Variability in venom volume, flow rate and duration in defensive stings of five scorpion species

A Sting Operation: Risk Assessment and Venom Expenditure by Arizona Bark Scorpions (Centruroides sculpturatus) in a Defensive Context

Scorpion antipredator behavior incorporates risk assessment that informs decision-making and venom usage. We quantified antipredator behaviors of the clinically significant Arizona bark scorpion (Centruroides sculpturatus) in their natural environment using exposure to two stimuli: a freshly thawed laboratory mouse (Mus musculus) and a membrane-covered glass beaker. We videotaped and compared envenomation behaviors between sexes (females, gravid females, and males), across sizes, and between animal orientations (on vertical or horizontal substrates). Results failed to show consistent support for any of our four hypotheses. Females (especially gravid females) were no more likely than males to exhibit higher levels of stinging and venom expenditure. Scorpions on horizontal surfaces compared to those on vertical surfaces, and larger scorpions compared to smaller ones, were likewise no more likely to exhibit higher levels of responsiveness. Mice were more likely to be stung than the membrane-covered beaker, but with fewer and briefer stings, suggesting the scorpions did not attempt to deliver more venom into the mice. Thus, we discerned no clear patterns in risk assessment, stinging, and venom use associated with sex, substrate orientation, body size, or threat stimuli. These findings contrasted with those of several prior laboratory studies. Variation from unaccounted environmental variables may have obfuscated divergent behavioral tactics. Nevertheless, the behaviors we document here provide insights on the range of defensive behaviors exhibited by C. sculpturatus under natural environmental conditions, including the frequency of dry stings (11.8%) to the membrane-covered beakers.

Molecular diversity assessed by MALDI mass spectrometry of two scorpion species venom from two different locations in Morocco

Scorpion venom is a cocktail of molecules whose composition is remarkably plastic, controlled by several factors. The Moroccan scorpion fauna is characterized by its richness and high rate of endemism and the venom molecular variability of many species is not yet well characterized. The aim of the present study was to highlight the molecular variability of the venom composition of Androctonus amoreuxi and Buthacus stockmanni (endemic species), both belonging to the Buthidae family, collected from two Moroccan regions, Zagora and Tan-tan. Characterization of the molecular mass fingerprints (MFPs) of each specimen was performed by Matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) using a sandwich (Sand) and a dried-droplet (DD) sample preparation and dilutions. Considering these two methods, a total of 828 ion signals were detected, and Sand method produced more adducts (56%) than DD (44%). We observed interspecific variations in the venom composition between these two species showing they share 235 ion signals, while 226 and 367 are specific for these two species, respectively. Moreover, B. stockmanni specimens showed a clear difference in their MFPs between the two geographical areas studied, suggesting intraspecific variations. Moreover, specimens from each population also show an intraspecific variability. In addition, for the same individual, a variation in the venom composition was also recorded depending on the milking frequency. Our results confirmed the presence of characteristic components in each extracted venom sample. In conclusion, MFPs assessed by MALDI-MS represent a fast, non-supervised, sensitive, reliable and cost-efficient approach for taxonomic identification and molecular variability characterization. This study undoubtedly represents a step forward for understanding the scorpion venom plasticity, intra/inter variations, and their temporal and geographical variability.

Linking toxicity and predation in a venomous arthropod: the case of Tityus fuhrmanni (Scorpiones: Buthidae), a generalist predator scorpion

Background:

Scorpions are arachnids that have a generalist diet, which use venom to subdue their prey. The study of their trophic ecology and capture behavior is still limited compared to other organisms, and aspects such as trophic specialization in this group have been little explored.

Methods:

In order to determine the relationship between feeding behavior and venom toxicity in the scorpion species Tityus fuhrmanni, 33 specimens were offered prey with different morphologies and defense mechanisms: spiders, cockroaches and crickets. In each of the experiments we recorded the following aspects: acceptance rate, immobilization time and the number of capture attempts. The median lethal dose of T. fuhrmanni venom against the three different types of prey was also evaluated.

Results:

We found that this species does not have a marked difference in acceptance for any of the evaluated prey, but the number of capture attempts of spiders is higher when compared to the other types of prey. The immobilization time is shorter in spiders compared to other prey and the LD₅₀ was higher for cockroaches.

Conclusions:

These results indicate that T. fuhrmanni is a scorpion with a generalist diet, has a venom with a different potency among prey and is capable of discriminating between prey types and employing distinct strategies to subdue them.

Comparison of biological activities of Tityus pachyurus venom from two Colombian regions

Background

In the present study, we have tested whether specimens of the medically relevant scorpion Tityus pachyurus, collected from two climatically and ecologically different regions, differ in the biological activities of the venom.

Methods

Scorpions were collected in Tolima and Huila, Colombia. Chemical profiles of the crude venom were obtained from 80 scorpions for each region, using SDS-PAGE and RP-HPLC. Assays for phospholipase A₂, direct and indirect hemolytic, proteolytic, neuromuscular, antibacterial, and insecticidal activities were carried out.

Results

The electrophoretic profiles of venom from the two regions showed similar bands of 6-14 kDa, 36-45 kDa, 65 kDa and 97 kDa. However, bands between 36 kDa and 65 kDa were observed with more intensity in venoms from Tolima, and a 95 kDa band occurred only in venoms from Huila. The chromatographic profile of the venoms showed differences in the intensity of some peaks, which could be associated with changes in the abundance of some components between both populations. Phospholipase A₂ and hemolytic activities were not observable, whereas both venoms showed proteolytic activity towards casein. Insecticidal activity of the venoms from both regions showed significant variation in potency, the bactericidal activity was variable and low for both venoms. Moreover, no differences were observed in the neuromuscular activity assay.

Conclusion

Our results reveal some variation in the activity of the venom between both populations, which could be explained by the ecological adaptations like differences in feeding, altitude and/or diverse predator exposure. However more in-depth studies are necessary to determine the drivers behind the differences in venom composition and activities.

Armed stem to stinger: a review of the ecological roles of scorpion weapons

Scorpions possess two systems of weapons: the pincers (chelae) and the stinger (telson). These are placed on anatomically and developmentally well separated parts of the body, that is, the oral appendages and at the end of the body axis. The otherwise conserved body plan of scorpions varies most in the shape and relative dimensions of these two weapon systems, both across species and in some cases between the sexes. We review the literature on the ecological function of these two weapon systems in each of three contexts of usage: (i) predation, (ii) defense and (iii) sexual contests. In the latter context, we will also discuss their usage in mating. We first provide a comparative background for each of these contexts of usage by giving examples of other weapon systems from across the animal kingdom. Then, we discuss the pertinent aspects of the anatomy of the weapon systems, particularly those aspects relevant to their functioning in their ecological roles. The literature on the functioning and ecological role of both the chelae and the telson is discussed in detail, again organized by context of usage. Particular emphasis is given on the differences in morphology or usage between species or higher taxonomic groups, or between genders, as such cases are most insightful to understand the roles of each of the two distinct weapon systems of the scorpions and their evolutionary interactions. We aimed to synthesize the literature while minimizing conjecture, but also to point out gaps in the literature and potential future research opportunities.

Scorpion envenomation: state of the art

Scorpion envenomation is common in the tropical and subtropical regions. It poses a major public health problem with some patients having serious clinical manifestations and severe complications including death. Old World and New World scorpions are usually contrasted because of differences in venom composition, clinical presentation and severity, and, accordingly, different therapeutic approaches. The majority of scorpion stings are either dry or result in low amounts of injected venom, thus explaining why up to 95% of scorpion stings ensue only in local signs. For a clinical envenomation to occur, it has been suggested that the interaction between the quantity of venom introduced in the body of the prey and the distribution volume should ensue in a critical threshold of scorpion toxin plasma concentration. In this case, there is a massive release of neurohormonal mediators (mainly catecholamine), with systemic vasoconstrictor effects eliciting a sharp increase in systemic arterial pressure and LV-filling pressure and decreased cardiac output. This early phase of cardiac dysfunction, also called "vascular phase", is followed by a severe cardiomyopathy, a form of Takotsubo cardiomyopathy, involving both ventricles and reversible in days to weeks. The more comprehensive understanding of the disease pathophysiology has allowed for a well-codified symptomatic treatment, thus contributing to a substantial reduction in the death toll of scorpion envenomation over the past few decades. The standard intensive-care treatment (when available) overcomes envenomation's consequences such as acute pulmonary edema and cardiogenic shock. Even though it continues to inspire many evaluative studies, immunotherapy seems less attractive because of the major role held by mediators in the pathogenesis of envenomation, and unfavorable pharmacokinetic properties to existing sera compared to venom. Meta-analyses of controlled trials of immunotherapy in severe scorpion envenomation reached similar conclusions: there is an acceptable level of evidence in favor of the use of scorpion antivenom (Fab'₂) against Centruroides sp. in USA/Mexico, while there is still a need for a higher level of evidence for immunotherapy in the Old World envenomation.

Molecular game theory for a toxin-dominant food chain model

Animal toxins that are used to subdue prey and deter predators act as the key drivers in natural food chains and ecosystems. However, the predators of venomous animals may exploit feeding adaptation strategies to overcome toxins their prey produce. Much remains unknown about the genetic and molecular game process in the toxin-dominant food chain model. Here, we show an evolutionary strategy in different trophic levels of scorpion-eating amphibians, scorpions and insects, representing each predation relationship in habitats dominated by the paralytic toxins of scorpions. For scorpions preying on insects, we found that the scorpion α-toxins irreversibly activate the skeletal muscle sodium channel of their prey (insect, BgNa_V1) through a membrane delivery mechanism and an efficient binding with the Asp/Lys-Tyr motif of BgNa_V1. However, in the predatory game between frogs and scorpions, with a single point mutation (Lys to Glu) in this motif of the frog's skeletal muscle sodium channel (fNa_V1.4), fNa_V1.4 breaks this interaction and diminishes muscular toxicity to the frog; thus, frogs can regularly prey on scorpions without showing paralysis. Interestingly, this molecular strategy also has been employed by some other scorpion-eating amphibians, especially anurans. In contrast to these amphibians, the Asp/Lys-Tyr motifs are structurally and functionally conserved in other animals that do not prey on scorpions. Together, our findings elucidate the protein-protein interacting mechanism of a toxin-dominant predator-prey system, implying the evolutionary game theory at a molecular level.

Target-Specificity in Scorpions; Comparing Lethality of Scorpion Venoms across Arthropods and Vertebrates

Scorpions use their venom in defensive situations as well as for subduing prey. Since some species of scorpion use their venom more in defensive situations than others, this may have led to selection for differences in effectiveness in defensive situations. Here, we compared the LD₅₀ of the venom of 10 species of scorpions on five different species of target organisms; two insects and three vertebrates. We found little correlation between the target species in the efficacy of the different scorpion venoms. Only the two insects showed a positive correlation, indicating that they responded similarly to the panel of scorpion venoms. We discuss the lack of positive correlation between the vertebrate target species in the light of their evolution and development. When comparing the responses of the target systems to individual scorpion venoms pairwise, we found that closely related scorpion species tend to elicit a similar response pattern across the target species. This was further reflected in a significant phylogenetic signal across the scorpion phylogeny for the LD₅₀ in mice and in zebrafish. We also provide the first mouse LD₅₀ value for Grosphus grandidieri.

A biomechanical view on stinger diversity in scorpions

Scorpions have elongated metasomas that bear a telson, which is used as a stinger for venom injection. There is a remarkable diversity in the use of the stinger among scorpions, comprising defensive behavior, prey subjugation and mating. This diversity could be reflected by the shape of the telson, as different stinging behaviors will result in very different functional demands. Here we explored the diversity of telson shapes in scorpions by providing morphological measurements, such as curvature and tip angle, as well as by testing stingers under load using finite element analysis (FEA). FEA models were loaded with forces scaled to the surface area of the models, to allow comparison of the relative strain energy based on shape alone. Load force angle was rotated to identify the optimal stinging angle based on the lowest strain energy. Aculeus length and mean aculeus height correlated with minimal strain energy. Optimal stinging angle correlated with tip angle, and differed from the tip angle by about 28.4 ± 6.22 °. We found that species that are more venomous have long aculei (stinger barbs) with a larger radius of curvature. FEA models of these longer aculei showed basal stress concentrations, indicating a potential greater risk of basal breakage due to shape alone. Telsons with shorter and thicker aculeus shapes showed stress concentrations at the tip only. Despite these marked differences in shape, we found no difference in the scaled strain energy between groups of species that are more venomous and less venomous groups of species. These results show that scorpion stingers may be biomechanically optimized, and this may indicate different usage of the stinger in different species.

Sex Differences in Defensive Behavior and Venom of The Striped Bark Scorpion Centruroides vittatus (Scorpiones: Buthidae)

Studies of venom variability have advanced from describing the mechanisms of action and relative potency of medically important toxins to understanding the ecological and evolutionary causes of the variability itself. While most studies have focused on differences in venoms among taxa, populations, or age-classes, there may be intersexual effects as well. Striped bark scorpions (Centruroides vittatus) provide a good model for examining sex differences in venom composition and efficacy, as this species exhibits dramatic sexual dimorphism in both size and defensive behavior; when threatened by an enemy, larger, slower females stand and fight while smaller, fleeter males prefer to run. We here add evidence suggesting that male and female C. vittatus indeed have different defensive propensities; when threatened via an electrical stimulus, females were more likely to sting than were males. We reasoned that intersexual differences in defensive phenotypes would select for venoms with different functions in the two sexes; female venoms should be effective at predator deterrence, whereas male venoms, less utilized defensively, might be better suited to capturing prey or courting females. This rationale led to our predictions that females would inject more venom and/or possess more painful venom than males. We were wrong. While females do inject more venom than males in a defensive sting, females are also larger; when adjusted for body size, male and female C. vittatus commit equal masses of venom in a sting to a potential enemy. Additionally, house mice (Mus musculus) find an injection of male venom more irritating than an equal amount of female venom, likely because male venom contains more of the toxins that induce pain. Taken together, our results suggest that identifying the ultimate causes of venom variability will, as we move beyond adaptive storytelling, be hard-won.

Tityus serrulatus venom--A lethal cocktail

Tityus serrulatus (Ts) is the main scorpion species of medical importance in Brazil. Ts venom is composed of several compounds such as mucus, inorganic salts, lipids, amines, nucleotides, enzymes, kallikrein inhibitor, natriuretic peptide, proteins with high molecular mass, peptides, free amino acids and neurotoxins. Neurotoxins are considered the most responsible for the envenoming syndrome due to their pharmacological action on ion channels such as voltage-gated sodium (Nav) and potassium (Kv) channels. The major goal of this review is to present important advances in Ts envenoming research, correlating both the crude Ts venom and isolated toxins with alterations observed in all human systems. The most remarkable event lies in the Ts induced massive releasing of neurotransmitters influencing, directly or indirectly, the entire body. Ts venom proved to extremely affect nervous and muscular systems, to modulate the immune system, to induce cardiac disorders, to cause pulmonary edema, to decrease urinary flow and to alter endocrine, exocrine, reproductive, integumentary, skeletal and digestive functions. Therefore, Ts venom possesses toxins affecting all anatomic systems, making it a lethal cocktail. However, its low lethality may be due to the low venom mass injected, to the different venom compositions, the body characteristics and health conditions of the victim and the local of Ts sting. Furthermore, we also described the different treatments employed during envenoming cases. In particular, throughout the review, an effort will be made to provide information from an extensive documented studies concerning Ts venom in vitro, in animals and in humans (a total of 151 references).