Spatial Ecology of North American Pitvipers (Viperidae: Crotalinae): A Review and Meta-Analysis

We studied the spatial and reproductive ecology of a population of Copperheads (Agkistrodon contortrix), a North American pitviper, in a basalt trap-rock ecosystem in the central Connecticut River Valley, a region that constitutes the northeastern extreme of this species' geographic range. Adult males (n = 20) and females (n = 15) were surgically implanted with radio-transmitters and tracked every 48 h during the active season (April through October) for three consecutive years (2001 to 2003). From late autumn to early spring (November through March), when snakes were hibernating and thus inactive, tracking was reduced to once per week. We generated data on movement and other spatial parameters for each subject using GPS coordinates. There were significant sex differences in activity range size and multiple movement parameters. Throughout the active season males had greater activity range sizes and showed greater movement than females. This trend was pronounced during the mating season, which...

Platelet and red cell responses to three North American pit vipers

Aim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacépède, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa.Location Midwestern and eastern North America.Methods We reconstructed maximum parsimony (MP) and maximum likelihood (ML) relationships based on 846 base pairs of mitochondrial DNA (mtDNA) ATPase 8 and ATPase 6 genes sequenced over 178 individuals. We quantified range expansions, demographic histories, divergence dates and potential size differences among clades since their last period of rapid expansion. We used the Shimodaira–Hasegawa (SH) test to compare our ML tree against three biogeographical hypotheses.Results A significant SH test supported diversification of A. contortrix from northeastern Mexico into midwestern–eastern North America, where its trajectory was sundered by two vicariant events. The first (c. 5.1 Ma) segregated clades at 3.1% sequence divergence (SD) along a continental east–west moisture gradient. The second (c. 1.4 Ma) segregated clades at 2.4% SD along the Mississippi River, coincident with the formation of the modern Ohio River as a major meltwater tributary. A single glacial refugium was detected within the Apalachicola region of southeastern North America. Significant support was also found for a hypothesis of trans‐Gulf rafting by the common ancestor of A. piscivorus from eastern Mexico (possibly the Yucatan Peninsula) to northern Florida. There, a Mid–Late Pliocene marine transgression separated it at 4.8% SD from mainland North America. Significant range expansions followed compressive glacial effects in three (of four) A. contortrix clades and in two (of three) A. piscivorus clades, with the Florida A. piscivorus clade exhibiting significant distributional stasis.Main conclusions Pliocene glaciations, rapidly developing western aridity, and Pleistocene glacial meltwaters seemingly led to the diversification of A. contortrix and A. piscivorus in North America. Both species were pushed southwards by Pleistocene climate change, with subsequent northward expansions uninhibited topographically. The subspecific taxonomy used for A. contortrix and A. piscivorus today, however, appear non‐representative. The monophyletic Florida subspecies of A. piscivorus may be a distinct species (at 4.8% SD), whereas two western subspecies of A. contortrix also appear to constitute a single distinct species, pending additional analyses. We conclude that both species of Agkistrodon can be used as suitable ectothermic models to gauge impacts of future climate change.

North American pit viper, or crotalid bites, remain a low-incidence and potentially high-consequence medical event. Although the venom of these snakes is known to cause tissue, hematologic, and neurologic toxicity, the published literature on North American crotalid bites remains limited. The National Poison Data System, the data repository for the 55 poison control centers in the United States, offers a unique opportunity to examine nationwide trends involving venomous snake bites. National Poison Data System cases involving North American crotalids from 2006 to 2020 were analyzed. Data collected included age and type of snake, date, geographic location, pertinent clinical characteristics, treatments administered, and medical outcomes including incidence of "dry" bites and death. A total of 55,914 cases were identified during the 15-year study period. Cases, especially those involving copperheads, increased during the study period. Most of the cases were reported in July. Cases were reported in all 50 states and Washington, DC, with Texas having the most cases (n = 9115). North Carolina had the largest increase in bites during the study period. Moderate or major medical outcomes were documented in 58% (n = 32,584) of cases, with 25% (n = 14,195) being admitted to a critical care unit. Puncture wound, edema, and pain were the most commonly documented symptoms. Antivenom was documented as being administered in 25% (n = 14,151) of cases. Dry bites were reported in <1.5% of cases. Thirty-two deaths were reported, 23 involving rattlesnakes. This study demonstrates that reported North American crotalid bites appear to be increasing over time and are associated with potentially significant morbidity. Mortality, however, remains low.

Sexual dimorphisms – phenotypic dissimilarities between the sexes – are common and widespread among plants and animals, and classical examples include differences in body size, colour, shape, ornamentation and behaviour. In general, sexual dimorphisms are hypothesized to evolve by way of sexual selection acting on one sex through priority‐of‐access for sexual partners via mate choice and/or intra‐sexual competition. In snakes, males are the mate‐searching sex and one form of sexual selection involves male–male competition in locating females by following pheromone trails using their forked tongues, the structure used to sample environmental chemicals for transduction in the vomeronasal chemosensory system (VNS). Based on several lines of empirical evidence, increased tongue forking (bifurcation) in snakes (and some lizard taxa) appears to enhance chemical trail‐following abilities through tropotaxis (the simultaneous comparison of stimulus intensities on two sides of the body) and thus aids in prey location and mate searching in males. We predicted that male copperheads, Agkistrodon contortrix, a North American pitviper, should have more deeply forked tongues than females owing to male–male competition for priority‐of‐access to widely dispersed females during the mating seasons. We examined formalin‐fixed, ethanol‐preserved museum specimens of adult A. contortrix for sexual size dimorphism (SSD) of the tongue. Tongue dimensions showed differences indicative of SSD, and the degree of bifurcation (i.e. mean tine length) was significantly greater in males. Various structures of the VNS and associated regions (e.g. muscles) in some vertebrate taxa show sexual dimorphism, but our study is the first to document dimorphism in the tongue of a tetrapod vertebrate.

Sexual Selection and Variance in Reproductive Success

Canebrake Rattlesnake Envenomation

Roads are associated with a blunted stress response in a North American pit viper

Chapter 74 - Snake Bite: North American Pit Vipers

Chapter 75 - Snake Bite: North American Pit Vipers

Coagulation abnormalities following crotaline (pit viper) snakebite have traditionally been considered short-lived, but laboratory studies have rarely been reported beyond the first few days of treatment for envenomation. During the course of an antivenom clinical trial, we observed coagulation defects as late as 2 weeks following envenomation. To document and characterize the recurrence or persistence of coagulopathy among patients envenomed by pit vipers and treated with a Fab antivenom. Patients with moderate pit viper envenomation were enrolled in a multicenter, prospective clinical trial. A Fab-based antivenom preparation, antivenom polyvalent crotalid (ovine) Fab, was administered in all cases. Platelet count, fibrinogen level, presence of fibrin split products, prothrombin time, and partial thromboplastin time were determined before treatment and at standard intervals during the following 2 weeks. Of 38 patients completing the study, 20 (53%) had recurrent, persistent, or late coagulopathy 2 to 14 days after envenomation. Thrombocytopenia occurred in patients with prior thrombocytopenia; hypofibrinogenemia occurred only in those with prior hypofibrinogenemia or positive fibrin split products. No patient experienced significant spontaneous bleeding. One patient with coagulopathy developed minor bleeding following minor surgery 12 days after envenomation. Prolonged or recurrent coagulopathy may occur after envenomation by North American pit vipers. Patients treated with Fab-based antivenom may benefit from periodic rather than single-bolus dosing. Patients with coagulopathy should undergo close monitoring during the first 2 weeks after snakebite.

The two current antivenom products available in the United States (US) for North American pit viper envenomation include ovine-derived Crotalidae polyvalent immune Fab (FabAV, Crofab®) and equine-derived Crotalidae Immune (F(ab′)2, Anavip®). Both products contain the oligosaccharide, galactose-alpha-1,3-galactose (alpha-gal), and may lead to a hypersensitivity reaction commonly referred to as alpha-gal syndrome (AGS). We report two patients receiving antivenom for pit viper envenomation who developed anaphylactic reactions and had confirmed abnormal titers of alpha-gal-specific IgE. We suggest clinicians seek a history of red meat allergy and administer AV cautiously in endemic areas of AGS.

Venomous snakebites are surprisingly common in the US. This article provides an overview of what to do when a patient has been bitten by a North American pit viper, a venomous subset of indigenous snakes.

North American pit vipers

Crotalidae polyvalent immune Fab (CroFab) is an antivenin that is FDA approved and commonly used to treat envenomations caused by North American pit vipers. Although CroFab has been widely used since the early 2000s, hypersensitivity reactions like type I, type IV, and angioedema have been reported in the literature. We present a case of CroFab induced hypersensitivity reaction in a 41-year-old male shortly after starting CroFab infusion. Furthermore, this patient developed anaphylaxis symptoms including: difficulty breathing, oropharyngeal edema, dysphagia, wheezing, and chest tightness. This was resolved upon stopping CroFab infusion and administering epinephrine, methylprednisolone, diphenhydramine, and famotidine. The reaction occurred again when CroFab was re-introduced despite infusing it at a much slower rate. Interestingly, this patient successfully tolerated crotalidae immune F(ab')2 (equine) antivenom (ANAVIP) upon switching him from CroFab. Hypersensitivity reactions to CroFab can be life-threatening and warrant immediate attention and treatment in a multidisciplinary setting.