The regenerated tail of juvenile leopard geckos (Gekkota: Eublepharidae: Eublepharis macularius) preferentially stores more fat than the original

The tail of many species of lizard is used as a site of fat storage, and caudal autotomy is a widespread phenomenon among lizards. This means that caudal fat stores are at risk of being lost if the tail is autotomized. For fat-tailed species, such as the leopard gecko, this may be particularly costly. Previous work has shown that tail regeneration in juveniles of this species is rapid and that it receives priority for energy allocation, even when dietary resources are markedly reduced. We found that the regenerated tails of juvenile leopard geckos are more massive than their original counterparts, regardless of dietary intake, and that they exhibit greater amounts of skeleton, inner fat, muscle and subcutaneous fat than original tails (as assessed through cross-sectional area measurements of positionally equivalent stations along the tail). Autotomy and regeneration result in changes in tail shape, mass and the pattern of tissue distribution within the tail. The regenerated tail exhibits enhanced fat storage capacity, even in the face of a diet that results in significant slowing of body growth. Body growth is thus sacrificed at the expense of rapid tail growth. Fat stores laid down rapidly in the regenerating tail may later be used to fuel body growth or reproductive investment. The regenerated tail thus seems to have adaptive roles of its own, and provides a potential vehicle for studying trade-offs that relate to life history strategy.     

Locomotor performance of sand lizards (Lacerta agilis): effects of predatory pressure and parasite load

Locomotor performance affects foraging efficiency, predator avoidance and consequently fitness. Agility and speed determine the animal's social status and reflect its condition. In this study, we test how predatory pressure and parasite load influences locomotor performance of wild specimens of the sand lizard Lacerta agilis. Animals were chased on a 2-metre racetrack. Lizards with autotomy ran significantly faster than lizards with an intact tail, but there was no significant difference in running speed between individuals with fresh caudal autotomy and regenerated tails. Parasite presence and load, age and sex had no significant effect on speed. Our results indicate that autotomy either alters locomotory behaviour or that individuals with autotomised tails were those that previously survived contact with predators, and therefore represented a subgroup of the fastest individuals. Therefore, in general, predatory pressure but not parasites affected locomotor performance in lizards.     

Some vaguely explored (but not trivial) costs of tail autotomy in lizards

Lizard tail autotomy is considered an efficient anti-predator strategy that allows animals to escape from a predator attack. However, since the tail also is involved in many alternative functions, tailless animals must cope with several costs following autotomy. Here we explicitly evaluate the consequences of tail autotomy for two costs that have been virtually unexplored: 1. we test whether the anatomical change that occurs after tail loss causes a reduction in the role of the tail as a distraction mechanism to predators; 2. we analyzed whether tail synthesis comprises an energetically costly process in itself, by directly comparing the cost of maintenance before and after autotomy. We found that original tails displace further and at greater velocity than regenerated tails, indicating that the anti-predation responses of a lizard probably changes according to whether its tail is original or regenerated. With regard to the energetic cost of tail synthesis, we observed a significant increase in the standard metabolic rate, which rose 36% in relation to the value recorded prior to tail loss. This result suggests that the energetic cost of tail synthesis itself could be enough to affect lizard fitness.     

Is partial tail loss the key to a complete understanding of caudal autotomy?

Autotomy, the self‐amputation of limbs or appendages, is a dramatic anti‐predator tactic that has repeatedly evolved in a range of invertebrate and vertebrate groups. In lizards, caudal autotomy enables the individual to break away from the predator's grasp, with the post‐autotomy thrashing of the tail distracting the attacker while the lizard makes its escape. This drastic defensive strategy should be selectively advantageous when the benefit (i.e. survival) exceeds the subsequent costs associated with tail loss. Here, we highlight how the position of autotomy along the length of the tail may influence the costs and benefits of the tactic, and thus the adaptive advantage of the strategy. We argue that most studies of caudal autotomy in lizards have focused on complete tail loss and failed to consider variation in the amount of tail shed, and, therefore, our understanding of this anti‐predator behaviour is more limited than previously thought. We suggest that future research should investigate how partial tail loss influences the likelihood of surviving encounters with a predator, and both the severity and duration of costs associated with caudal autotomy. Investigation of partial autotomy may also enhance our understanding of this defensive strategy in other vertebrate and invertebrate groups.     

Frequency of tail loss reflects variation in predation levels,predator efficiency,and the behaviour of three populations of brown anoles

We investigated two predictions regarding the incidence of tail regeneration in lizards for three populations of brown anoles exposed to varying predation levels from the same predator (cats). Firstly although inefficient predators are likely to increase the incidence of regenerated tails (i.e. lizards can escape through tail autotomy), highly efficient predators will kill and eat the lizard and thus leave no evidence of autotomy. At the site with no cats, only 4% of anoles demonstrated signs of tail regeneration. This value was not significantly different from the site where feral cats (i.e. ‘efficient’ predators that would capture prey to eat, as supported by behavioural observation) were present (7%). By contrast, 25% of anoles present at the site with pet cats (well‐fed domesticated cats that caught and played with anoles, i.e. were ‘inefficient’ predators) exhibited regenerated tails. Secondly, more obvious lizards are more susceptible to predation attempts. Supporting this hypothesis, our data indicate a higher incidence of regenerated tails (28%) was recorded amongst adult males (which are territorial, occupying exposed positions) compared to females and subadult males (17%) or juveniles (1%). In conclusion, the behaviour of both the predator and the lizard influences the frequency of regenerated tails in brown anoles. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 648–656.     

Energetic and locomotor costs of tail loss in the Chinese skink, Eumeces chinensis

Caudal autotomy is a defense mechanism used by numerous lizards to evade predators, but this entails costs. We collected 294 adult Chinese skinks (Eumeces chinensis) from a population in Lishui (eastern China) to evaluate energetic and locomotor costs of tail loss. Of the 294 skinks, 214 (c. 73%) had previously experienced caudal autotomy. Neither the proportion of individuals with regenerated tails nor the frequency distribution of locations of the tail break differed between sexes. We successively removed four tail segments from each of the 20 experimental skinks (adult males) initially having intact tails. Lipid content in each removed tail segment was measured, and locomotor performance (sprint speed, the maximal length traveled without stopping and the number of stops in the racetrack) was measured for each skink before and after each tail-removing treatment. Another independent sample of 20 adult males with intact tails was measured for locomotor performance to serve as controls for successive measurements taken for the experimental lizards. Caudal lipids were disproportionately stored along the length of the tail, with most lipids being aggregated in its proximal portion. Tail loss significantly affected sprint speed, but not the maximal length of, or the number of stops during the sprint. However, the adverse influence of tail loss on sprint speed was not significant until more than 51% of the tail (in length) was lost. Our data show that partial tail loss due to predatory encounters or other factors may not severely affect energy stores or locomotor performance in E. chinensis. As tail breaks occurred more frequently in the proximal portion of the tail in skinks collected from the field, we conclude that caudal autotomy occurring in nature often incurs substantial energetic and locomotor costs in E. chinensis.     

Unique Structural Features Facilitate Lizard Tail Autotomy

Autotomy refers to the voluntary shedding of a body part; a renowned example is tail loss among lizards as a response to attempted predation. Although many aspects of lizard tail autotomy have been studied, the detailed morphology and mechanism remains unclear. In the present study, we showed that tail shedding by the Tokay gecko (Gekko gecko) and the associated extracellular matrix (ECM) rupture were independent of proteolysis. Instead, lizard caudal autotomy relied on biological adhesion facilitated by surface microstructures. Results based on bio-imaging techniques demonstrated that the tail of Gekko gecko was pre-severed at distinct sites and that its structural integrity depended on the adhesion between these segments.     

TAIL SHEDDING IN ISLAND LIZARDS [LACERTIDAE, REPTILIA]: DECLINE OF ANTIPREDATOR DEFENSES IN RELAXED PREDATION ENVIRONMENTS

The ability of an animal to shed its tail is a widespread antipredator strategy among lizards. The degree of expression of this defense is expected to be shaped by prevailing environmental conditions including local predation pressure. We test these hypotheses by comparing several aspects of caudal autotomy in 15 Mediterranean lizard taxa existing across a swath of mainland and island localities that differ in the number and identity of predator species present. Autotomic ease varied substantially among the study populations, in a pattern that is best explained by the presence of vipers. Neither insularity nor the presence of other types of predators explain the observed autotomy rates. Final concentration of accumulated tail muscle lactate and duration of movement of a shed tail, two traits that were previously thought to relate to predation pressure, are in general not shaped by either predator diversity or insularity. Under conditions of relaxed predation selection, an uncoupling of different aspects of caudal autotomy exists, with some elements (ease of autotomy) declining faster than others (duration of movement, lactate concentration). We compared rates of shed tails in the field against rates of laboratory autotomies conducted under standardized conditions and found very high correlation values ( r > 0.96). This suggests that field autotomy rates, rather than being a metric of predatory attacks, merely reflect the innate predisposition of a taxon to shed its tail.     

Partial tail loss has no severe effects on energy stores and locomotor performance in a lacertid lizard, <Emphasis Type="Italic">Takydromus septentrionalis</Emphasis>

Many species of lizards use caudal autotomy as a defense strategy to avoid predation, but tail loss entails costs. These topics were studied experimentally in the northern grass lizard, Takydromus septentrionalis. We measured lipids in the three-tail segments removed from each of the 20 experimental lizards (adult females) initially having intact tails to evaluate the effect of tail loss on energy stores; we obtained data on locomotor performance (sprint speed, the maximal length traveled without stopping and the number of stops in the racetrack) for these lizards before and after the tail-removing treatments to evaluate the effect of tail loss on locomotor performance. An independent sample of 20 adult females that retained intact tails was measured for locomotor performance to serve as controls for successive measurements taken for the experimental lizards. The lipids stored in the removed tail was positively correlated with tailbase width when holding the tail length constant, indicating that thicker tails contained more lipids than did thinner tails of the same overall length. Most of the lipids stored in the tail were concentrated in the proximal portion of the tail. Locomotor performance was almost unaffected by tail loss until at least more than 71% of the tail (in length) was lost. Our data show that partial tail loss due to predatory encounters or other factors may not severely affect energy stores and locomotor performance in T. septentrionalis.     

Comparative postautotomy tail activity in six Mediterranean lacertid lizard species

Tail autotomy, the self-induced tail separation from the body, is a common and effective antipredator mechanism in lizards. In this study, we examine the muscle energetics of tail shedding in six lacertid lizard species (Podarcis erhardii, Podarcis peloponnesiaca, Podarcis muralis, Podarcis gaigeae, Podarcis milensis, and Lacerta graeca) from the northeast Mediterranean region. Very long periods of postautotomy tail movement were demonstrated for all species (range=6-8 min), and differences among species were not statistically significant. Postautotomy tail movement, powered by anaerobic muscle activity, resulted in a strong increase in lactate concentrations and a concomitant depletion of muscle glycogen of exhausted tails relative to resting tails. No significant differences were found in either lactate or glycogen concentrations among the species examined. Duration of movement was negatively correlated with final lactate concentrations. The lack of differentiation in postautotomy energetic physiology in this group of species that have evolved under very different predation environments indicates that postautotomy muscle metabolism involves an overall conservative suite of characters.     

Endoplasmin regulates differentiation of tonsil-derived mesenchymal stem cells into chondrocytes through ERK signaling

It is well-known that some species of lizard have an exceptional ability known as caudal autotomy (voluntary self-amputation of the tail) as an anti-predation mechanism. After amputation occurs, they can regenerate their new tails in a few days. The new tail section is generally shorter than the original one and is composed of cartilage rather than vertebrae bone. In addition, the skin of the regenerated tail distinctly differs from its original appearance. We performed a proteomics analysis for extracts derived from regenerating lizard tail tissues after amputation and found that endoplasmin (ENPL) was the main factor among proteins up-regulated in expression during regeneration. Thus, we performed further experiments to determine whether ENPL could induce chondrogenesis of tonsil-derived mesenchymal stem cells (T-MSCs). In this study, we found that chondrogenic differentiation was associated with an increase of ENPL expression by ER stress. We also found that ENPL was involved in chondrogenic differentiation of T-MSCs by suppressing extracellular signal-regulated kinase (ERK) phosphorylation.     

Patterns of caudal-autotomy evolution in lizards

Using comparative techniques to account for phylogenetic effects, I examined patterns of evolution of caudal autotomy and foraging in 39 lizard species to test the hypothesis that caudal autotomy has co-evolved with morphology, locomotor performance, and foraging behaviour. There were significant positive associations between evolution of the point on the tail (distance from cloaca) at which tail loss occurs (an indirect measure of caudal autotomy) and evolution of each of the following: tail length, caudifemoralis longus (CFL) muscle length, and jump distance. The correlation with the evolution of sprint speed approached significance. These relationships primarily were due to the influence of tail-length evolution on autotomy-point evolution. With the effect of tail-length evolution removed, autotomy-point evolution was negatively correlated with the evolution of tail-loss frequency. The CFL restricts tail loss to portions of the tail posterior to the most distal point of its insertion in the tail. In addition, with the effect of tail-length evolution removed, CFL length co-evolved with sprint speed. These results indicate that tail morphology has co-evolved with caudal autotomy such that the evolution of the CFL has reduced caudal autotomy in certain groups of lizards.
Ambush foraging, the ability to lose the tail, intermediate CFL length, and low locomotor performance (i.e. slow sprint speed and short jump distance) are hypothesized to be the ancestral conditions in lizards using outgroup rooting. The diversification of lizard taxa has resulted in some lineages moving away from ancestral character states (i.e. family Teiidae, superfamily Varanoidea), while others are very similar or identical to their ancestors (i.e. superfamily Iguania).     

Tail loss reduces home range size and access to females in male lizards, Psammodromus algirus

Numerous lizard species use caudal autotomy as an antipredatordevice even though there must be significant costs during theperiod of tail regeneration. Strategies used by tailless individualsto enhance survival in natural populations are still poorlyunderstood. We experimentally examine tail loss in large, dominantmales of Psammodromus algirus in the middle of the breedingseason in the field. We report data showing home range reductionof large dominant males after autotomy, reduction in the numberof females in the home ranges of manipulated males, and a potentialincrease in mating opportunities of small subordinate maleswith complete tails. We conclude that changes in home rangeuse because of desertion of areas with less cover can resultin decreased predation risk at the cost of decreased accessto females.     

Dynamics of Mara–Serengeti ungulates in relation to land use changes

Caudal autotomy, the ability to shed the tail, is common in lizards as a response to attempted predation. Since Arnold's substantial review of caudal autotomy as a defence in reptiles 20 years ago, our understanding of the costs associated with tail loss has increased dramatically. In this paper, we review the incidence of caudal autotomy among lizards (Reptilia Sauria) with particular reference to questions posed by Arnold. We examine tail break frequencies and factors that determine occurrence of autotomy in natural populations (including anatomical mechanisms, predation efficiency and intensity, microhabitat preference, sex and ontogenetic differences, as well as intraspecific aggression). We also summarize the costs associated with tail loss in terms of survivorship and reproduction, focusing on potential mechanisms that influence fitness (i.e. locomotion costs, behavioural responses and metabolic costs). Finally, we examine the factors that may influence the facility with which autotomy takes place, including regeneration rate, body form and adaptive behaviour. Taking Arnold's example, we conclude with proposals for future research.     

Tail injuries increase the risk of mortality in free-living lizards (Uta stansburiana)

Summary Caudal autotomy is an effective anti-predator mechanism used by many lizard species. Fitness benefits of surviving a predatory attack are obvious, although lizards that autotomize their tails may be at greater risk during subsequent encounters with predators than lizards with complete tails. In previous laboratory studies, tail-less lizards were more vulnerable to capture by predators, but little is known about the relative survival of tailed versus tail-less lizards in nature. This study reports on significant associations between naturally incurred tail injuries and the subsequent risk of mortality in 7 populations of the lizard Uta stansburiana. I used standard mark-recapture techniques to document survival and quantified tail injuries by estimating tail completeness. I then used sampled randomization tests to compare intitial tail completeness values of surviving versus non-surviving lizards. I evaluated overall patterns by comparising the means of tail completeness values of survivors versus non-survivors among mark-recapture sequences. Lizards with incomplete tails suffered higher mortality in the field, although this was not true for every comparison considered (i.e., for every mark-recapture sequence analyzed), and the overall trend was much stronger for adult males than for either adult females or juveniles. Higher mortality among lizards with incomplete tails is presumably a consequence of increased vulnerability to capture by predators. Vulnerability to predation of tail-injured lizards may be confounded by reduced social status in this species, because social subordination can result in the occupation of an inferior home range.     

No behavioural compensation for fitness costs of autotomy in a lizard

Abstract Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, but their use may be costly and decrease fitness. Fitness costs of antipredator mechanisms may, in turn, be defrayed by behavioural compensation. We used lizards as a model to measure behavioural fitness costs of the antipredator mechanism, autotomy, as they commonly lose their tails when attacked by predators. In addition, we examined whether male skinks, Carlia jarnoldae (Scincidae), behaviourally compensate for tail loss by comparing the behaviour of tailed and tailless males in experimental enclosures, either alone, with a conspecific male or female, or with a predator. Tailless males experience several costs of autotomy including reduced energy stores, and loss of autotomy as a defence. We identified an additional cost of tail loss: reduced mating success. However, this species did not behaviourally compensate these costs. Instead, characteristics of the ecology of C. jarnoldae may minimize the costs of autotomy. This species experiences an extended breeding season, which means that they experience reduced mating success for only 20% of this breeding season. Additionally, the presence of inguinal fat stores which supply energy in addition to stores in the tail reduce energetic costs.     

Muscle activity in autotomized tails of a lizard (Gekko gecko): a naturally occurring spinal preparation

We quantified muscle activity in tails of lizards (Gekko gecko) during running and after autotomy of the tail. We chose different animals and varied where we broke the tails in order to obtain three experimental preparations having: no regenerated tissue or prior tail loss (non-regenerated), a large regenerated portion and a few original caudal vertebrae (partially regenerated), and only regenerated tissue (fully regenerated). All observed axial motor patterns were rhythmic. During running of intact animals, muscles in non-regenerated tails were activated in an alternating, unilateral pattern that was propagated posteriorly. After autotomy, non-regenerated tails had unilateral muscle activity that alternated between the left and right sides and propagated anteriorly. Autotomized, partially regenerated tails had unilateral, alternating muscle activity that lacked any longitudinal propagation. Autotomized, fully regenerated tails had periodic muscle activity that occurred simultaneously for both left and right sides and all longitudinal positions. Neither tactile stimulation nor removal of the tail tip prior to autotomizing the tail affected the motor pattern. Several features of the motor pattern of autotomized tails changed significantly with increased time after autotomy. Autotomized tails with one or more spinal segments moved longer and more vigorously than autotomized tails consisting entirely of regenerated (unsegmented) tissue.Abbreviations AREA rectified integrated area - CYCDUR cycle duration or time between the onsets of successive bursts for a single channel - DUTY duty factor = EMG duration/CYCDUR - EMG electromyogram - EMGDUR EMG duration - INTENSITY = AREA/EMGDUR - ISPL intersegmental phase lag = PLAG/number of intervening muscle segments - LAG among site lag time = difference in onset times of adjacent ipsilateral electrode sites - PLAG phase lag = LAG/CYCDUR - RELISPL relative intersegmental phase lag = RELPLAG/number of intervening muscle segments - RELPLAG relative phase lag = LAG/EMGDUR     

Effects of size,caudal autotomy,and predator kairomones on the foraging behavior of Allegheny Mountain dusky salamanders (<Emphasis Type="Italic">Desmognathus ochrophaeus</Emphasis>)

Prey must balance the conflicting demands of foraging and defensive behavior. Foraging under the threat of predation may be further complicated among species that engage in caudal autotomy, the loss of a portion of the tail at preformed breakage planes, because the tail may serve as an important energy storage organ and contribute to motility, culminating in a trade-off between foraging and predator avoidance. As a result of the advantages conferred by the presence of a tail, individuals that have recently undergone autotomy may be more motivated to forage despite elevated levels of threat indicated by predator kairomones. We used a full factorial design to evaluate the combined effects of body size, exposure to predator kairomones, and experience with autotomy on the latency to strike at Drosophila prey, number of strikes, and prey captured per strike by Allegheny Mountain dusky salamanders (Desmognathus ochrophaeus). In our study, caudal autotomy was the only significant main effect and influenced both the latency to attack prey and the number of strikes attempted. In terms of latency to attack prey, there was a significant interaction between body size and autotomy such that “small” salamanders (≤3.2 cm SVL) without tails delayed their foraging behavior. In terms of the number of strikes toward prey, there was a significant interaction between autotomy and exposure to predator kairomones such that individuals with intact tails exhibited a greater number of strikes, with the exception of the “large” (>3.2 cm SVL) salamanders, which performed fewer strikes when exposed to the snake kairomones. There was no significant effect on foraging efficiency, although the trend in the data suggests that autotomized individuals forage more efficiently. This study was designed to evaluate the confluence of factors related to size, caudal autotomy, and exposure to stimuli from predators and hints at the magnitude of caudal autotomy on antipredator decision-making. Our data suggest that despite the importance of tail tissue for energy storage, locomotion, and mating, salamanders without tails are cautious when foraging under elevated risk.     

Multiple Roles of Tail Display by the Curly-Tailed Lizard Leiocephalus carinatus: Pursuit Deterrent and Deflective Roles of a Social Signal

The same display may be used in different contexts to convey different messages, or may have other, non-signaling functions. Several lines of evidence suggest that vertical tail curling, a previously documented social display in the lizard Leiocephalus carinatus , has antipredatory functions that may include pursuit deterrence and deflection of attacks from the body to the tail, which can be autotomized. An antipredatory role of tail curling is suggested by its more frequent occurrence when a predator is approaching than moving away, its greater frequency and intensity when a lizard is approached by a predator than when it moves spontaneously, and its greater frequency when the predator approaches directly rather than on a path bypassing the lizard. Evidence is presented contradicting use of tail curling for flash concealment or as an alarm signal to conspecifics. A pursuit-deterrent function of tail curling is suggested by its (1) more frequent use by lizards close to a refuge than those further from a refuge, (2) greater frequency during direct approaches by predators, and (3) much greater frequency when a predator is far enough away for pursuit to be deterred than when the predator is close enough to pose a high risk of capture. Lizards fled into a refuge without tail curling when the predator was very close, but often stopped outside a refuge while displaying the curled tail when the predator was farther away. Tail curling also may deflect attacks to the autotomizable tail, as suggested by its occurrence during spontaneous movements when no predator is approaching and by the high frequency of completely uncurled tails among individuals under bushes. The role of the tail in autotomy may facilitate evolution of pursuit-deterrent signals involving the tail.     

胎生蜥蜴断尾及再生的研究

对胎生蜥蜴的断尾及再生进行了统计和观察,结果表明：胎生蜥蜴幼体断尾率为28．26％,成体断尾率为45．45％。说明承受着很大的生存压力;断尾活动时间与断尾的长度及断尾部位有关;再生尾中有一节鳞片明显较其它鳞片长;再生尾明显较原尾生长速度快。