The Evolution of Fangs, Venom, and Mimicry Systems in Blenny Fishes

Condition-dependent trade-offs maintain honest signalling

How and why animals and humans signal reliably is a key issue in biology and social sciences that needs to be understood to explain the evolution of communication. In situations in which the receiver needs to differentiate between low- and high-quality signallers, once a ruling paradigm, the Handicap Principle has claimed that honest signals have to be costly to produce. Subsequent game theoretical models, however, highlighted that honest signals are not necessarily costly. Honesty is maintained by the potential cost of cheating: by the difference in the marginal benefit to marginal cost for low versus high-quality signallers; i.e. by differential trade-offs. Owing to the difficulties of manipulating signal costs and benefits, there is lack of empirical tests of these predictions. We present the results of a laboratory decision-making experiment with human participants to test the role of equilibrium signal cost and signalling trade-offs for the development of honest communication. We found that the trade-off manipulation had a much higher influence on the reliability of communication than the manipulation of the equilibrium cost of signal. Contrary to the predictions of the Handicap Principle, negative production cost promoted honesty at a very high level in the differential trade-off condition.

Condition-dependent trade-offs maintain honest signalling

How and why animals and humans signal reliably is a key issue in biology and social sciences that needs to be understood to explain the evolution of communication. In situations in which the receiver needs to differentiate between low- and high-quality signallers, once a ruling paradigm, the Handicap Principle has claimed that honest signals have to be costly to produce. Subsequent game theoretical models, however, highlighted that honest signals are not necessarily costly. Honesty is maintained by the potential cost of cheating: by the difference in the marginal benefit to marginal cost for low versus high-quality signallers; i.e. by differential trade-offs. Owing to the difficulties of manipulating signal costs and benefits, there is lack of empirical tests of these predictions. We present the results of a laboratory decision-making experiment with human participants to test the role of equilibrium signal cost and signalling trade-offs for the development of honest communication. We found that the trade-off manipulation had a much higher influence on the reliability of communication than the manipulation of the equilibrium cost of signal. Contrary to the predictions of the Handicap Principle, negative production cost promoted honesty at a very high level in the differential trade-off condition.

Vexitoxins: conotoxin-like venom peptides from predatory gastropods of the genus Vexillum

Venoms of predatory marine cone snails are intensely studied because of the biomedical applications of the neuropeptides that they contain, termed conotoxins. Meanwhile some gastropod lineages have independently acquired secretory glands strikingly similar to the venom gland of cone snails, suggesting that they possess similar venoms. Here we focus on the most diversified of these clades, the genus Vexillum. Based on the analysis of a multi-species proteo-transcriptomic dataset, we show that Vexillum species indeed produce complex venoms dominated by highly diversified short cysteine-rich peptides, vexitoxins. Vexitoxins possess the same precursor organization, display overlapping cysteine frameworks and share several common post-translational modifications with conotoxins. Some vexitoxins show sequence similarity to conotoxins and adopt similar domain conformations, including a pharmacologically relevant inhibitory cysteine knot motif. The Vexillum envenomation gland (gL) is a notably more recent evolutionary novelty than the conoidean venom gland. Thus, we hypothesize lower divergence between vexitoxin genes, and their ancestral 'somatic' counterparts compared to that in conotoxins, and we find support for this hypothesis in the evolution of the vexitoxin cluster V027. We use this example to discuss how future studies on vexitoxins can inform the origin of conotoxins, and how they may help to address outstanding questions in venom evolution.

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.

Molecular cloning and characterization of the two putative toxins expressed in the venom of the devil stinger Inimicus japonicus

Various proteins are involved in fish venom toxicity, but limited information is available regarding their structure and mode of action. Here, we analyzed RNA transcripts in the dorsal spine of the devil stinger Inimicus japonicus using next-generation sequencing (NGS), and identified two putative protein toxins, a natterin-like protein (Ij-natterin) and a phospholipase A₂ (Ij-PLA₂), as well as a previously reported stonustoxin-like protein. The deduced amino acid sequence of Ij-natterin suggested that it acts as a pore-forming toxin through the cooperation of the N-terminal lectin-like domain and the C-terminal pore-forming domain. Ij-PLA₂ showed significant homology with secreted Ca²⁺-dependent PLA₂s from snake venom and mammals (sPLA₂-I/II). The recombinant Ij-PLA₂ protein exhibited PLA₂ activity in the absence of Ca²⁺, in contrast to canonical sPLA₂-I/II. Comparison of the amino acid sequences of Ij-PLA₂ with the other sPLA₂-I/II suggests that the C-terminal extended peptide region of Ij-PLA₂ is involved in its Ca²⁺-independent activity.

Insights into how development and life-history dynamics shape the evolution of venom

Venomous animals are a striking example of the convergent evolution of a complex trait. These animals have independently evolved an apparatus that synthesizes, stores, and secretes a mixture of toxic compounds to the target animal through the infliction of a wound. Among these distantly related animals, some can modulate and compartmentalize functionally distinct venoms related to predation and defense. A process to separate distinct venoms can occur within and across complex life cycles as well as more streamlined ontogenies, depending on their life-history requirements. Moreover, the morphological and cellular complexity of the venom apparatus likely facilitates the functional diversity of venom deployed within a given life stage. Intersexual variation of venoms has also evolved further contributing to the massive diversity of toxic compounds characterized in these animals. These changes in the biochemical phenotype of venom can directly affect the fitness of these animals, having important implications in their diet, behavior, and mating biology. In this review, we explore the current literature that is unraveling the temporal dynamics of the venom system that are required by these animals to meet their ecological functions. These recent findings have important consequences in understanding the evolution and development of a convergent complex trait and its organismal and ecological implications.

A Comprehensive Multi-Omic Approach Reveals a Relatively Simple Venom in a Diet Generalist, the Northern Short-Tailed Shrew, Blarina brevicauda

Animals that use venom to feed on a wide diversity of prey may evolve a complex mixture of toxins to target a variety of physiological processes and prey-defense mechanisms. Blarina brevicauda, the northern short-tailed shrew, is one of few venomous mammals, and is also known to eat evolutionarily divergent prey. Despite their complex diet, earlier proteomic and transcriptomic studies of this shrew's venom have only identified two venom proteins. Here, we investigated with comprehensive molecular approaches whether B. brevicauda venom is more complex than previously understood. We generated de novo assemblies of a B. brevicauda genome and submaxillary-gland transcriptome, as well as sequenced the salivary proteome. Our findings show that B. brevicauda's venom composition is simple relative to their broad diet and is likely limited to seven proteins from six gene families. Additionally, we explored expression levels and rate of evolution of these venom genes and the origins of key duplications that led to toxin neofunctionalization. We also found three proteins that may be involved in endogenous self-defense. The possible synergism of the toxins suggests that vertebrate prey may be the main target of the venom. Further functional assays for all venom proteins on both vertebrate and invertebrate prey would provide further insight into the ecological relevance of venom in this species.

Solenodon genome reveals convergent evolution of venom in eulipotyphlan mammals

Venom systems are key adaptations that have evolved throughout the tree of life and typically facilitate predation or defense. Despite venoms being model systems for studying a variety of evolutionary and physiological processes, many taxonomic groups remain understudied, including venomous mammals. Within the order Eulipotyphla, multiple shrew species and solenodons have oral venom systems. Despite morphological variation of their delivery systems, it remains unclear whether venom represents the ancestral state in this group or is the result of multiple independent origins. We investigated the origin and evolution of venom in eulipotyphlans by characterizing the venom system of the endangered Hispaniolan solenodon (Solenodon paradoxus). We constructed a genome to underpin proteomic identifications of solenodon venom toxins, before undertaking evolutionary analyses of those constituents, and functional assessments of the secreted venom. Our findings show that solenodon venom consists of multiple paralogous kallikrein 1 (KLK1) serine proteases, which cause hypotensive effects in vivo, and seem likely to have evolved to facilitate vertebrate prey capture. Comparative analyses provide convincing evidence that the oral venom systems of solenodons and shrews have evolved convergently, with the 4 independent origins of venom in eulipotyphlans outnumbering all other venom origins in mammals. We find that KLK1s have been independently coopted into the venom of shrews and solenodons following their divergence during the late Cretaceous, suggesting that evolutionary constraints may be acting on these genes. Consequently, our findings represent a striking example of convergent molecular evolution and demonstrate that distinct structural backgrounds can yield equivalent functions.

Venomous Bites, Stings, and Poisoning: An Update

This article discusses the epidemiology, prevention, clinical features, and treatment of venomous bites by snakes, lizards, and spiders; stings by fish, jellyfish, echinoderms, insects, and scorpions; and poisoning by ingestion of fish, turtles, and shellfish. Invertebrate stings cause fatalities by anaphylaxis, secondary to acquired hypersensitivity (Hymenoptera, such as bees, wasps, and ants; and jellyfish), and by direct envenoming (scorpions, spiders, jellyfish, and echinoderms). Simple preventive techniques, such as wearing protective clothing, using a flashlight at night, and excluding venomous animals from sleeping quarters, are of paramount importance to reduce the risk of venomous bites and stings.

Integrating natural history collections and comparative genomics to study the genetic architecture of convergent evolution

Evolutionary convergence has been long considered primary evidence of adaptation driven by natural selection and provides opportunities to explore evolutionary repeatability and predictability. In recent years, there has been increased interest in exploring the genetic mechanisms underlying convergent evolution, in part, owing to the advent of genomic techniques. However, the current 'genomics gold rush' in studies of convergence has overshadowed the reality that most trait classifications are quite broadly defined, resulting in incomplete or potentially biased interpretations of results. Genomic studies of convergence would be greatly improved by integrating deep 'vertical', natural history knowledge with 'horizontal' knowledge focusing on the breadth of taxonomic diversity. Natural history collections have and continue to be best positioned for increasing our comprehensive understanding of phenotypic diversity, with modern practices of digitization and databasing of morphological traits providing exciting improvements in our ability to evaluate the degree of morphological convergence. Combining more detailed phenotypic data with the well-established field of genomics will enable scientists to make progress on an important goal in biology: to understand the degree to which genetic or molecular convergence is associated with phenotypic convergence. Although the fields of comparative biology or comparative genomics alone can separately reveal important insights into convergent evolution, here we suggest that the synergistic and complementary roles of natural history collection-derived phenomic data and comparative genomics methods can be particularly powerful in together elucidating the genomic basis of convergent evolution among higher taxa. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

Evolution: Fangtastic Venoms Underpin Parasitic Mimicry

Venomous teeth are rare in fishes, which typically utilise spines for defence. A new study reveals the evolutionary origins of fangs and venom in the Nemophini blennies and shows that, in contrast to snakes and lizards, the fangs pre-date the venom.

Investigation of the estuarine stonefish (Synanceia horrida) venom composition

The Estuarine stonefish (Synanceia horrida) is recognised as one of the most venomous fish species in the world but the overall venom composition has yet to be investigated using in-depth transcriptomic and proteomic methods. To date, known venom components are restricted to a hyaluronidase and a large, pore-forming toxin known as Stonustoxin (SNTX). Transcriptomic sequencing of the venom gland resulted in over 170,000 contigs with only 0.4% that were homologous to putative venom proteins. Integration of the transcriptomic data with proteomic data from the S. horrida venom confirmed the hyaluronidase and SNTX to be present, together with several other protein families including major contributions from C-type lectins. Other protein families observed included peroxiredoxin and several minor protein families such as Golgi-associated plant pathogenesis related proteins, tissue pathway factor inhibitors, and Kazal-type serine protease inhibitors that, although not putative venom proteins, may contribute to the venom's adverse effects. BIOLOGICAL SIGNIFICANCE: Proteomic analysis of milked Synanceia horrida venom, paired with transcriptomic analysis of the venom gland tissue revealed for the first time the composition of one of the world's most dangerous fish venoms. The results demonstrate that the venom is relatively less complex compared to other well-studied venomous animals with a number of unique proteins not previously found in animal venoms.

Evolutionary Ecology of Fish Venom: Adaptations and Consequences of Evolving a Venom System

Research on venomous animals has mainly focused on the molecular, biochemical, and pharmacological aspects of venom toxins. However, it is the relatively neglected broader study of evolutionary ecology that is crucial for understanding the biological relevance of venom systems. As fish have convergently evolved venom systems multiple times, it makes them ideal organisms to investigate the evolutionary ecology of venom on a broader scale. This review outlines what is known about how fish venom systems evolved as a result of natural enemy interactions and about the ecological consequences of evolving a venom system. This review will show how research on the evolutionary ecology of venom in fish can aid in understanding the evolutionary ecology of animal venoms more generally. Further, understanding these broad ecological questions can shed more light on the other areas of toxinology, with applications across multiple disciplinary fields.

Transcriptomic Characterization of the South American Freshwater Stingray Potamotrygon motoro Venom Apparatus

Venomous animals are found through a wide taxonomic range including cartilaginous fish such as the freshwater stingray Potamotrygon motoro occurring in South America, which can injure people and cause venom-related symptoms. Ensuring the efficacy of drug development to treat stingray injuries can be assisted by the knowledge of the venom composition. Here we performed a detailed transcriptomic characterization of the venom gland of the South American freshwater stingray Potamotrygon motoro. The transcripts retrieved showed 418 hits to venom components (comparably to 426 and 396 hits in other two Potamotrygon species), with high expression levels of hyaluronidase, cystatin and calglandulin along with hits uniquely found in P. motoro such as DELTA-alicitoxin-Pse1b, Augerpeptide hhe53 and PI-actitoxin-Aeq3a. We also identified undescribed molecules with extremely high expression values with sequence similarity to the SE-cephalotoxin and Rapunzel genes. Comparative analyses showed that despite being closely related, there may be significant variation among the venoms of freshwater stingrays, highlighting the importance of considering elicit care in handling different envenomation cases. Since hyaluronidase represents a major component of fish venom, we have performed phylogenetic and selective pressure analyses of this gene/protein across all fish with the available information. Results indicated an independent recruitment of the hyaluronidase into the stingray venom relative to that of venomous bony fish. The hyaluronidase residues were found to be mostly under negative selection, but 18 sites showed evidence of diversifying positive selection (P < 0.05). Our data provides new insight into stingray venom variation, composition, and selective pressure in hyaluronidase.

Comparative transcriptome analyses of venom glands from three scorpionfishes

Scorpionfishes (Scorpaenidae) are a relatively common cause of human envenomation. They often enter coastal waters and their stings can be quite hazardous, provoking extreme pain and causing the victims to take days to recover. There are few genomic resources available for the scorpionfishes. In this study, we elucidated the transcriptomic profile of the venom glands from three different scorpionfish species, namely Scorpaenopsis cirrosa, S. neglecta and S. possi. This is the first report of scorpionfish transcriptomes. After functional and pathway annotation, we employed toxin annotation to identify many species-specific (18, 13 and 19 respectively) and overlapping putative toxins among the three species. Our study represents a significant improvement in the genetic information about the venoms from these three species. Moreover, this work also provides an archive for future studies on evolution of fish toxins and can be used for comparative studies of other fishes.

Defining the pathogenic threat of envenoming by South African shield-nosed and coral snakes (genus Aspidelaps), and revealing the likely efficacy of available antivenom

While envenoming by the southern African shield-nosed or coral snakes (genus Aspidelaps) has caused fatalities, bites are uncommon. Consequently, this venom is not used in the mixture of snake venoms used to immunise horses for the manufacture of regional SAIMR (South African Institute for Medical Research) polyvalent antivenom. Aspidelaps species are even excluded from the manufacturer's list of venomous snakes that can be treated by this highly effective product. This leaves clinicians, albeit rarely, in a therapeutic vacuum when treating envenoming by these snakes. This is a significantly understudied small group of nocturnal snakes and little is known about their venom compositions and toxicities. Using a murine preclinical model, this study determined that the paralysing toxicity of venoms from Aspidelaps scutatus intermedius, A. lubricus cowlesi and A. l. lubricus approached that of venoms from highly neurotoxic African cobras and mambas. This finding was consistent with the cross-genus dominance of venom three-finger toxins, including numerous isoforms which showed extensive interspecific variation. Our comprehensive analysis of venom proteomes showed that the three Aspidelaps species possess highly similar venom proteomic compositions. We also revealed that the SAIMR polyvalent antivenom cross-reacted extensively in vitro with venom proteins of the three Aspidelaps. Importantly, this cross-genus venom-IgG binding translated to preclinical (in a murine model) neutralisation of A. s. intermedius venom-induced lethality by the SAIMR polyvalent antivenom, at doses comparable with those that neutralise venom from the cape cobra (Naja nivea), which the antivenom is directed against. Our results suggest a wider than anticipated clinical utility of the SAIMR polyvalent antivenom, and here we seek to inform southern African clinicians that this readily available antivenom is likely to prove effective for victims of Aspidelaps envenoming. BIOLOGICAL SIGNIFICANCE: Coral and shield-nosed snakes (genus Aspidelaps) comprise two species and several subspecies of potentially medically important venomous snakes distributed in Namibia, Botswana, Zimbabwe, Mozambique and South Africa. Documented human fatalities, although rare, have occurred from both A. lubricus and A. scutatus. However, their venom proteomes and the pathological effects of envenomings by this understudied group of nocturnal snakes remain uncharacterised. Furthermore, no commercial antivenom is made using venom from species of the genus Aspidelaps. To fill this gap, we have conducted a transcriptomics-guided comparative proteomics analysis of the venoms of the intermediate shield-nose snake (A. s. intermedius), southern coral snake (A. l. lubricus), and Cowle's shield snake (A. l. cowlesi); investigated the mechanism of action underpinning lethality by A. s. intermedius in the murine model; and assessed the in vitro immunoreactivity of the SAIMR polyvalent antivenom towards the venom toxins of A. l. lubricus and A. l. cowlesi, and the in vivo capability of this antivenom at neutralising the lethal effect of A. s. intermedius venom. Our data revealed a high degree of conservation of the global composition of the three Aspidelaps venom proteomes, all characterised by the overwhelming predominance of neurotoxic 3FTxs, which induced classical signs of systemic neurotoxicity in mice. The SAIMR polyvalent antivenom extensively binds to Aspidelaps venom toxins and neutralised, with a potency of 0.235 mg venom/mL antivenom, the lethal effect of A. s. intermedius venom. Our data suggest that the SAIMR antivenom could be a useful therapeutic tool for treating human envenomings by Aspidelaps species.

Studying Smaller and Neglected Organisms in Modern Evolutionary Venomics Implementing RNASeq (Transcriptomics)-A Critical Guide

Venoms are evolutionary key adaptations that species employ for defense, predation or competition. However, the processes and forces that drive the evolution of venoms and their toxin components remain in many aspects understudied. In particular, the venoms of many smaller, neglected (mostly invertebrate) organisms are not characterized in detail, especially with modern methods. For the majority of these taxa, even their biology is only vaguely known. Modern evolutionary venomics addresses the question of how venoms evolve by applying a plethora of -omics methods. These recently became so sensitive and enhanced that smaller, neglected organisms are now more easily accessible to comparatively study their venoms. More knowledge about these taxa is essential to better understand venom evolution in general. The methodological core pillars of integrative evolutionary venomics are genomics, transcriptomics and proteomics, which are complemented by functional morphology and the field of protein synthesis and activity tests. This manuscript focuses on transcriptomics (or RNASeq) as one toolbox to describe venom evolution in smaller, neglected taxa. It provides a hands-on guide that discusses a generalized RNASeq workflow, which can be adapted, accordingly, to respective projects. For neglected and small taxa, generalized recommendations are difficult to give and conclusions need to be made individually from case to case. In the context of evolutionary venomics, this overview highlights critical points, but also promises of RNASeq analyses. Methodologically, these concern the impact of read processing, possible improvements by perfoming multiple and merged assemblies, and adequate quantification of expressed transcripts. Readers are guided to reappraise their hypotheses on venom evolution in smaller organisms and how robustly these are testable with the current transcriptomics toolbox. The complementary approach that combines particular proteomics but also genomics with transcriptomics is discussed as well. As recently shown, comparative proteomics is, for example, most important in preventing false positive identifications of possible toxin transcripts. Finally, future directions in transcriptomics, such as applying 3rd generation sequencing strategies to overcome difficulties by short read assemblies, are briefly addressed.

The hidden half: ecology and evolution of cryptobenthic fishes on coral reefs

Teleost fishes are the most diverse group of vertebrates on Earth. On tropical coral reefs, their species richness exceeds 6000 species; one tenth of total vertebrate biodiversity. A large proportion of this diversity is composed of cryptobenthic reef fishes (CRFs): bottom-dwelling, morphologically or behaviourally cryptic species typically less than 50 mm in length. Yet, despite their diversity and abundance, these fishes are both poorly defined and understood. Herein we provide a new quantitative definition and synthesise current knowledge on the diversity, distribution and life history of CRFs. First, we use size distributions within families to define 17 core CRF families as characterised by the high prevalence (>10%) of small-bodied species (<50 mm). This stands in strong contrast to 42 families of large reef fishes, in which virtually no small-bodied species have evolved. We posit that small body size has allowed CRFs to diversify at extremely high rates, primarily by allowing for fine partitioning of microhabitats and facilitation of allopatric reproductive isolation; yet, we are far from understanding and documenting the biodiversity of CRFs. Using rates of description since 1758, we predict that approximately 30 new species of cryptobenthic species will be described per year until 2050 (approximately twice the annual rate compared to large fishes). Furthermore, we predict that by the year 2031, more than half of the described coral reef fish biodiversity will consist of CRFs. These fishes are the 'hidden half' of vertebrate biodiversity on coral reefs. Notably, global geographic coverage and spatial resolution of quantitative data on CRF communities is uniformly poor, which further emphasises the remarkable reservoir of biodiversity that is yet to be discovered. Although small body size may have enabled extensive diversification within CRF families, small size also comes with a suite of ecological challenges that affect fishes' capacities to feed, survive and reproduce; we identify a range of life-history adaptations that have enabled CRFs to overcome these limitations. In turn, these adaptations bestow a unique socio-ecological role on CRFs, which includes a key role in coral reef trophodynamics by cycling trophic energy provided by microscopic prey to larger consumers. Although small in body size, the ecology and evolutionary history of CRFs may make them a critical component of coral-reef food webs; yet our review also shows that these fishes are highly susceptible to a variety of anthropogenic disturbances. Understanding the consequences of these changes for CRFs and coral reef ecosystems will require us to shed more light on this frequently overlooked but highly diverse and abundant guild of coral reef fishes.

Buccal venom gland associates with increased of diversification rate in the fang blenny fish Meiacanthus (Blenniidae; Teleostei)

At the macroevolutionary level, many mechanisms have been proposed to explain explosive species diversification. Among them morphological and/or physiological novelty is considered to have a great impact on the tempo and the mode of diversification. Meiacanthus is a genus of Blenniidae possessing a unique buccal venom gland at the base of an elongated canine tooth. This unusual trait has been hypothesized to aid escape from predation and thus potentially play an important role in their pattern of diversification. Here, we produce the first time-calibrated phylogeny of Blenniidae and we test the impact of two morphological novelties on their diversification, i.e. the presence of swim bladder and buccal venom gland, using various comparative methods. We found an increase in the tempo of lineage diversification at the root of the Meiacanthus clade, associated with the evolution of the buccal venom gland, but not the swim bladder. Neither morphological novelty was associated with the pattern of size disparification in blennies. Our results support the hypothesis that the buccal venom gland has contributed to the explosive diversification of Meiacanthus, but further analyses are needed to fully understand the factors sustaining this burst of speciation.

Extreme dentition does not prevent diet and tooth diversification within combtooth blennies (Ovalentaria: Blenniidae)

The dentition of fishes can be quite striking and is often correlated with a specific diet. Combtooth blennies have long incisiform oral teeth, unlike most actinopterygians. It has been suggested that the long tooth morphology is an adaptation for detritivory, but given the diversity of diets (detritus, coral polyps, polychaetes, and pieces of other fishes), are blenny teeth indeed monomorphic? Or does tooth variation associated with diet still exist at this extreme? To explore tooth and diet diversification, we used a new phylogenetic hypothesis of Blenniidae, measured tooth shape, number, and mode of attachment, and quantified blenniid diet. The ancestral diet of blennies contained detritus and diversified into many different diets, including almost exclusively detritivory. Our results reveal a dental cline that may be constrained by tooth shape, but has not prevented diet diversification. Ancestral state reconstruction of tooth morphologies suggests that the ancestor of blennies had many unattached teeth and featured transitions to fewer attached teeth, with several transitions back to attached or unattached teeth. The dentition of blenniids is not monotypic; rather it is diverse and small changes in tooth shape are accompanied by changes in size, number, attachment, and often diet.

A Dipteran's Novel Sucker Punch: Evolution of Arthropod Atypical Venom with a Neurotoxic Component in Robber Flies (Asilidae, Diptera)

Predatory robber flies (Diptera, Asilidae) have been suspected to be venomous due to their ability to overpower well-defended prey. However, details of their venom composition and toxin arsenal remained unknown. Here, we provide a detailed characterization of the venom system of robber flies through the application of comparative transcriptomics, proteomics and functional morphology. Our results reveal asilid venoms to be dominated by peptides and non-enzymatic proteins, and that the majority of components in the crude venom is represented by just ten toxin families, which we have named Asilidin1-10. Contrary to what might be expected for a liquid-feeding predator, the venoms of robber flies appear to be rich in novel peptides, rather than enzymes with a putative pre-digestive role. The novelty of these peptides suggests that the robber fly venom system evolved independently from hematophagous dipterans and other pancrustaceans. Indeed, six Asilidins match no other venom proteins, while three represent known examples of peptide scaffolds convergently recruited to a toxic function. Of these, members of Asilidin1 closely resemble cysteine inhibitor knot peptides (ICK), of which neurotoxic variants occur in cone snails, assassin bugs, scorpions and spiders. Synthesis of one of these putative ICKs, U-Asilidin₁-Mar1a, followed by toxicity assays against an ecologically relevant prey model revealed that one of these likely plays a role as a neurotoxin involved in the immobilization of prey. Our results are fundamental to address these insights further and to understand processes that drive venom evolution in dipterans as well as other arthropods.

Venomics of Remipede Crustaceans Reveals Novel Peptide Diversity and Illuminates the Venom's Biological Role

We report the first integrated proteomic and transcriptomic investigation of a crustacean venom. Remipede crustaceans are the venomous sister group of hexapods, and the venom glands of the remipede Xibalbanus tulumensis express a considerably more complex cocktail of proteins and peptides than previously thought. We identified 32 venom protein families, including 13 novel peptide families that we name xibalbins, four of which lack similarities to any known structural class. Our proteomic data confirm the presence in the venom of 19 of the 32 families. The most highly expressed venom components are serine peptidases, chitinase and six of the xibalbins. The xibalbins represent Inhibitory Cystine Knot peptides (ICK), a double ICK peptide, peptides with a putative Cystine-stabilized α-helix/β-sheet motif, a peptide similar to hairpin-like β-sheet forming antimicrobial peptides, two peptides related to different hormone families, and four peptides with unique structural motifs. Remipede venom components represent the full range of evolutionary recruitment frequencies, from families that have been recruited into many animal venoms (serine peptidases, ICKs), to those having a very narrow taxonomic range (double ICKs), to those unique for remipedes. We discuss the most highly expressed venom components to shed light on their possible functional significance in the predatory and defensive use of remipede venom, and to provide testable ideas for any future bioactivity studies.