Crotalus Oreganus Research Articles

Snake Venomics of Crotalus tigris: The Minimalist Toxin Arsenal of the Deadliest Neartic Rattlesnake Venom. Evolutionary Clues for Generating a Pan-Specific Antivenom against Crotalid Type II Venoms

We report the proteomic and antivenomic characterization of Crotalus tigris venom. This venom exhibits the highest lethality for mice among rattlesnakes and the simplest toxin proteome reported to date. The venom proteome of C. tigris comprises 7-8 gene products from 6 toxin families; the presynaptic β-neurotoxic heterodimeric PLA(2), Mojave toxin, and two serine proteinases comprise, respectively, 66 and 27% of the C. tigris toxin arsenal, whereas a VEGF-like protein, a CRISP molecule, a medium-sized disintegrin, and 1-2 PIII-SVMPs each represent 0.1-5% of the total venom proteome. This toxin profile really explains the systemic neuro- and myotoxic effects observed in envenomated animals. In addition, we found that venom lethality of C. tigris and other North American rattlesnake type II venoms correlates with the concentration of Mojave toxin A-subunit, supporting the view that the neurotoxic venom phenotype of crotalid type II venoms may be described as a single-allele adaptation. Our data suggest that the evolutionary trend toward neurotoxicity, which has been also reported for the South American rattlesnakes, may have resulted by pedomorphism. The ability of an experimental antivenom to effectively immunodeplete proteins from the type II venoms of C. tigris, Crotalus horridus , Crotalus oreganus helleri, Crotalus scutulatus scutulatus, and Sistrurus catenatus catenatus indicated the feasibility of generating a pan-American anti-Crotalus type II antivenom, suggested by the identification of shared evolutionary trends among South and North American Crotalus species.

Experimentally Altered Navigational Demands Induce Changes in the Cortical Forebrain of Free-Ranging Northern Pacific Rattlesnakes (Crotalus o. oreganus)

The hippocampus of birds and mammals plays a crucial role in spatial memory and navigation. The hippocampus exhibits plasticity in adulthood in response to diverse environmental factors associated with spatial demands placed on an animal. The medial and dorsal cortices of the telencephalon of squamate reptiles have been implicated as functional homologues to the hippocampus. This study sought to experimentally manipulate the navigational demands placed on free-ranging northern Pacific rattlesnakes (Crotalus o. oreganus) to provide direct evidence of the relationship between spatial demands and neuroplasticity in the cortical telencephalon of the squamate brain. Adult male rattlesnakes were radio-tracked for 2 months, during which time 1 of 3 treatments was imposed weekly, namely 225-meter translocation in a random direction, 225-meter walk and release at that day’s capture site (handling control) or undisturbed (control). Snakes were then sacrificed and the brains were removed and processed for histological analysis of cortical features. The activity range was larger in the translocated (Tr) group compared to the handled (Hd) and undisturbed control (Cn) groups when measured via 95% minimum convex polygon (MCP). At the 100% MCP level, Tr snakes had larger activity ranges than the Cn snakes only. The volume of the medial cortex (MC) was larger in the Tr group compared to the Cn group. The MC of Hd snakes was not significantly different from that of either of the other groups. No differences in dorsal cortex (DC) or lateral cortex volumes were detected among the groups. Numbers of 5-bromo-2′-deoxyuridine (BrdU)-labeled cells in the MC and DC 3 weeks after BrdU injection were not affected by treatment. This study establishes a causal relationship between navigational demands and greater MC volume in a free-ranging reptile.

Northern Pacific Rattlesnakes (Crotalus oreganus) use thermal and structural cues to choose overwintering hibernacula

Hibernacula play an important role in the ecology of high-latitude snakes, and communally denning species may occupy their hibernacula for half the year or more. Because of the long duration spent at hibernacula, such sites can provide multiple benefits to snakes including shelter from lethal overwinter conditions, social opportunities, and basking sites important in thermoregulation. Adequate hibernacula seem to be limited on the landscape and individuals travel several kilometres to use and reuse specific sites. We investigate orientation, physical structure, and thermal properties of sites used as hibernacula by Northern Pacific Rattlesnakes ( Crotalus oreganus Holbrook, 1840), and compare them with random sites that appear to be similar but were not used for hibernation. Hibernacula occurred primarily on south-facing talus slopes, were oriented on less-steep slopes, and were composed of rocks that were intermediate in size to randomly occurring sites. Our results suggest that the orientation and physical composition of hibernacula allow them to be stable over time, allowing snakes to repeatedly locate the sites, as well as providing predictable overwinter refuge. Hibernacula were also warmer on the surface than north-facing random sites and provided increased basking opportunities for snakes thermoregulating in early spring after emergence from hibernation.

Isolation and identification of a snake venom metalloproteinase inhibitor from California ground squirrel (Spermophilus beecheyi) blood sera

California ground squirrels (Spermophilus beecheyi) show blood-based defenses to a variety of toxins in the venom of the Northern Pacific rattlesnake (Crotalus oreganus oreganus). In this study we demonstrate the presence of an effective snake venom metalloproteinase inhibitor (SVMPI) in S. beecheyi. The blood sera of California ground squirrels were effective at reducing the metalloproteinase activity of Northern Pacific (C. o. oreganus) and prairie rattlesnake (Crotalus viridis viridis) venoms by over 75%, significantly more than its ability to reduce the activity of western diamondback rattlesnake venom. We used anion exchange and affinity chromatography to isolate this protein from the blood sera of S. beecheyi. This SVMPI had a molecular mass of 108.3 kDa and a pI of 5.1. The IC50 of this inhibitor against whole venom from C. o. oreganus was determined to be 3.14 × 10−8 M. Subsequent LC MS/MS analysis of a CNBr/tryptic digest of the inhibitor yielded multiple internal peptide sequences. These sequences showed homology to three other known mammalian plasma proteins: inter-α trypsin inhibitor, and two hibernation-associated proteins, HP25 and HP27. The presence of SVMPI in S. beecheyi blood sera is consistent with the resistance of these animals to venom-induced hemorrhage and tissue damage, and consistent with the protective factors conferring venom resistance in other mammals. However, the variety of SVMPI identified to date from mammalian taxa suggests that different species have converged on neutralization of venom metalloproteinase activity as a key step in venom neutralization.

Isolation and Characterization of a Natriuretic Peptide from Crotalus oreganus abyssus (Grand Canyon Rattlesnake) and its Effects on Systemic Blood Pressure and Nitrite Levels

Studies on the therapeutic potential of venom peptides have significantly advanced the development of new peptide drugs. A good example is captopril, a synthetic peptide drug, which acts as an anti-hypertensive and potentiating bradykinin, inhibiting the angiotensin-converting enzyme, whose precursor was isolated from the venom of Bothrops jararacussu. The natriuretic peptide (NPs) family comprises three members, ANP (atrial natriuretic peptide), BNP (B-type natriuretic peptide) and CNP (C-type natriuretic peptide), and has an important role in blood pressure regulation and electrolyte homeostasis. In this study, we describe, for the first time, the isolation and characterization of a novel natriuretic-like peptide (Coa_NP), isolated from Crotalus Oreganus abyssus venom. The peptide has 32 amino acids and its complete sequence is SKRLSNGCFGLKLDRIGAMSGLGCWRLINESK. The Coa_NP has an average molecular mass of 3510.98 Da and its amino acid sequence presents the loop region that is characteristic of natriuretic peptides (17 amino acids, NP domain consensus; CFGXXXDRIXXXSGLGC). Coa_NP is a natriuretic peptide of the ANP/BNP-like family, since the carboxy terminal region of CNP has its own NP domain. The functional experiments showed that Coa_NP produced biological effects similar to those of the other natriuretic peptides: (1) a dose-dependent decrease in mean arterial pressure; (2) significant increases in plasma nitrite levels, and (3) vasorelaxation in thoracic aortic rings that were pre-contracted with phenylephrine. The structural and biological aspects confirm Coa_NP as a natriuretic peptide isolated from snake venom, thus expanding the diversification of venom components.

ALTERED NAVIGATIONAL DEMANDS INDUCE CHANGES IN A CORTICAL BRAIN REGION OF FREE-RANGING NORTHERN PACIFIC RATTLESNAKES (CROTALUS O. OREGANUS)

Event Abstract Back to Event ALTERED NAVIGATIONAL DEMANDS INDUCE CHANGES IN A CORTICAL BRAIN REGION OF FREE-RANGING NORTHERN PACIFIC RATTLESNAKES (CROTALUS O. OREGANUS) Matthew L. Holding1*, Kelsee M. Buskirk1, Emily N. Taylor1 and Christine R. Strand1 1 California Polytechnic State University, Biological Sciences, United States The cortical telencephalon of squamate reptiles has been implicated as a functional homologue to the avian and mammalian hippocampus. The role of the medial and dorsal cortices in spatial navigation and spatial memory has been demonstrated by multiple laboratory experiments and observational studies in the field. This study sought to experimentally manipulate the navigational demands placed on free-ranging northern Pacific rattlesnakes (Crotalus o. oreganus) to provide direct evidence of the relationship between spatial demands and neuroplasticity in the cortical telencephalon of the squamate brain. Twenty-two adult male snakes were radio-tracked for two months during which one of three treatments was imposed weekly. Treatments consisted of the following: 225 meter translocation in a random direction, 225 meter walk and release at that day’s capture site (handling control), and undisturbed control. Snakes were then sacrificed and brains were removed, embedded in gelatin, frozen, sectioned and Nissl-stained for quantification of cortical volumes. The volume of the medial cortex was significantly larger in the translocated group compared to undisturbed controls. No differences in dorsal or lateral cortical volume were detected among the groups. The range of the snakes measured by minimum convex polygon was larger in the translocated group compared to handled and undisturbed controls. A causal relationship between increased navigation in a free-ranging reptile and changes in brain morphology has been established. Furthermore, sex differences previously described in the medial cortex of Crotaline snakes may be a function of an increased amount of movement in males and not a genetically determined dimorphism. Acknowledgements National Science Foundation Pre-doctoral Fellowship to MLH Keywords: Medial Cortex, neuroplasticity, reptile, Spatial Ecology, translocation Conference: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology, Ann Arbor, United States, 11 Jul - 13 Jul, 2011. Presentation Type: Poster Topic: Brain and behavior Citation: Holding ML, Buskirk KM, Taylor EN and Strand CR (2011). ALTERED NAVIGATIONAL DEMANDS INDUCE CHANGES IN A CORTICAL BRAIN REGION OF FREE-RANGING NORTHERN PACIFIC RATTLESNAKES (CROTALUS O. OREGANUS). Front. Endocrinol. Conference Abstract: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology. doi: 10.3389/conf.fendo.2011.03.00019 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Jul 2011; Published Online: 09 Aug 2011. * Correspondence: Mr. Matthew L Holding, California Polytechnic State University, Biological Sciences, San Luis Obispo, CA, 93407-0401, United States, matthew.holding28@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Matthew L Holding Kelsee M Buskirk Emily N Taylor Christine R Strand Google Matthew L Holding Kelsee M Buskirk Emily N Taylor Christine R Strand Google Scholar Matthew L Holding Kelsee M Buskirk Emily N Taylor Christine R Strand PubMed Matthew L Holding Kelsee M Buskirk Emily N Taylor Christine R Strand Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Rock squirrel (Spermophilus variegatus) blood sera affects proteolytic and hemolytic activities of rattlesnake venoms

Rock squirrels (Spermophilus variegatus) from two sites in south central New Mexico, where prairie (Crotalus viridis viridis) and western diamondback (Crotalus atrox) rattlesnakes are common predators, were assayed for inhibition of rattlesnake venom digestive and hemostatic activities. At statistically significant levels rock squirrel blood sera reduced the metalloprotease and hemolytic activity of venoms from C. v. viridis and C. atrox more than venom from an allopatric snake species, the northern Pacific rattlesnake (Crotalus oreganus). In contrast, general proteolytic activity of venom from C. oreganus was inhibited more by S. variegatus serum defenses than activity of venom from sympatric snakes. For all three venoms, incubation with squirrel sera increased the level of fibrinolysis over venom-only treatments. These results suggest that rock squirrels (S. variegatus) can defend against metalloproteases and other proteases after envenomation from at least two of five rattlesnake predators they might encounter. However, there were statistically significant differences between general proteolytic activity and fibrinolytic activity of C. v. viridis and C. atrox venom, suggesting that rock squirrels might be differentially vulnerable to these two predators. The hypothesis that prey resistance influences snake venom evolution in a predator–prey arms race is given further support by the previously cryptic variation in venoms detected when assayed against prey defenses.

A population genetic analysis of the midget faded rattlesnake in Wyoming

Little is known about the population biology of midget faded rattlesnakes, a sensitive subspecies of the Western Rattlesnake, despite conservation efforts to protect them. We conducted a molecular genetic study of midget faded rattlesnakes in southwestern Wyoming to investigate population genetic structure in this area, particularly with reference to Flaming Gorge Reservoir and its associated human activities, and to document levels of genetic diversity. We genotyped 229 snakes from 11 sampling sites using 9 microsatellite loci. We found significant levels of genetic structure among sites that were better explained by geographic region and isolation by distance than by position relative to waterways. Sites on either side of the reservoir at its widest point were not significantly different. Six of the sites showed signatures of a population bottleneck using an alpha value of 0.05. Three of these bottlenecked sites (the three most northern) were the most genetically distinct and occur in areas of greatest impact from human activity.

Comparative study of anticoagulant and procoagulant properties of 28 snake venoms from families Elapidae, Viperidae, and purified Russell’s viper venom-factor X activator (RVV-X)

Snake venoms consist of numerous molecules with diverse biological functions used for capturing prey. Each component of venom has a specific target, and alters the biological function of its target. Once these molecules are identified, characterized, and cloned; they could have medical applications. The activated clotting time (ACT) and clot rate were used for screening procoagulant and anticoagulant properties of 28 snake venoms. Crude venoms from Daboia russellii siamensis, Bothrops asper, Bothrops moojeni, and one Crotalus oreganus helleri from Wrightwood, CA, had procoagulant activity. These venoms induced a significant shortening of the ACT and showed a significant increase in the clot rate when compared to the negative control. Factor X activator activity was also measured in 28 venoms, and D. r. siamensis venom was 5–6 times higher than those of B. asper, B. moojeni, and C. o. helleri from Wrightwood County. Russell’s viper venom-factor X activator (RVV-X) was purified from D. r. siamensis venom, and then procoagulant activity was evaluated by the ACT and clot rate. Other venoms, Crotalus atrox and two Naja pallida, had anticoagulant activity. A significant increase in the ACT and a significant decrease in the clot rate were observed after the addition of these venoms; therefore, the venoms were considered to have anticoagulant activity. Venoms from the same species did not always have the same ACT and clot rate profiles, but the profiles were an excellent way to identify procoagulant and anticoagulant activities in snake venoms.

Evolutionary trends in venom composition in the Western Rattlesnakes ( Crotalus viridis sensu lato): Toxicity vs. tenderizers

The Western Rattlesnake ( Crotalus viridis sensu lato, now including Crotalus oreganus) is broadly distributed across the western half of the United States, northwestern Mexico and southwestern Canada, and eight subspecies are currently recognized. Although some venom characteristics have been noted for most subspecies, a systematic study of venoms from all subspecies has not been reported. Venom was extracted from snakes collected from approximate geographic range centers for all subspecies and analyzed using SDS-PAGE, MALDI-TOF mass spectrometry, enzyme and toxicity assays. Electrophoretic and mass spectrometric analyses demonstrated that small myotoxins, disintegrins and PLA 2 were abundant in most venoms. PIII and PI metalloproteinases (∼54 kDa and 23 kDa, respectively) were common to all venoms except C. o. concolor, C. o. caliginis and C.o. helleri. Metalloproteinase activity was highest in C. o. cerberus and lowest in C. o. concolor venoms (∼100-fold difference). Conversely, C. o. concolor venom was the most toxic and C. o. cerberus venom was least toxic (15-fold difference). In general, venoms with high metalloproteinase activity were less toxic (type I venoms), while venoms which were highly toxic showed low protease activity (type II venoms). Within the C. viridis/ oreganus complex, these two extremes of venom compositional phenotypes are observed, and it appears that high metalloproteinase activity and high toxicity are incompatible qualities of these venoms. The functional significance of these biochemical characteristics likely relates to characteristics of prey consumed, and venoms with low metalloproteinase activity may constrain snake prey selection or foraging activity patterns.

Characterization of ten microsatellite loci in midget faded rattlesnake (Crotalus oreganus concolor)

Primers for 10 microsatellite loci were developed for midget faded rattlesnake (Crotalus oreganus concolor), a small bodied subspecies of the Western Rattlesnake, which is found in the Colorado Plateau of eastern Utah, western Colorado and southwestern Wyoming. In a screen of 23 individuals from the most northern portion of the subspecies range in southwestern Wyoming, the 10 loci were found to have levels of variability ranging from 4 to 11 alleles. No loci were found to be linked, although one locus revealed significant departures from Hardy–Weinberg equilibrium. These microsatellite loci will be applicable for population genetic analyses, which will ultimately aid in management efforts for this rare subspecies of rattlesnake.

The relationship between plasma steroid hormone concentrations and the reproductive cycle in the Northern Pacific rattlesnake, Crotalus oreganus

We describe the reproductive cycle of Northern Pacific rattlesnakes ( Crotalus oreganus) by quantifying steroid hormone concentrations and observing reproductive behaviors in free-ranging individuals. Additionally, we examined reproductive tissues from museum specimens. Plasma steroid hormone concentrations were quantified for both male and female snakes throughout the active season (March–October). We measured testosterone (T), 5α-dihydrotestosterone (DHT), and corticosterone (B) concentrations in both sexes and 17β-estradiol (E2) and progesterone (P) in females only. We observed reproductive behaviors (e.g., consortship, courtship, and copulation) in the field and measured testis and follicle size in male and female snakes from museum collections to relate steroid hormone concentrations to the timing of reproductive events. Our study revealed that C. oreganus in central California exhibits a bimodal pattern of breeding, with most mating behavior occurring in the spring and some incidences of mating behavior observed in late summer/fall. Each breeding period corresponded with elevated androgen (T or DHT) levels in males. Testes were regressed in the spring when the majority of reproductive behavior was observed in this population, and they reached peak volume in August and September during spermatogenesis. Although we did not detect seasonal variation in female hormone concentrations, some females had high E2 in the spring and fall, coincident with mating and with increased follicle size (indicating vitellogenesis) in museum specimens. Females with high E2 concentrations also had high T and DHT concentrations. Corticosterone concentrations in males and females were not related either to time of year or to concentrations of any other hormones quantified. Progesterone concentrations in females also did not vary seasonally, but this likely reflected sampling bias as females tended to be underground, and thus unobtainable, in summer months when P would be expected to be elevated during gestation. In females, P was positively correlated with T and DHT, and E2 was positively correlated with T.

Microgeographic Variation in Reproductive Characteristics among Western Rattlesnake (Crotalus oreganus) Populations

Studies on geographic variation in reproductive characteristics can contribute to an understanding of the effects of environmental factors on animal population structure and dynamics. Using a ten-year mark–recapture data set (1994–2003), we studied microgeographic variation in reproductive characteristics (body condition, growth, age to maturity, pregnancy interval, fecundity, and size of offspring) among three Western Rattlesnake (Crotalus oreganus) populations within 40 km of each other. Significant differences existed among snakes from the different den sites in length, body condition, growth rate, fecundity, and size and body condition of offspring. Furthermore, there was a consistent pattern in the variation among populations. Individuals from the population in the most disturbed area, were shorter, had lower body condition, grew slower, had lower fecundity, and had shorter and lower body condition offspring compared to other populations. The results from this study have important applied implications for understanding fine scale variation in reproductive characteristics. This study suggests that some rattlesnake populations have reproductive characteristics that may make them more susceptible to future disturbances.

Denim Clothing Reduces Venom Expenditure by Rattlesnakes Striking Defensively at Model Human Limbs

Venomous snakebites can be painful, costly, and potentially life threatening. We seek to learn whether ordinary clothing (denim material from blue jeans) interferes with the kinematics of venom delivery, thereby reducing the amount of venom injected by a representative viper into a human limb. In a laboratory study, we used model human limbs (warm, saline solution-filled gloves) to elicit defensive strikes from small and large southern Pacific rattlesnakes (Crotalus oreganus helleri). Each snake was videotaped biting a bare glove and a denim-covered glove. The snakes injected significantly less venom into denim-covered gloves than bare gloves during defensive strikes, with a 60% reduction for small snakes and 66% for large snakes. Latency to bite, number of bites, and duration of fang contact during the bite were similar for the 2 glove types, suggesting that the 2 targets elicited similar defensive behaviors and strikes. Several findings suggested that denim interfered with venom delivery, including the high proportion of dry bites for denim-covered gloves and the large quantity of venom spilled harmlessly on the denim cover. Large rattlesnakes struck more readily, maintained longer fang contact during the bite, and delivered 26 to 41 times more venom into gloves than small snakes. In our model, denim clothing proved effective at reducing venom injection by both small and large rattlesnakes. Wearing long denim pants as an alternative to shorts may provide a simple, low-cost means of reducing the severity of snakebites.

First Report of Scavenging by the Northern Pacific Rattlesnake (Crotalus oreganus oreganus) in the Wild

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Effectiveness of Short‐Distance Translocation and its Effects on Western Rattlesnakes

ABSTRACT Short‐distance translocation (SDT) is commonly used to mitigate snake‐human interactions, yet little is known about its effectiveness or its effects on behavior and welfare of snakes. Between April 2004 and October 2005, we evaluated SDT as a conservation and management tool by investigating how 500‐m SDT affected spatial ecology, body condition, and behavior of western rattlesnakes (Crotalus oreganus) surgically implanted with radiotransmitters in a field study near Osoyoos, British Columbia, Canada. Of 14 rattlesnakes subjected to SDT, 12 (85.7%) returned on ≥1 occasion (range 1–7 times) to the general area they were removed from. Rattlesnakes that underwent SDT showed an increase in total distance moved over an active season compared to non‐translocated snakes, but there was no evidence to suggest SDT had an effect on activity range size. There was no evidence to suggest SDT affected body condition, behavior, or mortality rates. Short‐distance translocation to high‐quality undisturbed habitats was unsuccessful as a long‐term solution to snake‐human conflict because most translocated snakes returned to conflict areas within a short time (x̄x = 19.9 ± 8.7 days). However, SDT may be an effective short‐term tool to manage snake‐human conflict in areas where human presence is seasonal or short‐lived if careful attention is paid to species‐specific biological needs, habitat quality at the release site, and the location of the release site in relation to conflict areas.

Quantitative Analysis of Snake Venoms Using Soluble Polymer-based Isotope Labeling

We present the design and synthesis of a new quantitative strategy termed soluble polymer-based isotope labeling (SoPIL) and its application as a novel and inclusive method for the identification and relative quantification of individual proteins in complex snake venoms. The SoPIL reagent selectively captures and isolates cysteine-containing peptides, and the subsequent tagged peptides are released and analyzed using nanoflow liquid chromatography-tandem mass spectrometry. The SoPIL strategy was used to quantify venom proteins from two pairs of venomous snakes: Crotalus scutulatus scutulatus type A, C. scutulatus scutulatus type B, Crotalus oreganus helleri, and Bothrops colombiensis. The hemorrhagic, hemolytic, clotting ability, and fibrinogenolytic activities of crude venoms were measured and correlated with difference in protein abundance determined by the SoPIL analysis. The SoPIL approach could provide an efficient and widely applicable tool for quantitative proteomics.

The forked tongue and edge detection in snakes (Crotalus oreganus): An experimental test.

Many stimulus-detection systems are lateralized to allow for simultaneous comparison of paired stimuli. It has been hypothesized that the deeply forked tongue of snakes and some derived lizards functions as a chemical edge detector where cues gathered by each tine are kept separate to provide two points of lateral odor assessment by the central nervous system via vomeronasal input. While following a chemical trail, one time can be on the trail, the other off, and such differential information prompts the snake to turn back to the trail. The authors tested this hypothesis in rattlesnakes within a predatory context by unilaterally severing the vomeronasal nerves. If edge detection is used by snakes during prey trailing, then unilateral denervation should disrupt trailing ability. The authors found no change in the seven separate trailing parameters measured. Therefore, they found no support for the edge detection hypothesis as it applies to prey trailing behavior. Instead, the deeply forked tongue may represent a chemosensory specialization to increase odor-sampling area, with snakes and derived lizards detecting only the concentration of chemical trails.

Rattlesnake Preference for Envenomated Prey: Species Specificity

Abstract Ten Prairie Rattlesnakes (Crotalus viridis viridis) and 10 Western Diamondback Rattlesnakes (Crotalus atrox) were offered choices between envenomated (E) and nonenvenomated (NE) mice. Both species preferred E over NE mice when envenomation was accomplished by a conspecific but not when envenomation was accomplished by the other species. However, when envenomation was accomplished by Crotalus oreganus oreganus, E mice were preferred by C. v. viridis but not by C. atrox. Accordingly, we conclude that rattlesnakes of closely related species recognize each other's E prey, whereas rattlesnakes of distantly related species do not.

Ground squirrels use an infrared signal to deter rattlesnake predation

The evolution of communicative signals involves a major hurdle; signals need to effectively stimulate the sensory systems of their targets. Therefore, sensory specializations of target animals are important sources of selection on signal structure. Here we report the discovery of an animal signal that uses a previously unknown communicative modality, infrared radiation or "radiant heat," which capitalizes on the infrared sensory capabilities of the signal's target. California ground squirrels (Spermophilus beecheyi) add an infrared component to their snake-directed tail-flagging signals when confronting infrared-sensitive rattlesnakes (Crotalus oreganus), but tail flag without augmenting infrared emission when confronting infrared-insensitive gopher snakes (Pituophis melanoleucus). Experimental playbacks with a biorobotic squirrel model reveal this signal's communicative function. When the infrared component was added to the tail flagging display of the robotic models, rattlesnakes exhibited a greater shift from predatory to defensive behavior than during control trials in which tail flagging included no infrared component. These findings provide exceptionally strong support for the hypothesis that the sensory systems of signal targets should, in general, channel the evolution of signal structure. Furthermore, the discovery of previously undescribed signaling modalities such as infrared radiation should encourage us to overcome our own human-centered sensory biases and more fully examine the form and diversity of signals in the repertoires of many animal species.