Diamondback Rattlesnake Crotalus Research Articles

BEYOND MYTHS: REDISCOVERY OF THE WESTERN DIAMONDBACK RATTLESNAKE Crotalus atrox (BAIRD & GIRARD, 1853) IN THE MEXICAN STATE OF OAXACA AFTER A SPAN OF 79 YEARS

We rediscovered and confirmed, after a span of 79 years, the presence of the Western Diamondback Rattlesnake Crotalus atrox in the Mexican state of Oaxaca. The record is based on six specimens found in an anthropized environment within the Base Aérea Militar II located in Ciudad Ixtepec, in the municipality of Asunción Ixtaltepec within the Isthmus of Tehuantepec region.

A novel broad spectrum venom metalloproteinase autoinhibitor in the rattlesnake Crotalus atrox evolved via a shift in paralog function

The complexity of snake venom composition reflects adaptation to the diversity of prey and may be driven at times by a coevolutionary arms race between snakes and venom-resistant prey. However, many snakes are also resistant to their own venom due to serum-borne inhibitors of venom toxins, which raises the question of how snake autoinhibitors maintain their efficacy as venom proteins evolve. To investigate this potential three-way arms race among venom, prey, and autoinhibitors, we have identified and traced the evolutionary origin of serum inhibitors of snake venom metalloproteinases (SVMPs) in the Western Diamondback rattlesnake Crotalus atrox which possesses the largest known battery of SVMP genes among crotalids examined. We found that C.atrox expresses five members of a Fetuin A-related metalloproteinase inhibitor family but that one family member, FETUA-3, is the major SVMP inhibitor that binds to approximately 20 different C.atrox SVMPs and inhibits activities of all three SVMP classes. We show that the fetua-3 gene arose deep within crotalid evolution before the origin of New World species but, surprisingly, fetua-3 belongs to a different paralog group than previously identified SVMP inhibitors in Asian and South American crotalids. Conversely, the C.atrox FETUA-2 ortholog of previously characterized crotalid SVMP inhibitors shows limited activity against C.atrox SVMPs. These results reveal that there has been a functional evolutionary shift in the major SVMP inhibitor in the C.atrox lineage as the SVMP family expanded and diversified in the Crotalus lineage. This broad-spectrum inhibitor may be of potential therapeutic interest.

Online and pet stores as sources of trade for reptiles in South Africa

The ever-increasing human population, globalisation, and desire to keep pets have resulted in the translocation of many species into non-native environments. As a result, some of the non-native reptile species have been introduced to South Africa through the pet trade. However, little is known about the extent of trade in reptiles via online and physical pet stores in South Africa and their potential climatically suitable areas. We assessed the physical pet store and online trade of reptiles in South Africa. We found 69 physical pet stores and 18 online advertising websites selling 1,912 individuals of 66 species and 859 individuals of 50 reptile species, respectively. In total, we found 88 unique species representing 18 families from both sources, of which 86.4% were non-native species and 32 species were CITES-listed. Snakes were the most dominant (76.1%) traded group. Ball python Python regius (n = 601), corn snake Pantherophis guttatus (n = 553) and central bearded dragon Pogona vitticeps (n = 419) were the most-traded reptiles. Prices ranged from ZAR100.00 to ZAR6,000.00, with sharp-nosed viper Deinagkistrodon acutus acutus being the most expensive species. For present distributions, the red-eared slider Trachemys scripta elegans, P. guttatus, and Western diamondback rattlesnake Crotalus atrox had the largest predicted climatic suitability. The future predictions for the latter two species were predicted to increase while red-eared slider suitability shifted. Most popular species were available in large volumes, sold at relatively low prices and had high climatic suitability, representing a high potential invasion risk. We, therefore, propose that the existing pet trade regulations should be revised to include a more restricted trade on the trade of endangered, non-CITES listed and potential invasive pet species.

Frequency of reproduction in female western diamond‐backed rattlesnakes from the Sonoran Desert of Arizona is variable in individuals: potential role of rainfall and prey densities

In many species of snakes, particularly viperids from temperate regions, production of offspring by individuals occurs on a less-than-annual schedule. Accordingly, acquiring sufficient energy and nutrient reserves for reproduction in females often requires more than a single active season. This is termed capital mode. Yet, in some instances, annual reproduction occurs under conditions where foraging success is high and environmental factors are compliant. This is termed income mode. Here, we addressed the hypothesis of annual versus less-than-annual reproduction from a long-term radio-telemetric study involving female western diamond-backed rattlesnakes Crotalus atrox from a population of the Sonoran Desert in Arizona. From 2001 to 2008, 16 of 20 radio-telemetered females produced 36 litters, which 32 were informative in addressing the hypothesis of reproductive frequency. In 14 females, litters were produced on a biennial or at-least-biennial (≥biennial) cycle. However, seven females demonstrated annual reproduction, of which several had previously reproduced on a biennial or greater cycle. Because our study was non-experimental, we were unable to unambiguously identify specific proximate factors that contributed to the shift in annual reproduction. Nonetheless, we established that greater annual rainfall was significantly correlated with shifts to annual reproduction. Based on other studies, we hypothesize that increased rainfall was causally linked with increases in rodent densities and the foraging success of female C. atrox, which in turn is linked to reproduction. We describe, moreover, several characteristics of female C. atrox that appear to facilitate the potential for annual reproduction. In long-lived species, such as C. atrox, our research underscores the necessity to follow individuals for extended periods to gain insights on reproductive cycles not captured by point sampling methods, such as short-term field studies or reliance on museum specimens.

Habitat specificity and home‐range size as attributes of species vulnerability to extinction: a case study using sympatric rattlesnakes

AbstractLarge home‐range size and habitat specificity are two commonly cited ecological attributes that are believed to contribute to species vulnerability. The eastern diamondback rattlesnake Crotalus adamanteus is a declining species that occurs sympatrically with the more abundant canebrake rattlesnake Crotalus horridus in a portion of the south‐eastern Coastal Plain, USA. In this study, we use the ecological similarities of the two species as experimental controls to test the role of home‐range size and habitat specificity in the imperilment of the eastern diamondback rattlesnake. We used analysis of variance to investigate differences in home‐range size between the two species, and home‐range selection was modeled as habitat use versus availability with a case control sampling design using logistic regression. We failed to detect differences in home‐range size between the two species; therefore, we could not identify home‐range size as an attribute contributing to the imperilment of eastern diamondback rattlesnakes. Eastern diamondback rattlesnakes selected pine savannas to a degree that suggests that the species is a habitat specialist. Of the two factors examined, habitat specificity to the imperiled longleaf pine ecosystem may be a significant contributor to the decline of the eastern diamondback rattlesnake.

Proteome analysis of the thermoreceptive pit membrane of the western diamondback rattlesnake Crotalus atrox.

Rattlesnakes detect their prey's temperature by means of a cavern-like structure, the pit organ. The sensory component of this organ lies within a thin membrane called the pit membrane. Proteome analysis conducted on this neurosensory tissue revealed only a relatively small number of proteins, thereby depicting its high degree of specialization. In addition to containing blood serum and structural proteins, the proteome of this membrane appears to be strikingly similar to that of isolated rattlesnake brain mitochondria. Indeed, our results show that over 80% of the detected tissue proteins are of mitochondrial origin. Fluorescence microscopy studies of these organelles indicate their dense arrangement and accumulation in structures which have been previously reported to be the terminal ends of free nerve fibers of the innervating trigeminal branches. Thus, original ultrastructural observations are paralleled by our findings at the molecular level.

Structural correlates of speed and endurance in skeletal muscle: the rattlesnake tailshaker muscle

The western diamondback rattlesnake Crotalus atrox can rattle its tail continuously for hours at frequencies approaching 90 Hz. We examined the basis of these fast sustainable contractions using electromyography, data on oxygen uptake and the quantitative ultrastructure of the tailshaker muscle complex. The tailshaker muscle has no apparent unique structures; rather, the relative proportions of the structures common to all skeletal muscles appear to be present (1) to minimize activation, contraction and relaxation times via an extremely high volume density of sarcoplasmic reticulum (26 %) as well as, (2) to maximize ATP resysnthesis via a high volume density of mitochondria (26 %). The high rate of ATP supply is reflected in the in vivo muscle mass-specific oxygen uptake of this group of muscles which, at 585 ml O2 kg-1 min-1 during rattling at 30 °C body temperature, exceeds that reported for other ectotherm and many endotherm muscles. Since the change in oxygen uptake paralleled that of the rattling frequency over the range of measured body temperatures, there was a nearly constant O2 cost per muscle contraction (0.139±0.016 µl O2 g-1). Electromyo-graphic analysis suggests that each of the six muscles that make up the shaker complex may be a single motor unit. Finally, the maximum rate of mitochondrial oxygen uptake is similar to that of various mammals, a hummingbird, a lizard, an anuran amphibian and of isolated mitochondria (at 10 000-40 000 molecules O2 s-1 µm2 of cristae surface area, when normalized to 30 °C), suggesting a shared principle of design of the inner mitochondrial membrane among the vertebrates.

Structural interaction of natural and synthetic inhibitors with the venom metalloproteinase, atrolysin C (form d).

The structure of the metalloproteinase and hemorrhagic toxin atrolysin C form d (EC 3.4.24.42), from the venom of the western diamondback rattlesnake Crotalus atrox, has been determined to atomic resolution by x-ray crystallographic methods. This study illuminates the nature of inhibitor binding with natural (< Glu-Asn-Trp, where < Glu is pyroglutamic acid) and synthetic (SCH 47890) ligands. The primary specificity pocket is exceptionally deep; the nature of inhibitor and productive substrate binding is discussed. Insights gained from the study of these complexes facilitate the design of potential drugs to treat diseases where matrix metalloproteinases have been implicated, e.g., arthritis and tumor metastasis.

Refined 2·0 Å X-ray Crystal Structure of the Snake Venom Zinc-endopeptidase Adamalysin II: Primary and Tertiary Structure Determination, Refinement, Molecular Structure and Comparison with Astacin, Collagenase and Thermolysin

Adamalysin II, alias proteinase II, a 24 kDa zinc-endopeptidase isolated from the snake venom of the Eastern diamondback rattlesnake Crotalus adamanteus, is a prototype, of the proteolytic domain of snake venom metalloproteinases and of domains found in mammalian reproductive tract proteins. Its 2·0 Å crystal and molecular structure was solved by multiple isomorphous replacement using six heavy-atom derivatives, and was refined to a crystallographic R-value of 0·172. 201 of the 203 amino acid residues of adamalysin II are defined by electron density; only the first two residues are disordered and crystallographically undefined in the crystal structure. Three-quarters of these crystallographic amino acid residue assignments were confirmed by chemical sequencing. In addition, the active-site zinc-ion, a heptaco-ordinated calcium ion, a fixed sulphate anion and 173 solvent molecules were localized in the structure.Adamalysin II is an ellipsoidal molecule with a relatively flat active-site cleft separating the "upper" main body from a small "lower" subdomain. The regularly folded N-terminal upper domain consists essentially of a central, highly twisted five-stranded β-pleated sheet flanked by a long and a short surface located helix on its convex side, and by two long helices, one of which represents the central "active site helix", on its concave side. The lower subdomain, comprising the last 50 residues, is organized in multiple turns, with the chain ending in a long C-terminal helix and an extended segment clamped to the upper domain via a disulphide bridge.The catalytic zinc-ion, located at the bottom of the active-site cleft, is almost tetrahedrally co-ordinated by His142, His146 and His152, and a water molecule anchored to an intermediate glutamic acid residue (Glu143), with the three imidazole Nε nitrogen atoms 2·1 Å and the solvent oxygen atom 2·4 Å away from the zinc ion. His142, Glu143 and His146 are part of the long active-site helix, which extends up to Gly149, where it turns sharply away towards His152. The importance of these residues for structure and activity of adamalysin II explains their occurrence in the HEXXHXXGXXH consensus sequence. Asp153, which is strictly conserved in these snake venom and reproductive tract metalloproteinases, is buried in the subdomain and seems to stabilize the hydrophobic active-site basement. Some residues behind, the adamalysin peptide chain folds into a characteristic 1,4-turn (the "Met-turn") containing the conserved Met166, which forms a hydrophobic basement for the three zinc-binding imidazoles. Adamalysin II shares a similar overall topology with astacin, with the collagenase catalytic domains and the P. aeruginosa alkaline proteinase, and exhibits a virtually identical zinc environment with these other "metzincins".The catalytic domains of the snake venom metalloproteinases and the corresponding domains of some reproductive tract proteins can be aligned with only a very few single residue insertions and deletions and with sequence identities mostly above 50%. All substitutions, including some novel cysteine residues engaged in additional disulphide bridges, are in agreement with the adamalysin 11 structure, which can therefore be considered as a prototype of these "adarnalysins".

Antihemorrhagic factors from the blood serum of the western diamondback rattlesnake Crotalus atrox

Several antihemorrhagic factors isolated from C. atrox serum are glycoproteins with mol. wt ranging from 65,000 to 80,000. The antihemorrhagic activity of these factors was stable at a pH range of 1.3–11.5 and at temperatures up to 85°C, for 30 min. The isolated antihemorrhagins also neutralized the proteolytic activity of C. atrox venom, as tested with azocollagen and gelatin, and formed a complex with hemorrhagic toxin e isolated from the same venom. The neutralization capacity of the isolated antihemorrhagins was six times as high as the commercial polyvalent antivenom produced for clinical use.

The refined crystal structure of dimeric phospholipase A2 at 2.5 A. Access to a shielded catalytic center.

The 2.5-A crystal structure of the calcium-free form of the dimeric venom phospholipase A2 from the Western Diamondback rattlesnake Crotalus atrox, has been refined to an R-factor of 17.8% (I greater than 2 sigma) and acceptable stereochemistry. The molecule is a nearly perfect 2-fold symmetric dimer in which most of the catalytic residues of both subunits face an internal cavity. The restricted access to the putative catalytic sites is especially puzzling as the optimal substrates for this and most other phospholipase A2 are phospholipids condensed in micellar or lamellar aggregates. We point out that substrate access to the internal cavity may be aided by calcium binding which can alter the intersubunit contacts that shield the catalytic network. We also suggest that a system of hydrogen-bonded moieties exists on the surface of the dimer that links the amino terminus to the catalytic system, through an invariant Gln 4 side chain and the backbone of the active center residue, Tyr 73. This hydrogen-bonded network is on a highly accessible surface of the dimer and would appear to contribute to the enzyme's (as opposed to the proenzyme's) special capacity to attack aggregated rather than monomeric substrate.