Osteoderms as calcium reservoirs: Insights from the lizard Ouroborus cataphractus.

The functional significance of osteoderms-bony elements embedded in the dermis-remains a topic of much debate. Although many hypotheses have been put forward in the past, the idea that osteoderms can serve as calcium reservoirs has received little experimental attention thus far. In this study, we use micro-computed tomography to investigate inter- and intrasexual variation in osteoderm density in the viviparous lizard Ouroborus cataphractus and conduct histochemical analyses to unravel the potential mechanism involved in mineral resorption from the osteoderms. Our results show that females have denser, more compact osteoderms than males of similar body sizes, regardless of the season during which they were collected and their reproductive state. Furthermore, a histochemical study demonstrates the presence of mononucleated TRAP-positive cells in the vascular canals of the osteoderms. Based on the findings of this study, we suggest that the mineral storage hypothesis merits further attention as a candidate explanation for osteoderm evolution.

Intraspecific competition: A missing link in dermal armour evolution?

Predation is widely regarded as an important selective force in the evolution and maintenance of dermal armour; yet, the basic premise that predation and armour are strongly linked to each other has proven to be difficult to assess. In this concept, I put forward the fighting-advantage hypothesis, the view that aggressive interactions with conspecifics, not predation, might have been a key selective pressure in the evolution of dermal armour. Considering intraspecific competition as a potential explanation could not only reveal previously overlooked aspects of the functional and evolutionary significance of dermal armour, but also advance the emerging field of biomimetics in which such knowledge forms the starting point of technological innovation.

On dangerous ground: the evolution of body armour in cordyline lizards.

Animal body armour is often considered an adaptation that protects prey against predatory attacks, yet comparative studies that link the diversification of these allegedly protective coverings to differential predation risk or pressure are scarce. Here, we examine the evolution of body armour, including spines and osteoderms, in Cordylinae, a radiation of southern African lizards. Using phylogenetic comparative methods, we attempt to identify the ecological and environmental correlates of body armour that may hint at the selective pressures responsible for defensive trait diversification. Our results show that species inhabiting arid environments are more likely to possess elaborated body armour, specifically osteoderms. We did not find any effect of estimated predation pressure or risk on the degree of body armour. These findings suggest that body armour might not necessarily evolve in response to direct interactions with predators, but rather as a result of increased habitat-mediated predation risk. Furthermore, we discuss the possibility that osteoderms might have been shaped by factors unrelated to predation.

Has snake fang evolution lost its bite? New insights from a structural mechanics viewpoint.

Venomous snakes-the pinnacle of snake evolution-are characterized by their possession of venom-conducting fangs ranging from grooved phenotypes characterizing multiple lineages of rear-fanged taxa to tubular phenotypes present in elapids, viperids and atractaspidines. Despite extensive research, controversy still exists on the selective pressures involved in fang phenotype diversification. Here, we test the hypothesis that larger fangs and consequently a shift to an anterior position in the maxilla evolved to compensate for the costs of structural changes, i.e. higher stress upon impact in tubular fangs compared to grooved fangs. Direct voxel-based stress simulations conducted on high-resolution µCT scans, analysed within a phylogenetic framework, showed no differences in stress distribution between the three fang phenotypes, despite differences in (relative) fang length. These findings suggest that additional compensatory mechanisms are responsible for the biomechanical optimization and that fang length might instead be related to differential striking behaviour strategies.

What doesn't kill you might make you stronger: functional basis for variation in body armour.

1. Predation has been proposed to be a selective agent in the evolution of morphological antipredator strategies in prey. Among vertebrates, one of the morphological traits that evolved multiple times is body armour, including carapaces, thickened keratinized scales and plates of dermal bone. 2. It has been generally assumed that body armour provides protection against a predatory attack; yet, few explicit tests of the hypothesis exist. Cordylidae, a relatively small family of southern African lizards, show considerable variation in the degree of body armour. Hence, this family provides an opportunity to test the hypothesis that body armour serves as protection against predators. 3. Experiments were conducted to test whether the bite forces of four species of mammalian predators were high enough to penetrate the skins of Karusasaurus polyzonus, Namazonurus peersi, Cordylus cordylus and Cordylus macropholis, as well as those of Ouroborus cataphractus individuals originating from three localities that differed in their predator diversity. Furthermore, histological techniques were used to test whether variation in skin toughness was associated with concomitant changes in the degree of epidermal (i.e. ß-keratin) and dermal (i.e. osteoderm) armour. 4. The skin toughness values for four out of five cordylid lizards tested in this study were well below the bite forces of the mammalian predators. In contrast, the thick osteoderms in the dermis of O. cataphractus can withstand bites from several mongoose species. However, the significant variation in body armour that is present between the three populations of O. cataphractus does not seem to be related to predator diversity. 5. It is concluded that body armour can serve as protection against predation in O. cataphractus, but that alternative selection pressures, such as thermoregulation or predation by snakes, presumably underlie variation in defensive morphology in the other cordylid lizards.

Biomimethics: a critical perspective on the ethical implications of biomimetics in technological innovation.

Biomimetics, bioinspiration, biomimicry, and related nature-inspired activities-collectively known as biom*-are witnessing an unprecedented surge in popularity, as they offer unparalleled opportunities for technological advancement, innovation, and sustainable development. The growing prevalence of biom*, however, has sparked moral debates regarding their approaches, emphasizing the need for universally applicable ethical guidelines that can effectively guide practitioners in their work. In this perspective, we outline some of the moral, ethical, and legal challenges associated with biom*, particularly the scientific discipline of biomimetics, focusing on various issues surrounding our motivations for pursuing these approaches, the valuation of nature within them, and regulations in the commercialization of biological knowledge. By highlighting the challenges inherent in biom*, this perspective aims to empower practitioners in the field to make informed decisions and take purposeful action. Specific recommendations are provided to guide them in choosing the right course of action for the right reasons.

Chromosome-Level Genome Assembly of the Cape Cliff Lizard (Hemicordylus capensis).

Squamates represent a highly diverse and species-rich vertebrate group that is remarkably understudied from a genomic perspective. A scarcity of genomic data is particularly evident for scincomorph lizards, which encompass over 10% of all living squamates, and for which high-quality genomic resources are currently lacking. To address this knowledge gap, we present the first chromosome-level reference genome for this group, generated from a male Cape cliff lizard (Hemicordylus capensis), using highly accurate PacBio HiFi long-read sequencing data, long-range Omni-C chromosomal conformation capture data and transcriptomic data for annotation. The rHemCap1.1 genome assembly spans 2.29 Gb, with a scaffold N50 of 359.65 Mb, and includes 25,300 protein-coding genes, with a BUSCO completeness score of 95.5% (sauropsida_odb10). We have generated the most contiguous and complete chromosome-level squamate reference genome assembly publicly available to date. Furthermore, we used short-read resequencing of 35 males and females and applied a differential coverage approach to infer the sex-determination system of the species, which was previously unknown. Our results suggest this species has XX/XY sex chromosomes, representing the first evidence of sex determination in the family Cordylidae. This reference genome will help to establish this species as an evolutionary model for studying variation in body armor, a key trait in cordylids and other squamate groups. Lastly, this is the first squamate reference genome from a continental African species and, as such, represents a valuable resource not only for further evolutionary research in cordylids but also in closely related groups.

Looking deep into nature: A review of micro-computed tomography in biomimicry.

Albert Einstein once said "look deep into nature, and then you will understand everything better". Looking deep into nature has in the last few years become much more achievable through the use of high-resolution X-ray micro-computed tomography (microCT). The non-destructive nature of microCT, combined with three-dimensional visualization and analysis, allows for the most complete internal and external "view" of natural materials and structures at both macro- and micro-scale. This capability brings with it the possibility to learn from nature at an unprecedented level of detail in full three dimensions, allowing us to improve our current understanding of structures, learn from them and apply them to solve engineering problems. The use of microCT in the fields of biomimicry, biomimetic engineering and bioinspiration is growing rapidly and holds great promise. MicroCT images and three-dimensional data can be used as generic bio-inspiration, or may be interpreted as detailed blueprints for specific engineering applications, i.e., reverse-engineering nature. In this review, we show how microCT has been used in bioinspiration and biomimetic studies to date, including investigations of multifunctional structures, hierarchical structures and the growing use of additive manufacturing and mechanical testing of 3D printed models in combination with microCT. The latest microCT capabilities and developments which might support biomimetic studies are described and the unique synergy between microCT and biomimicry is demonstrated. STATEMENT OF SIGNIFICANCE: This review highlights the growing use of X-ray micro computed tomography in biomimetic research. We feel the timing of this paper is excellent as there is a significant growth and interest in biomimetic research, also coupled with additive manufacturing, but still no review of the use of microCT in this field. The use of microCT for structural biomimetic and biomaterials research has huge potential but is still under-utilized, partly due to lack of knowledge of the capabilities and how it can be used in this field. We hope this review fills this gap and fuels further advances in this field using microCT.

A new Nucras Gray, 1838 (Squamata: Lacertidae) from the Strandveld of the Western Cape, South Africa.

A striking new sandveld lizard of the Nucras tessellata group is described from the Lambert's Bay Strandveld of the Western Cape Province, South Africa. It is sister to the clade N. livida + N. tessellata, and is phenetically most similar to N. tessellata, from which it differs in its more elongate body and possibly increased number of presacral vertebrae and patternless orange dorsal coloration. The form elegans, described as a species by Andrew Smith (1838), but treated as an infrasubspecific variant by Broadley (1972), also exhibits weak patterning, but is likely a regional color variant. Nucras aurantiaca sp. nov. is the ninth member of the genus found in southern Africa. Its discovery in the well-collected coastal Western Cape suggests that further herpetofaunal surveys are needed in this region, which is threatened by agricultural activity and tourism-related development.

Snake fangs: 3D morphological and mechanical analysis by microCT, simulation, and physical compression testing.

This Data Note provides data from an experimental campaign to analyse the detailed internal and external morphology and mechanical properties of venomous snake fangs. The aim of the experimental campaign was to investigate the evolutionary development of 3 fang phenotypes and investigate their mechanical behaviour. The study involved the use of load simulations to compare maximum Von Mises stress values when a load is applied to the tip of the fang. The conclusions of this study have been published elsewhere, but in this data note we extend the analysis, providing morphological comparisons including details such as curvature comparisons, thickness, etc. Physical compression results of individual fangs, though reported in the original paper, were also extended here by calculating the effective elastic modulus of the entire snake fang structure including internal cavities for the first time. This elastic modulus of the entire fang is significantly lower than the locally measured values previously reported from indentation experiments, highlighting the possibility that the elastic modulus is higher on the surface than in the rest of the material. The micro-computed tomography (microCT) data are presented both in image stacks and in the form of STL files, which simplifies the handling of the data and allows its re-use for future morphological studies. These fangs might also serve as bio-inspiration for future hypodermic needles.

Analyzing nature's protective design: The glyptodont body armor.

Many animal species evolved some form of body armor, such as scales of fish and bony plates or osteoderms of reptiles. Although a protective function is often taken for granted, recent studies show that body armor might comprise multiple functionalities and is shaped by trade-offs among these functionalities. Hence, despite the fact that natural body armor might serve as bio-inspiration for the development of artificial protective materials, focussing on model systems in which body armor serves a solely protective function might be pivotal. In this study, we investigate the osteoderms of Glyptotherium arizonae, an extinct armadillo-like mammal in which body armor evolved as protection against predators and/or tail club blows of conspecifics. By using a combination of micro-computed tomography, reverse-engineering, stress simulations and mechanical testing of 3D printed models, we show that the combination of dense compact layers and porous lattice core might provide an optimized combination of strength and high energy absorption.

Functional trade-off between strength and thermal capacity of dermal armor: Insights from girdled lizards.

The presence of dermal armor is often unambiguously considered the result of an evolutionary predator-prey arms-race. Recent studies focusing predominantly on osteoderms - mineralized elements embedded in the dermis layer of various extant and extinct vertebrates - have instead proposed that dermal armor might exhibit additional functionalities besides protection. Multiple divergent functionalities could impose conflicting demands on a phenotype, yet, functional trade-offs in dermal armor have rarely been investigated. Here, we use high-resolution micro-computed tomography and voxel-based simulations to test for a trade-off between the strength and thermal capacity of osteoderms using two armored cordylid lizards as model organisms. We demonstrate that high vascularization, associated with improved thermal capacity might limit the strength of osteoderms. These results call for a holistic, cautionary future approach to studies investigating dermal armor, especially those aiming to inspire artificial protective materials.

Laboratory x-ray micro-computed tomography: a user guideline for biological samples.

Laboratory x-ray micro-computed tomography (micro-CT) is a fast-growing method in scientific research applications that allows for non-destructive imaging of morphological structures. This paper provides an easily operated "how to" guide for new potential users and describes the various steps required for successful planning of research projects that involve micro-CT. Background information on micro-CT is provided, followed by relevant setup, scanning, reconstructing, and visualization methods and considerations. Throughout the guide, a Jackson's chameleon specimen, which was scanned at different settings, is used as an interactive example. The ultimate aim of this paper is make new users familiar with the concepts and applications of micro-CT in an attempt to promote its use in future scientific studies.

Evolutionary morphology of the lizard chemosensory system.

Foraging mode plays a pivotal role in traditional reconstructions of squamate evolution. Transitions between modes are said to spark concerted changes in the morphology, physiology, behaviour, and life history of lizards. With respect to their sensory systems, species that adopt a sit-and-wait strategy are thought to rely on visual cues primarily, while actively hunting species would predominantly use chemical information. The morphology of the tongue and the vomeronasal-organs is believed to mirror this dichotomy. Still, support for this idea of concerted evolution of the morphology of the lizard sensory system merely originates from studies comparing only a few, distantly related taxa that differ in many aspects of their biology besides foraging mode. Hence, we compared vomeronasal-lingual morphology among closely related lizard species (Lacertidae). Our findings show considerable interspecific variation indicating that the chemosensory system of lacertids has undergone substantial change over a short evolutionary time. Although our results imply independent evolution of tongue and vomeronasal-organ form, we find evidence for co-variation between sampler and sensor, hinting towards an 'optimization' for efficient chemoreception. Furthermore, our findings suggest species' degree of investment in chemical signalling, and not foraging behaviour, as a leading factor driving the diversity in vomeronasal-lingual morphology among lacertid species.

Author Correction: Evolutionary morphology of the lizard chemosensory system.

A correction to this article has been published and is linked from the HTML version of this paper. The error has not been fixed in the paper.

Enemy at the gates: Rapid defensive trait diversification in an adaptive radiation of lizards.

Adaptive radiation (AR), the product of rapid diversification of an ancestral species into novel adaptive zones, has become pivotal in our understanding of biodiversity. Although it has widely been accepted that predators may drive the process of AR by creating ecological opportunity (e.g., enemy-free space), the role of predators as selective agents in defensive trait diversification remains controversial. Using phylogenetic comparative methods, we provide evidence for an "early burst" in the diversification of antipredator phenotypes in Cordylinae, a relatively small AR of morphologically diverse southern African lizards. The evolution of body armor appears to have been initially rapid, but slowed down over time, consistent with the ecological niche-filling model. We suggest that the observed "early burst" pattern could be attributed to shifts in vulnerability to different types of predators (i.e., aerial versus terrestrial) associated with thermal habitat partitioning. These results provide empirical evidence supporting the hypothesis that predators or the interaction therewith might be key components of ecological opportunity, although the way in which predators influence morphological diversification requires further study.

Some Like It Hot: Camera Traps Unravel the Effects of Weather Conditions and Predator Presence on the Activity Levels of Two Lizards.

It is generally assumed that favourable weather conditions determine the activity levels of lizards, because of their temperature-dependent behavioural performance. Inactivity, however, might have a selective advantage over activity, as it could increase survival by reducing exposure to predators. Consequently, the effects of weather conditions on the activity patterns of lizards should be strongly influenced by the presence of predators. Using remote camera traps, we test the hypothesis that predator presence and weather conditions interact to modulate daily activity levels in two sedentary cordylid lizards, Karusasaurus polyzonus and Ouroborus cataphractus. While both species are closely related and have a fully overlapping distribution, the former is a fast-moving lightly armoured lizard, whereas the latter is a slow-moving heavily armoured lizard. The significant interspecific difference in antipredator morphology and consequently differential vulnerability to aerial and terrestrial predators, allowed us to unravel the effects of predation risk and weather conditions on activity levels. Our results demonstrate that K. polyzonus is predominantly active during summer, when ambient temperatures are favourable enough to permit activity. In contrast, a peak in activity during spring was observed in O. cataphractus, with individuals being inactive during most of summer. While favourable weather conditions had a strong effect on the activity levels of K. polyzonus, no such relationship was present in O. cataphractus. Contrary to our hypothesis, the presence of terrestrial predators does not seem to affect daily activity levels or alter the influence of weather conditions on activity levels. We conclude that inactivity in O. cataphractus appears to be related to seasonal differences in vulnerability to predators, rather than the presence of predators, and highlight the importance of additional selective pressures, such as food abundance, in determining the species' activity levels.

Generation gland morphology in cordylid lizards: an evolutionary perspective.

To elucidate the functional significance of the three distinct types of generation glands that have been identified among cordylid lizards, we mapped gland type to the terminal taxa in the most recent phylogenetic tree for the Cordylidae. We used the phylogenetic programme Mesquite and applied the principle of parsimony to infer character states for the ancestral nodes in the tree. For those species where information on gland type was not available from the literature, we conducted a histological investigation of generation gland morphology, using standard histological techniques. We included two species of the sister family Gerrhosauridae in the analysis to serve as outgroups. In both Gerrhosaurus typicus and G. flavigularis, scales immediately anterior to the femoral pores displayed glandular activity, but differed from generation glands of cordylids in the absence of mature glandular generations. Among the cordylids investigated, we identified a fourth type of generation gland in Pseudocordylus subviridis, P. spinosus, and in the two Hemicordylus species, one where the glands consistently comprise of two mature glandular generations. In H. capensis, both single- and two-layer type glands are present. Our reconstruction of ancestral character states suggests a minimum of six transformations from one gland type to another during the evolutionary history of the family. The reconstruction furthermore suggests that the single-layer type gland reappeared at least once (in Hemicordylus) in the Cordylinae after having been lost. The reconstruction also unequivocally shows that the pit-like multiple-layer type gland evolved directly from the single-layer type and not from the protruding multiple-layer type. The two-layer type gland appears to be an intermediary condition between the multiple-layer and single-layer types. The evolutionary transformation of generation gland type appears to be linked to changes in lifestyle and associated changes in degree of territoriality and the need for chemical communication.