Venom physiology and composition in a litter of Common Death Adders (Acanthophis antarcticus) and their parents

Contrasting patterns of venom regeneration in a centipede (Scolopendra viridis) and a scorpion (Centruroides hentzi)

As biochemical traits with clear fitness consequences, venoms serve a critical ecological role for the animals that produce them. Understanding how venoms are maintained and regenerated after use will, therefore, provide valuable insight into the ecology of venomous animals. Furthermore, most studies on venomous organisms often require removing animals from the wild and waiting extended periods of time between venom extractions. Uncovering the patterns of venom regeneration across different species will likely lead to the development of more efficient venom extraction protocols, reducing both experimental time and the number of animals required. Using reversed-phase high-performance liquid chromatography, we identified asynchronous regeneration of venom protein component abundances in the centipede Scolopendra viridis but found no evidence for asynchronous venom regeneration in the scorpion Centruroides hentzi. We also observed high levels of intraspecific venom variation in C. hentzi, emphasizing the importance of testing for intraspecific venom variation in studies evaluating the synchronicity of venom regeneration. Although the regeneration of relative venom protein component abundances is an asynchronous process in S. viridis, we provide evidence that the presence-absence of major venom components is not an asynchronous process and suggest that studies relying on just the presence/absence of individual proteins (e.g. bioprospecting, drug discovery) could use catch-and-release methods of venom extraction to reduce the number of animals removed from the wild.

Addressing the global snakebite crisis with geo-spatial analyses - Recent advances and future direction

Venomous snakebite is a neglected tropical disease that annually leads to hundreds of thousands of deaths or long-term physical and mental ailments across the developing world. Insufficient data on spatial variation in snakebite risk, incidence, human vulnerability, and accessibility of medical treatment contribute substantially to ineffective on-ground management. There is an urgent need to collect data, fill knowledge gaps and address on-ground management problems. The use of novel, and transdisciplinary approaches that take advantage of recent advances in spatio-temporal models, 'big data', high performance computing, and fine-scale spatial information can add value to snakebite management by strategically improving our understanding and mitigation capacity of snakebite. We review the background and recent advances on the topic of snakebite related geospatial analyses and suggest avenues for priority research that will have practical on-ground applications for snakebite management and mitigation. These include streamlined, targeted data collection on snake distributions, snakebites, envenomings, venom composition, health infrastructure, and antivenom accessibility along with fine-scale models of spatio-temporal variation in snakebite risk and incidence, intraspecific venom variation, and environmental change modifying human exposure. These measures could improve and 'future-proof' antivenom production methods, antivenom distribution and stockpiling systems, and human-wildlife conflict management practices, while simultaneously feeding into research on venom evolution, snake taxonomy, ecology, biogeography, and conservation.

Venom Use in Eulipotyphlans: An Evolutionary and Ecological Approach

Venomousness is a complex functional trait that has evolved independently many times in the animal kingdom, although it is rare among mammals. Intriguingly, most venomous mammal species belong to Eulipotyphla (solenodons, shrews). This fact may be linked to their high metabolic rate and a nearly continuous demand of nutritious food, and thus it relates the venom functions to facilitation of their efficient foraging. While mammalian venoms have been investigated using biochemical and molecular assays, studies of their ecological functions have been neglected for a long time. Therefore, we provide here an overview of what is currently known about eulipotyphlan venoms, followed by a discussion of how these venoms might have evolved under ecological pressures related to food acquisition, ecological interactions, and defense and protection. We delineate six mutually nonexclusive functions of venom (prey hunting, food hoarding, food digestion, reducing intra- and interspecific conflicts, avoidance of predation risk, weapons in intraspecific competition) and a number of different subfunctions for eulipotyphlans, among which some are so far only hypothetical while others have some empirical confirmation. The functions resulting from the need for food acquisition seem to be the most important for solenodons and especially for shrews. We also present several hypotheses explaining why, despite so many potentially beneficial functions, venomousness is rare even among eulipotyphlans. The tentativeness of many of the arguments presented in this review highlights our main conclusion, i.e., insights regarding the functions of eulipotyphlan venoms merit additional study.

Venom Profiling of the Insular Species Bothrops alcatraz: Characterization of Proteome, Glycoproteome, and N-Terminome Using Terminal Amine Isotopic Labeling of Substrates

Bothrops alcatraz, a species endemic to Alcatrazes Islands, is regarded as critically endangered due to its small area of occurrence and the declining quality of its habitat. We recently reported the identification of N-glycans attached to toxins of Bothrops species, showing similar compositions in venoms of the B. jararaca complex (B. jararaca, B. insularis, and B. alcatraz). Here, we characterized B. alcatraz venom using electrophoretic, proteomic, and glycoproteomic approaches. Electrophoresis showed that B. alcatraz venom differs from B. jararaca and B. insularis; however, N-glycan removal revealed similarities between them, indicating that the occupation of N-glycosylation sites contributes to interspecies variability in the B. jararaca complex. Metalloproteinase was the major toxin class identified in the B. alcatraz venom proteome followed by serine proteinase and C-type lectin, and overall, the adult B. alcatraz venom resembles that of B. jararaca juvenile specimens. The comparative glycoproteomic analysis of B. alcatraz venom with B. jararaca and B. insularis indicated that there may be differences in the utilization of N-glycosylation motifs among their different toxin classes. Furthermore, we prospected for the first time the N-terminome of a snake venom using the terminal amine isotopic labeling of substrates (TAILS) approach and report the presence of ∼30% of N-termini corresponding to truncated toxin forms and ∼37% N-terminal sequences blocked by pyroglutamic acid in B. alcatraz venom. These findings underscore a low correlation between venom gland transcriptomes and proteomes and support the view that post-translational processes play a major role in shaping venom phenotypes.

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.

Venom regeneration in the centipede Scolopendra polymorpha: evidence for asynchronous venom component synthesis

Venom regeneration comprises a vital process in animals that rely on venom for prey capture and defense. Venom regeneration in scolopendromorph centipedes likely influences their ability to subdue prey and defend themselves, and may influence the quantity and quality of venom extracted by researchers investigating the venom's biochemistry. We investigated venom volume and total protein regeneration during the 14-day period subsequent to venom extraction in the North American centipede Scolopendra polymorpha. We further tested the hypothesis that venom protein components, separated by reversed-phase fast protein liquid chromatography (RP-FPLC), undergo asynchronous (non-parallel) synthesis. During the first 48 h, volume and protein mass increased linearly. Protein regeneration lagged behind volume regeneration, with 65–86% of venom volume and 29–47% of protein mass regenerated during the first 2 days. No additional regeneration occurred over the subsequent 12 days, and neither volume nor protein mass reached initial levels 7 months later (93% and 76%, respectively). Centipede body length was negatively associated with rate of venom regeneration. Analysis of chromatograms of individual venom samples revealed that 5 of 10 chromatographic regions and 12 of 28 peaks demonstrated changes in percent of total peak area (i.e., percent of total protein) among milking intervals, indicating that venom proteins are regenerated asynchronously. Moreover, specimens from Arizona and California differed in relative amounts of some venom components. The considerable regeneration of venom occurring within the first 48 h, despite the reduced protein content, suggests that predatory and defensive capacities are minimally constrained by the timing of venom replacement.

Morphology, reproduction and diet in Australian and Papuan death adders (Acanthophis, Elapidae)

Death adders (genus Acanthophis) differ from most other elapid snakes, and resemble many viperid snakes, in their thickset morphology and ambush foraging mode. Although these snakes are widely distributed through Australia and Papua New Guinea, their basic biology remains poorly known. We report morphological and ecological data based upon dissection of >750 museum specimens drawn from most of the range of the genus. Female death adders grow larger than conspecific males, to about the same extent in all taxa (20% in mean adult snout-vent length,  =  SVL). Most museum specimens were adult rather than juvenile animals, and adult males outnumbered females in all taxa except A. pyrrhus. Females have shorter tails (relative to SVL) than males, and longer narrower heads (relative to head length) in some but not all species. The southern A. antarcticus is wider-bodied (relative to SVL) than the other Australian species. Fecundity of these viviparous snakes was similar among taxa (mean litter sizes 8 to 14). Death adders encompass a broad range of ecological attributes, taking a wide variety of vertebrate prey, mostly lizards (55%), frogs and mammals (each 21%; based on 217 records). Dietary composition differed among species (e.g. frogs were more common in tropical than temperate-zone species), and shifted with snake body size (endotherms were taken by larger snakes) and sex (male death adders took more lizards than did females). Overall, death adders take a broader array of prey types, including active fast-moving taxa such as endotherms and large diurnal skinks, than do most other Australian elapids of similar body sizes. Ambush foraging is the key to capturing such elusive prey.

Variation in venom yield and protein concentration of the centipedes Scolopendra polymorpha and Scolopendra subspinipes

Venom generally comprises a complex mixture of compounds representing a non-trivial metabolic expense. Accordingly, natural selection should fine-tune the amount of venom carried within an animal's venom gland(s). The venom supply of scolopendromorph centipedes likely influences their venom use and has implications for the severity of human envenomations, yet we understand very little about their venom yields and the factors influencing them. We investigated how size, specifically body length, influenced volume yield and protein concentration of electrically extracted venom in Scolopendra polymorpha and Scolopendra subspinipes. We also examined additional potential influences on yield in S. polymorpha, including relative forcipule size, relative mass, geographic origin (Arizona vs. California), sex, time in captivity, and milking history. Volume yield was linearly related to body length, and S. subspinipes yielded a larger length-specific volume than S. polymorpha. Body length and protein concentration were uncorrelated. When considering multiple influences on volume yield in S. polymorpha, the most important factor was body length, but yield was also positively associated with relative forcipule length and relative body mass. S. polymorpha from California yielded a greater volume of venom with a higher protein concentration than conspecifics from Arizona, all else being equal. Previously milked animals yielded less venom with a lower protein concentration. For both species, approximately two-thirds of extractable venom was expressed in the first two pulses, with remaining pulses yielding declining amounts, but venom protein concentration did not vary across pulses. Further study is necessary to ascertain the ecological significance of the factors influencing venom yield and how availability may influence venom use.

Investigating the chemical profile of regenerated scorpion (Parabuthus transvaalicus) venom in relation to metabolic cost and toxicity

We investigated the biochemical profile of regenerated venom of the scorpion Parabuthus transvaalicus in relation to its metabolic cost and toxicity. Using a closed-system respirometer, we compared oxygen consumption between milked and unmilked scorpions to determine the metabolic costs associated with the first 192 h of subsequent venom synthesis. Milked scorpions had a substantially (21%) higher mean metabolic rate than unmilked scorpions, with the largest increases in oxygen consumption occurring at approximately 120 h, 162 h, and 186 h post-milking. Lethality tests in crickets indicated that toxicity of the regenerated venom returned to normal levels within 4 d after milking. However, the chemical profile of the regenerated venom, as evaluated by FPLC and MALDI-TOF mass spectrometry, suggested that regeneration of different venom components was asynchronous. Some peptides regenerated quickly, particularly those associated with the scorpion's "prevenom," whereas others required much or all of this time period for regeneration. This asynchrony could explain the different spikes detected in oxygen consumption of milked scorpions as various peptides and other venom components were resynthesized. These observations confirm the relatively high metabolic cost of venom regeneration and suggest that greater venom complexity can be associated with higher costs of venom production.