Effects of tail autotomy on survival,growth and territory occupation in free‐ranging juvenile geckos (Oedura lesueurii)

Abstract Many animals autotomize their tails to facilitate escape from predators. Although tail autotomy can increase the likelihood of surviving a predatory encounter, it may entail subsequent costs, including reduced growth, loss of energy stores, a reduction in reproductive output, loss of social status and a decreased probability of survival during subsequent encounters with predators. To date, few studies have investigated the potential fitness costs of tail autotomy in natural populations. I investigated whether tail loss influenced survival, growth and territory occupation of juvenile velvet geckos Oedura lesueurii in a population where predatory snakes were common. During the 3‐year mark–recapture study, 32% of juveniles voluntarily autotomized their tails when first captured. Analysis of survival using the program mark showed that voluntary tail autotomy did not influence the subsequent survival of juvenile geckos. Survival was age‐dependent and was higher in 1‐year‐old animals (0.98) than in hatchlings (0.76), whereas recapture probabilities were time‐dependent. Growth rates of tailed and tailless juveniles were very similar, but tailless geckos had slow rates of tail regeneration (0.14 mm day⁻¹). Tail autotomy did not influence rock usage by geckos, and both tailed and tailless juveniles used few rocks as diurnal retreat sites (means of 1.64 and 1.47 rocks, respectively) and spent long time periods (85 and 82 days) under the same rocks. Site fidelity may confer survival advantages to juveniles in populations sympatric with ambush foraging snakes. My results show that two potential fitness costs of tail autotomy – decreased growth rates and a lower probability of survival – did not occur in juveniles from this population. However, compared with juveniles, significantly fewer adult geckos (17%) voluntarily autotomized their tails during capture. Because adults possess large tails that are used for lipid storage, the energetic costs of tail autotomy are likely to be much higher in adult than in juvenile O. lesueurii.     

Effect of hind-limb autotomy on calling and hiding behavior in the band-legged ground cricket, <Emphasis Type="Italic">Dianemobius nigrofasciatus</Emphasis>

Crickets can escape death by autotomizing a limb when attacked by predators. In contrast with this benefit, autotomized individuals pay an immediate cost of escape speed and mating ability. Therefore, an adaptive response compensating for the cost of autotomy might be advantageous in autotomized individuals. In this study, we examined whether autotomy induced behavioral plasticity compensating for future cost in the band-legged ground cricket Dianemobius nigrofasciatus. Behavioral traits of D. nigrofasciatus were compared between autotomized and intact individuals. Frequency of calling behavior was higher for autotomized males. This behavior might be advantageous because females prefer actively calling males. In contrast with calling behavior, the frequencies of hiding behavior did not vary between autotomized and intact crickets, irrespective of sex. It might be disadvantageous for both sexes to hide, because females could not find hiding males and hiding females could not find males. These results indicated autotomy-induced behavioral plasticity that might reduce the cost of autotomy.     

Hair-trigger autotomy in porcelain crabs is a highly effective escape strategy

The benefits of autotomy, the voluntary shedding of limbs, havebeen adequately demonstrated in vertebrates but are poorlystudied in invertebrates. We provide strong experimental evidencefor an antipredatory benefit to autotomy in two porcelain crabs(Petrolisthes cinctipes and P. manimaculis). Since the outcomeof autotomy depends critically on the species of predator andprey involved, we first surveyed field populations of porcelaincrabs to identify ecologically relevant predators to use insubsequent experiments. We then examined the escape tacticsof the porcelain crabs in response to the four potential predatorswe identified, all larger predatory crabs. Cheliped autotomywas induced by three of the predator species (Cancer antennarius,Hemigrapsus nudus, Pachygrapsus crassipes); the fourth didnot attack porcelain crabs. Autotomy occurred in response to34% of all attacks, and in 67% of attacks in which the preywas held at some point by only the cheliped. Autotomy was ahighly effective escape mechanism against these predators;58 of 59 crabs that autotomized escaped, usually while thepredator stopped pursuit to eat the shed cheliped. Relianceon autotomy as a primary mechanism for escaping predators maybe particularly common in small crabs that cannot adequatelydefend themselves by other means and in suspension-feedingcrabs that do not need their chelipeds for feeding.     

Regeneration,predatory–prey interaction,and evolutionary history of articulate crinoids

Regeneration and predatory–prey interaction of crinoids are reviewed. Crinoids have strong powers of regeneration, and arm regeneration is common in fossil and Recent crinoids. Regenerated arms commonly start from the ligamentary articulation called syzygy or cryptosyzygy, where crinoids can autotomize their arms. Therefore, regenerated arms can be formed after loss of arms by autotomy of arms, and such autotomy is commonly the response to predatory attacks. Thus, regenerated arms can be used as the clue to estimate the predatory frequencies. Regeneration of “correct” skeletal morphology as in the original depends on the existence of adoral nerve center. A stalk without the adoral nerve center cannot regenerate the “correct” morphology of the original skeleton, but forms of “callus” as skeletal overgrowth. The strong ability of regeneration is a key factor of the success of articulate crinoids in the geologic history since the Triassic onward.     

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.     

Autotomy reduces feeding, energy storage and growth of the sea star Stichaster striatus

We evaluated the effect of autotomy on feeding, energy storage and growth of juvenile Stichaster striatus kept in the laboratory for five months with a limited supply of the mussel Semimytilus algosus. Autotomy strongly decreased feeding, energy storage and growth. Intact juveniles showed a ∼ 3 fold higher feeding rate than autotomized individuals throughout the experiment. Intact juveniles also had a higher (∼ 5 fold) energy content per pyloric caeca in each arm. This was mainly due to higher lipid content, the main proximate constituent of pyloric caeca. Intact juveniles showed a greater growth rate and reached a greater size than autotomized individuals, more evident for underwater mass than radius length. The reduced capacity to feed reduced energy intake in autotomized individuals. However, low energy reserves along with low growth in autotomized sea stars, support the hypothesis that juveniles of this species allocate energy to regeneration to the detriment of growth. This was also supported by the ∼ 25% of arm length regeneration after 5 mo. Remaining small could increase risk of lethal predation, however, S. striatus may reduce predation risk by using crevices and kelp holdfasts as refuges from predators. Given the strong impact of autotomy on feeding, regeneration of arms to recover full capacity to forage and grow seems a better strategy for juvenile S. striatus, than merely growing.     

Patterns in the autotomized adults of two sympatric,closely related grasshopper species in their natural habitat

Insects have various defense responses to natural enemies, including autotomy. Detailed knowledge of autotomy patterns and frequencies in the wild is required to make reliable inferences concerning the fitness benefits and costs of the consequences of autotomy. However, few quantitative surveys have been conducted on the frequency of autotomized insects in the wild. Here, I examined data on autotomy in adult Parapodisma tanbaensis and Parapodisma subastris grasshoppers, which are sympatric, closely related species, collected over two consecutive years at three field sites in Kyoto, Japan. To investigate what traits were related to the frequency of autotomized adults, I recorded the species, sex, body size, and hind leg status after sampling adults because, according to previous research, these four parameters can be used to make predictions about the frequency of autotomized adults in the wild. There was a significant interaction effect between grasshopper sex and the sampling season on the frequency of autotomized adults and a non-linear increase in the frequency of autotomized adults as the season advanced. However, there were no significant effects caused by species or body size. Thus, a sexual difference existed in the occurrence and disappearance of autotomized adults in the wild as the season advanced. The ecological and evolutionary factors and mechanisms causing this pattern are discussed.     

Change in take‐off elevation angle after limb autotomy mitigates the reduction in jumping distance in rice grasshoppers Oxya yezoensis

Autotomy is the ability to spontaneously self‐amputate a limb or other appendage, often as a reflexive action. This limb amputation typically occurs as a specialized defensive response to an attack from a predator and thereby enables the prey to escape from predation. Despite the benefits of escape, autotomized organisms lose the body part and its associated function. Here, we investigated the jumping behavior and performance of one‐leg‐autotomized and intact rice grasshoppers, Oxya yezoensis, to examine changes in jumping behavior after autotomy. The take‐off elevation of autotomized grasshoppers was 7.8° lower than in intact grasshoppers, resulting in nearly a 45° angle of take‐off, which maximized the jumping distance. Kinematic analyses of the jumping manner revealed that the angle of the femur during jumping differed between intact and autotomized grasshoppers, suggesting that the grasshoppers behaviorally change the take‐off elevation after autotomy. According to analyses of jumping performance, the degree of decline in performance differed between horizontal distance and vertical height. Even though they jumped on only one hind leg, one‐leg‐autotomized grasshoppers realized 69% performance along a horizontal distance relative to intact grasshoppers. In contrast, autotomized grasshoppers realized only a 44% performance in vertical height compared to intact grasshoppers. The difference in take‐off elevation between autotomized and intact grasshoppers is likely related to the observed difference in the magnitude of the decline in performance between horizontal distance and vertical height. These results suggest that rice grasshoppers may alter their take‐off elevation after limb autotomy to minimize the reduction in jumping distance.     

Autotomy-induced life history plasticity in band-legged ground cricket Dianemobius nigrofasciatus

Crickets can autotomize their limbs when attacked by predators. This enables them to escape death, but imposes a short-term cost on their escape speed and a long-term cost on their future mating ability. Therefore, adaptive response compensated for the cost of autotomy might be advantageous for autotomized individuals. In the present study, we examined whether autotomy induced life history plasticities compensating for the future cost in the band-legged ground cricket Dianemobius nigrofasciatus . Life history traits of D. nigrofasciatus were compared between autotomized and intact individuals. The developmental time and head width of the individuals that were autotomized as fourth instar nymphs were significantly shorter and smaller, respectively, than those of intact individuals. However, the adult longevity, number of eggs laid and oviposition schedule did not vary between autotomized and intact individuals. In addition, there was no difference between individuals autotomized at the fourth instar and adult stages in these three traits. Early maturation in the autotomized individuals might be advantageous through reducing the risk of predation owing to the shorter period in nymphal stages. The cost of small body size in the autotomized females might not be so great because of no significant difference in fecundity between autotomized and intact individuals. However, the cost of small body size was unclear in the autotomized males because in general larger males were preferred by females. These results indicated autotomy-induced life history that might reduce the cost of autotomy.     

Regeneration of Walking Legs in the Fiddler Crab Uca pugilator

SYNOPSIS. Regeneration of walking legs in the fiddler crab Ucapugilator is most efficient when it follows autotomy (the reflexiveloss of a limb). Closure of the wound and would healing occurimmediately following autotomy and visible regeneration beginswithin a few days. Regeneration of the walking leg occurs intwo distinct stages: The first stage, called Basal Growth, involvesmitosis and differentiation. The second stage involves primarilyprotein synthesis and water uptake and is called ProecdysialGrowth. Proecdysial Growth is, in part, under direct hormonalstimulation.     

Effect of the degree of autotomy on feeding, growth, and reproductive capacity in the multi-armed sea star Heliaster helianthus

The term autotomy refers to the process by which some species lose limbs or parts of limbs in response to adverse biotic or abiotic conditions, as for example, predation or abnormally high temperatures. The multi-armed sea star Heliaster helianthus is a key predator of the intertidal and the shallow rocky subtidal communities of north-central Chile. Natural populations of this sea star have been found with up to 60% of the individuals showing some degree of autotomy. The present study evaluated the effects of autotomy on feeding rate and growth of juvenile and adult H. helianthus after experimentally induced autotomy of 17% and 33% of their arms, as well as on the energy content of the pyloric caeca and gonads of adults during the reproductive period. Experimental juvenile sea stars were maintained and fed in the laboratory over a period of five months and adult sea stars for one month, Intact individuals were maintained as parallel controls. The results showed that juveniles undergoing 33% autotomy decreased their feeding rates, and as a consequence showed lowered net individual growth. In contrast, adults with 17% and 33% autotomy showed marked reductions in feeding. The results showed that autotomized adults had between five and seven times lower contents of carbohydrates, lipids, and proteins (and thus energetic content) in their pyloric caeca and gonads. The loss of the arms not only decreased the capacity for feeding in sea stars, but also allocated energy away from growth and reproduction into the process of regeneration of arms. This suggests that autotomy reduces the fitness of H. helianthus. Growth was reduced in the juveniles, while adults became limited in their ability to store energy which then limited their reproductive potential. Finally, based on the important effect of autotomy on reducing the feeding capacity of H. helianthus, the role of this sea star as a predator in the environment may be strongly affected.     

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.     

Autotomy and its Effects on Wolf Spider Foraging Success

Few studies have attempted to determine how physical injury affects predators. One of the ways that physical injury can be expressed is by autotomy or the voluntary loss of a body part. Here, we examined whether the loss of specific legs affects the foraging success of the wolf spider Rabidosa santrita (predator) on another species, Pardosa valens (prey). We also wanted to identify whether the loss of legs in both the predator and prey would impact the outcome of a predation event. Both predator and prey were collected from a creek bed at Portal, AZ, in 2012. Predators were randomly assigned groups where all prey items were intact or all prey had one randomly chosen leg IV removed. Within these groups, predators were organized into a control, leg I autotomy, or leg IV autotomy treatment. All predators had their pre‐ and post‐foraging running speed determined. Predators were introduced into chambers with five prey items and allowed to forage for 1 h. The leg position autotomized or the comparison of pre‐ and post‐foraging trials had no effect on predator running speed. Additionally, there was no significant effect of either predator or prey leg treatment on the total proportion of prey items captured by the end of the foraging trials. Survival analyses indicated that intact prey items tended to have a higher survival rate when predators were missing a leg IV than when predators were intact. When both the predator and prey were missing legs, no significant difference in prey survival rates was detected. We suggest that for predators that inhabit complex, heterogeneous habitats and are classified as ambush predators, the loss of a limb may affect prey capture success, especially when the prey is intact, but that increased sample size is necessary to determine whether this trend is significant.     

The incidence of autotomy in Carcinus maenas (L.)

A total of 1023 individuals of the common shore crab, Carcinus maenas (L.), were obtained from the environs of Whitby Harbour and Robin Hood's Bay. The bulk of the sample was taken from the sublittoral zone, but crabs from a sheltered shore were included. Each crab was measured, sexed and examined for the incidence of autotomized and regenerated limbs.There was a positive correlation between the incidence of autotomy and carapace width for crabs in both the sublittoral zone and the exposed intertidal zone. In sublittoral crabs the males suffered a higher incidence of autotomy than did the females and the incidence of cheliped autotomy was higher than for the walking limbs. The discrepancy between the loss of the chelipeds and walking limbs was reflected in a similar disparity between the occurrence of the regenerated chelipeds and walking limbs.Crabs on an exposed shore suffered a higher incidence of autotomy than did those from a sheltered shore. There were more crabs with cumulative limb losses than would be expected which suggests that once a crab enters into a state of autotomy it becomes increasingly vulnerable to the loss of another limb. Only 1 % of the population of sublittoral crabs would be expected to carry the loss of five limbs at once. No crabs were found with six or more limbs missing.     

The cannibalistic snail Agaronia propatula (Caenogastropoda,Mollusca) is reluctant to feed on autotomized ‘tails’ of conspecifics

Autotomy and cannibalism increase the complexity of the life history, population structure, and population dynamics of a species. Species in which autotomy is triggered by cannibalism have rarely been studied. It has been hypothesized that in the intertidal gastropod Agaronia propatula, autotomized tissues are highly attractive to cannibals and so increase the victim’s chance to escape. We tested the hypothesis by presenting autotomized ‘tails’ to foraging animals. The attack rates on autotomized ‘tails’ were lower than those on artificial objects reported previously. Autonomously moving autotomized ‘tails’ were more frequently ignored than non-moving and artificially moved ‘tail’ pieces. Thus, autotomized tissue repelled rather than attracted potential cannibals. Autotomy in A. propatula does not help to defend against cannibalism by offering the cannibal an attractive food item for consumption. It seems possible, though, that autotomized conspecifics are less attractive to cannibals than intact ones due to a repelling action of autotomized tissues.     

Induced Response of Tomato Plants to Injury by Green and Red Strains of Tetranychus Urticae

We studied the induced response of tomato plants to the green strain and the red strain of the spider mite Tetranychus urticae. We focused on the olfactory response of the predatory mite Phytoseiulus persimilis to volatiles from T. urticae-infested tomato leaves in a Y-tube olfactometer. Tomato leaves attracted the predatory mites when slightly infested with the red strain, or moderately or heavily infested with the green strain. In contrast, neither leaves that were slightly infested with green-strain mites, nor leaves that were moderately or heavily infested with the red strain attracted the predators. We discuss the specific defensive responses of tomato plants to each of the two strains.     

Females of the marine amphipod Jassa marmorata mate multiple times with the same or different males

Cardiovascular and respiratory variables were recorded in the blue crab, Callinectes sapidus, during injury and subsequent autotomy of a chela. Cardiac function and haemolymph flow rates were measured using a pulsed-Doppler flowmeter. Oxygen uptake was recorded using an intermittent flow respirometry system. Crabs reacted to the loss of a chela with a rapid increase in heart rate, which was sustained for 2?h. Stroke volume of the heart also increased after the chela was autotomized. A combined increase in heart rate and stroke volume led to an increase in cardiac output, which was maintained for an hour after the loss of a chela. There was also differential haemolymph perfusion of various structures. There was no change in perfusion of the anterolateral arteries or posterior and anterior aortae, during injury of the chela or subsequent autotomy. Haemolymph flow rates did increase significantly through the sternal artery during injury and immediately following autotomy of the chela. This was at the expense of blood flow to the digestive gland: a sustained decrease in haemolymph flow through the hepatic arteries occurred for 3?h following autotomy. Fine-scale cardiac changes associated with the act of autotomy included a bradycardia and/or associated cardiac pausing before the chela was shed, followed by a subsequent increase in cardiac parameters. Changes in the cardiovascular physiology were paralleled by an increase in oxygen uptake, which was driven by an increased ventilation of the branchial chambers. Although limb loss is a major event, it appears that only acute changes in physiology occur. These may benefit the individual, allowing rapid escape following autotomy with a subsequent return to normal activity.     

Decapod crustacean chelipeds: an overview

The structure, growth, differentiation and function of crustacean chelipeds are reviewed. In many decapod crustaceans growth of chelae is isometric with allometry level reaching unity till the puberty moult. Afterwards the same trend continues in females, while in males there is a marked spurt in the level of allometry accompanied by a sudden increase in the relative size of chelae. Subsequently they are differentiated morphologically into crusher and cutter making them heterochelous and sexually dimorphic. Of the two, the major chela is used during agonistic encounters while the minor is used for prey capture and grooming. Various biotic and abiotic factors exert a negative effect on cheliped growth. The dimorphic growth pattern of chelae can be adversely affected by factors such as parasitic infection and substrate conditions. Display patterns of chelipeds have an important role in agonistic and aggressive interactions. Of the five pairs of pereiopods, the chelae are versatile organs of offence and defence which also make them the most vulnerable for autotomy. Regeneration of the autotomized chelipeds imposes an additional energy demand called “regeneration load” on the incumbent, altering energy allocation for somatic and/or reproductive processes. Partial withdrawal of chelae leading to incomplete exuviation is reported for the first time in the laboratory and field inMacrobrachiumspecies.     

The roles of top and intermediate predators in herbivore suppression: contrasting results from the field and laboratory

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