Costs Of Autotomy Research Articles

Frequency and latency of autotomy of a sexually selected fiddler crab appendage

Autotomy is a predator defence mechanism by which individuals voluntarily release an appendage to escape a predator or escape a fouled moult. The decision to autotomize is driven by the costs of autotomy (i.e., the loss of the appendage) vs. the risk of predation. In many cases, autotomized appendages have few alternative functions, yet male fiddler crabs autotomize the sexually selected large claw that is critical for mate attraction. We conducted an experiment with Austruca mjoebergi to understand the role of claw autotomy by males during the mating season. Males more readily autotomized a leg relative to the enlarged claw, reflecting the much greater cost of being without the major claw. Larger crabs had a lower probability of claw autotomy than did small crabs, reflecting the greater fitness cost of claw autotomy experienced by larger crabs. The sexually selected fiddler crab claw is a multifunction structure with benefits that may outweigh the survival probability resulting from autotomy when individuals are threatened by predation.

The dorso-ventral righting reflex of purple shore crabs is impeded by sexually selected claws but not by leg autotomy

ABSTRACTLocomotion has been a well-studied avenue for questions regarding the costs of autotomy. However, previous studies have focused on traditional means of locomotion such as walking, running, or swimming; an unexplored aspect of locomotion as it relates to the costs of autotomy is the dorso-ventral righting reflex, or DVRR. Using a comprehensive set of treatment groups, we explored how autotomy affects the DVRR in the crab Hemigrapsus nudus. Our results suggested that missing walking legs had no impact on an animal’s ability to complete the DVRR. However, the enlarged claws of males were shown to impede the speed at which males can right themselves out of the compromising, supine position. This is a novel example of how a sexually selected trait can negatively affect animal locomotion.

Effect of Caudal Autotomy on Aquatic and Terrestrial Locomotor Performance in Two Desmognathine Salamander Species

Plethodontid salamanders within the genus Desmognathus range from species that are primarily aquatic to species that are fully terrestrial. Thus, these species are a good model system to use for a comparison of the effect of tail loss on maximal swimming and running performance, and propensity for caudal autotomy in closely related species that primarily inhabit either aquatic or terrestrial environments. I examined the effect of caudal autotomy on maximal swimming and running speeds in D. quadramaculatus (a larger, more aquatic species) and in D. ocoee (a smaller, primarily terrestrial species). Prior to tail loss, aquatic burst speeds were greater than terrestrial burst speeds for individuals of D. quadramaculatus, but the converse was true for individuals of D. ocoee. During aquatic locomotion in each species, burst speed was significantly reduced after autotomy. With the loss of about 65% of tail length, swimming burst speed declined about 50% for D. quadramaculatus and 40% for D. ocoee. Terrestrial burst speed was not reduced in either species after autotomy. These results show that tail loss is costly for primarily aquatic desmognathine salamanders in terms of a reduction in maximal locomotor performance. The time required for caudal autotomy increased significantly with body size in each species, and larger individuals of D. quadramaculatus would bite prior to autotomy. Thus, larger individuals of D. quadramaculatus may utilize caudal autotomy less readily and rely more on alternative antipredator mechanisms such as biting, and this may be related to a higher locomotor cost of autotomy for such individuals.

Costs and economy of autotomy for tail movement and running speed in the skink Trachylepis maculilabris

Economy of autotomy (shedding less than complete tails) is advantageous via retention of ability to autotomize and reduction of costs, including lipid loss, regeneration, and decreased social status. We studied its effects on predator-distracting tail movements and running speed in the speckle-lipped mabuya ( Trachylepis maculilabris (Boettger, 1913)) by removing fractions of the autotomizable portion. Distance moved was shorter for autotomized tail segments one third of the total tail length than for longer segments. Movement duration did not vary with proportion removed. Longer movement suggests that shedding longer segments improves ability to distract predators, enhances difficulty of capturing a tail, and may require longer handling time. Tails were difficult to break in regenerated sections and did not move when broken. The lack of movement of regenerated portions after separation suggests permanent loss of capacity to distract predators. Decreased speed was confirmed as a cost of autotomy in lizards that lost at least two thirds of their tail. In lizards that lost one third of tails speed was intermediate to that of intact lizards and those that lost more. Graded decrease in speed as proportional loss increases is consistent with progressive loss of a counterweight that reduces lateral motion while running. Economy of autotomy entails trade-offs between immediate and long-term escape ability.

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

AbstractAutotomy, 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.

Autotomy reduces immune function and antioxidant defence

Costs of autotomy, an antipredator defence, are typically explained by impaired mobility; yet physiologically mediated costs may also play a role. Given the resemblance to wounding, a decreased immune function and an associated reduction in antioxidant defence is expected after autotomy. In line with this, after lamellae autotomy, larvae of the damselfly Lestes viridis showed lower levels of innate immunity (i.e. phenoloxidase, PO) and antioxidant defence (superoxide dismutase, SOD). Levels of catalase (CAT) remained, however, unaffected. In line with its cytotoxicity, PO covaried positively with CAT, yet negatively with SOD. We identified a novel cost of autotomy in terms of a reduced innate immunity, which may provide an alternative explanation for the often observed costs of autotomy and which may generate indirect interactions between predators and parasites.

The costs of autotomy and regeneration in animals: a review and framework for future research

Many organisms have the ability to shed an appendage (autotomy) to escape a predator or fouled molting event. Despite its immediate advantage on survivorship, autotomy can have important consequences for locomotion, foraging, survivorship, and/or reproduction. Thus, regeneration is a way that animals alleviate some of the costs associated with losing an appendage. Like autotomy, however, appendage regeneration can have important consequences for a variety of aspects of fitness; in a wide range of amphibians, reptiles, fishes, and arthropods, the allocation of resources to regenerate a lost appendage negatively affects somatic or reproductive growth. Previous research into the costs associated with regeneration has provided a strong framework to explore how trade-offs associated with regeneration may have influenced its evolution. However, all research to date describing the costs and benefits associated with autotomy and regeneration have compared individuals autotomizing and regenerating an appendage with individuals that have never lost an appendage. I suggest that for studies of the evolutionary significance of regeneration, an alternative comparison is between individuals experiencing autotomy without regeneration and individuals experiencing autotomy with regeneration. Future work in this direction promises new insights into the evolution of regenerative tendencies, as well as how regeneration may be influencing animal form and function.

Direct and indirect costs of limb autotomy in field crickets, Gryllus bimaculatus

Autotomy, found in multiple taxa, is the voluntary shedding of limbs and other appendages in response to predation, intraspecific conflicts and infection or damage. In a wild population of the field cricket, we found that 36% of 110 individuals of both sexes were missing at least one limb. We examined the speed to autotomize an entrapped limb and the costs of this autotomy in both sexes of a first-generation laboratory population of known age. We induced autotomy of either the two hindlegs or the two middle legs over 2 subsequent days. We found no sex differences in speed of autotomy, but hindlegs were autotomized faster than middle legs, and first legs were shed faster than second legs. Escape speed was significantly reduced by the loss of either middle or hindlegs, and number of jumps in the escape sprint was reduced. We found no significant effect of loss of two legs on male–male competitive ability, but loss of two legs in females significantly reduced mating ability by pairs. Males with autotomized middle legs showed reduced longevity, but neither sex showed a significant effect of autotomy on body mass. Gryllus bimaculatus, therefore, appears to incur both direct and indirect fitness costs from limb autotomy. This study has implications for understanding the general biology of crickets and contributes to our understanding of the role of autotomy as an evolutionary mechanism.

Autotomy shapes the trade-off between seeking cover and foraging in larval damselflies

Animals commonly choose between microhabitats that differ in foraging return and mortality hazard. I studied the influence of autotomy, the amputation of a body part, on the way larvae of the damselfly Lestes sponsa deal with the trade-off between foraging or seeking cover. Survival of Lestes larvae when confronted with the odonate predator Aeshna cyanea was higher in a complex than in a simple microhabitat, indicating that this more complex microhabitat was safer. Within the simple microhabitat, larvae without lamellae had a higher risk for mortality by predation than larvae with lamellae, showing a long-term cost of autotomy. When varying the foraging value (food present or absent) and predation risk (encaged predator or no predator) in the simple microhabitat, larvae with and without lamellae responded differentially to the imposed trade-off. All larvae spent more time in the simple microhabitat when food was present than when food was absent. Larvae without lamellae, however, only sporadically left the safe microhabitat, irrespective of the presence of the predator. In contrast, larvae with lamellae shifted more frequently towards the risky microhabitat than those without lamellae, and more often in the absence than in the presence of the predator. These decisions affected the foraging rates of the animals. I show for the first time that refuge use is higher after autotomy and that this is associated with the cost of reduced foraging success. The different microhabitat preferences for larvae with and without lamellae are consistent with their different vulnerabilities to predation and demonstrate the importance of intrinsic factors in establishing trade-offs.