Garter Snakes Thamnophis Sirtalis Research Articles

The effect of predator kairomones on caudal regeneration by Allegheny Mountain Dusky Salamanders (Desmognathus ochrophaeus)

Many prey use autotomy as an antipredator mechanism. Rapid regeneration of autotomized appendages is beneficial because forfeited tissues may serve as organs for energy storage, accessories for locomotion, or indicators of social status. We monitored levels of caudal regeneration by Allegheny Mountain Dusky Salamanders (Desmognathus ochrophaeus Cope, 1859) exposed to kairomones from predatory Eastern Garter Snakes (Thamnophis sirtalis (Linnaeus, 1758)). After the induction of autotomy, salamanders were exposed to one of three treatment regimens: blank (water), or acute (30 min per week) or chronic (constant) exposure to predator kairomones during a 12-week study period. Overall, the mean volume of regenerated tissue, as a percentage of the original tail volume, was highest for individuals exposed to the blank versus predator kairomones. When the combined effects of time elapsed since the induction of caudal autotomy and the different treatment regimens were considered, we found that the mean volume of regenerated tissue was significantly greater for control salamanders beginning 8 weeks after autotomy. The mechanism contributing to the differential rates of regeneration among individuals in our treatment groups is unknown, but previous work suggests that elevated stress related to predation threat can have detrimental effects on wound healing and growth in amphibians.

Comparing the Natural and Anthropogenic Sodium Channel Blockers Tetrodotoxin and Indoxacarb in Garter Snakes.

Synthetic chemicals, such as pesticides, are used in a variety of ways in the agricultural industry. Anthropogenic chemicals pose a unique challenge to organisms because of the lack of evolutionary history between the chemical and the organism. However, research has shown that some organisms have a resistance to these synthetic chemicals due to their evolved resistance to a natural compound with a similar structure or mode of action. Indoxacarb (INDOX) is a relatively new pesticide with a similar mode of action to that of tetrodotoxin (TTX). Tetrodotoxin is a naturally occurring toxin that is used as an antipredator defense in the rough-skinned newt (Taricha granulosa). Some populations of the common garter snake (Thamnophis sirtalis) have developed a resistance to tetrodotoxin. Here, we investigated the correlation between TTX and INDOX resistance in snakes. We hypothesized that INDOX would induce a much higher stress response than the naturally occurring TTX. We injected each snake with tetrodotoxin (1 mass-adjusted mouse unit). We did the same with mass-adjusted units of INDOX. We measured corticosterone, testosterone, and bactericidal ability. Our results show an acute stress response to INDOX, but not TTX through an elevate corticosterone and innate immune response, although there was no difference in testosterone concentration. These results suggest that, although INDOX may have a similar mechanism of action, garter snakes do not react in a similar manner as to TTX. This research gives a physiological perspective on the differences between naturally occurring compounds and synthetic compounds.

Parallel evolution of tetrodotoxin resistance in three voltage-gated sodium channel genes in the garter snake Thamnophis sirtalis.

Members of a gene family expressed in a single species often experience common selection pressures. Consequently, the molecular basis of complex adaptations may be expected to involve parallel evolutionary changes in multiple paralogs. Here, we use bacterial artificial chromosome library scans to investigate the evolution of the voltage-gated sodium channel (Nav) family in the garter snake Thamnophis sirtalis, a predator of highly toxic Taricha newts. Newts possess tetrodotoxin (TTX), which blocks Nav’s, arresting action potentials in nerves and muscle. Some Thamnophis populations have evolved resistance to extremely high levels of TTX. Previous work has identified amino acid sites in the skeletal muscle sodium channel Nav1.4 that confer resistance to TTX and vary across populations. We identify parallel evolution of TTX resistance in two additional Nav paralogs, Nav1.6 and 1.7, which are known to be expressed in the peripheral nervous system and should thus be exposed to ingested TTX. Each paralog contains at least one TTX-resistant substitution identical to a substitution previously identified in Nav1.4. These sites are fixed across populations, suggesting that the resistant peripheral nerves antedate resistant muscle. In contrast, three sodium channels expressed solely in the central nervous system (Nav1.1–1.3) showed no evidence of TTX resistance, consistent with protection from toxins by the blood–brain barrier. We also report the exon–intron structure of six Nav paralogs, the first such analysis for snake genes. Our results demonstrate that the molecular basis of adaptation may be both repeatable across members of a gene family and predictable based on functional considerations.

Facultative pheromonal mimicry in snakes: “she-males” attract courtship only when it is useful

Males of many animal species mimic females, and thereby deceive rival males. Facultative shifts in posture, color, or movement allow a male using visually-based mimicry to adopt and terminate mimicry rapidly. Pheromonal mimicry is rare in vertebrates perhaps because it is difficult to redeploy pheromones rapidly enough to adjust male tactics to local conditions. In Manitoba garter snakes (Thamnophis sirtalis parietalis), female mimicry benefits males immediately after they have emerged from hibernation. While the snakes are cold and slow, courtship warms them and protects them against predatory crows. This benefit disappears as soon as the snakes are warm. We show that (unlike females) she-male garter snakes attract courting males only when they are cold. Low temperatures may suppress volatility of “less attractive” components of the pheromones (saturated methyl ketones) that she-males use to attract courtship, allowing male snakes to function as transvestites only when this tactic is beneficial.

Temporal dynamics of relative-mass variation of red-sided garter snakes (Thamnophis sirtalis parietalis) at a communal hibernaculum in Manitoba

An animal's relative body mass (i.e., mass adjusted for length or some other size dimension) is a potential indicator of its body condition, which in turn can influence demographic traits. In this study, I revisited data collected in 1969–1970 on garter snakes, Thamnophis sirtalis parietalis, at a communal hibernaculum in Manitoba, to test hypotheses generated by more recent literature. First, I compared fall-through-spring variation in relative mass to a similar study of another species of Thamnophis in a milder, Mediterranean climate and found a similar temporal pattern, suggesting common features across a wide latitudinal range. Female snakes had a higher relative mass than males and experienced lower decline in relative mass overwinter and through the spring. This suggests different hibernation strategies of the 2 sexes, possibly involving different temperatures or differences in metabolism, and also reflects the preoccupation of males upon spring emergence with searching for mates, at energetic cost while not feeding. Comparison of my data with a second study of the same species at another den in Manitoba indicated nearly identical patterns of loss of mass, based on recaptures of males throughout the spring, and also corroborated that study's finding that initially relatively heavy males remained at the den longer. Thus, males that have accumulated more capital the previous year presumably have more opportunities to mate. Although recapture intervals of most males were only a few days long, similar to the previous study, some males remained in the vicinity of the den for up to 5 weeks. These findings underscore the fundamental differences between males and females in the temporal distribution of their costs of reproduction.

Toxic Prey and Predator Avoidance: Responses of Toxic Newts to Chemical Stimuli from a Predator and Injured Conspecifics

Abstract Predator avoidance behavior minimizes predation risk because the prey never enters the perceptual field of the predator. For toxic species, avoiding potential predators indiscriminately is unlikely to be the best predator avoidance strategy because many predators will be incapable of consuming the toxin. We investigated the role of chemical-based avoidance behavior in predator-prey interactions between a toxic prey species, the Rough-skinned Newt (Taricha granulosa), and its major predator, the Common Garter Snake (Thamnophis sirtalis). Terrestrial newts avoided predator kairomones only when the predator had recently consumed a conspecific, but did not avoid damage-released alarm cues. These results indicate newts may be able to chemically differentiate between toxin-resistant and toxin-sensitive snakes in the same population and avoid only those snakes actively preying upon their cohort.

Brain nuclei in actively courting red-sided garter snakes: A paradigm of neural trimorphism

During the breeding season, two distinct male phenotypes are exhibited by red-sided garter snakes (Thamnophis sirtalis parietalis), with courtship behavior being directed not only toward females, but also toward a sub-population of males called she-males. She-males are morphologically identical to other males except for a circulating androgen level three times that of normal males and their ability to produce a female-like pheromone. As in other vertebrates, limbic nuclei in the red-sided garter snake brain are involved in the control of sexual behaviors. For example, an intact anterior hypothalamus pre-optic area (AHPOA) is essential for the initiation and maintenance of reproduction. To determine if brain morphology varies among the three behavioral phenotypes (i.e., males, she-males, and females) during the breeding season, we examined the volume, cell size and cell density of the AHPOA as well as a control region, the external nucleus of the optic tract (ENOT). We used Luxol Fast Blue and Ziehl's Fuchsin to visualize neurons and glial cells, respectively. No significant differences were observed among the three behavioral phenotypes in the volume, cell size or density in the control region. In contrast, the volume, cell size and density of the AHPOA of she-males were significantly greater than those of both male and female snakes. While the volume of the AHPOA was significantly greater in females compared to males, no differences were observed in cell size or density. These differences in brain morphology suggest a possible underlying mechanism for phenotypic-specific behavioral patterns.

Biophysical costs associated with tetrodotoxin resistance in the sodium channel pore of the garter snake, Thamnophis sirtalis

Tetrodotoxin (TTX) is a potent toxin that specifically binds to voltage-gated sodium channels (NaV). TTX binding physically blocks the flow of sodium ions through NaV, thereby preventing action potential generation and propagation. TTX has different binding affinities for different NaV isoforms. These differences are imparted by amino acid substitutions in positions within, or proximal to, the TTX-binding site in the channel pore. These substitutions confer TTX-resistance to a variety of species. The garter snake Thamnophis sirtalis has evolved TTX-resistance over the course of an arms race, allowing some populations of snakes to feed on tetrodotoxic newts, including Taricha granulosa. Different populations of the garter snake have different degrees of TTX-resistance, which is closely related to the number of amino acid substitutions. We tested the biophysical properties and ion selectivity of NaV of three garter snake populations from Bear Lake, Idaho; Warrenton, Oregon; and Willow Creek, California. We observed changes in gating properties of TTX-resistant (TTXr) NaV. In addition, ion selectivity of TTXr NaV was significantly different from that of TTX-sensitive NaV. These results suggest TTX-resistance comes at a cost to performance caused by changes in the biophysical properties and ion selectivity of TTXr NaV.

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Predators Make (Temporary) Escape from Coevolutionary Arms Race

Influence of income and capital on reproduction in a viviparous snake: direct and indirect effects

AbstractA central issue in life‐history studies is the extent to which organisms are ‘capital’ versus ‘income’ breeders (i.e. using stored resources vs. current food intake). Snakes are primarily capital breeders, but income during vitellogenesis can also contribute to reproductive output. In Manitoba, the garter snake Thamnophis sirtalis has a short active season, with mating occurring upon emergence from hibernation and vitellogenesis shortly thereafter. Given the brevity of this sequence, animals in these populations should be almost exclusively capital breeders. Consistent with this prediction, in this experiment the reproductive output of recently mated snakes was influenced by mass of the mother at the time of mating but not by her food intake shortly after mating. Food eaten during pregnancy contributed significantly to postpartum mass but not to litter mass. However, the initial mass of snakes influenced both postpartum and litter mass. For snakes given a high ration of food, a female's relative mass (i.e. adjusted for body length) significantly influenced the actual amount she consumed (relatively lighter snakes ate more). Perhaps most important, among pregnant snakes, those that were initially relatively heavier gave birth substantially and significantly earlier. Thus, snakes that are relatively heavy when they mate may gain further fitness benefits following pregnancy (e.g. more time to acquire resources and for offspring to grow before winter), which can also be interpreted as indirect effects on reproduction. These life‐history variations may be relevant to population dynamics.

To avoid or not to avoid? Factors influencing the discrimination of predator diet cues by a terrestrial salamander

Many prey species use chemical cues deposited by predators to assess predation risk, and some prey are capable of discriminating among predator chemical traces based on the predator's recent diet. Here we test the influence of genetic relatedness (degree of genetic similarity between prey) and ecological relatedness (degree of refuge and trophic overlap between syntopic prey) on the evolution of predator-diet discrimination by red-backed salamanders, Plethodon cinereus. In experiment 1, we examined whether red-backed salamanders from Binghamton University (Binghamton, New York, U.S.A.) would differentially respond to chemical traces from garter snakes (Thamnophis sirtalis) fed conspecific P. cinereus from four populations belonging to three phylogenetic groups: Group II from Mountain Lake, Virginia, Group III from Binghamton University, New York, Group III from Hawk Mountain, Pennsylvania, and Group IV from Cherry Springs, Pennsylvania, U.S.A. The test salamanders only avoided chemical traces from garter snakes fed salamanders from the two Group III sites, although the response to the Group III-Hawk Mountain treatment was intermediate to that for the Group III-Binghamton University treatment and the Group II and IV treatments. In experiment 2, we examined whether red-backed salamanders collected from two subpopulations, syntopic or allotopic with two-lined salamanders, Eurycea bislineata, vary in their response to chemical cues from garter snakes foraging on two-lined salamanders. Only red-backed salamanders syntopic with E. bislineata avoided chemical traces from garter snakes fed E. bislineata. These results suggest that both genetic and ecological relatedness play a role in the evolution of predator-diet discrimination in red-backed salamanders.

COEVOLUTION OF DEADLY TOXINS AND PREDATOR RESISTANCE: SELF-ASSESSMENT OF RESISTANCE BY GARTER SNAKES LEADS TO BEHAVIORAL REJECTION OF TOXIC NEWT PREY

Deadly toxins and resistance to them are an evolutionary enigma. Selection for increased resistance does not occur if predators do not survive encounters with toxic prey. Similarly, deadly toxins are of no advantage to individual prey if it dies delivering the toxins. For individual selection to drive the coevolutionary arms race between resistant predators and lethal prey, the survivorship of individual predators must covary with their resistance. The extreme toxicity of the rough skinned newt Taricha granulosa appears to have coevolved with resistance in its predator, the common garter snake Thamnophis sirtalis, yet the mechanism by which individual selection can operate has been unclear in this and other lethal prey-predator systems. We show that individual snakes assess their own resistance relative to newt toxicity and reject prey too toxic to consume. Rejected newts all survived attacks and attempted ingestion by snakes that sometimes lasted over 50 min. Behavioral moderation of toxin exposure by snakes provides the association between individual resistance and fitness necessary for coevolution of lethal toxins and resistance to occur.

Differential effects of lesions of the vomeronasal and olfactory nerves on garter snake (Thamnophis sirtalis) responses to airborne chemical stimuli.

The roles of the main (MOS) and accessory (AOS) olfactory systems of garter snakes in response to airborne chemicals were investigated. Preoperatively, all snakes responded to airborne odors with increased tongue-flick rate and duration. Postoperatively, sham-operated snakes responded to airborne odors with increased tongue-flick rates, but snakes with main olfactory nerve cuts failed to respond to the odors, and snakes with vomeronasal nerve cuts responded to nonprey odors only. Preoperatively, exposure to earthworm odor produced more frequent and shorter duration tongue-flicks during locomotion compared with exposure to water. Postoperatively, only sham-lesioned snakes exhibited differential responding to earthworm odors. This study demonstrates that the MOS is critical for the initiation of tongue-flick behavior in response to airborne odors and that discrimination of odors with biological significance requires a functional AOS.

The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts.

The "geographic mosaic" approach to understanding coevolution is predicated on the existence of variable selection across the landscape of an interaction between species. A range of ecological factors, from differences in resource availability to differences in community composition, can generate such a mosaic of selection among populations, and thereby differences in the strength of coevolution. The result is a mixture of hotspots, where reciprocal selection is strong, and coldspots, where reciprocal selection is weak or absent, throughout the ranges of species. Population subdivision further provides the opportunity for nonadaptive forces, including gene flow, drift, and metapopulation dynamics, to influence the coevolutionary interaction between species. Some predicted results of this geographic mosaic of coevolution include maladapted or mismatched phenotypes, maintenance of high levels of polymorphism, and prevention of stable equilibrium trait combinations. To evaluate the potential for the geographic mosaic to influence predator-prey coevolution, we investigated the geographic pattern of genetically determined TTX resistance in the garter snake Thamnophis sirtalis over much of the range of its ecological interaction with toxic newts of genus Taricha. We assayed TTX resistance in over 2900 garter snakes representing 333 families from 40 populations throughout western North America. Our results provide dramatic evidence that geographic structure is an important component in coevolutionary interactions between predators and prey. Resistance levels vary substantially (over three orders of magnitude) among populations and over short distances. The spatial array of variation is consistent with two areas of intense evolutionary response by predators ("hotspots") surrounded by clines of decreasing resistance. Some general predictions of the geographic mosaic process are supported, including clinal variation in phenotypes, polymorphism in some populations, and divergent outcomes of the interaction between predator and prey. Conversely, our data provide little support for one of the major predictions, mismatched values of interacting traits. Two lines of evidence suggest selection is paramount in determining population variation in resistance. First, phylogenetic information indicates that two hotspots of TTX resistance have evolved independently. Second, in the one region that TTX levels in prey have been quantified, resistance and toxicity levels match almost perfectly over a wide phenotypic and geographic range. However, these results do not preclude the role the nonadaptive forces in generating the overall geographic mosaic of TTX resistance. Much work remains to fill in the geographic pattern of variation among prey populations and, just as importantly, to explore the variation in the ecology of the interaction that occurs within populations.

Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels.

Populations of the garter snake Thamnophis sirtalis have evolved geographically variable resistance to tetrodotoxin (TTX) in a coevolutionary arms race with their toxic prey, newts of the genus Taricha. Here, we identify a physiological mechanism, the expression of TTX-resistant sodium channels in skeletal muscle, responsible for adaptive diversification in whole-animal resistance. Both individual and population differences in the ability of skeletal muscle fibers to function in the presence of TTX correlate closely with whole-animal measures of TTX resistance. Demonstration of individual variation in an essential physiological function responsible for the adaptive differences among populations is a step toward linking the selective consequences of coevolutionary interactions to geographic and phylogenetic patterns of diversity.

Structural flexibility of the small intestine and liver of garter snakes in response to feeding and fasting.

Garter snakes Thamnophis sirtalis parietalis feed frequently but also tolerate extended periods of fasting when food is unavailable. We studied the dynamics, reversibility and repeatability of size changes of the small intestine and liver using ultrasonography. We employed light and transmission electron microscopy and flow cytometry to study the tissue mechanism that drives this flexibility. We compared garter snakes that fed every other day, snakes that fed once a week and fasting snakes. In all feeding trials, the size of the small intestine and the liver increased rapidly after feeding. Constantly feeding snakes maintained an elevated level of organ size, while snakes that were fed only once a week showed a marked up- and downregulation of organ size. Histology revealed the mucosal epithelium to be a transitional epithelium that can change cell configuration considerably to accommodate organ size changes. Upregulation of small intestine and liver size was always associated with the incorporation of lipid droplets into enterocytes and hepatocytes. Cell proliferation was not involved in upregulation of organ size. In contrast, cell proliferation increased during downregulation of organ size, indicating that cells worn out during digestion were replaced. The dynamics of flexibility and the functional features of the tissue were the same as described for the Burmese python Python molurus bivittatus. We suggest that garter snakes employ the same energetically cheap mechanism of organ size regulation as pythons, which allows for rapid, repeated and reversible size changes with no cell proliferation involved. Comparative evidence suggests that the transitional mucosal epithelium is an ancestral character of snakes and that feeding ecology is not directly related to the cytological features of the mucosal epithelium.

Comparisons between Toxic Effects of Tetrodotoxin Administered Orally and by Intraperitoneal Injection to the Garter Snake Thamnophis sirtalis

Comparisons between Toxic Effects of Tetrodotoxin Administered Orally and by Intraperitoneal Injection to the Garter Snake Thamnophis sirtalis

Recovery of Garter Snakes (Thamnophis sirtalis) from the Effects of Tetrodotoxin

km S Totontepec; 14169 UTA OAX, Sierra Mixe, 0.8 km S Totontepec; 14170 UTA OAX, Sierra Mixe, 0.8 km S Totontepec. Toluca conica: 2898 MZFC GRO, Chilpancingo, Omiltemi Salida E del pueblo; 2899 MZFC GRO, Chilpancingo, Omiltemi 2km E-SE; 2900 MZFC GRO, Chilpancingo, Omiltemi on trail to Las Joyas 500 m NW; 2901 MZFC GRO, Chilpancingo, Omiltemi Barranca de Potrerillos; 2902 MZFC GRO, Chilpancingo, Omiltemi 2 km E.

Recovery of Garter Snakes (Thamnophis sirtalis) from the Effects of Tetrodotoxin

Recovery of Garter Snakes (Thamnophis sirtalis) from the Effects of Tetrodotoxin

Comparisons between Toxic Effects of Tetrodotoxin Administered Orally and by Intraperitoneal Injection to the Garter Snake Thamnophis sirtalis

Comparisons between Toxic Effects of Tetrodotoxin Administered Orally and by Intraperitoneal Injection to the Garter Snake Thamnophis sirtalis