A Review of Rattlesnake Venoms

Venom components are invaluable in biomedical research owing to their specificity and potency. Many of these components exist in two genera of rattlesnakes, Crotalus and Sistrurus, with high toxicity and proteolytic activity variation. This review focuses on venom components within rattlesnakes, and offers a comparison and itemized list of factors dictating venom composition, as well as presenting their known characteristics, activities, and significant applications in biosciences. There are 64 families and subfamilies of proteins present in Crotalus and Sistrurus venom. Snake venom serine proteases (SVSP), snake venom metalloproteases (SVMP), and phospholipases A2 (PLA2) are the standard components in Crotalus and Sistrurus venom. Through this review, we highlight gaps in the knowledge of rattlesnake venom; there needs to be more information on the venom composition of three Crotalus species and one Sistrurus subspecies. We discuss the activity and importance of both major and minor components in biomedical research and drug development.

A Meta-Analysis of the Protein Components in Rattlesnake Venom

The specificity and potency of venom components give them a unique advantage in developing various pharmaceutical drugs. Though venom is a cocktail of proteins, rarely are the synergy and association between various venom components studied. Understanding the relationship between various components of venom is critical in medical research. Using meta-analysis, we observed underlying patterns and associations in the appearance of the toxin families. For Crotalus, Dis has the most associations with the following toxins: PDE; BPP; CRL; CRiSP; LAAO; SVMP P-I and LAAO; SVMP P-III and LAAO. In Sistrurus venom, CTL and NGF have the most associations. These associations can predict the presence of proteins in novel venom and understand synergies between venom components for enhanced bioactivity. Using this approach, the need to revisit the classification of proteins as major components or minor components is highlighted. The revised classification of venom components is based on ubiquity, bioactivity, the number of associations, and synergies. The revised classification can be expected to trigger increased research on venom components, such as NGF, which have high biomedical significance. Using hierarchical clustering, we observed that the genera's venom compositions were similar, based on functional characteristics rather than phylogenetic relationships.

Endoparasites of Crotalus tzabcan (Serpentes: Viperidae), with a checklist in rattlesnakes

The helminth and pentastomid fauna of 50 specimens of Crotalus tzabcan from the Yucatán Peninsula, Mexico is documented. The examination revealed the presence of three nematode species (Hastospiculum onchocercum, Hexametra boddaertii, and Travassosascaris araujoi), and one pentastomid (Porocephalus crotali). The threee nematode species had the same prevalence (2%), while the pentastomid had a higher prevalence (8%). The pentastomid P. crotali was the most abundant and intense parasite, although it was only found in four snake hosts. Crotalus tzabcan acts as definitive host for the adult helminths and pentastomids, with rodents as the probable intermediate hosts. This work represents the first systematic survey on the parasitic helminth and pentastomid fauna of C. tzabcan, and includes four new geographical records. Additionally, a checklist of helminths and pentastomids reported for Crotalus and Sistrurus is provided. To date, a total of 32 helminth and 7 pentastomid species have been recorded as parasites of rattlesnakes. Nematoda possessed the highest species richness. The genera with the highest number of host species were Mesocestoides and Hexametra, followed by Kalicephalus. The rattlesnake species with the highest number of reported parasites was C. durissus (18 nematodes and 2 pentastomids).

The importance of species: Pygmy rattlesnake venom toxicity differs between native prey and related non-native species

Venom toxicity assessments are often based upon non-native surrogate prey species that are not consumed in the wild by the venomous predator. This raises questions about the relevance of toxicity results on these "model" prey in addressing ecological or evolutionary questions about venom effects on native prey. We explore this issue by comparing the toxicity of venom from pygmy rattlesnakes (Sistrurus miliarius) on taxonomically-diverse sets of model (non-native) and native prey. Specifically, we compared rattlesnake venom toxicity for nine species from three broad taxonomic groups of prey (reptiles, mammals, and amphibians) to determine whether estimates of venom toxicity for the non-native model species of each group was representative of species which were native prey. In all three groups, model species (Anolis sagrei, Mus musculus, and Lithobates pipiens) had a significantly different mortality response from one or more of the native prey species (Anolis carolinensis, Peromyscus gossypinus, Lithobates sphenocephalus, Hyla cinerea, and Hyla squirella) that the models were meant to represent. Two features of our results suggest an importance of evolutionary history in understanding these differences. First, there was a phylogenetic component to prey responses to venom in that in each group, non-native models and congeneric native prey showed more similar responses than prey from other genera suggesting that venom may act on common prey targets that result from common ancestry. Second, native prey generally showed higher LD₅₀ values than their non-native counterparts, suggesting greater resistance to venom from a predator with which they interact in nature. Our results suggest that researchers should use native prey to generate measures of venom toxicity that are ecologically and evolutionarily relevant. If this is not possible using "model" prey species that are close taxonomic relatives to natural prey may be a reasonable alternative.

Demographic consequences of climate change and land cover help explain a history of extirpations and range contraction in a declining snake species

Developing conservation strategies for threatened species increasingly requires understanding vulnerabilities to climate change, in terms of both demographic sensitivities to climatic and other environmental factors, and exposure to variability in those factors over time and space. We conducted a range-wide, spatially explicit climate change vulnerability assessment for Eastern Massasauga (Sistrurus catenatus), a declining endemic species in a region showing strong environmental change. Using active season and winter adult survival estimates derived from 17 data sets throughout the species' range, we identified demographic sensitivities to winter drought, maximum precipitation during the summer, and the proportion of the surrounding landscape dominated by agricultural and urban land cover. Each of these factors was negatively associated with active season adult survival rates in binomial generalized linear models. We then used these relationships to back-cast adult survival with dynamic climate variables from 1950 to 2008 using spatially explicit demographic models. Demographic models for 189 population locations predicted known extant and extirpated populations well (AUC = 0.75), and models based on climate and land cover variables were superior to models incorporating either of those effects independently. These results suggest that increasing frequencies and severities of extreme events, including drought and flooding, have been important drivers of the long-term spatiotemporal variation in a demographic rate. We provide evidence that this variation reflects nonadaptive sensitivity to climatic stressors, which are contributing to long-term demographic decline and range contraction for a species of high-conservation concern. Range-wide demographic modeling facilitated an understanding of spatial shifts in climatic suitability and exposure, allowing the identification of important climate refugia for a dispersal-limited species. Climate change vulnerability assessment provides a framework for linking demographic and distributional dynamics to environmental change, and can thereby provide unique information for conservation planning and management.

Using rattlesnake microsatellites to determine paternity in captive bushmasters (Lachesis muta)

We used 10 microsatellite DNA markers originally described for two Crotalus and one Sistrurus species to infer paternity in a captive-hatched clutch of Lachesis muta. Although the dam was known, records listed two potential sires, which prevented the inclusion of those offspring in a captive breeding program. Samples were collected from both possible sires, the presumed dam and two offspring. Five of the ten markers were paternity informative and either unambiguously identified one of the two males as the sire of the offspring or excluded the other male. A sixth marker identified the sire in one of the two offspring. These results reveal rattlesnake DNA markers as a useful tool in paternity testing and captive breeding management of Lachesis muta. It also indicates that, within the American crotalid radiation, a selection of microsatellite DNA markers cross-amplify and provide useful genotypic information across species and genera.