France

Locomotion is a key aspect associated with ecologically relevant tasks for
many organisms, therefore, survival often depends on their ability to perform
well at these tasks. Despite this significance, we have little idea how
different performance tasks are weighted when increased performance in
one task comes at the cost of decreased performance in another. Additionally,
the ability for natural systems to become optimized to perform a
specific task can be limited by structural, historic or functional constraints.
Climbing lizards provide a good example of these constraints as climbing
ability likely requires the optimization of tasks which may conflict with
one another such as increasing speed, avoiding falls and reducing the cost
of transport (COT). Understanding how modifications to the lizard bauplan
can influence these tasks may allow us to understand the relative weighting
of different performance objectives among species. Here, we reconstruct
multiple performance landscapes of climbing locomotion using a 10 d.f.
robot based upon the lizard bauplan, including an actuated spine, shoulders
and feet, the latter which interlock with the surface via claws. This design
allows us to independently vary speed, foot angles and range of motion
(ROM), while simultaneously collecting data on climbed distance, stability
and efficiency. We first demonstrate a trade-off between speed and stability,
with high speeds resulting in decreased stability and low speeds an
increased COT. By varying foot orientation of fore- and hindfeet independently,
we found geckos converge on a narrow optimum of foot angles
(fore 20°, hind 100°) for both speed and stability, but avoid a secondary
wider optimum (fore −20°, hind −50°) highlighting a possible constraint.
Modifying the spine and limb ROM revealed a gradient in performance.
Evolutionary modifications in movement among extant species over time
appear to follow this gradient towards areas which promote speed
and efficiency.

SEB Annual Conference 2022

Using a biologically mimicking climbing robot to explore the performance landscape of climbing in lizards

Discover the art of creating extraordinary science at SEB’s Annual Conference at Le Corum Conference Center     in Montpellier, France from 5 to  8 July 2022.

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

2022 will find 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.
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Please register for the conference by clicking on this link:

https://www.sebiology.org/events/seb-annual-conference-2022/registration.html

The site will be open for registered participants closer to the event.

2022 will find 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

technical paper

The design of robotic manipulators is confronted with a seemingly unavoidable trade-off between the level of flexibility versus strength. Unsurprisingly, nature has already come up with a solution and encapsulated it in a particular group of organisms: the seahorses. A seahorse’s body is completely enclosed in a highly articulated body armour, made of similar and modular bony plates. Yet, the combination of regional variation in this skeletal anatomy and the soft tissue interconnecting the skeletal units provides a rigid, yet controllable and flexible tail. A seahorse tail thereby intriguingly integrates these two seemingly mutually exclusive properties. Although the seahorse can serve as a bio-inspired foundation for designing a novel type of robotic manipulator, its actual design is far from intuitive and hard to do manually. This raises the need for automated design methodologies. One domain, named Evolutionary Robotics, applies evolution as an optimisation technique to provide a holistic perspective to automated robot design. Evolutionary Robotics has already shown its potential in conventional rigid robotics and provided the necessary backbone for the optimisation of more recent alternatives such as soft robotics. Our work lies at the intersection of biology and robotics, as we aim to create a generic evolutionary brain-body co-optimisation framework. Using this framework, we pursue the automated design of a seahorse-tail inspired robotic manipulator. From there on, the framework maintains applicability to other biomimetic experiments, next to providing a testbed for in-silico evolutionary experiments in biology.

Evolutionary co-optimisation of robot morphology and control: toward a seahorse-tail inspired robotic manipulator

The lateral sequence walk is a widespread gait among mammals, but certain groups, such as adult primates and aardvarks, instead employ a diagonal sequence gait. It may be that caudally-shifted centers of mass and large whole-body moments of inertia in the latter groups make diagonal sequence gaits energetically favourable. To test this, we built a simple model of a generalized quadruped in OpenSim, consisting of two-link, four degree-of-freedom legs, and a two-link trunk with a spinal joint. We generate gaits to minimize various measures of effort cost, including torque-rate squared and joint work, by employing recent advances in trajectory optimization with algorithmic differentiation. We show how mass distribution affects gait choice in three dimensions, and compare these results to the gaits of various mammalian groups.

Effect of mass distribution on effort-optimizing gait in a 3D model

Both the teeth and the digestive tract show adaptations that are commonly interpreted in the context of trophic guilds – faunivory, herbivory, and omnivory. Teeth prepare the food for the digestive tract, and dental evolution focuses on increasing durability and functionality of teeth; in particular, size reduction of plant particles is an important preparation for microbial fermentative digestion. In narratives of digestive adaptations, microbes are typically considered service providers especially for herbivorous animals, facilitating digestion. The fact that the majority of herbivorous (and possibly omnivorous) mammals display adaptations to maximize the use of microbes themselves as prey, in terms of harvesting the microbes multiplying in their guts, is less emphasized, and is not reflected in the trophic label ‘herbivory’. Adaptations to maximize the harvest of the microbiome are widespread, and given the expansion of the nutritive niche – as compared to animals that cannot use this prey source – this appears self-evident. Harvesting of microbes occurs either in the form of coprophagy after a separation from indigestible material in the hindgut, by the ‘colonic separation mechanism’, or from a forestomach by a ‘washing mechanism’ that selectively removes fine material, including microbes, to the lower digestive tract. The evolution of this washing mechanism as part of the microbe farming niche opened the opportunity for the evolution of another mechanism that links teeth and guts in an innovative way – the sorting (and cleaning) of not-yet-sufficiently-size-reduced ingesta that is then re-submitted to repeated mastication (rumination), leading to unprecedented chewing and digestive efficiency.

Teeth and the gastrointestinal tract in mammals: when 1 + 1 = 3

Despite copious measuring of highly variable tooth wear patterns in numerous vertebrates, the etiology of dental wear caused by interactions between tooth and food material (incl. dust and grit) is still a matter of intense interdisciplinary debates. During the last decade, central questions regarding the relation between forage properties and the effect of abrasives on dental wear has been tested by new sets of in-vivo as well as in-vitro feeding experiments in mammals, birds and reptiles. In addition, data from recent field observations in primates provide new evidence that variation in feeding behaviors is another key player that is influenced by food geometric and material properties. Yet, these studies include usually highly precise but invasive animal experiments, access to the habitat and in the best-case long-term observations. Here, a comprehensive overview is given based on new insights from these studies and a set of testable tooth wear approximations is compiled. In order to provide a new and less invasive investigation option that combines the outcome of these studies, a new tool to simulate tooth wear during the masticatory process is introduced starting with selected model cases in equids. Simulation outcomes allowed the formulation of biomechanical explanations for the transition of the unworn (primary) occlusal surface into the functional, lateroventrally angulated (secondary) occlusal surface. The simulations are highly generalizable for many vertebrate groups, including possible morphological changes, simulating chewing as well as dental treatment options in a time reduced way.

Vertebrate tooth-grit-food interactions

Nutrition is a complex process of matching multiple and changing nutrient needs to variable and uncertain nutrient supply. Many behavioural and physiological mechanisms evolved to meet this challenge have been identified. However, little is known about how nutritional behaviour and physiology interact to produce an integrated, adapted nutritional phenotype, and how these integrated phenotypes vary with evolutionary and ecological circumstances. In this talk I present a series of studies that have used a framework from nutritional ecology, called nutritional geometry, to examine these issues. Examples span highly controlled laboratory studies of insect to observational studies of primates in the wild. I end by showing how this approach has been used to develop a new understanding of the human obesity epidemic

Towards an integrated understanding of nutritional phenotypes

The nutritional decisions of herbivores are inextricably tied to the thermal environment they experience. This pertains not just to the total energy eaten, but also to the macronutrients from which they choose to get that energy, and to the plant secondary metabolites (PSMs) that complicate the decision. The relationship between thermal physiology and nutritional ecology runs deeper than simply adjusting food intake to meet changes in metabolic rate. I will present results on how temperature-dependent toxicity applies to marsupial folivores ingesting diets high in plant secondary metabolites. Ambient temperature may also influence the mixing of macronutrients to minimise heat generation, and when a plant toxin is included in the diet, these feeding decisions can be further complicated. The addition of a plant secondary metabolite removed the effect of temperature on macronutrient balancing, so it may be that ingesting enough protein to deal with the cost of plant secondary metabolite ingestion overrides the desire to minimise the obligatory thermogenesis of a higher protein diet in warm conditions. Field data collected on koalas fitted with radio collars with microphones will be considered to observe this phenoma in a wild setting. Intake patterns of koalas were indeed influenced by temperature and plant secondary metabolite concentrations of available trees resulting in altered daily and per meal food intake. Temperature can have considerable impact on nutrition, and warming ambient temperatures due to climate change are likely to result in a new challenges for marsupial folivores and other herbivores, particularly those ingesting PSM rich diets.

Temperature-dependent toxicity and macronutrient selection in folivorous marsupials

Gabriella Willan (1), Catherine Williams (1,2), Shreya Rai (3), Arkhat Abzhanov (3), Loïc Kéver (4), Anthony Herrel (4,5), Arsalan Marghoub (6), Mehran Moazen (6), Susan Evans (7), Alex Kirby (8), Matt Vickaryous (1)
1 Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Canada
2 Zoophysiology, Faculty of Natural Science, Aarhus University, Denmark 
3 Department of Life Sciences, Faculty of Natural Sciences, Imperial College, London, UK
4 UMR 7179 MECADEV C.N.R.S/M.N.H.N., Département Adaptations du Vivant, France
5 Evolutionary Morphology of Vertebrates, Ghent University, Gent, Belgium 
6 Department of Mechanical Engineering, University College London, UK
7 Department of Cell and Developmental Biology, University College London, UK
8 Department of Medical Physics and Biomedical Engineering, University College London, UK 

	Osteoderms are bone-rich elements that form within the dermis of various vertebrates including many species of lizard. Among lizards, osteoderms demonstrate variability in size, shape, and body-wide distribution but a detailed comparative assessment of osteoderm microstructure is lacking. Here, we characterize the histological diversity of osteoderms from representative members of the lizard groups Gekkota (geckos), Anguimorpha (anguids, Shinisaurus, helodermatids, varanids), and Scincomorpha (scincids, cordylids, gerrhosaurids). In virtually all lizards, osteoderms are composed primarily of bone, albeit with a heterogenous and often laminated fibrillary organization. Histologically, most osteoderms are dominated by lamellar, woven-fibred and/or Sharpey-fibred bone, although details of the organization and relative contribution of each bone matrix differs between genera. In addition, we found that multiple genera from each major group also develop a highly mineralized, collagen and cell-poor capping tissue – a feature previously restricted to only a handful of species. Singularly, the osteoderm-like elements from the gekkotan Geckolepis entirely lack bone and instead are composed of a plate of collagen topped with mineralized capping tissue. Initial studies of osteoderm development in the lacertid Timon show that specific markers for osteoblast differentiation (Osterix and β-catenin) can be successfully detected surrounding the growing osteoderm, opening possibilities of dissecting whether developmental strategies vary in sync with histological appearance, under drivers such as phylogeny, ecology and function. 





Histological heterogeneity: development and tissue-level diversity of lizard osteoderms

Ossified dermal armor is found across the vertebrate tree of life. Despite bony plates being present in some of the earliest vertebrate ancestors (with dermal armor preceding jaws and even ossified skeletons in the evolution of the group), the ossified armor seen in modern actinopteryiigian fish, frogs, lizards, mammals, crocodiles and turtles appear to be apomorphic, having independently evolved in at least 25 lineages. Squamates—whose very name is derived from their scaly armor— have a particularly complex pattern of armor evolution, with members of 12 extant families possessing some form of osteoderms. These structures strengthen the integument, provide additional ornamentation in the form of spines or keels, and may play a role in calcium sequestration and thermoregulation. This study employs comparative phylogenetic analyses of micro-computed tomography (μCT) datasets to quantify and investigate the diversity of dermal armor across Squamata, with broad sampling in the families that are known to possess osteoderms. Our analysis reveals seven independent origins of osteoderms within the order, with three clades—Cordylidae, Anguidae and egerniine skinks—displaying increased rate-shifts in the distribution and extent of their armor. To better understand the mechanisms generating this variation, we sequenced the transcriptome of mammalian osteoderms and identified several pathways known to be involved in the growth of endochondral bone. Ongoing transcriptomic analysis of osteoderm development and selection analysis within the three rate-shifted squamates lineages hints at a universal mechanism for the repeated re-evolution of dermal armor in amniotes.

Scaled up defenses: Patterns and drivers of dermal armor in lizards

Biomechanical behaviour of lizard osteoderms and skin under external loading
Loïc Kéver1, Olivier Damien2, Arsalan Marghoub3, Mehran Moazen3, Susan Evans3, Matthew K. Vickaryous 4, Arkhat Abzhanov5, Anthony Herrel 1,6 
1National Museum of Natural History, France
2CONACyT Autonomous University of Baja California Sur, Mexico
3University College London, UK
4University of Guelph, Canada
5Imperial College London, UK
6Ghent University, Belgium
Dermal bony plates also known as osteoderms are present in several distantly related vertebrate taxa and they are particularly common and diverse among extant lizards. Lizard osteoderms have classically been considered to be protective elements against predator attacks. However, empirical data supporting this hypothesis are scant and one of the basic questions pertaining to their diversity has never been addressed: are there interspecific differences in the deformation of lizard osteoderms under external loading? We sampled formalin fixed specimens from eleven species of lizards with osteoderms of different morphologies, instrumented one of the temporal osteoderms with a rectangular rosette strain gauge and loaded different areas of their head to better understand the mechanical responses of osteoderms to loading. Our goals were to 1) test whether loadings applied in different locations of the head (including on the instrumented osteoderm) generated strains in the instrumented osteoderm, 2) explore whether species differed in the relative stiffness of their osteoderm and skin and 3) provide insights into the morphological features and patterns of organization associated with variation in stiffness. We show that loading neighboring osteoderms can generate large strains in the instrumented osteoderm. Moreover, despite a large overlap between some species, the strains recorded showed interspecific differences in magnitude. Smaller strains were recorded in species with relatively thick osteoderms including Heloderma suspectum, H. horridum and Tiliqua rugosa. 






Biomechanical behaviour of lizard osteoderms and skin under external loading

Osteoderms (ODs) are calcified hard tissues that develop directly within the dermis of many lizards. They can be found all over the body, or only on some parts of the body (like the head, where intimate connections with the bones of the skull are common). OD’s main role has been commonly considered to be mainly protective, however there are some evidences that they can also have other functions. We investigated the potential role of calvarial ODs in the biomechanics of feeding. Two lizard species were selected: one that has ODs all over its head (Tiliqua scincoides), and one that has ODs only over its temporal region (Timon lepidus). Several experiments were performed to quantify the level of principal strains on one of the temporal ODs while measuring bite force. At the same time, finite element models of both lizards were developed based on micro-CT images. After being validated against the experimental measurements, finite element models were used to further investigate several hypothetical scenarios regarding the function of the ODs, such as having no ODs. Our results show that ODs can have a significant role in reducing the level of strain across the skull during feeding. Perhaps the possession of cranial ODs can enhance the biting performance of some lizards.

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Using a biologically mimicking climbing robot to explore the performance landscape of climbing in lizards

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