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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.

SEB Annual Conference 2022

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

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

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

Biological armours, unlike architectural skins, face a curious structural paradox, in that they must continue to provide protection and support even as the structure they cover grows. (This is akin to the challenge of keeping fast-growing toddlers clothed.) Tessellated armours have evolved multiple times in animals as solutions for this problem, the gaps between tiles creating zones for activity (e.g. movement, growth), albeit perhaps at the expense of overall armour integrity. Our extended workgroup uses biological tessellations as model systems to explore form-function relationships and constraints in tissues, factors regulating mineralisation and growth, and material properties of biological composites. I discuss these functional morphological concepts in the context of biological tilings, drawing on examples from diverse systems and size scales, to offer perspectives on growth-mechanics trade-offs (both inside and outside the body), while reflecting on the value of cross-disciplinary bridges to invigorate the study of biological tissues.

Tales of tiled tissue trade-offs: Biological tessellations as architectural balance acts of growth and mechanics

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.

Calvarial osteoderms and their potential role in Lizard feeding biomechanics

Humans are drawn to patterns and hierarchies in nature, mimicking them particularly in decoration and architecture. Natural patterns, however, are never purely aesthetic and, since evolution works towards optimising a variety of factors simultaneously, natural structural systems are intrinsically multi-functional. In this study, we examine and classify biological tessellations or ‘tilings’: rather than starting from a specific anatomical feature or function, we focus on this unexpectedly ubiquitous natural structural motif and show its prevalence and function across the Tree of Life. Drawing on more than 100 examples, from viruses to vertebrates and over 8 orders of magnitude in size scale, we construct a hierarchical system of classification for this diverse, but largely unexamined trope in biological patterning. We detail our novel classification scheme, which captures tessellation morphology through a set of seven variables, detailing the material, form and function of tiled natural architectures. Examining the relationships of variables in a Multiple Correspondences Analysis, we observe broad structural correlations across and between taxonomic groups (e.g. materials common to particular taxonomic groups, tiling features that tend to co-occur), but also capture links between anatomical characteristics and particular functions (e.g. tiling morphologies associated with structural support or mobility). Our resulting collection of natural tessellations and its companion website are multidisciplinary meeting points, offering new windows for exploring selective pressures and trade-offs that shape anatomical evolution in nature, for interpreting man-made tessellations in history, and for guiding novel approaches in design and architecture.

Tessellated Material Systems: A Catalogue to Explore the Multifunctionality and Biodiversity of a Universal Motif

Impacts of changing environment on fitness are mediated by changes in energy acquisition and allocation within an organism. Maintenance energy costs constitute a substantial part of individual's energy budget. Therefore, individual variation in standard metabolic rate plays an important role in understanding how ectotherms adapt to environmental changes. Despite considerable efforts in this area, many issues remain unresolved. In this talk, I (1) introduce the theoretical framework for the link between environmental change, individual metabolic variation and fitness, (2) present the latest findings in this field, and (3) highlight priorities for future research.

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

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