Leg Autotomy Research Articles

Juvenile leg autotomy predicts adult male morph in a New Zealand harvestman with weapon polymorphism.

Intraspecific weapon polymorphisms that arise via conditional thresholds may be affected by juvenile experience such as predator encounters, yet this idea has rarely been tested. The New Zealand harvestman Forsteropsalis pureora has three male morphs: majors (alphas and betas) are large-bodied with large chelicerae used in male-male contests, while minors (gammas) are small-bodied with small chelicerae and scramble to find mates. Individuals use leg autotomy to escape predators and there is no regeneration of the missing leg. Here, we tested whether juvenile experience affects adult morph using leg autotomy scars as a proxy of predator encounters. Juvenile males that lost at least one leg (with either locomotory or sensory function) had a 45 times higher probability of becoming a minor morph at adulthood than intact juvenile males. Leg loss during development may affect foraging, locomotion, and/or physiology, potentially linking a juvenile's predator encounters to their final adult morph and future reproductive tactic.

Effects of molting on the expression of ecdysteroid biosynthesis genes in the Y-organ of the blackback land crab, Gecarcinus lateralis

A pair of Y-organs (YOs) synthesize ecdysteroids that initiate and coordinate molting processes in decapod crustaceans. The YO converts cholesterol to secreted products through a biosynthetic pathway involving a Rieske oxygenase encoded by Neverland (Nvd) and cytochrome P450 monooxygenases encoded by Halloween genes Spook (Spo; Cyp307a1), Phantom (Phm; Cyp306a1), Disembodied (Dib; Cyp302a1), and Shadow (Sad; Cyp315a1). NAD kinase (NADK) and 5-aminolevulinic acid synthase (ALAS) support ecdysteroid synthesis in insects. A 20-hydroxylase, encoded by Shed in decapods and Shade in insects, converts ecdysone to the active hormone 20-hydroxyecdysone (20E). 20E is inactivated by cytochrome P450 26-hydroxylase (Cyp18a1). Contigs encoding these eight proteins were extracted from a Gecarcinus lateralis YO transcriptome and their expression was quantified by quantitative polymerase chain reaction. mRNA levels of Gl-Spo and Gl-Phm were four orders of magnitude higher in YO than those in nine other tissues, while mRNA levels of Gl-NADK and Gl-ALAS were similar in all ten tissues. In G. lateralis induced to molt by multiple leg autotomy, YO mRNA levels of Gl-Nvd, Gl-Spo, Gl-Phm, Gl-NADK, and Gl-ALAS were highest in intermolt and premolt stages and lower in postmolt. Gl-Dib mRNA level was not affected by molt stage. mRNA level of Gl-Sad, which converts 2-deoxyecdysone to ecdysone, was higher in mid- and late premolt stages, when YO ecdysteroidogenic capacity is greatest. Gl-Cyp18a1 mRNA level was highest in intermolt, decreased in premolt stages, and was lowest in postmolt. In animals induced to molt by eyestalk ablation, YO mRNA levels of all eight genes were not correlated with increased hemolymph 20E titers. These results suggest that YO ecdysteroidogenic genes are differentially regulated at transcriptional and translational levels.

High incidence of leg autotomy in urban crickets

Abstract Predation is an important selection pressure affecting animals. Predation has both consumptive and non-lethal effects. Because it is often difficult to estimate the extent to which non-lethal effects occur, we focused on autotomy as an indicator of non-lethal effects occurring in urban habitats. Autotomy is expected to indicate that individuals have escaped from predators. The incidence of leg autotomy in the cricket Dianemobius nigrofasciatus was compared between urban and rural habitats. The incidence of autotomy was higher in urban than in rural habitats. Failure to moult and conspecific aggressive interactions were not the main factors contributing to the incidence of autotomy in these crickets. The ease of autotomy and risk-taking tendencies did not differ among habitats. These results indicate that the incidence of autotomy reflects predation failure, and the non-lethal effects of predation are more likely to occur in urban habitats.

No risk to scrambling? Mating tactic does not affect the frequency of leg autotomy in a New Zealand harvestman

Intense sexual selection on males may drive the evolution of exaggerated weaponry, typically used in contests for females or reproductive sites. In some species, males have discontinuous variation in weapon morphology that is accompanied by alternative reproductive tactics (ARTs). Major males with enlarged weapons usually exhibit a mating tactic based on female or resource defence, which makes them relatively sedentary. Minor males with reduced or absent weapons may exhibit a scramble competition mating tactic, which involves increased movement in search of females. Thus, the main costs paid by majors involve the expression/maintenance of exaggerated structures and potential injuries during contests. In turn, the main costs paid by minors are likely related to increased exposure to predation during mate search, yet this cost has rarely been considered for minors. Harvestmen are an arachnid group with diverse male weaponry, including many cases of male polymorphism associated with ARTs. Species of the suborder Eupnoi use leg autotomy as a common antipredator defence. Here we investigated whether leg autotomy (a proxy for predation risk) is more frequent in minors of the weapon polymorphic harvestman Forsteropsalis pureora , which has three male morphs with drastically different cheliceral size and morphology. Leg autotomy was very common, with 54% of wild-caught individuals missing at least one leg (mostly leg II), but we found no evidence for differential predation risk between male morphs during adulthood. In a predator simulation experiment, we found no difference in the likelihood or latency to autotomize a leg between male morphs or leg types (legs I, II, III or IV). However, males already missing legs were more reluctant to autotomize an additional leg. Our results suggest that while leg autotomy is a common antipredator strategy, with no difference between male tactics, costs are compounded as additional legs are autotomized and males may strategically decide not to autotomize in future predator encounters. • New Zealand harvestmen autotomize (lose) legs to escape predators. • This defence strategy is common in wild populations. • Sensory legs are lost more often than locomotory legs. • Harvestmen that have lost legs in the past take longer to drop an additional leg. • Male reproductive strategy does not affect autotomy risk.

Diet, predators, and defensive behaviors of New Zealand harvestmen (Opiliones: Neopilionidae)

The Neopilionidae is a highly diversified harvestman family in New Zealand, comprising eight genera and 28 species. Although individuals of many species are abundant in the field, basic information on their natural history is absent. Here we describe the diet, predators, and defensive behaviors of 13 species across three genera, Forsteropsalis Taylor, 2013, Mangatangi Taylor, 2013, and Pantopsalis Simon, 1879. Using three years of field observations, we first identify food items for this family, finding that New Zealand neopilionids are opportunistic, generalist foragers with a diet composed of a wide variety of prey and scavenged soft-bodied invertebrates, including worms, amphipods, species from nine orders of insects, and two orders of arachnids (including conspecifics). We then describe the first known invertebrate predators of New Zealand harvestmen, including seven spider species, and conduct a review of the literature to collate a list of 32 species of native and non-native vertebrates (frogs, lizards, fish, birds, and mammals) that prey on harvestmen, including neopilionids. Finally, we describe the defensive behaviors of neopilionids, providing the first reports of autotomy and thanatosis in the family. In general, the diet of New Zealand neopilionids is similar to other harvestman species, and the list of predators includes mostly insectivorous taxa known to feed on harvestmen elsewhere. The defensive repertoire of neopilionids includes behaviors recorded for other species of Eupnoi, such as leg autotomy, but also unique behaviors that are only known for species of Dyspnoi and Laniatores, such as thanatosis.

Characterization of Shed genes encoding ecdysone 20-monooxygenase (CYP314A1) in the Y-organ of the blackback land crab, Gecarcinus lateralis

Molting in decapod crustaceans is controlled by ecdysteroid hormones synthesized and secreted by the molting gland, or Y-organ (YO). Halloween genes encode cytochrome P450 enzymes in the ecdysteroid synthetic pathway. The current paradigm is that YOs secrete an inactive precursor (e.g., ecdysone or E), which is hydroxylated at the #20 carbon to form an active hormone (20-hydroxyecdysone or 20E) by a mitochonrial 20-monooxygenase (CYP314A1) in peripheral tissues. 20-Monooxygenase is encoded by Shed in decapods and Shade in insects. We used eastern spiny lobster Shed sequences to extract six orthologs in the G. lateralis YO transcriptome. Phylogenetic analysis of the deduced amino acid sequences from six decapod species organized the Sheds into seven classes (Sheds 1–7), resulting in the assignment of the G. lateralis Sheds to Gl-Shed1, 2, 4A, 4B, 5A, and 5B. The mRNA levels of the six Gl-Sheds in the YO of intermolt animals were comparable to those in nine other tissues that included hepatopancreas and muscle. qPCR was used to compare the effects of molt induction by multiple leg autotomy (MLA) and eyestalk ablation (ESA) on Gl-Shed mRNA levels in the YO. Molt stage had little effect on Gl-Shed1 and Gl-Shed5B expression in the YO of MLA animals. Gl-Shed5A was expressed at the highest mRNA levels in the YO and was significantly increased during early and mid premolt stages. By contrast, ESA ± SB431542 had no effect on Gl-Shed expression at 1, 3, 5, and 7 days post-ESA. SB431542, which inhibits Transforming Growth Factor-β/activin signaling and blocks YO commitment, decreased Gl-Shed2 and Gl-Shed4A mRNA levels at 14 days post-ESA. A targeted metabolomic analysis showed that YOs cultured in vitro secreted E and 20E to the medium. These data suggest that the YO expresses 20-monooygenases that can convert E to 20E, which may contribute to the increase in active hormone in the hemolymph during premolt.

Proteomic analysis of the crustacean molting gland (Y-organ) over the course of the molt cycle

Molting in crustaceans is a highly complex physiological process involving regulation by two paired endocrine glands, the X-organ/sinus gland complex (XO/SG) and the Y-organ (YO). The XO/SG complex is responsible for making molt-inhibiting hormone, which negatively regulates synthesis of molting hormones, ecdysteroids, by the YO. In this study, changes in protein abundance in the YO were characterized over the course of a molt cycle induced by multiple leg autotomy in the blackback land crab, Gecarcinus lateralis. In all, 457 distinct protein spots were detected using two-dimensional gel electrophoresis, of which 230 (50%) changed significantly in abundance over the course of the molt cycle. Protein abundance differed most notably between intermolt and the three premolt stages, indicative of a biological ‘on-off’ switch. Changes in hemolymph proteins were correlated with stage-specific processes of sclerotization and melanization that facilitate cuticle hardening and support immune reactions. An abundance of cytoskeletal proteins were identified, which corresponded with glandular hypertrophy associated with synthesis and secretion of ecdysteroids. Many proteins involved in energetic pathways including glycolysis, the citric acid cycle, amino acid metabolism, and one‑carbon metabolism changed in abundance in response to increasing energy demands and the requirement for precursors of macromolecular synthesis. Several proteins involved in immune, proteostasis, and oxidative stress responses were correlated with the dynamic and demanding cellular changes associated with ecdysteroidogenesis. These changes in diverse physiological pathways represent the complexity involved with molecular regulation of the YO in decapod crustaceans.

The frequency of leg autotomy and its influence on survival in natural populations of the wolf spider Pardosa valens

Autotomy occurs when an animal intentionally sacrifices an appendage to escape predation or free a limb. While immediately beneficial, loss of an appendage can lead to a variety of future costs. In many spiders, leg autotomy is common; previous work has sometimes demonstrated autotomy costs in some behaviors, while other times, no costs of autotomy occur. We examined frequency of autotomy in two riparian zone populations of the wolf spider Pardosa valens Barnes, 1959 and then used both mark–recapture work at these sites and laboratory predation trials to determine whether autotomy affected survival. Autotomy occurred in 31% of spiders; males were more likely than females to have a missing leg, but female reproductive status (carrying an egg sac or not) was unrelated to leg loss status. At both sites, survival over 1 week in the field was significantly higher for intact spiders than for spiders missing a leg, for both sexes and both female reproductive states. Additionally, when we paired intact and autotomized spiders with a predator (the larger wolf spider Rabidosa santrita (Chamberlin & Ivie, 1942)), autotomized spiders were more likely to be attacked and eaten. Our results suggest that leg autotomy in P. valens leads to a significant future survival cost, and we discuss how this cost may affect males and females differently.

Interacting Effects of Leg Autotomy and Exposure to Predator Cues on Survival in A Wolf Spider (Pardosa valens)

Chemical cues from predators (kairomones) are used by many aquatic and terrestrial animals when deciding on behavioral responses to predation threats. These responses may also be affected by the animal’s physiological state (e.g., nutrition level, parasitism, or prior injury), which could alter normal responses to kairomones. In this study, we examined effects of leg autotomy (the voluntary sacrifice of a leg) on subsequent responses to predator chemical cues in females of the riparian-zone wolf spider Pardosa valens. In a fully-crossed design, spiders with all legs intact or with one leg removed were exposed to one of two cue treatments for 90 min: a control (no predator cue) or one with chemical cues (silk and excreta) from a larger sympatric wolf spider, Rabidosa santrita. We then introduced an R. santrita into each container, and recorded subsequent survival of P. valens. Survivorship was significantly higher for individuals previously exposed to predator cues than for those in the control group; however, autotomy had no effect on survivorship, which was similar for both intact and autotomized spiders in both the predator-cue and control treatments. In addition, although P. valens were more likely to be found off the substrate than on it when the predator was added in each of the four treatment pairings, this initial position did not influence survivorship. These results therefore indicate that P. valens can behaviorally respond to predator kairomones in ways that reduce their risk of predation, but that this response is unaffected by the prior sacrifice of a leg.

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.

The force needed for leg autotomy in the crab Hemigrapsus nudus

ABSTRACTAutotomy is the ability to shed an appendage, and arthropods can autotomize to escape predation or a fouled molting event. Myriad aspects of autotomy have been previously explored, yet quantitative data on the force needed to induce autotomy is lacking. We tested three leg types in Hemigrapsus nudus, and our results showed that hind legs require the most amount of force to autotomize (~45 N-s) compared to claws (~28 N-s) or middle walking legs (~22 N-s). These results rejected our null hypothesis that all legs require an equal amount of force to autotomize as well as our alternate hypothesis that larger legs would require more force than smaller legs. Previous research has suggested that the propensity to autotomize could correlate with the type of appendage, and while we are unable to provide an evolutionary explanation for our results, it is exciting to have some quantitative force data for future studies.

Elevated expression of neuropeptide signaling genes in the eyestalk ganglia and Y-organ of Gecarcinus lateralis individuals that are refractory to molt induction

Molting is induced in decapod crustaceans via multiple leg autotomy (MLA) or eyestalk ablation (ESA). MLA removes five or more walking legs, which are regenerated and become functional appendages at ecdysis. ESA eliminates the primary source of molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH), which suppress the production of molting hormones (ecdysteroids) from the molting gland or Y-organ (YO). Both MLA and ESA are effective methods for molt induction in Gecarcinus lateralis. However, some G. lateralis individuals are refractory to MLA, as they fail to complete ecdysis by 12weeks post-MLA; these animals are in the “blocked” condition. Quantitative polymerase chain reaction was used to quantify mRNA levels of neuropeptide and mechanistic target of rapamycin (mTOR) signaling genes in YO, eyestalk ganglia (ESG), thoracic ganglion (TG), and brain of intact and blocked animals. Six of the seven neuropeptide signaling genes, three of four mTOR signaling genes, and Gl-elongation factor 2 (EF2) mRNA levels were significantly higher in the ESG of blocked animals. Gl-MIH and Gl-CHH mRNA levels were higher in the TG and brain of blocked animals and levels increased in both control and blocked animals in response to ESA. By contrast, mRNA levels of Gl-EF2 and five of the 10 MIH signaling pathway genes in the YO were two to four orders of magnitude higher in blocked animals compared to controls. These data suggest that increased MIH and CHH synthesis in the ESG contributes to the prevention of molt induction by MLA in blocked animals. The up-regulation of MIH signaling genes in the YO of blocked animals suggests that the YO is more sensitive to MIH produced in the ESG, as well as MIH produced in brain and TG of ESA animals. Both the up-regulation of MIH signaling genes in the YO and of Gl-MIH and Gl-CHH in the ESG, TG, and brain appear to contribute to some G. lateralis individuals being refractory to MLA and ESA.

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.

Patterns of autotomy and regeneration in Hemigrapsus nudus

Leg autotomy and regeneration can have severe impacts on survival and reproduction, and these impacts may be even more pronounced in animals with multifarious legs, such as decapods. Thus, determining the patterns and frequency of autotomy and regeneration could reveal the effects of these processes on the individual and population level. We investigated whether some legs are lost more often than others and if all legs are equally likely to be regenerated. We sampled nearly 500 purple shore crabs (Hemigrapsus nudus) and showed that (1) most animals are found with at least one injured leg, (2) the patterns of autotomy differ between males and females, and (3) successful claw regeneration is unlikely in both males and females. Future work with H. nudus and other grapsid crabs will elucidate how patterns seen here relate to other developmental and ecological factors.

Defensive Responses of Neotropical Harvestmen (Arachnida, Opiliones) to Generalist Invertebrate Predators

Abstract Descriptions of defensive behaviors used by Neotropical harvestmen are rarely based upon direct observations of encounters between individuals and syntopic predators. In this study, we investigated the defensive responses exhibited by five harvestman species from Costa Rica in interactions with ctenid spiders (Cupiennius spp.), whip spiders (Phrynus pseudoparvulus), onychophorans (Epiperipatus sp.), and centipedes (Scolopendra sp.). We also observed interactions between harvestmen and a non-predatory invertebrate, the millipede Nyssodesmus python. In 64 encounters, ctenid spiders consumed 11 harvestmen, including eight Prionostemma sp., two Cynorta marginalis, and one Eupoecilaema magnum. The most frequent defensive behavior exhibited by harvestmen was fleeing. Other behaviors included aggression (striking with leg II), bobbing, leg autotomy, lying flat, and thanatosis. Prionostemma exhibited the most variable responses, especially in the presence of ctenid spiders. In addition to the lab-based e...

Molt regulation in green and red color morphs of the crab,Carcinus maenas: gene expression of molt-inhibiting hormone signaling components

In decapod crustaceans, regulation of molting is controlled by the X-organ/sinus gland complex in the eyestalks. The complex secretes molt-inhibiting hormone (MIH), which suppresses production of ecdysteroids by the Y-organ (YO). MIH signaling involves nitric oxide and cGMP in the YO, which expresses nitric oxide synthase (NOS) and NO-sensitive guanylyl cyclase (GC-I). Molting can generally be induced by eyestalk ablation (ESA), which removes the primary source of MIH, or by multiple leg autotomy (MLA). In our work on Carcinus maenas, however, ESA has limited effects on hemolymph ecdysteroid titers and animals remain in intermolt at 7 days post-ESA, suggesting that adults are refractory to molt induction techniques. Consequently, the effects of ESA and MLA on molting and YO gene expression in C. maenas green and red color morphotypes were determined at intermediate (16 and 24 days) and long-term (~90 days) intervals. In intermediate-interval experiments, ESA of intermolt animals caused transient twofold to fourfold increases in hemolymph ecdysteroid titers during the first 2 weeks. In intermolt animals, long-term ESA increased hemolymph ecdysteroid titers fourfold to fivefold by 28 days post treatment, but there was no late premolt peak (>400 pg μl(-1)) characteristic of late premolt animals and animals did not molt by 90 days post-ESA. There was no effect of ESA or MLA on the expression of Cm-elongation factor 2 (EF2), Cm-NOS, the beta subunit of GC-I (Cm-GC-Iβ), a membrane receptor GC (Cm-GC-II) and a soluble NO-insensitive GC (Cm-GC-III) in green morphs. Red morphs were affected by prolonged ESA and MLA treatments, as indicated by large decreases in Cm-EF2, Cm-GC-II and Cm-GC-III mRNA levels. ESA accelerated the transition of green morphs to the red phenotype in intermolt animals. ESA delayed molting in premolt green morphs, whereas intact and MLA animals molted by 30 days post treatment. There were significant effects on YO gene expression in intact animals: Cm-GC-Iβ mRNA increased during premolt and Cm-GC-III mRNA decreased during premolt and increased during postmolt. Cm-MIH transcripts were detected in eyestalk ganglia, the brain and the thoracic ganglion from green intermolt animals, suggesing that MIH in the brain and thoracic ganglion prevents molt induction in green ESA animals.

The effect of leg autotomy on terrestrial and aquatic locomotion in the wolf spider Pardosa valens (Araneae: Lycosidae)

Many species use autotomy, the self-amputation of an appendage, as a last-gasp method to escape a predator. Although this behavior can have immediate survival benefits, it can also negatively affect future survival or reproduction. The wolf spider Pardosa valens Barnes 1959 occurs along small mountain streams in southeastern Arizona, where it moves both on cobble along the stream and on top of the water's surface. Autotomy of legs is common in this species, and we hypothesized that such leg loss could lead to decreased sprint speed in both terrestrial and aquatic locomotion. We examined burst speed in the laboratory on artificial terrestrial and aquatic racetracks during 2005 (both males and females) and 2006 (females only). In 2005 terrestrial trials, intact spiders were faster than autotomized spiders, but there was no effect of sex on speed. In contrast, 2005 aquatic trials revealed that females ran faster than males, but that autotomy had a negative impact on the speed of females only. Additionally, female spiders generally ran faster on the terrestrial track later in the day than earlier in the day, suggesting that environmental variables such as temperature may have some influence on spider locomotion. Males were less likely to run on water than were females, and ran shorter distances when they did run. Results for females during 2006 also showed a decline in speed with autotomy, and an increase during later trials, although the results were weaker than during 2005, with only the aquatic trials showing a significant difference. These results suggest that leg autotomy in this spider does have a cost, but that the magnitude of this cost depends on aspects of the spider (e.g., sex) and habitat (e.g., substrate and environmental conditions).

Rheb, an activator of target of rapamycin, in the blackback land crab,Gecarcinus lateralis: cloning and effects of molting and unweighting on expression in skeletal muscle

Molt-induced claw muscle atrophy in decapod crustaceans facilitates exuviation and is coordinated by ecdysteroid hormones. There is a 4-fold reduction in mass accompanied by remodeling of the contractile apparatus, which is associated with an 11-fold increase in myofibrillar protein synthesis by the end of the premolt period. Loss of a walking limb or claw causes a loss of mass in the associated thoracic musculature; this unweighting atrophy occurs in intermolt and is ecdysteroid independent. Myostatin (Mstn) is a negative regulator of muscle growth in mammals; it suppresses protein synthesis, in part, by inhibiting the insulin/metazoan target of rapamycin (mTOR) signaling pathway. Signaling via mTOR activates translation by phosphorylating ribosomal S6 kinase (s6k) and 4E-binding protein 1. Rheb (Ras homolog enriched in brain), a GTP-binding protein, is a key activator of mTOR and is inhibited by Rheb-GTPase-activating protein (GAP). Akt protein kinase inactivates Rheb-GAP, thus slowing Rheb-GTPase activity and maintaining mTOR in the active state. We hypothesized that the large increase in global protein synthesis in claw muscle was due to regulation of mTOR activity by ecdysteroids, caused either directly or indirectly via Mstn. In the blackback land crab, Gecarcinus lateralis, a Mstn-like gene (Gl-Mstn) is downregulated as much as 17-fold in claw muscle during premolt and upregulated 3-fold in unweighted thoracic muscle during intermolt. Gl-Mstn expression in claw muscle is negatively correlated with hemolymph ecdysteroid level. Full-length cDNAs encoding Rheb orthologs from three crustacean species (G. lateralis, Carcinus maenas and Homarus americanus), as well as partial cDNAs encoding Akt (Gl-Akt), mTOR (Gl-mTOR) and s6k (Gl-s6k) from G. lateralis, were cloned. The effects of molting on insulin/mTOR signaling components were quantified in claw closer, weighted thoracic and unweighted thoracic muscles using quantitative polymerase chain reaction. Gl-Rheb mRNA levels increased 3.4-fold and 3.9-fold during premolt in claw muscles from animals induced to molt by eyestalk ablation (ESA) and multiple leg autotomy (MLA), respectively, and mRNA levels were positively correlated with hemolymph ecdysteroids. There was little or no effect of molting on Gl-Rheb expression in weighted thoracic muscle and no correlation of Gl-Rheb mRNA with ecdysteroid titer. There were significant changes in Gl-Akt, Gl-mTOR and Gl-s6k expression with molt stage. These changes were transient and were not correlated with hemolymph ecdysteroids. The two muscles differed in terms of the relationship between Gl-Rheb and Gl-Mstn expression. In thoracic muscle, Gl-Rheb mRNA was positively correlated with Gl-Mstn mRNA in both ESA and MLA animals. By contrast, Gl-Rheb mRNA in claw muscle was negatively correlated with Gl-Mstn mRNA in ESA animals, and no correlation was observed in MLA animals. Unweighting increased Gl-Rheb expression in thoracic muscle at all molt stages; the greatest difference (2.2-fold) was observed in intermolt animals. There was also a 1.3-fold increase in Gl-s6k mRNA level in unweighted thoracic muscle. These data indicate that the mTOR pathway is upregulated in atrophic muscles. Gl-Rheb, in particular, appears to play a role in the molt-induced increase in protein synthesis in the claw muscle.

Toxicity of Field-Aged Permethrin-Loaded Attracticides on Choristoneura rosaceana (HARRIS) and Pandemis pyrusana Kearfott (Lepidoptera: Tortricidae) Adult Males and Females

Lethal and sub lethal effects were evaluated in the laboratory on Choristoneura rosaceana (Harris) and Pandemis pyrusana Kearfott males exposed to an attracticide loaded with permethrin and aged in the field. The effect of pairing conspecific females with previously intoxicated males was also evaluated. In both species a significantly greater mortality of male moths (≥ 95%) was observed 24 h after exposure to the attracticide formulation. Likewise, high levels of knock down (≥ 75%) were observed in males of both species 1 h after attracticide exposure. In females, knock down was ≥ 2.5% and mortality ≥ 3.3% after pairing with intoxicated males. Leg autotomy in males was at least 73% in C. rosaceana and ≥ 41% in P. pyrusana, 24 h after attracticide exposure; whereas it was only ≥ 10% among females of both species after pairing with intoxicated males. Moths exposed to an attracticide blank (permethrin-free) showed significantly lower effects in all parameters (0-3.3%). Fecundity and fertility were also significantly affected after pairing females with intoxicated males. There was no significant decrease in mortality, leg autotomy, and fecundity associated with age of the attracticide. Results suggest a high potential for the use of attracticides against these two tortricid species.

When predators become prey: flight decisions in jumping spiders

Current optimal escape theory focuses on economic distance-based models that predict that animals will flee at greater distances when risk of capture is greater. Although these models have been tested extensively on vertebrate prey animals using large approaching stimuli (e.g., humans), it has never been tested on an invertebrate generalist predator with a stimulus that is in the size range of potential prey. I presented adult jumping spiders, Phidippus princeps, with a small black model to test flight decisions when physically handicapped, under different levels of threat, and on surfaces that potentially hindered escape. Predator approach speed, running surface texture, and leg autotomy had no effect on flight decisions. I also measured running distance and speed under different levels of hunger and energy state to test how these variables affect the decision to flee or to turn and defend oneself against a predator. When prodded, larger spiders fled shorter distances before switching to a defensive posture, hungry spiders fled longer distances than sated spiders, and rested spiders ran faster than tired spiders. There is likely a trade-off between body size and energy stores when deciding to flee from a threat or turning to defend oneself. These findings 1) reflect differences in how predators and prey assess risk in their environment and the distances at which they treat an approaching object as threatening and 2) suggest that future studies should focus on how animals optimize escape decisions in ways other than traditional distance-based economic models (e.g., relying absolutely on crypsis). Copyright 2009, Oxford University Press.