Toxicity in animals. Trends in evolution?

Prey Shifts Drive Venom Evolution in Cone Snails

Venom systems are complex traits that have independently emerged multiple times in diverse plant and animal phyla. Within each venomous lineage there typically exists interspecific variation in venom composition where several factors have been proposed as drivers of variation, including phylogeny and diet. Understanding these factors is of broad biological interest and has implications for the development of antivenom therapies and venom-based drug discovery. Because of their high species richness and the presence of several major evolutionary prey shifts, venomous marine cone snails (genus Conus) provide an ideal system to investigate drivers of interspecific venom variation. Here, by analyzing the venom gland expression profiles of ∼3,000 toxin genes from 42 species of cone snail, we elucidate the role of prey-specific selection pressures in shaping venom variation. By analyzing overall venom composition and individual toxin structures, we demonstrate that the shifts from vermivory to piscivory in Conus are complemented by distinct changes in venom composition independent of phylogeny. In vivo injections of venom from piscivorous cone snails in fish further showed a higher potency compared with venom of nonpiscivores demonstrating a selective advantage. Together, our findings provide compelling evidence for the role of prey shifts in directing the venom composition of cone snails and expand our understanding of the mechanisms of venom variation and diversification.

Where Does All the Poison Go? Investigating Toxicokinetics of Newt (Taricha) Tetrodotoxin (TTX) in Garter Snakes (Thamnophis)

Animals that consume toxic diets provide models for understanding the molecular and physiological adaptations to ecological challenges. Garter snakes (Thamnophis) in western North America prey on Pacific newts (Taricha), which employ tetrodotoxin (TTX) as an antipredator defense. These snakes possess mutations in voltage-gated sodium channels (Nav), the molecular targets of TTX, that decrease the binding ability of TTX to sodium channels (target-site resistance). However, genetic variation at these loci that cannot explain all the phenotypic variation in TTX resistance in Thamnophis. We explored a separate means of resistance, toxin metabolism, to determine if TTX-resistant snakes either rapidly remove TTX or sequester TTX. We examined the metabolism and distribution of TTX in the body (toxicokinetics), to determine differences between TTX-resistant and TTX-sensitive snakes in the rates at which TTX is eliminated from organs and the whole body (using TTX half-life as our metric). We assayed TTX half-life in snakes from TTX-resistant and TTX-sensitive populations of three garter snake species with a coevolutionary history with newts (T. atratus, T. couchii, T. sirtalis), as well as two non-resistant "outgroup" species (T. elegans, Pituophis catenifer) that seldom (if ever) engage newts. We found TTX half-life varied across species, populations, and tissues. Interestingly, TTX half-life was shortest in T. elegans and P. catenifer compared to all other snakes. Furthermore, TTX-resistant populations of T. couchii and T. sirtalis eliminated TTX faster (shorter TTX half-life) than their TTX-sensitive counterparts, while populations of TTX-resistant and TTX-sensitive T. atratus showed no difference rates of TTX removal (same TTX half-life). The ability to rapidly eliminate TTX may have permitted increased prey consumption, which may have promoted the evolution of additional resistance mechanisms. Finally, snakes still retain substantial amounts of TTX, and we projected that snakes could be dangerous to their own predators days to weeks following the ingestion of a single newt. Thus, aspects of toxin metabolism may have been key in driving predator-prey relationships, and important in determining other ecological interactions.

Red-on-Yellow Queen: Bio-Layer Interferometry Reveals Functional Diversity Within Micrurus Venoms and Toxin Resistance in Prey Species

Snakes in the family Elapidae largely produce venoms rich in three-finger toxins (3FTx) that bind to the α 1 subunit of nicotinic acetylcholine receptors (nAChRs), impeding ion channel activity. These neurotoxins immobilize the prey by disrupting muscle contraction. Coral snakes of the genus Micrurus are specialist predators who produce many 3FTx, making them an interesting system for examining the coevolution of these toxins and their targets in prey animals. We used a bio-layer interferometry technique to measure the binding interaction between 15 Micrurus venoms and 12 taxon-specific mimotopes designed to resemble the orthosteric binding region of the muscular nAChR subunit. We found that Micrurus venoms vary greatly in their potency on this assay and that this variation follows phylogenetic patterns rather than previously reported patterns of venom composition. The long-tailed Micrurus tend to have greater binding to nAChR orthosteric sites than their short-tailed relatives and we conclude this is the likely ancestral state. The repeated loss of this activity may be due to the evolution of 3FTx that bind to other regions of the nAChR. We also observed variations in the potency of the venoms depending on the taxon of the target mimotope. Rather than a pattern of prey-specificity, we found that mimotopes modeled after snake nAChRs are less susceptible to Micrurus venoms and that this resistance is partly due to a characteristic tryptophan → serine mutation within the orthosteric site in all snake mimotopes. This resistance may be part of a Red Queen arms race between coral snakes and their prey.

Eco-Metabolomics Applied to the Chemical Ecology of Poison Frogs (Dendrobatoidea)

Amphibians are one of the most remarkable sources of unique natural products. Biogenic amines, peptides, bufodienolides, alkaloids, and volatile organic compounds have been characterized in different species. The superfamily Dendrobatoidea represents one of the most enigmatic cases of study in chemical ecology because their skin secretome is composed by a complex mixture (i.e. cocktail) of highly lethal and noxious unique alkaloid structures. While chemical defences from dendrobatoids (families Dendrobatidae and Aromobatidae) have been investigated employing ecological, behavioral, phylogenetic and evolutionary perspectives, studies about the analytical techniques needed to perform the chemical characterization have been neglected for many years. Therefore, our aim is to summarize the current methods applied for the characterization of chemical profiles in dendrobatoids and to illustrate innovative Eco-metabolomics strategies that could be translated to this study model. This approach could be extended to natural products other than alkaloids and implemented for the chemical analysis of different species of dendrobatoids employing both low- and high-resolution mass spectrometers. Here, we overview important biological features to be considered, procedures that could be applied to perform the chemical characterization, steps and tools to perform an Eco-metabolomic analysis, and a final discussion about future perspectives.

The best of both worlds? Rattlesnake hybrid zones generate complex combinations of divergent venom phenotypes that retain high toxicity

Studying the consequences of hybridization between closely related species with divergent traits can reveal patterns of evolution that shape and maintain extreme trophic adaptations. Snake venoms are an excellent model system for examining the evolutionary and ecological patterns that underlie highly selected polymorphic traits. Here we investigate hybrid venom phenotypes that result from natural introgression between two rattlesnake species that express highly divergent venom phenotypes: Crotalus o. concolor and C. v. viridis. Though not yet documented, interbreeding between these species may lead to novel venom phenotypes with unique activities that break the typical trends of venom composition in rattlesnakes. The characteristics of these unusual phenotypes could unveil the roles of introgression in maintaining patterns of venom composition and variation, including the near ubiquitous dichotomy between neurotoxic or degradative venoms observed across rattlesnakes. We use RADseq data to infer patterns of gene flow and hybrid ancestry between these diverged lineages and link these genetic data with analyses of venom composition, biological activity, and whole animal model toxicity tests to understand the impacts of introgression on venom composition. We find that introgressed populations express admixed venom phenotypes that do not sacrifice biological activity (lethal toxicity) or overall abundance of dominant toxins compared to parental venoms. These hybridized venoms therefore do not represent a trade-off in functionality between the typical phenotypic extremes but instead represent a unique combination of characters whose expression appears limited to the hybrid zone.

Phylogeny-Related Variations in Venomics: A Test in a Subset of Habu Snakes (Protobothrops)

We conducted a comparative analysis to unveil the divergence among venoms from a subset of Old World habu snakes (Protobothrops) in terms of venomic profiles and toxicological and enzymatic activities. A total of 14 protein families were identified in the venoms from these habu snakes, and 11 of them were shared among these venoms. The venoms of five adult habu snakes were overwhelmingly dominated by SVMP (32.56 ± 13.94%), PLA₂ (22.93 ± 9.26%), and SVSP (16.27 ± 4.79%), with a total abundance of over 65%, while the subadult P. mangshanensis had an extremely low abundance of PLA₂ (1.23%) but a high abundance of CTL (51.47%), followed by SVMP (22.06%) and SVSP (10.90%). Apparent interspecific variations in lethality and enzymatic activities were also explored in habu snake venoms, but no variations in myotoxicity were found. Except for SVSP, the resemblance of the relatives within Protobothrops in other venom traits was estimated to deviate from Brownian motion evolution based on phylogenetic signals. A comparative analysis further validated that the degree of covariation between phylogeny and venom variation is evolutionarily labile and varies among clades of closely related snakes. Our findings indicate a high level of interspecific variation in the venom proteomes of habu snakes, both in the presence or absence and the relative abundance of venom protein families, and that these venoms might have evolved under a combination of adaptive and neutral mechanisms.

Maternal chemical defenses predict offspring defenses in a dendrobatid poison frog

Within and among populations, alkaloid defenses of the strawberry poison frog (Oophaga pumilio) vary spatially, temporally, and with life history stage. Natural variation in defense has been implicated as a critical factor in determining the level of protection afforded against predators and pathogens. Oophaga pumilio tadpoles sequester alkaloids from nutritive eggs and are, thus, entirely dependent on their mothers for their defense. However, it remains unclear how tadpole alkaloid composition relates to that of its mother and how variation in maternally provisioned defenses might result in varying levels of protection against predators. Here, we demonstrate that natural variation in the alkaloid composition of a mother frog is reflected as variation in her tadpole's alkaloid composition. Tadpoles, like mother frogs, varied in their alkaloid composition but always contained the identical alkaloids found in their mother. Alkaloid quantity in tadpoles was highly correlated with alkaloid quantity in their mothers. Additionally, alkaloid quantity was the best predictor of tadpole palatability, wherein tadpoles with higher alkaloid quantities were less palatable. Mother frogs with greater quantities of alkaloids are, thus, providing better protection for their offspring by provisioning chemical defenses during one of the most vulnerable periods of life.

Transcriptomic analysis reveals potential candidate pathways and genes involved in toxin biosynthesis in true toads

Synthesized chemical defenses have broadly evolved across countless taxa and are important in shaping evolutionary and ecological interactions within ecosystems. However, the underlying genomic mechanisms by which these organisms synthesize and utilize their toxins are relatively unknown. Herein, we use comparative transcriptomics to uncover potential toxin synthesizing genes and pathways, as well as interspecific patterns of toxin synthesizing genes across ten species of North American true toads (Bufonidae). Upon assembly and annotation of the ten transcriptomes, we explored patterns of relative gene expression and possible protein-protein interactions across the species to determine what genes and/or pathways may be responsible for toxin synthesis. We also tested our transcriptome dataset for signatures of positive selection to reveal how selection may be acting upon potential toxin producing genes. We assembled high quality transcriptomes of the bufonid parotoid gland, a tissue not often investigated in other bufonid related RNAseq studies. We found several genes involved in metabolic and biosynthetic pathways (e.g. steroid biosynthesis, terpenoid backbone biosynthesis, isoquinoline biosynthesis, glucosinolate biosynthesis) that were functionally enriched and/or relatively expressed across the ten focal species that may be involved in the synthesis of alkaloid and steroid toxins, as well as other small metabolic compounds that cause distastefulness in bufonids. We hope that our study lays a foundation for future studies to explore the genomic underpinnings and specific pathways of toxin synthesis in toads, as well as at the macroevolutionary scale across numerous taxa that produce their own defensive toxins.

Antibacterial activities of two potential peptides extracted from Polistes wattii Cameron, 1900 (Vespidae: Polistinae) wasp venom collected at Eastern Province, Saudi Arabia

Alternatives of conventional antibiotics have become an urgent need to control drug-resistant bacteria. Therefore, search for new antibacterial agents has become a trend in several microbiological and pharmaceutical scientific works. Insects, one of the most successful and evolved species on earth is known to be an effective natural source of several medically useful chemicals including antibacterial agents. There is considerable evidence of using wasp venom against medical ailments in several parts of the world. In this work venom from Polistes wattii Cameron, 1900 collected from Eastern Province, Saudi Arabia was evaluated for its antibacterial activities. Such activity was tested against four pathogenic bacteria: two-gram positive Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175) and two gram-negative (Salmonella typhimurium NCTC 12023 ATCC 14028 and Enterobacter cloacae (RCMB 001(1) ATCC 23355). Also, chemical characterization of wasp venom was done using HPLC and two isolated peptides were sequenced. The result indicates the potent anti-microbial effect of the venom against the four tested bacteria. The most sensitive bacteria were Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175). The sequence of the two purified peptides indicates that they belong to mastoparan. The study results may pave way to use this wasp venom in future antibiotics especially in controlling skin infection by Staphylococcus aureus.

The relationships between toad behaviour, antipredator defences, and spatial and sexual variation in predation pressure

BACKGROUND

Animal behaviour is under strong selection. Selection on behaviour, however, might not act in isolation from other fitness-related traits. Since predators represent outstanding selective forces, animal behaviour could covary with antipredator defences, such that individuals better suited against predators could afford facing the costs of riskier behaviours. Moreover, not all individuals undergo equivalent degrees of predation pressure, which can vary across sexes or habitats. Individuals under lower predation pressure might also exhibit riskier behaviours.

METHODS

In this work, I tested these hypotheses on natterjack toads (Epidalea calamita). Specifically, I gauged activity time, exploratory behaviour and boldness in standard laboratory conditions, and assessed whether they correlated with body size and antipredator strategies, namely sprint speed, parotoid gland area and parotoid gland colour contrast. Additionally, I compared these traits between sexes and individuals from an agrosystem and pine grove, since there is evidence that males and agrosystem individuals are subjected to greater predation pressure.

RESULTS

Sprint speed as well as parotoid gland contrast and size appeared unrelated to the behavioural traits studied. In turn, body mass was negatively related to activity time, boldness and exploration. This trend is consistent with the fact that larger toads could be more detectable to their predators, which are mostly gape unconstrained and could easily consume them. As predicted, females exhibited riskier behaviours. Nonetheless, agrosystem toads did not differ from pine grove toads in the behavioural traits measured, despite being under stronger predation pressure.

Toxic Relationships and Arms-Race Coevolution Revisited

Toxin evolution in animals is one of the most fascinating and complex subjects of scientific inquiry today. Gaining an understanding of toxins poses a multifaceted challenge given the diverse modes of acquisition, evolutionary adaptations, and abiotic components that affect toxin phenotypes. Here, we highlight some of the main genetic and ecological factors that influence toxin evolution and discuss the role of antagonistic interactions and coevolutionary dynamics in shaping the direction and extent of toxicity and resistance in animals. We focus on toxic Pacific newts (family Salamandridae, genus Taricha) as a system to investigate and better evaluate the widely distributed toxin they possess, tetrodotoxin (TTX), and the hypothesized model of arms-race coevolution with snake predators that is used to explain phenotypic patterns of newt toxicity. Finally, we propose an alternative coevolutionary model that incorporates TTX-producing bacteria and draws from an elicitor-receptor concept to explain TTX evolution and ecology.

Sex and habitat differences in size and coloration of an amphibian's poison glands match differential predator pressures

Chemical defenses are frequently accompanied by salient color patterns actively avoided by predators, a phenomenon referred to as aposematism. However, the production of both chemical defenses and pigments is costly, and is thus expected to be reduced under mild predator pressure. In this work, I compared the size and coloration of parotoid glands (2 dorsal, external swollen structures that secrete toxins in toads) of male and female Epidalea calamita toads from agrosystems and from pine groves. I also quantified the predator attacks received by plasticine toad models, whose "parotoid glands" differed in size and color conspicuousness, exposed in each habitat. Predators avoided models with large and conspicuous parotoid glands, but models in agrosystems were more often attacked. Concerning actual toads, agrosystem and male individuals had larger parotoid glands, presumably implying greater production of chemical defenses than in pine grove and female conspecifics. These findings are aligned with previous research suggesting that both agrosystem toads and males in this system are subjected to a more intense predator pressure. Difference between parotoid gland and dorsum coloration was greater in agrosystem toads. A marked internal pattern could function as an aposematic signal, which could counteract increased predator pressure.

Mutual enlightenment: A toolbox of concepts and methods for integrating evolutionary and clinical toxinology via snake venomics and the contextual stance

Snakebite envenoming is a neglected tropical disease that may claim over 100,000 human lives annually worldwide. Snakebite occurs as the result of an interaction between a human and a snake that elicits either a defensive response from the snake or, more rarely, a feeding response as the result of mistaken identity. Snakebite envenoming is therefore a biological and, more specifically, an ecological problem. Snake venom itself is often described as a "cocktail", as it is a heterogenous mixture of molecules including the toxins (which are typically proteinaceous) responsible for the pathophysiological consequences of envenoming. The primary function of venom in snake ecology is pre-subjugation, with defensive deployment of the secretion typically considered a secondary function. The particular composition of any given venom cocktail is shaped by evolutionary forces that include phylogenetic constraints associated with the snake's lineage and adaptive responses to the snake's ecological context, including the taxa it preys upon and by which it is predated upon. In the present article, we describe how conceptual frameworks from ecology and evolutionary biology can enter into a mutually enlightening relationship with clinical toxinology by enabling the consideration of snakebite envenoming from an "ecological stance". We detail the insights that may emerge from such a perspective and highlight the ways in which the high-fidelity descriptive knowledge emerging from applications of -omics era technologies - "venomics" and "antivenomics" - can combine with evolutionary explanations to deliver a detailed understanding of this multifactorial health crisis.

Gallic acid anti-myotoxic activity and mechanism of action, a snake venom phospholipase A2 toxin inhibitor, isolated from the medicinal plant Anacardium humile

Snakebite envenoming is the cause of an ongoing health crisis in several regions of the world, particularly in tropical and neotropical countries. This scenario creates an urgent necessity for new practical solutions to address the limitations of current therapies. The current study investigated the isolation, phytochemical characterization, and myotoxicity inhibition mechanism of gallic acid (GA), a myotoxin inhibitor obtained from Anacardium humile. The identification and isolation of GA was achieved by employing analytical chromatographic separation, which exhibited a compound with retention time and nuclear magnetic resonance spectra compatible with GA's commercial standard and data from the literature. GA alone was able to inhibit the myotoxic activity induced by the crude venom of Bothrops jararacussu and its two main myotoxins, BthTX-I and BthTX-II. Circular dichroism (CD), fluorescence spectroscopy (FS), dynamic light scattering (DLS), and interaction studies by molecular docking suggested that GA forms a complex with BthTX-I and II. Surface plasmon resonance (SPR) kinetics assays showed that GA has a high affinity for BthTX-I with a K_D of 9.146 × 10^-7 M. Taken together, the two-state reaction mode of GA binding to BthTX-I, and CD, FS and DLS assays, suggest that GA is able to induce oligomerization and secondary structure changes for BthTX-I and -II. GA and other tannins have been shown to be effective inhibitors of snake venoms' toxic effects, and herein we demonstrated GA's ability to bind to and inhibit a snake venom PLA₂, thus proposing a new mechanism of PLA₂ inhibition, and presenting more evidence of GA's potential as an antivenom compound.

Electric Blue: Molecular Evolution of Three-Finger Toxins in the Long-Glanded Coral Snake Species Calliophis bivirgatus

The genus Calliophis is the most basal branch of the family Elapidae and several species in it have developed highly elongated venom glands. Recent research has shown that C. bivirgatus has evolved a seemingly unique toxin (calliotoxin) that produces spastic paralysis in their prey by acting on the voltage-gated sodium (NaV) channels. We assembled a transcriptome from C. bivirgatus to investigate the molecular characteristics of these toxins and the venom as a whole. We find strong confirmation that this genus produces the classic elapid eight-cysteine three-finger toxins, that δδ-elapitoxins (toxins that resemble calliotoxin) are responsible for a substantial portion of the venom composition, and that these toxins form a distinct clade within a larger, more diverse clade of C. bivirgatus three-finger toxins. This broader clade of C. bivirgatus toxins also contains the previously named maticotoxins and is somewhat closely related to cytotoxins from other elapids. However, the toxins from this clade that have been characterized are not themselves cytotoxic. No other toxins show clear relationships to toxins of known function from other species.

The genus Orobanche as food and medicine: An ethnopharmacological review

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Orobanche consists of annual, biennial or perennial fleshy parasitic herb species, many of which are in use as traditional medicines and wild gathered foods since a long time. Recently, Orobanche spp. are increasingly accepted as edible medicines with nourishing properties. However, there is a lack of comprehensive understanding of their ethnopharmacological background.

AIM OF THE REVIEW

This review focuses on the advancements in botanical classification, and summary of traditional use, phytochemistry, pharmacology and toxicology of Orobanche species, in order to check for scientific support of their traditional uses and the safe treatment of human ailments and diseases.

MATERIALS AND METHODS

In this review, the results of a systematic and comprehensive literature survey about Orobanche spp over the past 60 years (from 1960 to 2020) is presented. The selected literature includes periodicals, doctoral dissertations, master dissertations conference papers and various books. The literature was identified through search engine websites and a cross-checked with the Chinese pharmacopeia, classic Chinese and European herbals, regional medicinal monographs, and online ethnobotanical databases.

RESULTS

The literature about the traditional uses revealed that Orobanche spp. were used as medicine and food in many regions of the world, but mainly in China and North America while in Europe they were primarily used as food items. Phenylpropanoid derivatives and alkaloids, were reported as their main bioactive compounds, showing antioxidant, immune system enhancing, androgenic, antibacterial and antiviral properties.

CONCLUSIONS

Orobanche spp. are increasingly being used for tonic purposes in China. Their ethnopharmacological background suggests potential usages as healthy foods and food supplements. They have the potential to be developed into herbal medicines for tonifying the kidney, against impotence and spermatorrhea, dermatological problems and wounds, as well as infantile diarrhoea. However, the pharmacological studies conducted with extracts derived from Orobanche spp. were not useful for rationally explaining the traditional uses. More investigations are required to provide a pharmacological basis for the traditional claims and the relationship between traditional uses, clinical uses, phytochemistry and pharmacological properties. Additionally, quality control should be emphasized to ensure the safe and effective use of Orobanche derived products.

Variation in Bufadienolide Composition of Parotoid Gland Secretion From Three Taxa of Japanese Toads

Toads of the genus Bufo synthesize and accumulate bufadienolides (BDs) in their parotoid glands. BDs are cardiotonic steroids that play an important role in defense against the toads' predators. Three bufonid taxa occur in mainland Japan, Bufo japonicus formosus, B. j. japonicus, and B. torrenticola. The chemical structures of BDs isolated from B. j. formosus were studied several decades ago, but there is no further information on the toxic components of Japanese toads and their metabolism. In this study, we analyzed BDs of toads from throughout Japan and compared the BD profiles by liquid chromatography/mass spectrometry (LC/MS) and hierarchical cluster analysis (HCA). We observed BDs in three taxa of Japanese toads, and identified five of the most common BDs by nuclear magnetic resonance (NMR) analyses. Of the five BDs, only bufalin was detected in all individuals. HCA of individual BD profiles divided the three taxa into five primary clusters and several subclusters. This result indicates that BD profiles differ both among and within the taxa. The clustering pattern of BDs is generally concordant with a phylogenetic tree reconstructed from the mitochondrial cytochrome b gene of Japanese toads. Our results suggest that the BDs of Japanese toads have diversified not in response to specific selective pressures, but simply due to population structuring over evolutionary time.

A Venomics Approach Coupled to High-Throughput Toxin Production Strategies Identifies the First Venom-Derived Melanocortin Receptor Agonists

Animal venoms are rich in hundreds of toxins with extraordinary biological activities. Their exploitation is difficult due to their complexity and the small quantities of venom available from most venomous species. We developed a Venomics approach combining transcriptomic and proteomic characterization of 191 species and identified 20,206 venom toxin sequences. Two complementary production strategies based on solid-phase synthesis and recombinant expression in Escherichia coli generated a physical bank of 3597 toxins. Screened on hMC4R, this bank gave an incredible hit rate of 8%. Here, we focus on two novel toxins: N-TRTX-Preg1a, exhibiting an inhibitory cystine knot (ICK) motif, and N-BUTX-Ptr1a, a short scorpion-CSαβ structure. Neither N-TRTX-Preg1a nor N-BUTX-Ptr1a affects ion channels, the known targets of their toxin scaffolds, but binds to four melanocortin receptors with low micromolar affinities and activates the hMC1R/Gs pathway. Phylogenetically, these two toxins form new groups within their respective families and represent novel hMC1R agonists, structurally unrelated to the natural agonists.

A Multiomics Approach Unravels New Toxins With Possible In Silico Antimicrobial, Antiviral, and Antitumoral Activities in the Venom of Acanthoscurria rondoniae

The Araneae order is considered one of the most successful groups among venomous animals in the world. An important factor for this success is the production of venoms, a refined biological fluid rich in proteins, short peptides and cysteine-rich peptides (CRPs). These toxins may present pharmacologically relevant biological actions, as antimicrobial, antiviral and anticancer activities, for instance. Therefore, there is an increasing interest in the exploration of venom toxins for therapeutic reasons, such as drug development. However, the process of peptide sequencing and mainly the evaluation of potential biological activities of these peptides are laborious, considering the low yield of venom extraction and the high variability of toxins present in spider venoms. Here we show a robust methodology for identification, sequencing, and initial screening of potential bioactive peptides found in the venom of Acanthoscurria rondoniae. This methodology consists in a multiomics approach involving proteomics, peptidomics and transcriptomics analyses allied to in silico predictions of antibacterial, antifungal, antiviral, and anticancer activities. Through the application of this strategy, a total of 92,889 venom gland transcripts were assembled and 84 novel toxins were identified at the protein level, including seven short peptides and 10 fully sequenced CRPs (belonging to seven toxin families). In silico analysis suggests that seven CRPs families may have potential antimicrobial or antiviral activities, while two CRPs and four short peptides are potentially anticancer. Taken together, our results demonstrate an effective multiomics strategy for the discovery of new toxins and in silico screening of potential bioactivities. This strategy may be useful in toxin discovery, as well as in the screening of possible activities for the vast diversity of molecules produced by venomous animals.

Interspecific and intraspecific venom enzymatic variation among cobras (Naja sp. and Ophiophagus hannah)

The genera Ophiophagus and Naja comprise part of a clade of snakes referred to as cobras, dangerously venomous front-fanged snakes in the family Elapidae responsible for significant human mortality and morbidity throughout Asia and Africa. We evaluated venom enzyme variation for eleven cobra species and three N. kaouthia populations using SDS-PAGE venom fingerprinting and numerous enzyme assays. Acetylcholinesterase and PLA₂ activities were the most variable between species, and PLA₂ activity was significantly different between Malaysian and Thailand N. kaouthia populations. Venom metalloproteinase activity was low and significantly different among most species, but levels were identical for N. kaouthia populations; minor variation in venom L-amino acid oxidase and phosphodiesterase activities were seen between cobra species. Naja siamensis venom lacked the α-fibrinogenolytic activity common to other cobra venoms. In addition, venom from N. siamensis had no detectable metalloproteinase activity and exhibited an SDS-PAGE profile with reduced abundance of higher mass proteins. Venom profiles from spitting cobras (N. siamensis, N. pallida, and N. mossambica) exhibited similar reductions in higher mass proteins, suggesting the evolution of venoms of reduced complexity and decreased enzymatic activity among spitting cobras. Generally, the venom proteomes of cobras show highly abundant three-finger toxin diversity, followed by large quantities of PLA₂s. However, PLA₂ bands and activity were very reduced for N. haje, N. annulifera and N. nivea. Venom compositionalenzy analysis provides insight into the evolution, diversification and distribution of different venom phenotypes that complements venomic data, and this information is critical for the development of effective antivenoms and snakebite treatment.

Relationships Between Chemical Defenses of Common Toad (Bufo bufo) Tadpoles and Bacterial Community Structure of their Natural Aquatic Habitat

Many organisms synthesize secondary metabolites against natural enemies. However, to which environmental factors the production of these metabolites is adjusted to is poorly investigated in animals, especially so in vertebrates. Bufadienolides are steroidal compounds that are present in a wide range of plants and animals and, if present in large quantities, can provide protection against natural enemies, such as pathogens. In a correlative study involving 16 natural populations we investigated how variation in bufadienolide content of larval common toads (Bufo bufo) is associated with the bacterial community structure of their aquatic environment. We also evaluated pond size, macrovegetation cover, and the abundance of predators, conspecifics and other larval amphibians. We measured toxin content of tadpoles using HPLC-MS and determined the number of bufadienolide compounds (NBC) and the total quantity of bufadienolides (TBQ). AICc-based model selection revealed strong relationships of NBC and TBQ with bacterial community structure of the aquatic habitat as well as with the presence of conspecific tadpoles. The observed relationships may have arisen due to adaptation to local bacterial communities, phenotypic plasticity, differential biotransformation of toxin compounds by different bacterial communities, or a combination of these processes. Bacterial groups that contribute to among-population variation in toxin content remain to be pinpointed, but our study suggesting that toxin production may be influenced by the bacterial community of the environment represents an important step towards understanding the ecological and evolutionary processes leading to microbiota-mediated variation in skin toxin profiles of aquatic vertebrates.

Diet Breadth Mediates the Prey Specificity of Venom Potency in Snakes

Venoms are best known for their ability to incapacitate prey. In predatory groups, venom potency is predicted to reflect ecological and evolutionary drivers relating to diet. While venoms have been found to have preyspecific potencies, the role of diet breadth on venom potencies has yet to be tested at large macroecological scales. Here, using a comparative analysis of 100 snake species, we show that the evolution of prey-specific venom potencies is contingent on the breadth of a species' diet. We find that while snake venom is more potent when tested on species closely related to natural prey items, we only find this prey-specific pattern in species with taxonomically narrow diets. While we find that the taxonomic diversity of a snakes' diet mediates the prey specificity of its venom, the species richness of its diet was not found to affect these prey-specific potency patterns. This indicates that the physiological diversity of a species' diet is an important driver of the evolution of generalist venom potencies. These findings suggest that the venoms of species with taxonomically diverse diets may be better suited to incapacitating novel prey species and hence play an important role for species within changing environments.

Chemical defense of toad tadpoles under risk by four predator species

Many organisms use inducible defenses as protection against predators. In animals, inducible defenses may manifest as changes in behavior, morphology, physiology, or life history, and prey species can adjust their defensive responses based on the dangerousness of predators. Analogously, prey may also change the composition and quantity of defensive chemicals when they coexist with different predators, but such predator-induced plasticity in chemical defenses remains elusive in vertebrates. In this study, we investigated whether tadpoles of the common toad (Bufo bufo) adjust their chemical defenses to predation risk in general and specifically to the presence of different predator species; furthermore, we assessed the adaptive value of the induced defense. We reared tadpoles in the presence or absence of one of four caged predator species in a mesocosm experiment, analyzed the composition and quantity of their bufadienolide toxins, and exposed them to free-ranging predators. We found that toad tadpoles did not respond to predation risk by upregulating their bufadienolide synthesis. Fishes and newts consumed only a small percentage of toad tadpoles, suggesting that bufadienolides provided protection against vertebrate predators, irrespective of the rearing environment. Backswimmers consumed toad tadpoles regardless of treatment. Dragonfly larvae were the most voracious predators and consumed more predator-naïve toad tadpoles than tadpoles raised in the presence of dragonfly cues. These results suggest that tadpoles in our experiment had high enough toxin levels for an effective defense against vertebrate predators even in the absence of predator cues. The lack of predator-induced phenotypic plasticity in bufadienolide synthesis may be due to local adaptation for constantly high chemical defense against fishes in the study population and/or due to the high density of conspecifics.

Enhancing Acute Oral Toxicity Predictions by using Consensus Modeling and Algebraic Form-Based 0D-to-2D Molecular Encodes

Quantitative structure-activity relationships (QSAR) are introduced to predict acute oral toxicity (AOT), by using the QuBiLS-MAS (acronym for quadratic, bilinear and N-Linear maps based on graph-theoretic electronic-density matrices and atomic weightings) framework for the molecular encoding. Three training sets were employed to build the models: EPA training set (5931 compounds), EPA-full training set (7413 compounds), and Zhu training set (10 152 compounds). Additionally, the EPA test set (1482 compounds) was used for the validation of the QSAR models built on the EPA training set, while the ProTox (425 compounds) and T3DB (284 compounds) external sets were employed for the assessment of all the models. The k-nearest neighbor, multilayer perceptron, random forest, and support vector machine procedures were employed to build several base (individual) models. The base models with R_EPA-training ≥ 0.75 ( R = correlation coefficient) and MAE_EPA-training ≤ 0.5 (MAE = mean absolute error) were retained to build consensus models. As a result, two consensus models based on the minimum operator and denoted as M19 and M22, as well as a consensus model based on the weighted average operator and denoted as M24, were selected as the best ones for each training set considered. According to the applicability domain (AD) analysis performed, model M19 (built on the EPA training set) has MAE_test-AD = 0.4044, MAE_ProTox-AD = 0.4067 and MAE_T3DB-AD = 0.2586 on the EPA test set, ProTox external set, and T3DB external set, respectively; whereas model M22 (built on the EPA-full set) and model M24 (built on the Zhu set) present MAE_ProTox-AD = 0.3992 and MAE_T3DB-AD = 0.2286, and MAE_ProTox-AD = 0.3773 and MAE_T3DB-AD = 0.2471 on the two external sets accounted for, respectively. These outcomes were compared and statistically validated with respect to 14 QSAR methods (e.g., admetSAR, ProTox-II) from the literature. As a result, model M22 presents the best overall performance. In addition, a retrospective study on 261 withdrawn drugs due to their toxic/side effects was performed, to assess the usefulness of prospectively using the QSAR models proposed in the labeling of chemicals. A comparison with regard to the methods from the literature was also made. As a result, model M22 has the best ability of labeling a compound as toxic according to the globally harmonized system of classification and labeling of chemicals. Therefore, it can be concluded that the models proposed, especially model M22, constitute prominent tools for studying AOT, at providing the best results among all the methods examined. A freely available software was also developed to be used in virtual screening tasks ( http://tomocomd.com/apps/ptoxra ).

Experimental evidence for maternal provisioning of alkaloid defenses in a dendrobatid frog

Dendrobatid frogs sequester alkaloid defenses from dietary arthropods. Here, we provide experimental evidence that mother strawberry poison frogs (Oophaga pumilio) provision alkaloids to tadpoles. Captive-raised females were fed the synthetic alkaloid decahydroquinoline (DHQ), which we subsequently quantified in their skin, eggs, and developing tadpoles. DHQ quantity was positively associated with tadpole mass/development, suggesting high sequestration rates by tadpoles. These data confirm that tadpoles obtain nutrition and alkaloids by feeding exclusively on maternally provisioned eggs.

Changes in Toxin Quantities Following Experimental Manipulation of Toxin Reserves in Bufo bufo Tadpoles

Possessing toxins can contribute to an efficient defence against various threats in nature. However, we generally know little about the energy- and time-demands of developing toxicity in animals, which determines the efficiency of chemical defence and its trade-off with other risk-induced phenotypic responses. In this study we examined how immersion into norepinephrine solution inducing the release of stored toxins, administration of mild stress mimicking predator attack or simple handling during experimental procedure affected the quantity and number of toxin compounds present in common toad (Bufo bufo) tadpoles as compared to undisturbed control individuals, and investigated how fast toxin reserves were restored. We found that total bufadienolide quantity (TBQ) significantly decreased only in the norepinephrine treatment group immediately after treatment compared to the control, but this difference disappeared after 12 h; there were no consistent differences in TBQ between treatments at later samplings. Interestingly, in the norepinephrine treatment approximately half of the compounds characterized by >700 m/z values showed the same changes in time as TBQ, but several bufadienolides characterized by <600 m/z values showed the opposite pattern: they were present in higher quantities immediately after treatment. The number of bufadienolide compounds was not affected by any treatments, but was positively related to TBQ. Our study represents the first experimental evidence that toxin quantities returned to the original level following induced toxin release within a very short period of time in common toad tadpoles and provide additional insights into the physiological background of chemical defence in this model vertebrate species.

Snake venom potency and yield are associated with prey-evolution, predator metabolism and habitat structure

Snake venom is well known for its ability to incapacitate and kill prey. Yet, potency and the amount of venom available varies greatly across species, ranging from the seemingly harmless to those capable of killing vast numbers of potential prey. This variation is poorly understood, with comparative approaches confounded by the use of atypical prey species as models to measure venom potency. Here, we account for such confounding issues by incorporating the phylogenetic similarity between a snake's diet and the species used to measure its potency. In a comparative analysis of 102 species we show that snake venom potency is generally prey-specific. We also show that venom yields are lower in species occupying three dimensional environments and increases with body size corresponding to metabolic rate, but faster than predicted from increases in prey size. These results underline the importance of physiological and environmental factors in the evolution of predator traits.

The evolution and origin of tetrodotoxin acquisition in the blue-ringed octopus (genus Hapalochlaena)

Tetrodotoxin is a potent non-proteinaceous neurotoxin, which is commonly found in the marine environment. Synthesised by bacteria, tetrodotoxin has been isolated from the tissues of several genera including pufferfish, salamanders and octopus. Believed to provide a defensive function, the independent evolution of tetrodotoxin sequestration is poorly understood in most species. Two mechanisms of tetrodotoxin resistance have been identified to date, tetrodotoxin binding proteins in the circulatory system and mutations to voltage gated sodium channels, the binding target of tetrodotoxin with the former potentially succeeding the latter in evolutionary time. This review focuses on the evolution of tetrodotoxin acquisition, in particular how it may have occurred within the blue-ringed octopus genus (Hapalochlaena) and the subsequent impact on venom evolution.

Genuine and Sequestered Natural Products from the Genus Orobanche (Orobanchaceae, Lamiales)

The present review gives an overview about natural products from the holoparasitic genus Orobanche (Orobanchaceae). We cover both genuine natural products as well as compounds sequestered by Orobanche taxa from their host plants. However, the distinction between these two categories is not always easy. In cases where the respective authors had not indicated the opposite, all compounds detected in Orobanche taxa were regarded as genuine Orobanche natural products. From the about 200 species of Orobanche s.l. (i.e., including Phelipanche) known worldwide, only 26 species have so far been investigated phytochemically (22 Orobanche and four Phelipanche species), from 17 Orobanche and three Phelipanche species defined natural products (and not only natural product classes) have been reported. For two species of Orobanche and one of Phelipanche dedicated studies have been performed to analyze the phenomenon of natural product sequestration by parasitic plants from their host plants. In total, 70 presumably genuine natural products and 19 sequestered natural products have been described from Orobanche s.l.; these form the basis of 140 chemosystematic records (natural product reports per taxon). Bioactivities described for Orobanche s.l. extracts and natural products isolated from Orobanche species include in addition to antioxidative and anti-inflammatory effects, e.g., analgesic, antifungal and antibacterial activities, inhibition of amyloid β aggregation, memory enhancing effects as well as anti-hypertensive effects, inhibition of blood platelet aggregation, and diuretic effects. Moreover, muscle relaxant and anti-spasmodic effects as well as anti-photoaging effects have been described.

The protective effect exerted by ascorbic acid on DNA fragmentation of human leukocytes induced by Lachesis muta muta venom

The objective of this study was to evaluate the genotoxic and mutagenic effects of the toxins present in Lachesis muta muta's venom on human peripheral blood leukocytes and the protective potential of ascorbic acid on DNA fragmentation. The venom of L. muta muta was incubated in different concentrations (1, 2.5, 5, 7.5, 10, 15, 20, 30, 40, 50, 60, and 120 µg/mL) with human blood to evaluate DNA fragmentation using the comet, agarose gel electrophoresis, and micronucleus assays. In these concentrations evaluated, the venom of L. muta muta induced genotoxicity (comet assay and agarose gel electrophoresis) and mutagenicity (micronucleus test), but they were not cytotoxic, as they did not change the rate of cell proliferation after cytokinesis blockade with cytochalasin B. The ascorbic acid significantly inhibited the genotoxicity induced by L. muta muta venom in the proportions evaluated (1:0.1 and 1:0.5, venom/ascorbic acid - w/w). Thus, future studies are needed to elucidate the protective mechanisms of ascorbic acid on the genotoxic effects induced by toxins present in snake venoms.

Venom of prey-specialized spiders is more toxic to their preferred prey: A result of prey-specific toxins

In specialized predators, a variety of adaptations have evolved to such a level of specificity that they allow very effective exploitation of focal prey. Venom is an essential adaptive trait of predatory venomous species, such as spiders, yet our knowledge of spider venom is incomplete. In agreement with the prey preference hypothesis, we expected that the venom of spider specialists should be more toxic to focal than to alternative prey, because it is composed of prey-specific toxins. Here we used spiders with three types of trophic specializations: specialists that were ant-eating, termite-eating and spider-eating. We compared the efficacy of prey capture of preferred and alternative prey (measured as paralysis latency) with that of related generalists and profiled the venom of the studied species using proteomic methods. We used 22 spider species: six myrmecophagous, two termitophagous, three araneophagous and 11 euryphagous generalist species belonging to different families. We found that ten of the eleven specialist species induced significantly shorter paralysis latency in preferred prey than in alternative prey. Generalists exhibited either similar efficiency on both prey types or slightly higher efficiency on preferred prey. Multivariate analysis of proteomic profiles (peptides and proteins) revealed significant differences between trophic specializations, particularly in peptides. Specialists appear to have venom composed of unique specific compounds as revealed by the multivariate ordination and indicator analysis. These components are likely prey-specific toxins.

Population Genomic Analysis of a Pitviper Reveals Microevolutionary Forces Underlying Venom Chemistry

Venoms are among the most biologically active secretions known, and are commonly believed to evolve under extreme positive selection. Many venom gene families, however, have undergone duplication, and are often deployed in doses vastly exceeding the LD₅₀ for most prey species, which should reduce the strength of positive selection. Here, we contrast these selective regimes using snake venoms, which consist of rapidly evolving protein formulations. Though decades of extensive studies have found that snake venom proteins are subject to strong positive selection, the greater action of drift has been hypothesized, but never tested. Using a combination of de novo genome sequencing, population genomics, transcriptomics, and proteomics, we compare the two modes of evolution in the pitviper, Protobothrops mucrosquamatus. By partitioning selective constraints and adaptive evolution in a McDonald–Kreitman-type framework, we find support for both hypotheses: venom proteins indeed experience both stronger positive selection, and lower selective constraint than other genes in the genome. Furthermore, the strength of selection may be modulated by expression level, with more abundant proteins experiencing weaker selective constraint, leading to the accumulation of more deleterious mutations. These findings show that snake venoms evolve by a combination of adaptive and neutral mechanisms, both of which explain their extraordinarily high rates of molecular evolution. In addition to positive selection, which optimizes efficacy of the venom in the short term, relaxed selective constraints for deleterious mutations can lead to more rapid turnover of individual proteins, and potentially to exploration of a larger venom phenotypic space.

Sequestered Alkaloid Defenses in the Dendrobatid Poison Frog Oophaga pumilio Provide Variable Protection from Microbial Pathogens

Most amphibians produce their own defensive chemicals; however, poison frogs sequester their alkaloid-based defenses from dietary arthropods. Alkaloids function as a defense against predators, and certain types appear to inhibit microbial growth. Alkaloid defenses vary considerably among populations of poison frogs, reflecting geographic differences in availability of dietary arthropods. Consequently, environmentally driven differences in frog defenses may have significant implications regarding their protection against pathogens. While natural alkaloid mixtures in dendrobatid poison frogs have recently been shown to inhibit growth of non-pathogenic microbes, no studies have examined the effectiveness of alkaloids against microbes that infect these frogs. Herein, we examined how alkaloid defenses in the dendrobatid poison frog, Oophaga pumilio, affect growth of the known anuran pathogens Aeromonas hydrophila and Klebsiella pneumoniae. Frogs were collected from five locations throughout Costa Rica that are known to vary in their alkaloid profiles. Alkaloids were isolated from individual skins, and extracts were assayed against both pathogens. Microbe subcultures were inoculated with extracted alkaloids to create dose-response curves. Subsequent spectrophotometry and cell counting assays were used to assess growth inhibition. GC-MS was used to characterize and quantify alkaloids in frog extracts, and our results suggest that variation in alkaloid defenses lead to differences in inhibition of these pathogens. The present study provides the first evidence that alkaloid variation in a dendrobatid poison frog is associated with differences in inhibition of anuran pathogens, and offers further support that alkaloid defenses in poison frogs confer protection against both pathogens and predators.

Age- and environment-dependent changes in chemical defences of larval and post-metamorphic toads

BACKGROUND

Chemical defences are widespread in animals, but how their production is adjusted to ecological conditions is poorly known. Optimal defence theory predicts that inducible defences are favoured over constitutive defences when toxin production is costly and the need for it varies across environments. However, if some environmental changes occur predictably (e.g. coupled to transitions during ontogeny), whereas others are unpredictable (e.g. predation, food availability), changes in defences may have constitutive as well as plastic elements. To investigate this phenomenon, we raised common toad (Bufo bufo) tadpoles with ad libitum or limited food and in the presence or absence of chemical cues on predation risk, and measured their toxin content on 5 occasions during early ontogeny.

RESULTS

The number of compounds showed limited variation with age in tadpoles and was unaffected by food limitation and predator cues. The total amount of bufadienolides first increased and later decreased during development, and it was elevated in young and mid-aged tadpoles with limited food availability compared to their ad libitum fed conspecifics, whereas it did not change in response to cues on predation risk. We provide the first evidence for the active synthesis of defensive toxin compounds this early during ontogeny in amphibians. Furthermore, the observation of increased quantities of bufadienolides in food-restricted tadpoles is the first experimental demonstration of resource-dependent induction of elevated de novo toxin production, suggesting a role for bufadienolides in allelopathy.

CONCLUSIONS

Our study shows that the evolution of phenotypic plasticity in chemical defences may depend on the ecological context (i.e. predation vs. competition). Our results furthermore suggest that the age-dependent changes in the diversity of toxin compounds in developing toads may be fixed (i.e., constitutive), timed for the developmental stages in which they are most reliant on their chemical arsenal, whereas inducible plasticity may prevail in the amount of synthesized compounds.

Relationship between food and venom production in the estuarine stonefish Synanceia horrida

BACKGROUND

The potential costs of venom production may be significant to many marine venomous taxa. In general, the parameters that influence the rate of venom production are poorly understood, but seem to be related to feeding frequency.

METHODS

This study examines the effects of starvation on venom profile and venom yield on the estuarine stonefish (Synanceia horrida). In total, the venom of eight stonefishes was tested under two feeding regimes. Over a four week period, one of the two groups underwent an episode of suspended feeding, while the other was fed on a daily basis. The effect of time on venom replacement was determined by a paired T-test. ANOVA was performed to analyze differences in venom weight between fed and unfed treatments.

RESULTS

Nutritional suspension was found to have a significant effect on the quantity of venom produced. SDS-PAGE gel and FPLC revealed that the components of the venom collected from both groups were similar, indicating that four weeks is an adequate time to regenerate key venom components but not replenish initial venom quantities.

CONCLUSIONS

Venom production was found to be affected by starvation.

Proteomic analysis of venom variability and ontogeny across the arboreal palm-pitvipers (genus Bothriechis)

Bothriechis is a genus of eleven currently recognized slender and arboreal venomous snakes, commonly called palm-pitvipers that range from southern Mexico to northern South America. Despite dietary studies suggesting that palm-pitvipers are generalists with an ontogenetic shift toward endothermic prey, venom proteomic analyses have revealed remarkable divergence between the venoms of the Costa Rican species, B. lateralis, B. schlegelii, B. supraciliaris, and B. nigroviridis. To achieve a more complete picture of the venomic landscape across Bothriechis, the venom proteomes of biodiversity of the northern Middle American highland palm-pitvipers, B. thalassinus, B. aurifer, and B. bicolor from Guatemala, B. marchi from Honduras, and neonate Costa Rican B. lateralis and B. schlegelii, were investigated. B. thalassinus and B. aurifer venoms are comprised by similar toxin arsenals dominated by SVMPs (33-39% of the venom proteome), CTLs (11-16%), BPP-like molecules (10-13%), and CRISPs (5-10%), and are characterized by the absence of PLA₂ proteins. Conversely, the predominant (35%) components of B. bicolor are D49-PLA₂ molecules. The venom proteome of B. marchi is similar to B. aurifer and B. thalassinus in that it is rich in SVMPs and BPPs, but also contains appreciable amounts (14.3%) of PLA₂s. The major toxin family found in the venoms of both neonate B. lateralis and B. schlegelii, is serine proteinase (SVSP), comprising about 20% of their toxin arsenals. The venom of neonate B. schlegelii is the only palm-pitviper venom where relative high amounts of Kunitz-type (6.3%) and γPLA₂ (5.2%) inhibitors have been identified. Despite notable differences between their proteomes, neonate venoms are more similar to each other than to adults of their respective species. However, the ontogenetic changes taking place in the venom of B. lateralis strongly differ from those that occur in the venom of B. schlegelii. Thus, the ontogenetic change in B. lateralis produces a SVMP-rich venom, whereas in B. schlegelii the age-dependent compositional shift generates a PLA₂-rich venom. Overall, genus-wide venomics illustrate the high evolvability of palm-pitviper venoms. The integration of the pattern of venom variation across Bothriechis into a phylogenetic and biogeographic framework may lay the foundation for assessing, in future studies, the evolutionary path that led to the present-day variability of the venoms of palm-pitvipers.

SIGNIFICANCE

Bothriechis represents a monophyletic basal genus of eleven arboreal palm-pitvipers that range from southern Mexico to northern South America. Despite palm-pitvipers' putative status as diet generalists, previous proteomic analyses have revealed remarkable divergence between the venoms of Costa Rican species, B. lateralis, B. schlegelii, B. supraciliaris, and B. nigroviridis. Our current proteomic study of Guatemalan species, B. thalassinus, B. aurifer, and B. bicolor, Honduran B. marchi, and neonate B. lateralis and B. schlegelii from Costa Rica was undertaken to deepen our understanding of the evolutionary pattern of venom proteome diversity across Bothriechis. Ancestral characters are often, but not always, preserved in an organism's development. Venoms of neonate B. lateralis and B. schlegelii are more similar to each other than to adults of their respective species, suggesting that the high evolvability of palm-pitviper venoms may represent an inherent feature of Bothriechis common ancestor. Our genus-wide data identified four nodes of venom phenotype differentiation across the phylogeny of Bothriechis. Integrated into a phylogenetic and biogeographic framework, the pattern of venom variation across Bothriechis may lay the groundwork to establish whether divergence was driven by selection for efficient resource exploitation in arboreal 'islands', thereby contributing to the ecological speciation of the genus.

Canopy Venom: Proteomic Comparison among New World Arboreal Pit-Viper Venoms

Central and South American pitvipers, belonging to the genera Bothrops and Bothriechis, have independently evolved arboreal tendencies. Little is known regarding the composition and activity of their venoms. In order to close this knowledge gap, venom proteomics and toxin activity of species of Bothriechis, and Bothrops (including Bothriopsis) were investigated through established analytical methods. A combination of proteomics and bioactivity techniques was used to demonstrate a similar diversification of venom composition between large and small species within Bothriechis and Bothriopsis. Increasing our understanding of the evolution of complex venom cocktails may facilitate future biodiscoveries.

Tempo and Mode of the Evolution of Venom and Poison in Tetrapods

Toxic weaponry in the form of venom and poison has evolved in most groups of animals, including all four major lineages of tetrapods. Moreover, the evolution of such traits has been linked to several key aspects of the biology of toxic animals including life-history and diversification. Despite this, attempts to investigate the macroevolutionary patterns underlying such weaponry are lacking. In this study we analyse patterns of venom and poison evolution across reptiles, amphibians, mammals, and birds using a suite of phylogenetic comparative methods. We find that each major lineage has a characteristic pattern of trait evolution, but mammals and reptiles evolve under a surprisingly similar regime, whilst that of amphibians appears to be particularly distinct and highly contrasting compared to other groups. Our results also suggest that the mechanism of toxin acquisition may be an important distinction in such evolutionary patterns; the evolution of biosynthesis is far less dynamic than that of sequestration of toxins from the diet. Finally, contrary to the situation in amphibians, other tetrapod groups show an association between the evolution of toxic weaponry and higher diversification rates. Taken together, our study provides the first broad-scale analysis of macroevolutionary patterns of venom and poison throughout tetrapods.

Nomenclatural instability in the venomous snakes of the Bothrops complex: Implications in toxinology and public health

Since nomenclature is intended to reflect the evolutionary history of organisms, advances in our understanding of historical relationships may lead to changes in classification, and thus potentially in taxonomic instability. An unstable nomenclature for medically important animals like venomous snakes is of concern, and its implications in venom/antivenom research and snakebite treatment have been extensively discussed since the 90´s. The taxonomy of the pitvipers of the Bothrops complex has been historically problematic and different genus-level rearrangements were proposed to rectify the long-standing paraphyly of the group. Here we review the toxinological literature on the Bothrops complex to estimate the impact of recent proposals of classification in non-systematic research. This assessment revealed moderate levels of nomenclatural instability in the last five years, and the recurrence of some practices discussed in previous studies regarding the use of classifications and the information provided about the origin of venom samples. We briefly comment on a few examples and the implications of different proposals of classifications for the Bothrops complex. The aim of this review is to contribute to the reduction of adverse effects of current taxonomic instability in a group of medical importance in the Americas.

Lepidopteran defence droplets - a composite physical and chemical weapon against potential predators

Insects often release noxious substances for their defence. Larvae of Zygaena filipendulae (Lepidoptera) secrete viscous and cyanogenic glucoside-containing droplets, whose effectiveness was associated with their physical and chemical properties. The droplets glued mandibles and legs of potential predators together and immobilised them. Droplets were characterised by a matrix of an aqueous solution of glycine-rich peptides (H-WG11-NH2) with significant amounts of proteins and glucose. Among the proteins, defensive proteins such as protease inhibitors, proteases and oxidases were abundant. The neurotoxin β-cyanoalanine was also found in the droplets. Despite the presence of cyanogenic glucosides, which release toxic hydrogen cyanide after hydrolysis by a specific β-glucosidase, the only β-glucosidase identified in the droplets (ZfBGD1) was inactive against cyanogenic glucosides. Accordingly, droplets did not release hydrogen cyanide, unless they were mixed with specific β-glucosidases present in the Zygaena haemolymph. Droplets secreted onto the cuticle hardened and formed sharp crystalline-like precipitates that may act as mandible abrasives to chewing predators. Hardening followed water evaporation and formation of antiparallel β-sheets of the peptide oligomers. Consequently, after mild irritation, Zygaena larvae deter predators by viscous and hardening droplets that contain defence proteins and β-cyanoalanine. After severe injury, droplets may mix with exuding haemolymph to release hydrogen cyanide.

Age-related association of venom gene expression and diet of predatory gastropods

Background

Venomous organisms serve as wonderful systems to study the evolution and expression of genes that are directly associated with prey capture. To evaluate the relationship between venom gene expression and prey utilization, we examined these features among individuals of different ages of the venomous, worm-eating marine snail Conus ebraeus. We determined expression levels of six genes that encode venom components, used a DNA-based approach to evaluate the identity of prey items, and compared patterns of venom gene expression and dietary specialization.

Results

C. ebraeus exhibits two major shifts in diet with age—an initial transition from a relatively broad dietary breadth to a narrower one and then a return to a broader diet. Venom gene expression patterns also change with growth. All six venom genes are up-regulated in small individuals, down-regulated in medium-sized individuals, and then either up-regulated or continued to be down-regulated in members of the largest size class. Venom gene expression is not significantly different among individuals consuming different types of prey, but instead is coupled and slightly delayed with shifts in prey diversity.

Conclusion

These results imply that changes in gene expression contribute to intraspecific variation of venom composition and that gene expression patterns respond to changes in the diversity of food resources during different growth stages.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0592-5) contains supplementary material, which is available to authorized users.

Taxonomic distribution of defensive alkaloids in Nearctic oribatid mites (Acari, Oribatida)

The opisthonotal (oil) glands of oribatid mites are the source of a wide diversity of taxon-specific defensive chemicals, and are likely the location for the more than 90 alkaloids recently identified in oribatids. Although originally recognized in temperate oribatid species, alkaloids have also been detected in related lineages of tropical oribatids. Many of these alkaloids are also present in a worldwide radiation of poison frogs, which are known to sequester these defensive chemicals from dietary arthropods, including oribatid mites. To date, most alkaloid records involve members of the superfamily Oripodoidea (Brachypylina), although few species have been examined and sampling of other taxonomic groups has been highly limited. Herein, we examined adults of more than 60 species of Nearctic oribatid mites, representing 46 genera and 33 families, for the presence of alkaloids. GC-MS analyses of whole body extracts led to the detection of 15 alkaloids, but collectively they occur only in members of the genera Scheloribates (Scheloribatidae) and Protokalumma (Parakalummidae). Most of these alkaloids have also been detected previously in the skin of poison frogs. All examined members of the oripodoid families Haplozetidae and Oribatulidae were alkaloid-free, and no mites outside the Oripodoidea contained alkaloids. Including previous studies, all sampled species of the cosmopolitan oripodoid families Scheloribatidae and Parakalummidae, and the related, mostly tropical families Mochlozetidae and Drymobatidae contain alkaloids. Our findings are consistent with a generalization that alkaloid presence is widespread, but not universal in Oripodoidea. Alkaloid presence in tropical, but not temperate members of some non-oripodoid taxa (in particular Galumnidae) deserves further study.