High Specific Efficiency of Venom of Two Prey-Specialized Spiders

Prey specificity of predatory venoms

Venom represents a key adaptation of many venomous predators, allowing them to immobilise prey quickly through chemical rather than physical warfare. Evolutionary arms races between prey and a predator are believed to be the main factor influencing the potency and composition of predatory venoms. Predators with narrowly restricted diets are expected to evolve specifically potent venom towards their focal prey, with lower efficacy on alternative prey. Here, we evaluate hypotheses on the evolution of prey-specific venom, focusing on the effect of restricted diet, prey defences, and prey resistance. Prey specificity as a potential evolutionary dead end is also discussed. We then provide an overview of the current knowledge on venom prey specificity, with emphasis on snakes, cone snails, and spiders. As the current evidence for venom prey specificity is still quite limited, we also overview the best approaches and methods for its investigation and provide a brief summary of potential model groups. Finally, possible applications of prey-specific toxins are discussed.

Venom extraction method influences venom composition and potency in the giant house spider Eratigena atrica (C. L. Koch, 1843)

Extraction is the first step when investigating venom composition and function. In small invertebrates, widely used extraction methods include electrostimulation and venom gland extraction, however, the influence of these methods on composition and toxicology is poorly understood. Using the Giant House Spider Eratigena atrica as a model, we show that electrostimulation and venom gland removal extraction methods produce different protein profiles as assessed by Coomassie-stained SDS-PAGE and significantly different potencies in the cricket Acheta domesticus.

Dynamic evolution of size and colour in the highly specialized Zodarion ant-eating spiders

Ecological specialists constitute relevant case studies for understanding the mechanisms, potential and limitations of evolution. The species-rich and strictly myrmecophagous spiders of the genus Zodarion show diversified defence mechanisms, including myrmecomorphy of different ant species and nocturnality. Through Hybridization Capture Using RAD Probes (hyRAD), a phylogenomic technique designed for sequencing poorly preserved specimens, we reconstructed a phylogeny of Zodarion using 52 (approx. a third of the nominal) species that cover its phylogenetic and distributional diversity. We then estimated the evolution of body size and colour, traits that have diversified noticeably and are linked to defence mechanisms, across the group. Our genomic matrix of 300 loci led to a well-supported phylogenetic hypothesis that uncovered two main clades inside Zodarion. Ancestral state estimation revealed the highly dynamic evolution of body size and colour across the group, with multiple transitions and convergences in both traits, which we propose is likely indicative of multiple transitions in ant specialization across the genus. Our study will allow the informed targeted selection of Zodarion taxa of special interest for research into the group's remarkable adaptations to ant specialization. It also exemplifies the utility of hyRAD for phylogenetic studies using museum material.

Lampshade web spider Ectatosticta davidi chromosome-level genome assembly provides evidence for its phylogenetic position

The spider of Ectatosticta davidi, belonging to the lamp-shade web spider family, Hypochilidae, which is closely related to Hypochilidae and Filistatidae and recovered as sister of the rest Araneomorphs spiders. Here we show the final assembled genome of E. davidi with 2.16 Gb in 15 chromosomes. Then we confirm the evolutionary position of Hypochilidae. Moreover, we find that the GMC gene family exhibit high conservation throughout the evolution of true spiders. We also find that the MaSp genes of E. davidi may represent an early stage of MaSp and MiSp genes in other true spiders, while CrSp shares a common origin with AgSp and PySp but differ from MaSp. Altogether, this study contributes to addressing the limited availability of genomic sequences from Hypochilidae spiders, and provides a valuable resource for investigating the genomic evolution of spiders.

Intersexual Differences in the Gene Expression of Phoneutria depilata (Araneae, Ctenidae) Toxins Revealed by Venom Gland Transcriptome Analyses

The wandering spider, Phoneutria depilata, is one of Colombia's most active nocturnal arthropod predators of vertebrates and invertebrates. Its venom has been a relevant subject of study in the last two decades. However, the scarcity of transcriptomic data for the species limits our knowledge of the distinct components present in its venom for linking the mainly neurotoxic effects of the spider venom to a particular molecular target. The transcriptome of the P. depilata venom gland was analyzed to understand the effect of different diets or sex and the impact of these variables on the composition of the venom. We sequenced venom glands obtained from ten males and ten females from three diet treatments: (i) invertebrate: Tenebrio molitor, (ii) vertebrate: Hemidactylus frenatus, and (iii) mixed (T. molitor + H. frenatus). Of 17,354 assembled transcripts from all samples, 65 transcripts relating to venom production differed between males and females. Among them, 36 were classified as neurotoxins, 14 as serine endopeptidases, 11 as other proteins related to venom production, three as metalloprotease toxins, and one as a venom potentiator. There were no differences in transcripts across the analyzed diets, but when considering the effect of diets on differences between the sexes, 59 transcripts were differentially expressed. Our findings provide essential information on toxins differentially expressed that can be related to sex and the plasticity of the diet of P. depilata and thus can be used as a reference for venomics of other wandering spider species.

Composition and toxicity of venom produced by araneophagous white-tailed spiders (Lamponidae: Lampona sp.)

Prey-specialised spiders are adapted to capture specific prey items, including dangerous prey. The venoms of specialists are often prey-specific and less complex than those of generalists, but their venom composition has not been studied in detail. Here, we investigated the venom of the prey-specialised white-tailed spiders (Lamponidae: Lampona), which utilise specialised morphological and behavioural adaptations to capture spider prey. We analysed the venom composition using proteo-transcriptomics and taxon-specific toxicity using venom bioassays. Our analysis identified 208 putative toxin sequences, comprising 103 peptides < 10 kDa and 105 proteins > 10 kDa. Most peptides belonged to one of two families characterised by scaffolds containing eight or ten cysteine residues. Toxin-like proteins showed similarity to galectins, leucine-rich repeat proteins, trypsins and neprilysins. The venom of Lampona was shown to be more potent against the preferred spider prey than against alternative cricket prey. In contrast, the venom of a related generalist was similarly potent against both prey types. These data provide insights into the molecular adaptations of venoms produced by prey-specialised spiders.

The ontogenetic dietary shift from non-dangerous to dangerous prey in predator-eating predators under capture risk

Evaluating the patterns and generality of ontogenetic dietary shifts (ODSs) contributes to understanding prey-predator interactions and food web dynamics. Numerous studies have focused on predators that target distinctively lower trophic-level organisms. However, the ODS of predators that routinely prey on organisms at similar trophic levels (i.e., predator-eating predators) have been neglected in ODS research. The ODS patterns of predator eaters may not fit into conventional frameworks owing to constraints of potential capture risk (e.g., deadly counterattack from prey) and body size. We aimed to reveal the ODS patterns of predator eaters and determine whether the patterns were affected by body size and capture risk. Assuming that capture risk is a significant factor in ODS patterns, we expected: (1) juvenile araneophagic spiders to forage on non-dangerous prey (insects) and capture larger non-dangerous prey more frequently than dangerous prey (spiders); and (2) as they grow, their prey types will shift from non-dangerous to dangerous prey because larger predators will be able to capture dangerous prey as the optimal food. As a result of field observations, we revealed that the major ODS pattern in these spiders changed from a mixed (both insect and spider) to a spider-dominant diet. The model selection approach showed that this diet shift was partly due to predator size, and the relative importance of predator size was higher than the life stage per se and almost equal to species identity. In these spiders, the body size of spider prey tended to be smaller than that of insects when the predators were small, suggesting that capture risk may be a critical factor in determining the ODS patterns of these predators. Therefore, our study adds to the evidence that the capture risk is crucial in comprehensively understanding the mechanisms determining ODS patterns in natural systems.

Ecological specialization and reproductive isolation among closely related sympatric ant-eating spiders

Biological divergence results from several mechanisms. Defensive mechanisms, such as Batesian mimicry, can cause reproductive isolation via temporal segregation in foraging activity, particularly, in species that closely associate with their model. This seems to be the case of ant-eating spiders, which can be inaccurate Batesian mimics of their prey. Here, we focused on Zodarion nitidum, which has two forms occurring in sympatry, black and yellow. Given the expected noticeable impact of their colour differences on the spiders' interactions with their potential predators and prey, we investigated whether these morphotypes have diverged in other aspects of their biology. We measured the two morphotypes' phenotypic resemblance to a mimetic model, tested whether they were protected from predators, investigated their circadian activity, surveyed the prey they hunted, modelled their distributions, performed crossing experiments and estimated their degree of genetic differentiation. We found that the black morphotype is ant-like, resembling Messor ants, and it was not distinguishable from their ant models by four potential predators. In contrast, the yellow morphotype seems to use predator avoidance as a defensive strategy. Additionally, the two morphotypes differ in their circadian activity, the yellow morphotype being nocturnal and the black one being diurnal. The two morphotypes hunt and associate with different ant prey and possess marked differences in venom composition. Finally, crossing trials showed complete pre-mating isolation between the two morphotypes, but there was no evidence of genetic (mitochondrial data) or environmental niche differentiation. We conclude that the two morphotypes show evidence of a deep differentiation in morphological, behavioural, physiological and ecological traits that evolved together as part of the spider's diverging lifestyles.

Phylogenomics and loci dropout patterns of deeply diverged Zodarion ant-eating spiders suggest a high potential of RAD-seq for genus-level spider phylogenetics

RAD sequencing yields large amounts of genome-wide data at a relatively low cost and without requiring previous taxon-specific information, making it ideal for evolutionary studies of highly diversified and neglected organisms. However, concerns about information decay with phylogenetic distance have discouraged its use for assessing supraspecific relationships. Here, using Double Digest Restriction Associated DNA (ddRAD) data, we perform the first deep-level approach to the phylogeny of Zodarion, a highly diversified spider genus. We explore the impact of loci and taxon filtering across concatenated and multispecies coalescent reconstruction methods and investigate the patterns of information dropout in reference to both the time of divergence and the mitochondrial divergence between taxa. We found that relaxed loci-filtering and nested taxon-filtering strategies maximized the amount of molecular information and improved phylogenetic inference. As expected, there was a clear pattern of allele dropout towards deeper time and mitochondrial divergences, but the phylogenetic signal remained strong throughout the phylogeny. Therefore, we inferred topologies that were almost fully resolved, highly supported, and noticeably congruent between setups and inference methods, which highlights overall inconsistency in the taxonomy of Zodarion. Because Zodarion appears to be among the oldest and most mitochondrially diversified spider genera, our results suggest that ddRAD data show high potential for inferring intra-generic relationships across spiders and probably also in other taxonomic groups.

Special Issue: Evolutionary Ecology of Venom

This Special Issue of Toxins aims to increase the profile and understanding of how ecology shapes the evolution of venom systems, and also how venom influences the ecological attributes of and interactions among species [...].

Complex precursor structures of cytolytic cupiennins identified in spider venom gland transcriptomes

Analysis of spider venom gland transcriptomes focuses on the identification of possible neurotoxins, proteins and enzymes. Here, the first comprehensive transcriptome analysis of cupiennins, small linear cationic peptides, also known as cytolytic or antimicrobial peptides, is reported from the venom gland transcriptome of Cupiennius salei by 454- and Illumina 3000 sequencing. Four transcript families with complex precursor structures are responsible for the expression of 179 linear peptides. Within the transcript families, after an anionic propeptide, cationic linear peptides are separated by anionic linkers, which are transcript family specific. The C-terminus of the transcript families is characterized by a linear peptide or truncated linkers with unknown function. A new identified posttranslational processing mechanism explains the presence of the two-chain CsTx-16 family in the venom. The high diversity of linear peptides in the venom of a spider and this unique synthesis process is at least genus specific as verified with Cupiennius getazi.

Poor performance of DNA barcoding and the impact of RAD loci filtering on the species delimitation of an Iberian ant-eating spider

Genomic data provide unprecedented power for species delimitation. However, current implementations are still time and resource consuming. In addition, bioinformatic processing is contentious and its impact on downstream analyses is insufficiently understood. Here we employ ddRAD sequencing and a thorough sampling for species delimitation in Zodarion styliferum, a widespread Iberian ant-eating spider. We explore the influence of the loci filtering strategy on the downstream phylogenetic analyses, genomic clustering and coalescent species delimitation. We also assess the accuracy of one mitochondrial (COI) and one nuclear (ITS) barcode for fast and inexpensive species delineation in the group. Our genomic data strongly support two morphologically cryptic but ecologically divergent lineages, mainly restricted to the central-eastern and western parts of the Iberian Peninsula, respectively. Larger matrices with more missing data showed increased genomic diversity, supporting that bioinformatic strategies to maximize matrix completion disproportionately exclude loci with the highest mutation rates. Moderate loci filtering gave the best results across analyses: although larger matrices returned concatenated phylogenies with higher support, middle-sized matrices performed better in genetic structure analyses. COI displayed high diversity and a conspicuous barcode gap, revealing 13 mitochondrial lineages. Mitonuclear discordance is consistent with ancestral isolation in multiple groups, probably in glacial refugia, followed by range expansion and secondary contact that produced genomic homogenization. Several apparently (unidirectionally) introgressed specimens further challenge the accuracy of species identification through mitochondrial barcodes in the group. Conversely, ITS failed to separate both lineages of Z. styliferum. This study shows an extreme case of mitonuclear discordance that highlights the limitations of single molecular barcodes for species delimitation, even in presence of distinct barcode gaps, and brings new light on the effects of parameterization on shallow-divergence studies using RAD data.

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.