The integrative biology of decoy coloration in lizards

Anti-predator coloration is a widespread phenomenon that includes such tactics as aposematism, crypsis and mimicry. Most research on colorful anti-predator traits has focused on these well-known and well-studied tactics. One anti-predator trait that is found in diverse taxa yet is still poorly understood is anti-predator decoys. New advances in phylogenetics, genomics and molecular biology have allowed for an enriched understanding of the integrative biology of this type of anti-predator trait, particularly in lizards. While anti-predator decoy coloration is present in multiple taxa across the animal tree of life, it is particularly prevalent among lizards, which use both color and behavior to attract predator attention to the tail, which is often autotomizable and can regrow. In this Review, we discuss the integrative biology of decoy coloration in lizards, including the role of color, ontogenetic variation, gene expression and genomics. We begin by reviewing the mechanisms of the production of decoy coloration in lizards then discuss the function and macroevolution of decoy coloration. Finally, we suggest potentially fruitful avenues for future research on anti-predator decoys in lizards and other animal taxa.

Why some hearts heal and others don't: The phylogenetic landscape of cardiac regenerative capacity

The limited ability of adult humans to replenish lost heart muscle cells after a heart attack has attracted scientists to explore natural heart regeneration capabilities in the animal kingdom. In particular, research has accelerated since the landmark discovery more than twenty years ago that zebrafish can completely regrow myocardial tissue. In this review, we survey heart regeneration studies in diverse model and non-model animals, aiming to gain insights into both the evolutionary trends in cardiac regenerative potential and the variations among closely related species. Differences in cardiomyogenesis, vasculature formation, and the communication between cardiovascular cells and other players have been investigated to understand the cellular basis, although the precise molecular and genetic causes underlying the stark differences in cardiac regenerative potential among certain close cousins remain largely unknown. By studying cardiovascular regeneration and repair in diverse organisms, we may uncover distinct mechanisms, offering new perspectives for advancing regenerative medicine.

The influence of the post-autotomy regeneration of a sexual trait and mating tactics in a fiddler crab

Male fiddler crabs own an enlarged claw which is a weapon and an ornament. The enlargement of this claw begins from the juvenile stage and continues throughout life. Males may voluntarily lose (i.e., autotomize) this claw. After several molts males may regenerate a new claw, called leptochelous, which acquires a similar length but a lower muscle mass area than the original one, called brachychelous. In some species, regenerated claws develop permanently as leptochelous, the population having 2 discrete claw morphologies. Other species present morphological variations with leptochelous and brachychelous being 2 ends of a continuum. In the species Leptuca uruguayensis, we studied the morphological variation of this enlarged claw, whether it may be caused by its regeneration at different male sizes, and its consequences on mating success. We found that claws could not be discriminated as discrete morphs, suggesting a morphological continuum from brachychelous to leptochelous. Regenerated claws in the laboratory were initially small and proportional to body size, although a field experiment confirmed that claw size is recovered after several molts. Morphological variation may be caused by energetic limitations where males of different sizes must differently trade-off between restitution of claw length (ornament function) or claw muscle area (weapon function). Fiddler crabs use 2 mating tactics with different levels of female choice. However, regardless of the mating tactic, leptochelous males were at a disadvantage at high densities, although not at low densities, suggesting that the consequences of autotomy and regeneration on mating success may depend on the social context.

Tokay gecko tail regeneration involves temporally collinear expression of HOXC genes and early expression of satellite cell markers

BACKGROUND

Regeneration is the replacement of lost or damaged tissue with a functional copy. In axolotls and zebrafish, regeneration involves stem cells produced by de-differentiation. These cells form a growth zone which expresses developmental patterning genes at its apex. This system resembles an embryonic developmental field where cells undergo pattern formation. Some lizards, including geckos, can regenerate their tails, but it is unclear whether they show a "development-like" regeneration pathway.

RESULTS

Using the tokay gecko (Gekko gecko) model species, we examined seven stages of tail regeneration, and three stages of embryonic tail bud development, using transcriptomics, single-cell sequencing, and in situ hybridization. We find no apical growth zone in the regenerating tail. The transcriptomes of the regenerating vs. embryonic tails are quite different with respect to developmental patterning genes. Posterior HOXC genes were activated in a temporally collinear sequence in the regenerating tail. The major precursor populations were stromal cells (regenerating tail) vs. pluripotent stem cells (embryonic tail). Segmented skeletal muscles were regenerated with no expression of classical segmentation genes, but with the early activation of satellite cell markers.

CONCLUSIONS

Our study suggests that tail regeneration in the tokay gecko-unlike tail development-might rely on the activation of resident stem cells, guided by pre-existing positional information.

Robustness to Leg Loss in Opiliones: A Review and Framework Considerations for Future Research

Animals have evolved behavioral and morphological traits that allow them to respond to environmental challenges. However, these traits may have long-term consequences that could impact an animal's performance, fitness, and welfare. Several species in a group of the arachnid order of Opiliones release their legs voluntarily to escape predators. These animals use their legs for locomotion, sensation, and reproduction. Here, we first compile data across species in the suborder Eupnoi, showing that more than half of individuals are found missing legs. Then, we review recent work on the ultimate and proximate implications of leg loss in Opiliones. Field and laboratory experiments showed that leg loss (a) did not affect their survival or mating success and (b) compromised the kinematics and energetics of locomotion, but individuals recovered velocity and acceleration quickly. These findings demonstrate that these animals display robustness, that is, the ability to withstand and overcome the potential consequences of bodily damage. This may explain why leg loss is so prevalent in Opiliones. Additionally, we encourage researchers to consider expanding their hypotheses beyond traditional adaptationist and ableist lenses and incorporate a comprehensive examination of animal welfare when studying animals' responses to bodily damage. Finally, we highlight avenues for future research in Opiliones, namely assessing how individuals move in three-dimensional environments, the neural plasticity aiding recovery post-leg loss, applications for bio-inspired design, and evidence-based animal welfare measures.

Role of Tail Dynamics on the Climbing Performance of Gecko-Inspired Robots: A Simulation and Experimental Study

Geckos are renowned for their exceptional climbing abilities, enabled by their specialized feet with hairy toes that attach to surfaces using van der Waals forces. Inspired by these capabilities, various gecko-like robots have been developed for high-risk applications, such as search and rescue. While most research has focused on adhesion mechanisms, the gecko's tail also plays a critical role in maintaining balance and stability. In this study, we systematically explore the impact of tail dynamics on the climbing performance of gecko-inspired robots through both simulation and experimental analysis. We developed a dynamic climbing simulation system that models the robot's specialized attachment devices and predicts contact failures. Additionally, an adjustable-angle force measurement platform was constructed to validate the simulation results. Our findings reveal the significant influence of the tail on the robot's balance, stability, and maneuverability, providing insights for further optimizing climbing robot performance.

The effect of tail stiffness on a sprawling quadruped locomotion

A distinctive feature of quadrupeds that is integral to their locomotion is the tail. Tails serve many purposes in biological systems, including propulsion, counterbalance, and stabilization while walking, running, climbing, or jumping. Similarly, tails in legged robots may augment the stability and maneuverability of legged robots by providing an additional point of contact with the ground. However, in the field of terrestrial bio-inspired legged robotics, the tail is often ignored because of the difficulties in design and control. In this study, we test the hypothesis that a variable stiffness robotic tail can improve the performance of a sprawling quadruped robot by enhancing its stability and maneuverability in various environments. In order to validate our hypothesis, we integrated a cable-driven, flexible tail with multiple segments into the underactuated sprawling quadruped robot, where a single servo motor working alongside a reel and cable mechanism regulates the tail's stiffness. Our results demonstrated that by controlling the stiffness of the tail, the stability of locomotion on rough terrain and the climbing ability of the robot are improved compared to the movement with a rigid tail and no tail. Our findings highlight that constant ground support provided by the flexible tail is key to maintaining stable locomotion. This ensured a predictable gait cycle, eliminating unexpected turning and slipping, resulting in an increase in locomotion speed and efficiency. Additionally, we observed the robot's enhanced climbing ability on surfaces inclined up to 20°. The flexibility of the tail enabled the robot to overcome obstacles without external sensing, exhibiting significant adaptability across various terrains.

Past energy allocation overwhelms current energy stresses in determining energy allocation trade-offs

Regeneration of lost appendages is a gradual process in many species, spreading energetic costs of regeneration through time. Energy allocated to the regeneration of lost appendages cannot be used for other purposes and, therefore, commonly elicits energetic trade-offs in biological processes. We used limb loss in the Asian shore crab Hemigrapsus sanguineus to compare the strength of energetic trade-offs resulting from historic limb losses that have been partially regenerated versus current injuries that have not yet been repaired. Consistent with previous studies, we show that limb loss and regeneration results in trade-offs that reduce reproduction, energy storage, and growth. As may be expected, we show that trade-offs in these metrics from historic limb losses far outweigh trade-offs from current limb losses, and correlate directly with the degree of historic limb loss that has been regenerated. As regenerating limbs get closer to their normal size, these historical injuries get harder to detect, despite the continued allocation of additional resources to limb development. Our results demonstrate the importance of and a method for identifying historic appendage losses and of quantifying the amount of regeneration that has already occurred, as opposed to assessing only current injury, to accurately assess the strength of energetic trade-offs in animals recovering from nonlethal injury.

Integrative biology of injury in animals

Mechanical injury is a prevalent challenge in the lives of animals with myriad potential consequences for organisms, including reduced fitness and death. Research on animal injury has focused on many aspects, including the frequency and severity of wounding in wild populations, the short- and long-term consequences of injury at different biological scales, and the variation in the response to injury within or among individuals, species, ontogenies, and environmental contexts. However, relevant research is scattered across diverse biological subdisciplines, and the study of the effects of injury has lacked synthesis and coherence. Furthermore, the depth of knowledge across injury biology is highly uneven in terms of scope and taxonomic coverage: much injury research is biomedical in focus, using mammalian model systems and investigating cellular and molecular processes, while research at organismal and higher scales, research that is explicitly comparative, and research on invertebrate and non-mammalian vertebrate species is less common and often less well integrated into the core body of knowledge about injury. The current state of injury research presents an opportunity to unify conceptually work focusing on a range of relevant questions, to synthesize progress to date, and to identify fruitful avenues for future research. The central aim of this review is to synthesize research concerning the broad range of effects of mechanical injury in animals. We organize reviewed work by four broad and loosely defined levels of biological organization: molecular and cellular effects, physiological and organismal effects, behavioural effects, and ecological and evolutionary effects of injury. Throughout, we highlight the diversity of injury consequences within and among taxonomic groups while emphasizing the gaps in taxonomic coverage, causal understanding, and biological endpoints considered. We additionally discuss the importance of integrating knowledge within and across biological levels, including how initial, localized responses to injury can lead to long-term consequences at the scale of the individual animal and beyond. We also suggest important avenues for future injury biology research, including distinguishing better between related yet distinct injury phenomena, expanding the subjects of injury research to include a greater variety of species, and testing how intrinsic and extrinsic conditions affect the scope and sensitivity of injury responses. It is our hope that this review will not only strengthen understanding of animal injury but will contribute to building a foundation for a more cohesive field of 'injury biology'.

Biomimicking interfacial fracture behavior of lizard tail autotomy with soft microinterlocking structures

Biological soft interfaces often exhibit complex microscale interlocking geometries to ensure sturdy and flexible connections. If needed, the interlocking can rapidly be released on demand leading to an abrupt decrease of interfacial adhesion. Here, inspired by lizard tail autotomy where such apparently tunable interfacial fracture behavior can be observed, we hypothesized an interlocking mechanism between the tail and body based on the muscle-actuated mushroom-shaped microinterlocks along the fracture planes. To mimic the fracture behavior of the lizard tail, we developed a soft bilayer patch that consisted of a dense array of soft hemispherical microstructures in the upper layer acting as mechanical interlocks with the counter body part. The bottom control layer contained a microchannel that allowed to deflect the upper layer when applying the negative pressure, thus mimicking muscle contraction. In the microinterlocked condition, the biomimetic tail demonstrated a 2.7-fold and a three-fold increase in adhesion strength and toughness, respectively, compared to the pneumatically released microinterlocks. Furthermore, as per the computational analysis, the subsurface microchannel in the control layer enabled augmented adhesion by rendering the interface more compliant as a dissipative matrix, decreasing contact opening and strain energy dissipation by 50%. The contrasting features between the microinterlocked and released cases demonstrated a highly tunable adhesion of our biomimetic soft patch. The potential applications of our study are expected in soft robotics and prosthetics.

Microscopical observations on the regenerating tail of tsinling dwarf skink (Scincella tsinlingensis)

Although the key steps of tail regeneration in lizards are well understood, further investigations involving skinks can provide the field of regeneration research with additional information. In order to characterize the cytoarchitecture of tail regeneration in Scincella tsinlingensis, an endemic species in China, its histological events and growth trends are investigated. The rate of tail regeneration varies with the season: it proceeds faster in summer and autumn than it does in winter and spring. Tail regeneration of S. tsinlingensis is summarized as wound healing, blastema formation, cell differentiation and tail growth, which can be subdivided into seven stages. Wound healing following tail loss, begins with an obvious outgrowth undergoing re-epithelialization. Numerous proliferating mesenchymal-like cells aggregate near the distal end of the severed spinal cord to form the blastema. The expanding blastema is invaded by blood vessels, nerves and ependyma. A cartilaginous skeleton is formed around the ependymal tube and the muscle starts to differentiate. The keratinization of epidermis coincides with scale formation. Pigmentation eventually occurs in the regenerated tail. Tail regeneration in S. tsinlingensis is an epimorphic kind of regeneration that is also known as blastema-mediated. Structure and composition of the regenerated tail, including its cytoarchitecture, represent a conserved pattern of regeneration also known from other lizards.

At What Cost? Trade-Offs and Influences on Energetic Investment in Tail Regeneration in Lizards Following Autotomy

Caudal autotomy, the ability to shed a portion of the tail, is a widespread defence strategy among lizards. Following caudal autotomy, and during regeneration, lizards face both short- and long-term costs associated with the physical loss of the tail and the energy required for regeneration. As such, the speed at which the individual regenerates its tail (regeneration rate) should reflect the fitness priorities of the individual. However, multiple factors influence the regeneration rate in lizards, making inter-specific comparisons difficult and hindering broader scale investigations. We review regeneration rates for lizards and tuatara from the published literature, discuss how species' fitness priorities and regeneration rates are influenced by specific, life history and environmental factors, and provide recommendations for future research. Regeneration rates varied extensively (0-4.3 mm/day) across the 56 species from 14 family groups. Species-specific factors, influencing regeneration rates, varied based on the type of fracture plane, age, sex, reproductive season, and longevity. Environmental factors including temperature, photoperiod, nutrition, and stress also affected regeneration rates, as did the method of autotomy induction, and the position of the tail also influenced regeneration rates for lizards. Additionally, regeneration could alter an individual's behaviour, growth, and reproductive output, but this varied depending on the species.

Behavioral patterns in the early-stage antipredator response change after tail autotomy in adult wall lizards

Autotomy is a drastic antipredator defense consisting of the voluntary shedding of a body part to escape from the predators. The loss of a body part may impair locomotion, feeding or mating, so animals may face a higher predation risk shortly after autotomy. Thus, until regeneration is completed, prey may adjust their behavior to reduce predation risk, and this could involve secondary costs. We assessed the effect of tail loss on the antipredator behavior of wall lizards (Podarcis muralis), comparing the behavior of tailed and tailless individuals exposed to a predatory snake (Coronella austriaca) scent, under controlled experimental conditions. Tailless lizards spent significantly more time performing behaviors with antipredatory significance (e.g., moving slowly), whereas tailed individuals performed exploratory walking for significantly more time. Moreover, tailless lizards spent more time basking, which probably increases the effectiveness of their cryptic design and decreases detection by predators. Lizards intensified the tongue flick rates when exposed to a pungent control or snake scents, as compared to their response to a neutral control. Besides, both tailed and tailless lizards intensified some aspects of their antipredator behavior (walking slowly and avoiding refuge use) when exposed to snake scent, which indicates discrimination of the smell of predatory snakes. Lizards decreased refuge use when exposed to predator scents, probably because the refuges are evaluated as unsafe due to a high concentration of snake scents. To conclude, our experiments showed that, after losing their tails, wall lizards modify their behavior in a way that likely minimizes predation risk.

Future Tail Tales: A Forward-Looking, Integrative Perspective on Tail Research

Synopsis Tails are a defining characteristic of chordates and show enormous diversity in function and shape. Although chordate tails share a common evolutionary and genetic-developmental origin, tails are extremely versatile in morphology and function. For example, tails can be short or long, thin or thick, and feathered or spiked, and they can be used for propulsion, communication, or balancing, and they mediate in predator-prey outcomes. Depending on the species of animal the tail is attached to, it can have extraordinarily multi-functional purposes. Despite its morphological diversity and broad functional roles, tails have not received similar scientific attention as, for example, the paired appendages such as legs or fins. This forward-looking review article is a first step toward interdisciplinary scientific synthesis in tail research. We discuss the importance of tail research in relation to five topics: (1) evolution and development, (2) regeneration, (3) functional morphology, (4) sensorimotor control, and (5) computational and physical models. Within each of these areas, we highlight areas of research and combinations of long-standing and new experimental approaches to move the field of tail research forward. To best advance a holistic understanding of tail evolution and function, it is imperative to embrace an interdisciplinary approach, re-integrating traditionally siloed fields around discussions on tail-related research.

Tail Autotomy Alters Prey Capture Performance and Kinematics, but not Success, in Banded Geckos

Tails are versatile structures with diverse forms and functions across vertebrates. They are involved in almost all behaviors critical to survival including locomotion, feeding, and predator avoidance. Although the tail's role in locomotion and stability has been widely studied, its role in prey capture is relatively unknown. Lizards are an ideal system to examine the tail's impact on prey capture as most are capable of autotomizing, or dropping, their tail in response to predation and intraspecific competition. Tail autotomy can lower reproduction, decrease locomotor performance, impart instability during jumping, and decrease social status. Desert banded geckos (Coleonyx variegatus) frequently capture evasive prey in nature and appear to use their tail during strikes. However, it is unclear if these tail movements are important for the strike itself, or if they simply draw attention to that part of the body. We used high-speed 3D videography to quantify prey capture performance and kinematics of C. variegatus striking at crickets before and after total caudal autotomy. Trials were conducted within 2 h of autotomy and then repeatedly over a 2-week period. Overall, prey capture success was unaffected by caudal autotomy. However, maximum strike velocity decreased significantly after autotomy, highlighting the importance of the tail during prey capture. Strike kinematics were altered after autotomy in several ways, including geckos adopting a more sprawled posture. Maximum pectoral girdle and mid-back height were significantly lower during post-autotomy strikes, whereas maximum pelvic girdle height was unaffected. However, individual variation was considerable. This downward pitching of the body after tail loss suggests that the tail is necessary for counterbalancing the anterior portion of the body and resisting the rotational inertia incurred after pushing off with the hindlimbs. Utilizing autotomy to test tail function in prey capture can provide valuable insight into how the tail is used in terrestrial predation across a wide variety of species and ecological niches.

The power of community science to quantify ecological interactions in cities

Studying animals in urban environments is especially challenging because much of the area is private property not easily accessible to professional scientists. In addition, collecting data on animals that are cryptic, secretive, or rare is also challenging due to the time and resources needed to amass an adequate dataset. Here, we show that community science can be a powerful tool to overcome these challenges. We used observations submitted to the community science platform iNaturalist to assess predation and parasitism across urbanization gradients in a secretive, 'hard-to-study' species, the Southern Alligator Lizard (Elgaria multicarinata). From photographs, we quantified predation risk by assessing tail injuries and quantified parasitism by counting tick loads on lizards. We found that tail injuries increased with age and with urbanization, suggesting that urban areas are risky habitats. Conversely, parasitism decreased with urbanization likely due to a loss of hosts and anti-tick medications used on human companion animals. This community science approach generated a large dataset on a secretive species rapidly and at an immense spatial scale that facilitated quantitative measures of urbanization (e.g. percent impervious surface cover) as opposed to qualitative measures (e.g. urban vs. rural). We therefore demonstrate that community science can help resolve ecological questions that otherwise would be difficult to address.

Autotomy and Regeneration in Squamate Reptiles (Squamata, Reptilia): Defensive Behavior Strategies and Morphological Characteristics (Using Computer Microtomography Methods)

Abstract

It has been noted that caudal autotomy as a way of defending against predators in recent reptiles is characteristic solely of lepidosaurs and is absent in crocodiles and turtles. It was found that, in the order Rhynchocephalia and in representatives of the majority of families of lizards, intravertebral (IntraVB) autotomy is a widespread phenomenon, whereas agamid lizards and some snakes do not have a break plane, and their tails break between adjacent vertebrae (intervertebral (InterVB) autotomy). The frequencies of occurrence of InterVB autotomy and regeneration in six species of agamas of the genus Paralaudakia were analyzed. Six types of regenerate’s characteristic of the studied group and the anatomical structure of the knob -shaped jagged regenerate are described on the basis of the results of computed microtomography (micro-CT). Phenomena of autotomy and regeneration are discussed in the phylogenetic context.

Relative fitness of decoy coloration is mediated by habitat type

Predator-prey interactions can be important drivers of morphological evolution, and antipredator traits in particular. Further, ecological context can be an important factor shaping the evolution of these traits. However, the role of ecological factors such as habitat structure in altering predator-based selection is not well known for antipredator traits such as decoy coloration. We used a combination of a natural history collection survey and a clay model experiment in open- and closed-canopy habitats to study how ecological context alters the fitness benefit of either red or blue decoy coloration in skinks. We found that the development and ecology of red decoy coloration of mole skinks differed substantially from blue tail coloration of other sympatric skink species. Mole skinks do not reach the body size of sympatric species of skinks and retain decoy coloration throughout development. Both patterns of scarring in museum specimens and attacks on plasticine models suggest that red coloration serves as a decoy, attracting attacks to the autotomous tail. While predation rates were similar across habitats, models with red tails were attacked far less frequently in open habitats than models with blue tails, while attack rates were similar in closed habitats. Our results suggest that red decoy coloration in mole skinks could be an adaptation to relatively open-canopy habitats. Our study has important implications for understanding how habitat structure and predator-based selection can alter the evolutionary dynamics of decoy coloration.

When one tail isn't enough: abnormal caudal regeneration in lepidosaurs and its potential ecological impacts

Abnormal caudal regeneration, the production of additional tails through regeneration events, occurs in lepidosaurs as a result of incomplete autotomy or sufficient caudal wound. Despite being widely known to occur, documented events generally are limited to opportunistic single observations - hindering the understanding of the ecological importance of caudal regeneration. Here we compiled and reviewed a robust global database of both peer-reviewed and non-peer reviewed records of abnormal regeneration events in lepidosaurs published over the last 400 years. Using this database, we qualitatively and quantitatively assessed the occurrence and characteristics of abnormal tail regeneration among individuals, among species, and among populations. We identified 425 observations from 366 records pertaining to 175 species of lepidosaurs across 22 families from 63 different countries. At an individual level, regenerations ranged from bifurcations to hexafurcations; from normal regeneration from the original tail to multiple regenerations arising from a single point; and from growth from the distal third to the proximal third of the tail. Species showing abnormal regenerations included those with intra-vertebral, inter-vertebral or no autotomy planes, indicating that abnormal regenerations evidently occur across lepidosaurs regardless of whether the species demonstrates caudal autotomy or not. Within populations, abnormal regenerations were estimated at a mean ± SD of 2.75 ± 3.41% (range 0.1-16.7%). There is a significant lack of experimental studies to understand the potential ecological impacts of regeneration on the fitness and life history of individuals and populations. We hypothesised that abnormal regeneration may affect lepidosaurs via influencing kinematics of locomotion, restrictions in escape mechanisms, anti-predation tactics, and intra- and inter-specific signalling. Behaviourally testing these hypotheses would be an important future research direction.

Morphological and ecological divergence in two populations of European glass lizard, Pseudopus apodus (Squamata: Anguidae)

The European glass lizard, Pseudopus apodus (Pallas, 1775), is a large, legless lizard with wide distribution across south-eastern Europe and eastern and central Asia. To date, morphological diversification among populations on a geographically small scale has not yet been reported in this lizard. Thus, we investigated the morphological variations and corresponding differences in habitat utilization between two populations of P. apodus inhabiting the same biogeographical zone within a relatively close geographic area. We hypothesized that minor differences in habitat could induce a significant level of morphological differentiation, thus indicating morphological plasticity in this species on a small geographical scale. We sampled 164 individuals (92 from the Croatian mainland and 72 from the island of Cres). Results showed that P. apodus indeed exhibited morphological differences between populations in the same biogeographical zone within a relatively close geographic area, with the Cres Island individuals being generally larger than the individuals from the mainland. Some ecological characteristics were similar in both populations (e.g., soil temperature, distance to hiding place), whereas others were distinct (e.g., air temperature and humidity). In addition, vegetation cover differed between the two sites, with more vegetation present on the mainland than on the island. Furthermore, the Cres Island population showed clear sexual dimorphism, which was absent in the mainland population.

Ultraviolet reflectance and pattern properties in leopard geckos (Eublepharis macularius)

Complex visual signaling through various combinations of colors and patterns has been well documented in a number of diurnal reptiles. However, there are many nocturnal species with highly sensitive vision, being able to discriminate colors in night conditions, as was shown in geckos. Because of their sensitivity to chromatic signals, including UV (ultraviolet), they may have potential hidden features in their coloration, which may play role in intraspecific communication (e.g. mate choice) or interspecific signals (e.g. antipredatory function). We explored this hypothesis in nocturnal Leopard geckos (Eublepharis macularius), a species using visual signals in both antipredation defense and courtship, having ontogenetic color change accompanied by a shift in behavior. We used UV photography and visual modeling in order to compare various aspects of their coloration (luminance, contrast, color proportions) between sexes, age groups and populations. We found that Leopard geckos have considerable UV reflectance in white patches on their tails (and on the head in juveniles). Though, no prominent differences were detected in their coloration between various groups. We hypothesize that the limitation of UV reflectance to the head and tail, which are both actively displayed during defense, especially in juveniles, might potentially boost the effect of antipredation signaling.

Tail regeneration in Lepidosauria as an exception to the generalized lack of organ regeneration in amniotes

The present review hypothesizes that during the transition from water to land, amniotes lost part of the genetic program for metamorphosis utilized in larvae of their amphibian ancestors, a program that in extant fish and amphibians allows organ regeneration. The direct development of amniotes, with their growth from embryos to adults, occurred with the elimination of larval stages, increases the efficiency of immune responses and the complexity of nervous circuits. In amniotes, T-cells and macrophages likely eliminate embryonic-larval antigens that are replaced with the definitive antigens of adult organs. Among lepidosaurians numerous lizard families during the Permian and Triassic evolved the process of tail autotomy to escape predation, followed by tail regeneration. Autotomy limits inflammation allowing the formation of a regenerative blastema rich in the immunosuppressant and hygroscopic hyaluronic acid. Expression loss of developmental genes for metamorphosis and segmentation in addition to an effective immune system, determined an imperfect regeneration of the tail. Genes involved in somitogenesis were likely lost or are inactivated and the axial skeleton and muscles of the original tail are replaced with a nonsegmented cartilaginous tube and segmental myotomes. Lack of neural genes, negative influence of immune system, and isolation of the regenerating spinal cord within the cartilaginous tube impede the production of nerve and glial cells, and a stratified spinal cord with ganglia. Tissue and organ regeneration in other body regions of lizards and other reptiles is relatively limited, like in the other amniotes, although the cartilage shows a higher regenerative capability than in mammals.

The ecology and evolution of autotomy

Autotomy, the self-induced loss of a body part, occurs throughout Animalia. A lizard dropping its tail to escape predation is an iconic example, however, autotomy occurs in a diversity of other organisms. Octopuses can release their arms, crabs can drop their claws, and bugs can amputate their legs. The diversity of organisms that can autotomize body parts has led to a wealth of research and several taxonomically focused reviews. These reviews have played a crucial role in advancing our understanding of autotomy within their respective groups. However, because of their taxonomic focus, these reviews are constrained in their ability to enhance our understanding of autotomy. Here, we aim to synthesize research on the ecology and evolution of autotomy throughout Animalia, building a unified framework on which future studies can expand. We found that the ability to drop an appendage has evolved multiple times throughout Animalia and that once autotomy has evolved, selection appears to act on the removable appendage to increase the efficacy and/or efficiency of autotomy. This could explain why some autotomizable body parts are so elaborate (e.g. brightly coloured). We also show that there are multiple benefits, and variable costs, associated with autotomy. Given this variation, we generate an economic theory of autotomy (modified from the economic theory of escape) which makes predictions about when an individual should resort to autotomy. Finally, we show that the loss of an autotomizable appendage can have numerous consequences on population and community dynamics. By taking this broad taxonomic approach, we identified patterns of autotomy that transcend specific lineages and highlight clear directions for future research.

Establishment and characterization of rough-tailed gecko original tail cells

Some of lizard species have the ability to lose their tail in order to defend against predators and regenerate the new tail. Lizard's regenerated tail has attracted scientists' attention for unraveling the regeneration process, but less information is known about the cellular characterization and cell growth properties of original tail. This research aimed to report cell culture and banking process of rough-tailed gecko or Cyrtopodion scabrum's original tail cell sample from inner tissue without skin using tissue explant technique. For banking reports, it is essential to analyze this cells' potential to proliferate, to investigate biological aspects such as cell culture features, differentiation and chromosome number and to report its species identification and quality control. To achieve optimal growth conditions, three different temperatures for incubation including 18, 23 and 37 °C and two different media including DMEM and L-15 were applied. The expanded cells were studied for their potential to adipose and osteoblast differentiation. Results indicated that lizard's original tail cells could be successfully obtained by explant technique. The cells demonstrated fibroblast like morphology with population doubling times of approximately 24 ± 0.5 h. Karyotyping analysis showed a distribution of 2n = 40 chromosome number for this cell line. The comparison of different incubation media and temperatures showed that cell growth is equally optimal in all mentioned conditions according to growth curves. Adipose and osteoblast differentiation was obviously observed in these cells which confirms the hint of stem-ness in the produced mixed cells. According to cell banking policies, produced cells were also checked for bacterial, fungal, yeast and mycoplasma contaminations and no contamination was observed. Multiplex PCR for identification of species confirmed the species of lizard with no cross-contamination with other cells in the cell bank. Establishment of authenticated and well-characterized lizard's original tail cell line will provide a valuable source for subsequent in vitro regenerative research and molecular studies which are not feasible in in vivo methods. This finding will allow us to get an opportunity to create and preserve a new collection of lizard cell lines in the future.

Tail regeneration after autotomy revives survival: a case from a long-term monitored lizard population under avian predation

Caudal autotomy in lizards has intrigued scientists for more than 100 years. Because of the relative lack of literature under natural conditions, the complicated association among field autotomy rate, real predation pressure, the long-term cost of tail loss, and the benefit of regeneration remains equivocal. In this study, we conducted a 7-year capture-mark-recapture (CMR) programme with a wild population of a sexually dichromatic lizard, Takydromus viridipunctatus We used autotomy indexes and a contemporary bird census mega-dataset of four predatory birds as predictors to examine the association between tail loss and predation pressure. We further estimated the survival cost of tail loss and alleviation by regeneration under natural conditions through CMR modelling. We found that large and small avian predators affect lizard survival through the following two routes: the larger-sized cattle egret causes direct mortality while the smaller shrikes and kestrels are the major causes of autotomy. Following autotomy, the survival rate of tailless individuals over the next month was significantly lower than that of tailed individuals, especially males during the breeding season, which showed a decline of greater than 30%. This sex-related difference further demonstrated the importance of reproductive costs for males in this sexually dichromatic species. However, the risk of mortality returned to baseline after the tails were fully grown. This study indicates the benefit of tail regeneration under natural conditions, which increases our understanding of the cost-benefit dynamics of caudal autotomy and further explains the maintenance of this trait as an evolutionarily beneficial adaption to long-term predator-prey interactions.

Neuromuscular control of locomotion is altered by tail autotomy in geckos

Animal locomotion is driven by underlying axial and appendicular musculature. In order for locomotion to be effective, these muscles must be able to rapidly respond to changes in environmental and physiological demands. Although virtually unstudied, muscles must also respond to morphological changes, such as those that occur with tail autotomy in lizards. Tail autotomy in leopard geckos (Eublepharis macularius) results in a 25% loss of caudal mass and significant kinematic alterations to maintain stability. To elucidate how motor control of the locomotor muscles is modulated with these shifts, we used electromyography (EMG) to quantify patterns of in vivo muscle activity in fore- and hind limb muscles before and after autotomy. Forelimb muscles (biceps brachii and triceps brachii) exhibited no changes in motor recruitment, consistent with unaltered kinematics after autotomy. Amplitude of activity of propulsive muscles of the hind limbs (caudofemoralis and gastrocnemius) was significantly reduced and coincided with decreases in the propulsive phases of femur retraction and ankle extension, respectively. The puboischiotibialis did not exhibit these changes, despite significant reductions in femur depression and knee angle, suggesting that reduction in mass and vertical ground-reaction force by autotomy allows for the maintenance of a more sprawled and stable posture without increasing motor recruitment of the support muscles. These results highlight the significant neuromuscular shifts that occur to accommodate dramatic changes in body size and mass distribution, and illuminate the utility of tail autotomy as a system for studying the neuromuscular control of locomotion.

Lateral movements of a massive tail influence gecko locomotion: an integrative study comparing tail restriction and autotomy

Tails are an intricate component of the locomotor system for many vertebrates. Leopard geckos (Eublepharis macularius) possess a large tail that is laterally undulated during steady locomotion. However, the tail is readily shed via autotomy, resulting in the loss of tail function, loss in body mass, and a cranial shift in the center of mass. To elucidate the function of tail undulations, we investigated changes in limb kinematics after manipulating the tail artificially by restricting tail undulations and naturally by removing the tail via autotomy. Restricting tail undulations resulted in kinematic adjustments similar to those that occur following tail autotomy, characterized by more flexed hind limb joints. These data suggest that effects of autotomy on locomotion may be linked to the loss of tail movements rather than the loss of mass or a shift in center of mass. We also provide empirical support for the link between lateral tail undulations and step length through the rotation of the pelvic girdle and retraction of the femur. Restriction and autotomy of the tail limits pelvic rotation, which reduces femur retraction and decreases step length. Our findings demonstrate a functional role for tail undulations in geckos, which likely applies to other terrestrial vertebrates.

Consequences of lost endings: caudal autotomy as a lens for focusing attention on tail function during locomotion

Autotomy has evolved in many animal lineages as a means of predator escape, and involves the voluntary shedding of body parts. In vertebrates, caudal autotomy (or tail shedding) is the most common form, and it is particularly widespread in lizards. Here, we develop a framework for thinking about how tail loss can have fitness consequences, particularly through its impacts on locomotion. Caudal autotomy is fundamentally an alteration of morphology that affects an animal's mass and mass distribution. These morphological changes affect balance and stability, along with the performance of a range of locomotor activities, from running and climbing to jumping and swimming. These locomotor effects can impact on activities critical for survival and reproduction, including escaping predators, capturing prey and acquiring mates. In this Commentary, we first review work illustrating the (mostly) negative effects of tail loss on locomotor performance, and highlight what these consequences reveal about tail function during locomotion. We also identify important areas of future study, including the exploration of new behaviors (e.g. prey capture), increased use of biomechanical measurements and the incorporation of more field-based studies to continue to build our understanding of the tail, an ancestral and nearly ubiquitous feature of the vertebrate body plan.

Regenerating tail muscles in lizard contain Fast but not Slow Myosin indicating that most myofibers belong to the fast twitch type for rapid contraction

During tail regeneration in lizards a large mass of muscle tissue is formed in form of segmental myomeres of similar size located under the dermis of the new tail. These muscles accumulate glycogen and a fast form of myosin typical for twitch myofibers as it is shown by light and ultrastructural immunocytochemistry using an antibody directed against a Fast Myosin Heavy Chain. High resolution immunogold labeling shows that an intense labeling for fast myosin is localized over the thick filaments of the numerous myofibrils in about 70% of the regenerated myofibers while the labeling becomes less intense in the remaining muscle fibers. The present observations indicate that at least two subtypes of Fast Myosin containing muscle fibers are regenerated, the prevalent type was of the fast twitch containing few mitochondria, sparse glycogen, numerous smooth endoplasmic reticulum vesicles. The second, and less frequent type was a Fast-Oxidative-Glycolitic twitch fiber containing more mitochondria, a denser cytoplasm and myofibrils. Since their initial differentiation, myoblasts, myotubes and especially the regenerated myofibers do not accumulate any immuno-detectable Slow Myosin Heavy Chain. The study indicates that most of the segmental muscles of the regenerated tail serve for the limited bending of the tail during locomotion and trashing after amputation of the regenerated tail, a phenomenon that facilitates predator escape.

The regeneration blastema of lizards: an amniote model for the study of appendage replacement

Although amniotes (reptiles, including birds, and mammals) are capable of replacing certain tissues, complete appendage regeneration is rare. Perhaps the most striking example is the lizard tail. Tail loss initiates a spontaneous epimorphic (blastema‐mediated) regenerative program, resulting in a fully functional but structurally non‐identical replacement. Here we review lizard tail regeneration with a particular focus on the blastema. In many lizards, the original tail has evolved a series of fracture planes, anatomical modifications that permit the tail to be self‐detached or autotomized. Following tail loss, the wound site is covered by a specialized wound epithelium under which the blastema develops. An outgrowth of the spinal cord, the ependymal tube, plays a key role in governing growth (and likely patterning) of the regenerate tail. In some species (e.g., geckos), the blastema forms as an apical aggregation of proliferating cells, similar to that of urodeles and teleosts. For other species (e.g., anoles) the identification of a proliferative blastema is less obvious, suggesting an unexpected diversity in regenerative mechanisms among tail‐regenerating lizards.

Density and distribution of cutaneous sensilla on tails of leopard geckos (Eublepharis macularius) in relation to caudal autotomy

The lizard tail is well known for its ability to autotomize and regenerate. Physical contact of the tail by a predator may induce autotomy at the location at which the tail is grasped, and upon detachment the tail may undergo violent, rapid, and unpredictable movements that appear to be, to some degree, regulated by contact with the physical environment. Neither the mechanism by which tail breakage at a particular location is determined, nor that by which environmental feedback to the tail is received, are known. It has been suggested that mechanoreceptors (sensilla) are the means of mediation of such activities, and reports indicate that the density of sensilla on the tail is high. To determine the feasibility that mechanoreceptors are involved in such phenomena, we mapped scale form and the size, density, distribution, and spacing of sensilla on the head, body, limbs, and tail of the leopard gecko. This species has a full complement of autotomy planes along the length of the tail, and the postautotomic behavior of its tail has been documented. We found that the density of sensilla is highest on the tail relative to all other body regions examined; a dorsoventral gradient of caudal sensilla density is evident on the tail; sensilla are more closely spaced on the dorsal and lateral regions of the tail than elsewhere and are carried on relatively small scales; and that the whorls of scales on the tail bear a one to one relationship with the autotomy planes. Our results are consistent with the hypotheses of sensilla being involved in determining the site at which autotomy will occur, and with them being involved in the mediation of tail behavior following autotomy. These findings open the way for experimental neurological investigations of how autotomy is induced and how the detached tail responds to external environmental input.

Tail autotomy and subsequent regeneration alter the mechanics of locomotion in lizards

Animals undergo significant weight change due to a variety of causes. Autotomy, the voluntary shedding of an appendage in response to a predator stimulus, provides an effective model for measuring the effects of rapid weight change on locomotor behavior and the responses to more gradual weight gain, particularly in lizards capable of both autotomizing and regenerating their tail. Although the general effects of autotomy on locomotor performance are commonly explored, we investigated changes in locomotor mechanics associated with tail loss and long-term regeneration for the first time by measuring morphology, 3D kinematics, and ground reaction forces (GRFs) in the leopard gecko, Eublepharis macularius. Tail autotomy resulted in a 13% anterior shift in the center of mass (CoM), which only partially recovered after full regeneration of the tail. Although no changes in body or forelimb kinematics were evident, decreases in hindlimb joint angles signify a more sprawled posture following autotomy. Changes in hindlimb GRFs resulted in an increase in weight-specific propulsive force, without a corresponding change in locomotor speed. Hindlimb kinematics and GRFs following autotomy recovered to pre-autotomy values as the tail regenerated. These results suggest an active locomotor response to tail loss that demonstrates the causal relationships between morphological, kinematic, and force variation.