activated protein kinase signalling pathways through stimulation of mechanosensitive membrane proteins and the release of TGF-B. The end result is changes in the expression of gene transcripts and cellular proteins that support an increase in collagen deposition including matrix metalloproteinases, and collagen monomers. It was also found that cellular pathways associated with the deposition of collagen are stimulated by physiologically relevant levels of testosterone, and that these can be reversed through the expression of microRNA-29b. These studies suggest that the phenotypic response of the heart to a change in environmental temperature is under complex regulatory control that is sex specific.  

Mechanotransduction and the regulation of collagen deposition by trout cardiac fibroblasts during thermal acclimation

Climate change is increasing the frequency of heat extremes, and therefore the overheating risk of wildlife. Latitudinal patterns of overheating risk are expected, and many analyses have concluded that tropical organisms are at greater risk because they live in environments closer to their thermal limits (i.e., have lower warming tolerance).  Overheating risk should be dictated by interactions between mean habitat temperature, habitat temperature variation, organismal heat tolerance limits, and tolerance plasticity. How these factors collectively dictate overheating risk and responses to warming requires greater scrutiny, however. To address this issue, we combined data on physiological heat tolerance, heat tolerance plasticity, and temporally fine-scaled operative thermal environments for terrestrial ectotherm populations across a 120° latitudinal range. Consistent with previous research, we find that tropical organisms have lower warming tolerance than temperate organisms based on mean thermal conditions. However, temperate taxa currently have greater overheating risk than tropical taxa and will experience greater increases in overheating risk with warming because of differences in thermal variation between the regions. These results show that characterizing thermal variation and incorporating it into predictions of global change responses is critical, as doing so can alter predictions about global patterns of vulnerability to global change. 

How temperature variation drives latitudinal differences in ectotherm sensitivity to heat extremes

Although there is much controversy regarding the effects of ocean acidification on the behaviour of marine fish, marine invertebrates have been much less studied. Dungeness crabs, Metacarcinus magister, are found on the West coast of North American and their commercial and recreational fishery is one of the most valuable fishery in the Pacific region, with annual revenues of $220 million. Dungeness crabs live in the deep-sea and enter intertidal areas in order to find food. Previous studies have found that they routinely encounter pCO2 concentrations of up to 1300 µatm in their coastal habitat and that these levels of ocean acidification can affect larval development and mechanoreceptors. We exposed adult Dungeness crabs to control (600 µatm) and high pCO2 (1300 µatm) for 10 days and assessed their behaviour and physiology using electrophysiology, gene expression, immunohistochemistry and transmission electron microscopy of their olfactory organs, the antennules. Dungeness crabs exposed to high pCO2 had a 25% lower rate of antennular flicking rate in response to all concentrations of cadaverine, a food cue, than crabs exposed to control pCO2. No differences in antennular flicking were found in response to ammonium chloride, a deterant, however there was a large increase in the expression of Rh proteins that function as ammonia transporters in their antennules indicating a potential compensatory mechanism. We propose that a more holistic approach to the overall question of the effects of ocean acidification needs to be taken at multiple levels of biological organization and using environmentally relevant odorants and concentrations.

The effects of simulated ocean acidification on the behaviour and physiology of the economically important Dungeness crab, Metacarcinus magister

A central prediction of recent climate change models is that there will be an increase in thermal unpredictability and heatwave events. Sessile intertidal organisms experience a high degree of thermal unpredictability due to combined effects of solar radiation and tidal movement. How thermal unpredictability operates in microhabitats with different media, such as tidepool (aquatic) or tidally exposed (aerial) environments is poorly understood, especially when coupled with other important determinants of performance, such as food availability. Understanding how these factors interact to influence performance is essential towards understanding the effects of climate change on intertidal communities. We examined how acclimation to different levels of thermal predictability (no, predictable, unpredictable) with high and low food availability shape performance during a three-day heatwave in Mytilus californianus in two microhabitat treatments: tidepool and tidally exposed. During the heatwave, mussels were warmed to 35C each daytime low tide in their respective medium (water or air). Tissues samples were taken for biochemical analyses the day before, each day during, and the day after the heatwave. We found that microhabitat was the strongest driving factor for shaping physiological performance in Mytilus californianus. Food availability played a larger role in shaping performance in tidally exposed mussels, and the influence of thermal predictability depended on heatwave day. Our results suggest that the predicted increases in heatwave events and thermal unpredictability from climate change will not have a uniform effect in different microhabitats, which could have severe consequences for intertidal community and composition.

Heatwaves in the intertidal: how microhabitat, thermal unpredictability, and food availability shape physiological performance in mussels

Fluid mechanics is an important tool for understanding the biology and ecology of marine life. A major challenge in studying how microscopic aquatic organisms function in their natural habitats is integrating the different scales at which critical physical and biological processes occur. How can we make large-scale field measurements and models that include the behaviors and physical features of real organisms? Conversely, how can we design small-scale experiments to measure those biological factors under hydrodynamic conditions that reflect what the organisms actually experience in the large- scale ocean? I will discuss examples of some of the approaches we have used to span different scales in our studies of how the interaction between the locomotion of microscopic organisms and the turbulent, wave-driven water flow around them determines how they move through the environment. We studied how the microscopic larvae of bottom-dwelling marine animals navigate to suitable habitats on the sea floor by combining field flow measurements in marine environments with flume studies, experiments in fluidic devices, experiments with dynamically-scaled physical models, and agent-based models of different locomotory strategies in measured turbulent flow fields. 

Locomoting in a turbulent environment: Ways to study microscale processes in a large-scale ocean

Dynamic soaring harvests energy from a spatiotemporal wind gradient, allowing albatrosses to glide over vast distances. However, its use is challenging to demonstrate empirically, and has yet to be confirmed in other seabirds. We investigate how flap-gliding Manx Shearwaters optimize their flight for dynamic soaring. We do so by deriving a new metric, the horizontal wind effectiveness, that quantifies how effectively flight harvests energy from a shear layer. We evaluate this metric empirically for fine-scale trajectories reconstructed from bird-borne video data using a simplified flight dynamics model. We find that the birds’ undulations are phased with their horizontal turning to optimize energy harvesting. We also assess the opportunity for energy harvesting in long-range, GPS-logged foraging trajectories, and find that Manx Shearwaters optimize their flight to increase the opportunity for dynamic soaring during favourable wind conditions. Our results show how small-scale dynamic soaring impacts large-scale Manx Shearwater distribution at sea.




Optimisation of dynamic soaring in a flap-gliding seabird impacts its distribution at sea

Plants grow continuously throughout their life cycle. Plant cells within meristems- the actively growing regions at the tips of shoots and roots- undergo repeated division cycles to provide the cells needed for growth.  Division must be coordinated with cell growth because cells within a meristem maintain their average size when conditions are constant. However in response to changes in environmental conditions or in different genotype backgrounds, cell size is reset to a new average. Using combined modeling and imaging approaches, we have been studying the relationship between cell size control and cell cycle progression and we find evidence for two cell size control points within the Arabidopsis cell cycle at both the G1/S phase and G2/M phase boundaries, and that the adaptation of cell size to changing conditions appears to be an emergent property of the overall system of cell cycle control.

Decisions, decisions, decisions: Cell division and cell size control in Arabidopsis.

Spatial transcriptomics is a new technology for capturing and mapping whole transcriptome gene expression on histological sections close to single-cell resolution. This technique allows researchers to gain insight into organs’ molecular morphology, as well as regional changes in gene expression during disease progression, development, and evolution. We apply this technique to the light-absorbing retina within the developing mouse eye. The mouse retina lacks internal blood vessels at birth but develops these structures over the first four weeks, which changes the diffusion dynamics for O2 and nutrients and affects the metabolic phenotypes of the retinal cells. Using spatial transcriptomics, we have generated spatial molecular atlases of the retina and extracted combined information on nutrient diffusion distances and whole transcriptome gene expression. With this technique, we can now provide a new quantitative understanding of the cellular responses to changes in O2 and nutrient availabilities during organ development. 

Tracing the development of the eye using spatial transcriptomics

We have developed a super resolution cryo-fluorescence optical microscope in order to perform correlative imaging with the cryo Soft X-ray Tomography (SXT) beamline at the Diamond Light Source. Using Structured Illumination Microscopy (SIM) the microscope generates images at almost twice the achievable conventional optical resolution in 3 dimensions. By reducing the gap between the resolution in optical fluorescence images and the X-ray tomography significantly more information can be extracted from the correlated image sets. However, there are many barriers to reliably produce high quality fluorescence images of 3D samples in cryo while preserving the sample integrity. The sample must be kept cold, condensation must be avoided on both the sample and the optics, sample position must be highly stable and light must be collected at as high a numerical aperture as possible. We have open source control software providing a simple interface with high speed control of the wide range of hardware involved as well as a high degree of flexibility to provide a range of experimental options. Despite, these challenges we have been able to reliably produce images with sub 200 nm resolution and achieve correlative alignment at sub 100 nm. The CryoSIM and cryoSXT instruments are available for open access via peer revied applications.

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