Crotalus Horridus Research Articles

Population Isolation and Genetic Subdivision of Timber Rattlesnakes (Crotalus horridus) in the New Jersey Pine Barrens

Abstract: Timber Rattlesnakes, Crotalus horridus, are an endangered species in New Jersey, where high human population density places extraordinary pressures on natural populations. Disjunct populations are found in both the northern part of the state and a few scattered locations in the southern Pine Barrens. The Pine Barrens populations were previously shown to have reduced levels of genetic diversity compared to other populations in the Mid-Atlantic region. In this study, we used microsatellite DNA to examine the remaining six known C. horridus populations in the Pine Barrens and two in the northern part of the state. Bayesian analysis, genetic distance analysis, and factorial component analysis were performed, and the results indicated that the sampled populations represented four genetic subgroups, the two northern populations comprised one subgroup and the remaining six Pine Barrens populations comprised the other subgroups. Although there was evidence for isolation by distance among the Pine Barre...

Male Snakes Allocate Time and Energy according to Individual Energetic Status: Body Condition, Steroid Hormones, and Reproductive Behavior in Timber Rattlesnakes, Crotalus horridus.

Life-history theory predicts that organisms will hedge current reproductive investment against potential costs in terms of survivorship and future fecundity. However, little is known regarding the endocrine mechanisms underlying bet-hedging strategies in free-ranging male vertebrates. We examined the relationships among individual energetic status, steroid hormones, mate search, and reproductive behavior in free-ranging male timber rattlesnakes. Snakes were monitored over four active seasons in order to test two hypotheses: (1) males adjust the amount of time and energy allocated toward reproduction according to the level of individual energy stores, and (2) observed condition-dependent reproductive allocation is associated with circulating concentrations of steroid hormones (testosterone and corticosterone) thought to regulate reproductive behaviors in vertebrates. A positive relationship between body condition and testosterone was observed in both the field and the laboratory. Male mate search effort was positively correlated with both body condition and testosterone. Body condition and testosterone concentrations were negatively related to time allocated toward foraging during the breeding season. A strong effect of year was observed in the analysis of testosterone and search effort, suggesting that multiple environmental factors impact hormone production and reproductive investment. Corticosterone was not related to any measured variable. Therefore, our results did not indicate a clear role of corticosterone in mediating observed relationships between energetic status and behavior. Observed relationships are consistent with the hypothesis that males allocate time and energy toward reproduction according to individual energetic status and that testosterone plays a role in mediating the trade-off between current reproductive investment and residual reproductive value.

Nowhere to Go but Up: Impacts of Climate Change on Demographics of a Short-Range Endemic (Crotalus willardi obscurus) in the Sky-Islands of Southwestern North America.

Biodiversity elements with narrow niches and restricted distributions (i.e., ‘short range endemics,’ SREs) are particularly vulnerable to climate change. The New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus, CWO), an SRE listed under the U.S. Endangered Species Act within three sky islands of southwestern North America, is constrained at low elevation by drought and at high elevation by wildfire. We combined long-term recapture and molecular data with demographic and niche modeling to gauge its climate-driven status, distribution, and projected longevity. The largest population (Animas) is numerically constricted (N = 151), with few breeding adults (Nb = 24) and an elevated inbreeding coefficient (ΔF = 0.77; 100 years). Mean home range (0.07km2) is significantly smaller compared to other North American rattlesnakes, and movements are within, not among sky islands. Demographic values, when gauged against those displayed by other endangered/Red-Listed reptiles [e.g., Loggerhead Sea Turtle ( Caretta caretta )], are either comparable or markedly lower. Survival rate differs significantly between genders (female<male) and life history stages (juvenile<adult) while a steadily declining population trajectory (r = -0.20±0.03) underscores the shallow predicted-time-to-extinction (17.09±2.05 years). Core habitat is receding upwards in elevation and will shift 750km NW under conservative climate estimates. While survival is significantly impacted by wildfire at upper elevations, the extinction vortex is driven by small population demographics, a situation comparable to that of the European Adder (Vipera berus), a conservation icon in southern Sweden. Genetic rescue, a management approach successfully employed in similar situations, is ill advised in this situation due to climate-driven habitat change in the sky islands. CWO is a rare organism in a unique environment, with a conserved niche and a predisposition towards extinction. It is a bellwether for the eventual climate-driven collapse of the Madrean pine-oak ecosystem, one of Earth’s three recognized megadiversity centers.

Ophidiomyces ophiodiicola dermatitis in eight free-ranging timber rattlesnakes (Crotalus horridus) from Massachusetts.

Eight free-ranging timber rattlesnakes (Crotalus horridus) from two geographically isolated Massachusetts populations were observed with skin lesions located primarily on the head but occasionally also on the lateral and ventral surfaces of the body. The snakes underwent health assessments that included physical examination, clinical pathology, full body radiographs, and full thickness biopsies of skin lesions. Each snake had fungal elements present histologically in tissue sections from skin lesions. Ophidiomyces ophiodiicola was identified from skin lesions using polymerase chain reaction in all eight snakes.

Caryospora bigenetica (Apicomplexa: Eimeriidae) in South America: new hosts and distribution records.

The coccidian Caryospora bigenetica was first described in the snake Crotalus horridus (Viperidae) from United States of America. This study represents the first record of the occurrence of C. bigenetica in snakes in South America. Feces were sampled between November 2013 and May 2014 from 256 wild snakes maintained in scientific breeding facilities in the states of Mato Grosso do Sul (MS; n = 214) and Rio de Janeiro (RJ; n = 42), Brazil. Caryospora bigenetica was found in 14 (5.6%) snakes, all belonging to the family Viperidae. Ten Bothrops moojeni and two Crotalus durissus from MS were infected. The coccidian was also found in one C. durissus and in one Bothrops jararacussu from the state of RJ. The oocysts were spherical with a double wall, the exterior lightly mammillated, striations apparent in transverse view, 13.0 µm (12 - 14); polar granule fixed in the internal wall. Sporocysts oval or pyriform, 10.0 × 8.0 µm (9 - 11 × 8 - 9); Stieda body discoid; sub-Stieda body present; sporocyst residuum present, formed by a group of spheroid bodies between sporozoites. This study increases the number of viperid hosts of C. bigenetica and expands the geographical distribution to South America.

The transcriptomic and proteomic basis for the evolution of a novel venom phenotype within the Timber Rattlesnake (Crotalus horridus).

The genetics underlying adaptive trait evolution describes the intersection between the probability that particular types of mutation are beneficial and the rates they arise. Snake venoms can vary in a directly meaningful manner through coding mutations and regulatory mutations. The amounts of different components determine venom efficacy, but point mutations in coding sequences can also change efficacy and function. The Timber Rattlesnake (Crotalus horridus) has populations that have evolved neurotoxic venom from the typical hemorrhagic rattlesnake venom present throughout most of its range. We identified only a handful of nonsynonymous differences in just five loci between animals with each venom type, and these differences affected lower-abundance toxins. Expression of at least 18 loci encoding hemorrhagic toxins was severely reduced in the production of neurotoxic venom. The entire phospholipase A2 toxin family was completely replaced in the neurotoxic venom, possibly through intergeneric hybridization. Venom paedomorphosis could, at best, explain only some of the loss of expression of hemorrhagic toxins. The number of potential mechanisms for altering venom composition and the patterns observed for C.horridus suggest that rapid venom evolution should occur primarily through changes in venom composition, rather than point mutations affecting coding sequences.

Metagenomic analysis of the gut microbiota of the Timber Rattlesnake, Crotalus horridus.

Snakes are capable of surviving long periods without food. In this study we characterized the microbiota of a Timber Rattlesnake (Crotalus horridus), devoid of digesta, living in the wild. Pyrosequencing-based metagenomics were used to analyze phylogenetic and metabolic profiles with the aid of the MG-RAST server. Pyrosequencing of samples taken from the stomach, small intestine and colon yielded 691696, 957756 and 700419 high quality sequence reads. Taxonomic analysis of metagenomic reads indicated Eukarya was the most predominant domain, followed by bacteria and then viruses, for all three tissues. The most predominant phylum in the domain Bacteria was Proteobacteria for the tissues examined. Functional classifications by the subsystem database showed cluster-based subsystems were most predominant (10-15 %). Almost equally predominant (10-13 %) was carbohydrate metabolism. To identify bacteria in the colon at a finer taxonomic resolution, a 16S rRNA gene clone library was created. Proteobacteria was again found to be the most predominant phylum. The present study provides a baseline for understanding the microbial ecology of snakes living in the wild.

Early significant ontogenetic changes in snake venoms.

Snake venom plays a critical role in food acquisition, digestion, and defense. Venoms are known to change throughout the life of some snake species, but nothing is known about the venom composition of hatchling/neonate snakes prior to and just after their first shedding cycle, despite this being a critical time in the life of the snake. Using a cohort of Crotalus horridus and two cohorts of Crotalus adamanteus, we showed for the first time that snakes undergo significant changes in venom composition after the postnatal shedding event. The number of changes among cohorts ranged widely and there was wide variation in the direction of protein regulation, which appeared to be on a locus-specific level rather than protein-family level. These significant venom composition changes that take place in the first few weeks of life most likely play critical roles in venom economy and resource conservation and may partially explain the rare, post-birth maternal care found in some venomous species.

Genetic Structure of Timber Rattlesnake (Crotalus horridus) Populations: Physiographic Influences and Conservation Implications

The distribution and genetic structure of wildlife populations may be impacted by landscape features and anthropogenic factors. The role of these factors in the genetic relationships among Timber Rattlesnakes (Crotalus horridus) from 21 locations in Pennsylvania, New Jersey, and Virginia was investigated using microsatellite genetic markers. Evidence for null alleles was found in 8 of the 21 populations studied, with frequencies ranging from 0.018 to 0.185. However, the presence of null alleles appeared to have no effect on the interpretation of the patterns of genetic relationships among the populations studied. The analyses showed that the overall extent of genetic differentiation was consistent with isolation by distance; however, a substantial amount of among-groups variation could not be accounted for by geographic distance alone. Bayesian analysis (STRUCTURE), genetic distance analysis, and factorial correspondence analysis (FCA) all indicated that the sampled populations represented three genetic g...

Seasonal variation in hematology and blood plasma chemistry values of the timber rattlesnake (Crotalus horridus).

Hematology, biochemical analyses, and body condition indices are useful tools for describing animal health, especially when making management decisions for species of conservation concern. We report hematologic, biochemical, and body condition index data for 13 free-ranging timber rattlesnakes (Crotalus horridus) sampled repeatedly over an active season in Indiana, USA.

Natural variation in steroid hormone profiles of male Timber Rattlesnakes, Crotalus horridus, in northwest Arkansas

We describe the seasonal profile of circulating steroid hormones (testosterone and corticosterone) in relation to the breeding season in free ranging male Timber Rattlesnakes, Crotalus horridus, over the course of three active seasons. In addition, we examine variation in steroid concentrations across years and in relation to body condition. We found that seasonal profiles of plasma testosterone were different compared to other crotalines with similar mating patterns. Concentrations of testosterone were elevated above baseline in the three months leading up to the single late summer breeding season. Testosterone peaked in July at the onset of the breeding season and dropped to baseline during the peak months of breeding (August and September). Testosterone concentrations also varied annually. Although the exact cause of annual variation could not be established, our results indicate that weather patterns may have driven observed differences. Testosterone concentrations were positively related to body condition, indicating that testosterone production is modulated according to energetic status (particularly in the two months prior to the breeding season). Corticosterone did not vary seasonally or with any measured variable, a result similar to other studied crotalines. Our results highlight the importance of long-term descriptive studies of the regulatory mechanisms that underlie behavior and physiology in diverse taxa, as these mechanisms can vary greatly within and among populations and are valuable in elucidating the intrinsic and extrinsic sources of such variation.

Growth of Timber Rattlesnakes (Crotalus horridus) in an Agriculturally Fragmented and a Contiguously Forested Habitat

Habitat loss and fragmentation threaten Timber Rattlesnake (Crotalus horridus) populations in contiguous, mature forests of eastern North America, yet information regarding the life history of C. horridus in fragmented habitats is sparse. In this study, we used mark–recapture data on body size and rattle morphology to compare the size at birth and per ecdysis growth rates of C. horridus from a fragmented habitat in west-central Missouri (MO) with those from a closed-canopy forest in northwest Arkansas (AR). The MO population is typically exposed to a shorter frost-free period than the AR population, so individuals may have less time to acquire prey. At birth, snakes in the MO population were significantly shorter than those from AR, but MO snakes increased in length more rapidly than AR snakes through their first eight ecdyses. Sexual size dimorphism was apparent in the MO population when males and females diverged in size between the fifth and sixth ecdyses, whereas growth trajectories of AR males and females remained indistinguishable through the first eight ecdyses. Crotalus horridus in the agriculturally fragmented habitat may have grown faster than their forest-dwelling counterparts because fields and edges provide prey with stable food sources, unlike the boom and bust production typical of acorn mast crops. Although previous studies have demonstrated that C. horridus growth rates vary along latitudinal and elevational gradients due to climatic constraints on foraging, our study suggests that prey abundance may be just as important in shaping variation in life history both within and among populations.

Black Bear Reactions to Venomous and Non-venomous Snakes in Eastern North America.

Bears are often considered ecological equivalents of large primates, but the latter often respond with fear, avoidance, and alarm calls to snakes, both venomous and non-venomous, there is sparse information on how bears respond to snakes. We videotaped or directly observed natural encounters between black bears (Ursus americanus) and snakes. Inside the range of venomous snakes in Arkansas and West Virginia, adolescent and adult black bears reacted fearfully in seven of seven encounters upon becoming aware of venomous and non-venomous snakes; but in northern Michigan and Minnesota where venomous snakes have been absent for millennia, black bears showed little or no fear in four encounters with non-venomous snakes of three species. The possible roles of experience and evolution in bear reactions to snakes and vice versa are discussed. In all areas studied, black bears had difficulty to recognize non-moving snakes by smell or sight. Bears did not react until snakes moved in 11 of 12 encounters with non-moving timber rattlesnakes (Crotalus horridus) and four species of harmless snakes. However, in additional tests in this study, bears were repulsed by garter snakes that had excreted pungent anal exudates, which may help explain the absence of snakes, both venomous and harmless, in bear diets reported to date.

Isolation of Lactococcus garvieae Strain TRF1 from the Fecal Material of a Timber Rattlesnake

In certain species of fish, such as rainbow trout, infection by the Firmicutes Lactococcus garvieae is problematic. This organism is the causative agent of lactococcosis disease in fish, and it is also considered a potential zoonotic bacterium, since it can cause several opportunistic infections in humans. In this study, L. garvieae strain TRF1 was grown and isolated in pure culture from the fecal material of a Timber Rattlesnake (Crotalus horridus), living in the wild. The presence/absence of several putative virulence factors was identified using staining, PCR amplification, and the construction of a draft genome. Strain TRF1 shared several putative virulence factors with strain Lg2, a known fish pathogen. However, the capsule gene cluster, found in strain Lg2, was not found in strain TRF1. Since this gene cluster is absent in several non-pathogenic strains of L. garvieae, it suggests strain TRF1 may not be pathogenic. However, this hypothesis will have to be tested in an animal model.

A Case of Neurotoxicity Following Envenomation by the Sidewinder Rattlesnake, Crotalus cerastes

North American rattlesnake envenomations typically result in local tissue injury and hematologic derangements. Neurotoxicity is uncommon but when present often manifests as fasciculations and paresthesias. Neurotoxicity following Sidewinder (Crotalus cerastes) envenomation has not been previously reported. A 56-year-old man bitten on the right foot developed painful paresthesias, weakness and fasciculations of the right lower extremity, and involuntary muscle contractions of the anterior thigh. Local tissue effects and hemotoxicity never developed. The patient was discharged 5days after the bite with resolution of fasciculations but continued to have right-sided weakness. The snake was identified as a Sidewinder, C. cerastes, by the patient and two independent herpetologists. This is the first reported case of a Sidewinder rattlesnake envenomation resulting in neurotoxicity.

Draft Genome Sequence of Clostridium mangenotii TR, Isolated from the Fecal Material of a Timber Rattlesnake

Here, we report the draft genome sequence of Clostridium mangenotii strain TR, which was isolated from the fecal material of a timber rattlesnake. This bacterium is nonpathogenic but contains 68 genes involved in virulence, disease, and defense.

Helminths of the Speckled Rattlesnake,Crotalus mitchellii(Squamata: Viperidae)

Fifty-six speckled rattlesnakes, Crotalus mitchellii, from western North America were examined for helminths. One species of Cestoda (tetrathyridia of Mesocestoides sp.) and 5 species of Nematoda (gravid adults of Abbreviata terrapenis, Physaloptera abjecta, Thubunaea cnemidophorus, and Travassoascaris araujoi and larvae of Physocephalus sp.) were found. Travassoascaris araujoi had the highest prevalence and greatest mean intensity of helminths infecting C. mitchellii. Three new host records for C. mitchellii are reported. As has been reported for other North American rattlesnakes, C. mitchellii is parasitized by “generalist” helminths.

Facial Diplegia, Pharyngeal Paralysis, and Ophthalmoplegia After a Timber Rattlesnake Envenomation

The timber rattlesnake, also known as Crotalus horridus, is well known to cause significant injury from toxins stored within its venom. During envenomation, toxic systemic effects immediately begin to cause damage to many organ systems including cardiovascular, hematologic, musculoskeletal, respiratory, and neurologic. One defining characteristic of the timber rattlesnake is a specific neurotoxin called crotoxin, or the "canebrake toxin," which is a potent β-neurotoxin affecting presynaptic nerves that can cause paralysis by inhibiting appropriate neuromuscular transmission. We present an unusual case of an 8-year-old boy bitten twice on his calf by a timber rattlesnake, who presented with a life-threatening envenomation and suffered multisystem organ failure as well as a prominent presynaptic neurotoxicity resulting in facial diplegia, pharyngeal paralysis, and ophthalmoplegia.

Snake co‐occurrence patterns are best explained by habitat and hypothesized effects of interspecific interactions

Snakes often occur in species-rich assemblages, and sympatry is thought to be facilitated primarily by low diet overlap, not interspecific interactions. We selected, a priori, three species pairs consisting of species that are morphologically and taxonomically similar and may therefore be likely to engage in interspecific, consumptive competition. We then examined a large-scale database of snake detection/nondetection data and used occupancy modelling to determine whether these species occur together more or less frequently than expected by chance while accounting for variation in detection probability among species and incorporating important habitat categories in the models. For some snakes, we obtained evidence that the probabilities that habitat patches are used are influenced by the presence of potentially competing congeneric species. Specifically, timber rattlesnakes (Crotalus horridus) were less likely than expected by chance to use areas that also contained eastern diamond-backed rattlesnakes (Crotalus adamanteus) when the proportion of evergreen forest was relatively high. Otherwise, they occurred together more often than expected by chance. Complex relationships were revealed between habitat use, detection probabilities and occupancy probabilities of North American racers (Coluber constrictor) and coachwhips (Coluber flagellum) that indicated the probability of competitive exclusion increased with increasing area of grassland habitat, although there was some model uncertainty. Cornsnakes (Pantherophis guttatus or Pantherophis slowinskii) and ratsnakes (Pantherophis alleghaniensis, Pantherophis spiloides, or Pantherophis obsoletus) exhibited differences in habitat selection, but we obtained no evidence that patterns of use for this species pair were influenced by current interspecific interactions. Overall, our results are consistent with the hypothesis that competitive interactions influence snake assemblage composition; the strength of these effects was affected by landscape-scale habitat features. Furthermore, we suggest that current interspecific interactions may influence snake occupancy, challenging the paradigm that contemporary patterns of snake co-occurrence are largely a function of diet partitioning that arose over evolutionary time.

How Frequently Do Cottonmouths (Agkistrodon piscivorus) Bask in Trees?

A common belief in the southeastern United States is that Cottonmouths (Agkistrodon piscivorus) bask frequently in tree branches over the water's edge and are therefore of considerable hazard for anglers and boaters. Although this notion is almost certainly based upon observations of nonvenomous watersnakes (Nerodia spp.), there are no quantitative data that specifically address this belief. I analyzed a 7-yr dataset on Cottonmouths from two populations (Georgia and Alabama) to determine the frequency of this behavior by Cottonmouths. I recorded behavioral and substrate information for 804 separate observations on Cottonmouths. Only two of these Cottonmouths were exhibiting arboreal behavior (0.25% of observations)—snakes observed over the ground or water surface on branches narrower than their own bodies—confirming that this is indeed a very rare tendency in this species and not likely to be observed by the public. Instead, I frequently encountered Cottonmouths on the ground along the water's edge in their characteristic ambush posture, uncoiled in aquatic situations, or coiled on elevated platforms (e.g., hummocks, piles of driftwood, logs, beaver lodges). This demonstrates that Cottonmouths have the capacity to climb but are not likely to be observed in arboreal situations. Few snakes in North America are as easily observed, frequently encountered, and misunderstood by the public as Cottonmouths (Agkistrodon piscivorus). Previous research has demonstrated that anecdotal accounts of aggressive behavior in this species—widely believed by the general public throughout the range of this snake—are unfounded (Gibbons and Dorcas, 2002; Glaudas, 2004; but see Means, 2010). Although factual information is becoming available through television and internet media, additional research is necessary to dispel myths regarding this and other snake species. Another widespread belief common in the Southeast is that Cottonmouths bask in the branches of trees and shrubs at the water's edge and often fall on hapless boaters. This belief has been articulated to J. W. Gibbons (Savannah River Ecology Laboratory, pers. comm.), J. B. Jensen (Georgia Department of Natural Resources, pers. comm.), C. Guyer (Auburn University, pers. comm.), and myself (pers. obs.). Although this belief is most likely a myth based upon encounters or stories involving misidentified watersnakes, there are currently no published data that refute the assertion that Cottonmouths bask in trees. Moreover, while several reviews of Cottonmouth natural history suggest that this species is generally found at the water's edge, floating on water, or lying on terrestrial substrates (Gloyd and Conant, 1990; Campbell and Lamar, 2004; Ernst and Ernst, 2004; Gibbons and Dorcas, 2005), these sources also mention that Cottonmouths are occasionally observed in trees and shrubs near the water's edge. These assertions are based largely on anecdotal observations and could be misinterpreted by lay readers who frequently misidentify watersnakes (Nerodia spp.) as Cottonmouths (Gibbons and Dorcas, 2004), which frequently bask from such perches (Tiebout and Cary, 1987; Gibbons and Dorcas, 2004). To date, no quantitative comparison of arboreal versus terrestrial (or aquatic) tendencies in the Cottonmouth is available. Reports of other terrestrial pit vipers exhibiting surprisingly arboreal feats (e.g., Timber Rattlesnake, Crotalus horridus; Coupe, 2001, Rudolph et al., 2004) further indicate the need for accurate information about Cottonmouths. To determine the frequency that observers might expect to find Cottonmouths basking above the water surface in vegetation, I analyzed my own observations of 804 encounters with Cottonmouths during 2003-09 from sites in Georgia and Alabama. I analyzed the frequency with which I found Cottonmouths in arboreal, aquatic, or elevated substrates and the behaviors they were exhibiting from these positions.