断尾对蓝尾石龙子能量储存和运动表现的影响

在许多蜥蜴种类中,尾自切是一种主要的逃避天敌捕食的防御性策略。虽然断尾使蜥蜴获得短期的生存利益,但同时也需为此承受多方面的代价。利用从丽水采集的117条蓝尾石龙子来评价该种动物断尾的能量和运动代价。81条(约69%)石龙子至少经历过1次尾自切。断尾个体中,原先断尾事件的发生频率在不同尾区间存在显著差别,但两性间无差别。将实验组17条具完整尾的石龙子依次切去3个尾段,然后测定断尾前后石龙子的运动表现以及每个尾段、身体各部分中的脂肪含量。另15条具完整尾的石龙子作为对照组,仅测量其运动表现。尾部的脂肪含量与尾基部宽呈正相关,说明具较粗尾部的石龙子一般具有相当较多的尾部储能。尾部脂肪含量随尾长呈非等比例分布,大部分脂肪集中于尾近基部端。断尾几乎不影响蓝尾石龙子的运动表现,仅当大部分尾部被切除时疾跑速有较小程度的降低。显示了蓝尾石龙子因遭遇天敌捕食攻击或其它因素作用而产生的部分断尾可能并不会导致严重的能量和运动代价。由于野外种群蓝尾石龙子个体的断尾情况主要发生在尾近基部或中部位置,因此可以认为自然条件下该种动物的尾自切通常会遭受明显的能量和运动代价。     

Sex, Reproductive Status, and Cost of Tail Autotomy via Decreased Running Speed in Lizards

Autotomy, voluntary shedding of body parts to permit escape, is a theoretically interesting defense because escape benefit is offset by numerous costs, including impaired future escape ability. Reduced sprint speed is a major escape cost in some lizards. We predicted that tail loss causes decreased speed in males and previtellogenic females, but not vitellogenic females already slowed by mass gain. In the striped plateau lizard, Sceloporus virgatus , adults of both sexes are subject to autotomy, and females undergo large increases in body condition (mass/length) during vitellogenesis. Time required for running 1 m was similar in intact autotomized males and previtellogenic females, but increased by nearly half after autotomy. Vitellogenic females were slower than other lizards when intact, but their speed was unaffected by autotomy. Following autotomy, speeds of all groups were similar. Thus, speed costs of autotomy vary with sex and reproductive condition: decreased running speed is not a cost of autotomy in vitellogenic females or presumably gravid females. Costs of autotomy are more complex than previously known. Speed and other costs might interact in unforseen ways, making it difficult to predict whether strategies to compensate for diminished escape ability differ with reproductive condition in females.     

Tail Autotomy Plays No Important Role in Influencing Locomotor Performance and Anti‐Predator Behavior in a Cursorial Gecko

We used the frog‐eyed sand gecko (Teratoscincus scincus) as a model system to evaluate the locomotor costs of tail loss, and to examine whether tailless geckos use alternative anti‐predator behavior to compensate for the costs of tail loss. Of the 16 field‐captured geckos, eight were used as experimental animals and the remaining ones as controls. Locomotor performance, activity level and anti‐predator behavior were measured for experimental geckos before and after the tail‐removing treatment. Control geckos never undergoing the tail‐removing manipulation were measured to serve as controls for the measurements taken at the same time for experimental geckos. Experimental geckos did not differ from controls in activity level before they underwent the tail‐removing manipulation, but became less active thereafter. The mean locomotor stamina of tailless geckos was reduced by about 30% of the mean value for tailed ones. However, as the maximum stamina predicted from the laboratory trials is seldom required in nature, we expect that the costs associated with the reduced locomotor stamina may be relatively minor in T. scincus. All other examined locomotor (overall speed, maximal speed and stride length) and behavioral (distance to refuge, approach distance and flight distance) traits were not affected by the tail‐removing manipulation. Overall, our results suggest that tail autotomy plays no important role in influencing locomotor performance and anti‐predator behavior in lizards where the tail has no direct role in locomotion but is used to direct predatory strikes away from the torso.     

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.     

The Influence of Tail Autotomy on the Escape Response of the Cape Dwarf Gecko, Lygodactylus capensis

Tail autotomy as a defence against predators occurs in many species of lizard. Although tail autotomy may provide an immediate benefit in terms of survival it may nevertheless be costly due to other functions of the tail. For example, tail autotomy may affect the locomotory performance of lizards during escape. We investigated the influence of tail autotomy on the escape performance of the Cape Dwarf Gecko, Lygodactylus capensis, on a vertical and a horizontal surface. Autotomized geckos were significantly slower than intact geckos during vertical escape, whereas tail autotomy did not influence the horizontal escape speed. Backward falling of the autotomized geckos on the vertical platform may explain the reduced speed. In addition, tail autotomy did not significantly affect body curvature and stride length of the geckos. The observed decrease of escape speed on a vertical platform may influence the habitat use and behaviour of these geckos. Ecological consequences resulting from tail autotomy are discussed in light of these findings.     

Reduced tail regeneration in the Common Lizard, Lacerta vivipara, parasitized by blood parasites

1. Many lizards will lose their tail through autotomy as an antipredator device even though there must be significant costs during tail regeneration.
2. Parasites are energetically costly to the host, and may reduce the rate of cell regeneration. The relation between the presence of haemogregarines (phylum Sporozoa) and the rate of tail regeneration in the Common Lizard Lacerta vivipara (Jacquin) was examined.
3. Experimentally induced autotomy in parasitized lizards resulted in a significantly reduced rate of tail regeneration compared with non-parasitized lizards. On the other hand, tail loss was not associated with an abnormal increase of parasite load, suggesting that the physiological stress (induced by tail loss) did not cause a decrease in parasite defence.     

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.     

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.     

Effects of Microhabitat‐Dependent Predation Risk on Vigilance during Intermittent Locomotion in Psammodromus algirus Lizards

Animals should be able to adjust their behavior by tracking changes in predation risk level continuously. Many animals show a pattern of intermittent locomotion with short pauses that may increase detection and vigilance of predators. These locomotor patterns may depend on the microhabitat structure, which affect predation risk levels. We examined in detail in the laboratory the characteristics of spontaneous locomotion, scanning behavior, and the escape performance of Psammodromus algirus lizards moving in two different microhabitats (leaf litter patches and open sand areas). Results showed that in leaf litter, lizards moved at slower speed and had shorter bursts of locomotion both in distance and duration, than in sand substrates. This locomotor pattern allowed lizards to increase scanning rate and total time spent in vigilance behavior. When lizards were forced to flee, they escaped to longer distances and during more time in open sand areas, but lizards were able to attain similar escape speed in the two substrates. Lizards may be able to compensate the cost of moving between different microhabitats with different predation risk by behaviorally changing their locomotor and vigilance patterns. However, complex interactions between the visibility of lizards to predators and the ability of lizards to detect predators, together with the need of attending simultaneously to other conflicting demands, may lead to apparently non‐intuitive solutions in locomotor patterns and the rate of vigilance behavior.     

The movement patterns of lacertid lizards: speed, gait and pauses in Lacerta vivipara

Lacerta vivipara moving across an open space at their normal activity temperature alternate bursts of locomotion with short pauses which tend to occur at the extremes of the limb cycle, i.e. when individual limbs are maximally adducted or retracted and the spinal cord is maximally flexed in the lateral plane. The movement bursts and pauses in adult lizards have mean durations of 0–30 and 012 s, respectively, and within bursts the lizards move at a mean speed of 14–6 cm s^-1. Movement in juvenile lizards is 2–5 times faster (relative to body length) and the pauses are of longer duration (mean = 019 s), giving the locomotion of juveniles a more jerky appearance. Lizards which are chasing crickets increase the speed and the duration of locomo-tory bursts, although the pauses persist. Lizards which are searching for a previously perceived cricket increase pause duration (mean = 0–40 s). Lizards which are fleeing from a sudden disturbance move at almost twice (juveniles) or 3–7 times (adults) the speed of foraging animals: the pauses persist, although at much reduced frequency. Increases in speed result from increases in both stride length (Λ) and stride frequency (n); the ratio Λ/ n appears to remain constant at 006. The significance of these observations is discussed, although the functions of the pauses cannot yet be explained.     

The m. caudifemoralis longus and its relationship to caudal autotomy and locomotion in lizards (Reptilia: Sauna)

Although the phenomenon of tail autotomy has traditionally been viewed in a purely adaptive light, functional constraints imposed by the locomotor system appear to have influenced the presence and extent of autotomy in lizards. Them. caudifemoralis longus is an unsegmented hind limb retractor that originates from the caudal vertebrae. It does not participate in autotomy and thus limits the proximal position of autotomic septa. Variation in the extent of the m. caudifemoralis is correlated with locomotor type. The muscle is large and originates from a long series of caudal vertebrae in fast moving lizards with powerful limb retraction, as exemplified by taxa capable of bipedal running. In slower lizards with sprawling postures, such as geckos, the m. caudifemoralis is small and restricted to the first few postsacral vertebrae. Autotomy is typically restricted or absent in the former lizards, while in the latter only the most proximal vertebrae are incapable of autotomy. In the evolution of existing patterns of caudal autotomy, functional demands intrinsic to the tail may be subservient to locomotor constraints imposed on the tail base by the m. caudifemoralis longus .     

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).     

Impact of tail loss on the behaviour and locomotor performance of two sympatric Lampropholis skink species

Caudal autotomy is an anti-predator behaviour that is used by many lizard species. Although there is an immediate survival benefit, the subsequent absence of the tail may inhibit locomotor performance, alter activity and habitat use, and increase the individuals' susceptibility to future predation attempts. We used laboratory experiments to examine the impact of tail autotomy on locomotor performance, activity and basking site selection in two lizard species, the delicate skink (Lampropholis delicata) and garden skink (L. guichenoti), that occur sympatrically throughout southeastern Australia and are exposed to an identical suite of potential predators. Post-autotomy tail movement did not differ between the two Lampropholis species, although a positive relationship between the shed tail length and distance moved, but not the duration of movement, was observed. Tail autotomy resulted in a substantial decrease in sprint speed in both species (28-39%), although this impact was limited to the optimal performance temperature (30°C). Although L. delicata was more active than L. guichenoti, tail autotomy resulted in decreased activity in both species. Sheltered basking sites were preferred over open sites by both Lampropholis species, although this preference was stronger in L. delicata. Caudal autotomy did not alter the basking site preferences of either species. Thus, both Lampropholis species had similar behavioural responses to autotomy. Our study also indicates that the impact of tail loss on locomotor performance may be temperature-dependent and highlights that future studies should be conducted over a broad thermal range.     

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.     

Flip,flop and fly: modulated motor control and highly variable movement patterns of autotomized gecko tails

Many animals lose and regenerate appendages, and tail autotomy in lizards is an extremely well-studied example of this. Whereas the energetic, ecological and functional ramifications of tail loss for many lizards have been extensively documented, little is known about the behaviour and neuromuscular control of the autotomized tail. We used electromyography and high-speed video to quantify the motor control and movement patterns of autotomized tails of leopard geckos (Eublepharis macularius). In addition to rhythmic swinging, we show that they exhibit extremely complex movement patterns for up to 30 min following autotomy, including acrobatic flips up to 3 cm in height. Unlike the output of most central pattern generators (CPGs), muscular control of the tail is variable and can be arrhythmic. We suggest that the gecko tail is well suited for studies involving CPGs, given that this spinal preparation is naturally occurring, requires no surgery and exhibits complex modulation.     

Caudal autotomy and regeneration in lizards

Caudal autotomy, or the voluntary self-amputation of the tail, is an anti-predation strategy in lizards that depends on a complex array of environmental, individual, and species-specific characteristics. These factors affect both when and how often caudal autotomy is employed, as well as its overall rate of success. The potential costs of autotomy must be weighed against the benefits of this strategy. Many species have evolved specialized behavioral and physiological adaptations to minimize or compensate for any negative consequences. One of the most important steps following a successful autotomous escape involves regeneration of the lost limb. In some species, regeneration occurs rapidly; such swift regeneration illustrates the importance of an intact, functional tail in everyday experience. In lizards and other vertebrates, regeneration is a highly ordered process utilizing initial developmental programs as well as regeneration-specific mechanisms to produce the correct types and pattern of cells required to sufficiently restore the structure and function of the sacrificed tail. In this review, we discuss the behavioral and physiological features of self-amputation, with particular reference to the costs and benefits of autotomy and the basic mechanisms of regeneration. In the process, we identify how these behaviors could be used to explore the neural regulation of complex behavioral responses within a functional context.     

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.     

Handling-related tail loss in an endangered skink: incidence, correlates and a possible solution

Caudal autotomy (tail loss) during capture and handling is widely reported among several families of lizards. Autotomy causes elevated stress levels in lizards, and imposes a significant fitness cost on autotomized individuals. Despite these detrimental impacts, conservation and ethical issues associated with handling-related tail loss have received little attention. We assessed the incidence and correlates of tail autotomy during capture and handling in an endangered skink, the alpine she-oak skink Cyclodomorphus praealtus . A significant proportion (9.3%) of lizards autotomized their tails during capture and handling. Medium-sized lizards were more likely to lose their tails during handling, and this effect was exacerbated at intermediate body temperatures. Probability of autotomy had a complex relationship with cumulative observer experience, independent of other risk factors. Based on the modelled relationship of autotomy with body temperature, we propose that alpine she-oak skinks be cooled immediately after capture to reduce rates of autotomy during subsequent handling.     

Interactive effects of leg autotomy and incline on locomotor performance and kinematics of the cellar spider,Pholcus manueli

Leg autotomy can be a very effective strategy for escaping a predation attempt in many animals. In spiders, autotomy can be very common (5–40% of individuals can be missing legs) and has been shown to reduce locomotor speeds, which, in turn, can reduce the ability to find food, mates, and suitable habitat. Previous work on spiders has focused mostly on the influence of limb loss on horizontal movements. However, limb loss can have differential effects on locomotion on the nonhorizontal substrates often utilized by many species of spiders. We examined the effects of leg autotomy on maximal speed and kinematics while moving on horizontal, 45° inclines, and vertical (90°) inclines in the cellar spider Pholcus manueli, a widespread species that is a denizen of both natural and anthropogenic, three‐dimensional microhabitats, which frequently exhibits autotomy in nature. Maximal speeds and kinematic variables were measured in all spiders, which were run on all three experimental inclines twice. First, all spiders were run at all inclines prior to autotomization. Second, half of the spiders had one of the front legs removed, while the other half was left intact before all individuals were run a second time on all inclines. Speeds decreased with increasing incline and following autotomy at all inclines. Autotomized spiders exhibited a larger decrease in speed when moving horizontally compared to on inclines. Stride length decreased at 90° but not after autotomy. Stride cycle time and duty factor increased after autotomy, but not when moving uphill. Results show that both incline and leg autotomy reduce speed with differential effects on kinematics with increasing incline reducing stride length, but not stride cycle time or duty factor, and vice versa for leg autotomy. The lack of a significant influence on a kinematic variable could be evidence for partial compensation to mitigate speed reduction.     

Take this broken tail and learn to jump: the ability to recover from reduced in‐air stability in tailless green anole lizards [Anolis carolinensis (Squamata: Dactyloidae)]

Locomotion is involved in various fitness‐related tasks, such as foraging, acquiring mates, and escaping from predators. Despite the importance of locomotor performance in determining fitness, animals often encounter situations in nature during which their locomotor performance is severely compromised. For animals that actively discard appendages as an anti‐predator strategy, the loss of appendages can cause a severe reduction in locomotor performance. However, whether animals can compensate for the impact on locomotor performance after autotomy is still unclear. A previous study has shown that tailless green anole lizards suffered from reduced in‐air stability during jumping. In this study, we monitored jump kinematics in three groups of Anolis carolinensis for five consecutive weeks to test two hypotheses: first, whether tailless green anoles can recover from reduced in‐air stability before their tails can regenerate; and second, whether gaining locomotor experience facilitates locomotor recovery. Our results revealed extensive individual variation in the ability to compensate for reduced in‐air stability. Some individuals did improve in‐air stability during the study period, whereas others showed no sign of improvement. Moreover, the acquisition of locomotor experience did not facilitate the recovery process. Our findings suggested that tail autotomy in green anoles probably imposes a long‐term fitness disadvantage. The utility of other compensatory mechanisms, such as altering behaviour, might play a role in natural populations to minimize the impact of autotomy on individual fitness. Our findings also shed light on the independent evolutionary losses of the ability to autotomize within lizards. Comparative studies which test whether species that autotomize more frequently/easily can better compensate for the effect of autotomy would be a fruitful direction of future research. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 583–592.