Thamnophis Ordinoides Research Articles

Edge-habitat Use by Northwestern Gartersnakes (<i>Thamnophis ordinoides</i>) in Saanich, British Columbia

Understanding habitat requirements of species is fundamental for their conservation and urban parks can provide key habitat for species in otherwise disturbed settings. Northwestern Gartersnakes (Thamnophis ordinoides) are common in parks in Saanich, British Columbia, but their specific habitat requirements are poorly understood. Based on previous studies and thermoregulatory needs of snakes, we predicted that edges, particularly field margins, would be heavily used by active snakes. We therefore used surveys that focused on edges to find snakes and measured edge-habitat use by comparing habitat variables at locations where snakes were found to the same variables at nearby random locations. Habitat variables included composition and structure of vegetation, substrate temperature, aspect, and slope. Overall, litter depth, canopy cover, a lack of bare ground and woody vegetation were the most important habitat variables for determining where snakes were found. our results provide a preliminary assessment to improve our understanding of habitat use for this species. The abundance of snakes found while surveying edges supports our initial assumption that edges are important habitat features but more work is required using multiple survey methods to further test this hypothesis.

Species specificity of methyl ketone profiles in the skin lipids of female garter snakes, genus Thamnophis

One of the relatively few vertebrate pheromones to be chemically identified, the female sex pheromone of the red-sided garter snake (Thamnophis sirtalis parietalis) is a series of saturated and monounsaturated methyl ketones contained within female skin lipids. During the breeding season, this pheromone is responsible for eliciting male courtship behaviors and males are able to utilize pheromonal variation to discriminate among females. While the pheromone system of the red-sided garter snake has been the subject of many studies, relatively little is known about the pheromone systems of other garter snakes. Through chemical analyses, we demonstrate that female skin lipids of the red-spotted garter snake (Thamnophis sirtalis concinnus), northwestern garter snake (Thamnophis ordinoides), and plains garter snake (Thamnophis radix) contain similar methyl ketones. The methyl ketone profiles of these snakes differ qualitatively from one another and from the methyl ketone profiles of red-sided garter snakes with differences particularly pronounced between sympatric species. Our results provide evidence that the use of methyl ketones in sexual signaling may be ubiquitous for Thamnophis species and suggest that these compounds could play a role in reproductive isolation between species in this genus.

Using Mitochondrial DNA to Determine the Identity and Origin of a Gartersnake Found in Alaska

In an era of rapidly changing environments and greater human mobility and penetration into wild areas, organisms are being discovered in increasingly unexpected places. One such finding is a road-killed juvenile gartersnake (Thamnophis) outside of Haines, Alaska, in August 2005. The poor condition of the specimen prevented a positive identification based on morphology alone. Furthermore, no snakes are known to be native to this region. We therefore undertook a molecular approach to determine the species and geographic origin of the individual. We sequenced two partial loci of mitochondrial DNA (cytochrome b and NADH subunit 2) from the Alaska specimen and seven specimens from localities in the lower northwestern United States. Phylogenetic reconstruction using our sequences and additional GenBank samples unambiguously revealed that the Alaska specimen is Thamnophis ordinoides and that it shares a haplotype with the northernmost sampled Washington population of T. ordinoides. In light of these analyses, we assess the likelihood that the specimen represents a relict population, a recent natural colonization, or a fresh introduction.

The Energetic Advantages of Slug Specialization in Garter Snakes (Genus Thamnophis)

We tested the hypothesis that dietary specialization by foraging garter snakes is accompanied by increased assimilation efficiency on specialist prey items. Our comparison included two closely related garter snake species considered to be slug specialists (Thamnophis ordinoides and Thamnophis elegans terrestris), one fish specialist (Thamnophis couchii), and one diet generalist (Thamnophis elegans elegans). Our results suggest that slug specialists have an energetic advantage over non-slug-eating snakes when both eat slugs. Slug specialists T. ordinoides and T. e. terrestris both have higher assimilation and net assimilation efficiencies when eating slugs than do generalists T. e. elegans and T. couchii. The slug specialists did not experience decreased efficiency when eating fish. Therefore, there was no apparent digestive trade-off for the slug specialists when eating other prey.

Experimental evidence that oral secretions of northwestern ring-necked snakes ( Diadophis punctatus occidentalis) are toxic to their prey

Ring-necked snakes ( Diadophis punctatus) are suspected of being venomous because their Duvernoy's gland secretions have high levels of phospholipase activity, which is characteristic of many viperid and elapid venoms, and because anecdotal reports of feeding behavior are consistent with the use of a venom. We tested the toxicity of northwestern ring-necked snake oral secretions to a natural prey species, northwestern garter snakes ( Thamnophis ordinoides), by injecting 2–35 μl of oral secretions intraperitoneally. All doses were 100% lethal within 180 min. The dose significantly affected the time to loss of a righting response. Neither injection of saline nor denatured oral secretions resulted in loss of a righting response or any visible detrimental effects. We suggest that northwestern ring-necked snakes may have evolved venom to subdue larger prey items than the snake would otherwise be capable of taking.

The effects of body size, age, and food intake during pregnancy on reproductive traits of a viviparous snake, Thamnophis ordinoides

:Litter characteristics of viviparous snakes presumably can be influenced by the mother’s state (e.g., mass) at the onset of pregnancy, by food acquired during vitellogenesis, or by food eaten by the mother during pregnancy and delivered to the developing embryos via the placenta. Alternatively, food consumed while pregnant could be allocated to the female herself, potentially influencing her future survivorship and/or reproduction. We tested the effects of food consumption during pregnancy on litter traits of the garter snake, Thamnophis ordinoides, along with the effects of body size and age of mother. We also measured trade-offs between traits. Age was significantly correlated with body size of female snakes, but it had no direct influence on reproductive traits. Initial body size, by contrast, especially snout-vent length, significantly and positively influenced litter size and mass. Food intake by gravid females declined during pregnancy, and snakes became relatively anorexic prior to giving birth; their appetite resumed following parturition. Snakes offered smaller amounts of food while pregnant ate less than those fed ad lib, but had similar postpartum appetites. Higher food intake during pregnancy resulted in higher postpartum mass of females, but not higher litter mass or size of offspring. There was strong evidence of a trade-off between litter size and offspring size and between postpartum mass and litter mass. Overall, our data are consistent with the hypothesis that reproductive traits of viviparous snakes are determined proximately by previously accumulated stores (capital) and/or food consumed during vitellogenesis (income), but not by resources acquired during pregnancy.

Pulmonary Surfactant Lipids in the Faveolar and Saccular Lung Regions of Snakes

We examined the composition and function of pulmonary surfactant located within the faveolar and saccular regions of the garter snake Thamnophis ordinoides and the rattlesnake Crotalus atrox lung. While the faveolar region is well vascularized and septated and is used in gas exchange, the saccular lung is a thin-walled, smooth bag with very little vascularization that functions as a bellows and in gas storage. Both regions of the lungs of the two snake species contained large amounts of surfactant. The rattlesnake faveolar lung contained 2419.9 ± 260.0 μg of phospholipidper gram of wet lung mass, a value among the largest ever recorded for any species. However, snake faveolar lung surfactant is markedly different from all other vertebrate surfactants reported to date because it contains relatively little cholesterol (3%-8%). Faveolar lung surfactant of the rattlesnake had a greater phospholipid saturation level than that of the garter snake. The phospholipid profile of garter snake faveolar lung surfactant was very similar to that reported for most other nonmammalian vertebrates, with phosphatidylcholine (PC) the predominant phospholipid (64%), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and sphingomyelin (S) either absent or present only in trace amounts (1%-4%), and intermediate (17%) levels ofphosphatidylinositol (PI). The phospholipid profile of rattlesnake faveolar lung surfactant, on the other hand, differed greatlyfrom that of most other vertebrates in that it contained unusually high levels of lysophosphatidylcholine (LPC) and S (12%-18%), whereas PG and PI were virtually absent (0%-1.4%). Removal of surfactant by lavage increased the opening pressure (the initial pressure required to commence the inflation of a collapsed lung) of both regions of the garter snake lung (faveolar region, 1.32-4.51 cm H₂0; saccular region, 1.55-2.19 cm H₂O). However, the rattlesnake faveolar region did not collapse even after lavage, and an opening pressure was never obtained. The opening pressure for the rattlesnake saccular lungs (2.78 cm H₂O) was not increased by lavage (3.0 cm H₂O). The filling pressures were greater for the faveolar lung than for the saccular lung for both species. Filling pressure of the two lung regions was not affected by lavage in either snake.

Orientation Abilities and Mechanisms in Nonmigratory Populations of Garter Snakes (Thamnophis sirtalis and T. ordinoides)

I tested the navigational abilities in nonmigratory populations of garter snakes (Thamnophis sirtalis and T. ordinoides) from Spectacle Lake Provincial Park on Vancouver Island, British Columbia, Canada. Displacement studies were carried out from 1986-88 to determine the level of orientational abilities present in each species and to examine potential orientation cues. Snakes were displaced from their home range and tested in an arena under a variety of conditions. The results demonstrated that nonmigratory T. sirtalis possessed advanced navigational abilities. Advanced abilities may be absent in T. ordinoides. Thamnophis sirtalis demonstrated time-compensated solar orientation as determined by 6-h phase-delayed tests. Pheromone trails produced by gravid females, but not by males, may also provide an orientation guide for T. sirtalis under some conditions. Thamnophis ordinoides did not respond in a discernible way to either solar or pheromonal cues. The findings of this study were compared with similar tests performed on a migratory population of T. sirtalis. Navigational skills vary little between migrating and nonmigrating populations of the same species but may be poorly developed in nonmigratory species.

HOMOGENEITY OF THE GENETIC VARIANCE-COVARIANCE MATRIX FOR ANTIPREDATOR TRAITS IN TWO NATURAL POPULATIONS OF THE GARTER SNAKE THAMNOPHIS ORDINOIDES.

Quantitative genetic models of evolution rely on the genetic variance-covariance matrix to predict the phenotypic response to selection. Both prospective and retrospective studies of phenotypic evolution across generations rely on assumptions about the constancy of patterns of genetic covariance through time. In the absence of robust theoretical predictions about the stability of genetic covariances, this assumption must be tested with empirical comparisons of genetic parameters among populations and species. Genetic variance-covariance matrices were estimated for a suite of antipredator traits in two populations of the northwestern garter snake, Thamnophis ordinoides. The characters studied include color pattern and antipredator behaviors that interact to facilitate escape from predators. Significant heritabilities for all traits were detected in both populations. Genetic correlations and covariances were found among behaviors in both populations and between color pattern and behavior in one of the populations. Phenotypic means differed among populations, but pairwise comparisons revealed no heterogeneity of genetic parameters between the populations. The structure of the genetic variance-covariance matrix has apparently not changed significantly during the divergence of these two populations.

Consistency of individual differences in anti-predator behaviour and colour pattern in the garter snake, Thamnophis ordinoides

Abstract. The importance of individual variation in behaviour as both an ingredient and a consequence of natural selection has only recently received much attention from empirical researchers. The manner in which individual differences change ontogenetically and how such changes may affect an individual's fitness are still largely unknown. This study investigates the development of anti-predator behaviour and colour pattern in the northwestern garter snake, Thamnophis ordinoides, during the first 2 years of life under laboratory conditions and in the wild. Several aspects of escape behaviour were examined, including the maximum sprint speed, the distance crawled until an anti-predator display was performed (stamina), and the tendency to perform stereotypical evasive manoeuvres during flight (reversals). These aspects of escape behaviour and the stripedness of colour pattern showed significant changes during this time, although the specific changes varied between laboratory and field conditions. Many of the developmental changes were associated with growth. Traits generally showed strong positive correlations across ages, both in the laboratory and in the field. Individual differences in anti-predator behaviour and colour pattern in this species of snake appear to be relatively consistent throughout the first 2 years of life. Using neonate trait values to estimate selection during this time will provide accurate representations of the form of selection because the ontogenetic trajectories of individuals are parallel.

CORRELATIONAL SELECTION FOR COLOR PATTERN AND ANTIPREDATOR BEHAVIOR IN THE GARTER SNAKE THAMNOPHIS ORDINOIDES.

Correlational selection favors combinations of traits and is a key element of many models of phenotypic and genetic evolution. Multiple regression techniques for measuring selection allow for the direct estimation of correlational selection gradients, yet few studies in natural populations have investigated this process. Color patterns and antipredator behaviors of snakes are thought to function interactively in predator escape and therefore may be subject to correlational selection. To investigate this hypothesis, I studied the survivorship of juvenile garter snakes, Thamnophis ordinoides, as a function of a suite of escape behaviors and color pattern. The only natural selection detected favored opposite combinations of stripedness of the color pattern and the tendency to perform during escape evasive behaviors called reversals. This selection presumably results from optical illusions created by moving patterns and their effects on visually foraging predators. Analysis of the bivariate selection surface shows that pure correlational selection can be thought of as a series of linear selection functions on one trait whose slopes depend on the value of the second trait. Alternatively, viewing the selection surface along its major axes reveals stabilizing and disruptive components of correlational selection. It is further shown that correlational selection alone can promote genetic variance and covariance within a generation. This phenomenon may be partially responsible for the extreme variation in color pattern and the genetic covariance between color pattern and behavior observed in natural populations of T. ordinoides.

Nutritional Provision to Embryos in a Predominantly Lecithotrophic Placental Reptile, Thamnophis ordinoides (Squamata: Serpentes)

Quantitative analysis of the composition of eggs and their sibling neonates in the viviparous natricine snake Thamnophis ordinoides revealed that yolk provided the principal source of organic nutrition but that embryos received a substantial allotment of inorganic nutrients from the placentas. The placental provision of water and sodium equaled or exceeded yolk supplies, and placental transport accounted for 23% of neonatal calcium composition. There was no difference between egg and newborn quantities of total phosphorus or total potassium, whereas neonates contained less total magnesium than eggs. The mode of embryonic nutrition in this species is characterized as predominantly lecithotrophic, yet placental nutrient provision contributes significantly to embryonic nourishment. Placental transport of sodium and embryonic uptake of water was greater in recently ovulated eggs that contained relatively low levels of sodium and water respectively. Thus, placental sources compensated for low yolk provision. P...

TETRODOTOXIN RESISTANCE IN GARTER SNAKES: AN EVOLUTIONARY RESPONSE OF PREDATORS TO DANGEROUS PREY.

The use of the "arms race" analogy as a conceptualization of evolutionary predator-prey interactions has been criticized because of the lack of evidence that predators can and do adapt to increased antipredator ability of prey. We present evidence that the garter snake Thamnophis sirtalis has evolved resistance to tetrodotoxin (TTX) in response to the toxicity of the newt Taricha granulosa on which the snake feeds. A bioassay (locomotor performance before and after injection of TTX) was used to obtain repeated measures of resistance for individual snakes. We studied interpopulation and interspecific variation by comparing resistance in Thamnophis sirtalis from populations occurring sympatrically and allopatrically with Taricha granulosa, and in Thamnophis ordinoides (which does not feed on the newt) occurring sympatrically with Taricha granulosa. We also examined intrapopulation variation in TTX resistance using snakes from a population known to feed on Taricha granulosa. Resistance differed significantly among individuals and litters; repeatability and heritability estimates of the assay were significantly different from zero, demonstrating the potential for response to selection. The population of Thamnophis sirtalis that occurs with Taricha granulosa exhibited levels of resistance much greater than either of the other groups. These results suggest that the predator-prey arms race analogy may be applicable to this system.

Genetic correlations between morphology and antipredator behaviour in natural populations of the garter snake Thamnophis ordinoides.

The genetic coupling of morphology and behaviour means that the evolution of the two types of traits will not be independent: changes in behaviour will result in changes in morphology and vice versa. This might explain nonadaptive differences in morphology through indirect selection on correlated characters of other categories. Genetic correlations between morphology and behaviour are also the basis for some models of sympatric speciation and of the stability of polymorphisms. Morphology and behaviour are often correlated in nature and a genetic basis for such couplings has been demonstrated. I present here evidence that colour pattern and antipredator behaviour are genetically coupled in natural populations of the garter snake Thamnophis ordinoides. Similar phenotypic correlations between pattern and behaviour exist among species of North American snakes, indicating that selection for particular combinations of traits may help to maintain genetic covariances and colour polymorphism in Thamnophis ordinoides.

Antipredator strategies of salamanders: individual and geographical variation in responses of Eurycea bislineata to snakes

Adult two-lined salamanders, Eurycea bislineata, displayed alternative antipredator behaviour to garter snake, Thamnophis ordinoides, predators. In response to snake tongue-flicks, individual salamanders either ran, jumped or remained immobile. Different populations and individuals within populations exhibited different propensities for the alternative behaviours. Individuals from an area with a high density of garter snakes ran more often than those from another area. The kind of behaviour exhibited was also correlated with the physical ability of the salamander. Those individuals that ran in response to garter snake tongue-flicks were able to run faster than those that exhibited immobility. Individual salamanders that run when tongue-flicked by garter snakes accrue a survival advantage over those that remain immobile. The survival advantages of alternative patterns of antipredator behaviour should vary greatly as a function of differing local selection regimens.

Behavioral Modification as a Means of Reducing the Cost of Reproduction

Because relative clutch mass (RCM) adversely affects locomotor performance, and therefore presumably the survival rate of pregnant females, it is assumed to be constrained by natural selection. I propose that changes in antipredator tactics during pregnancy can reduce females' dependence on locomotion, thereby alleviating selection acting on RCM. Such a behavioral shift would be a more likely response to selection against poor locomotor ability because reductions in RCM have obvious disadvantages (i.e., decreasing fecundity) and can only partially improve speed and endurance. Comparisons of the locomotor performance and antipredator behaviors of pregnant female garter snakes (Thamnophis ordinoides) before and after parturition indicate that locomotor ability declines and that antipredator tactics change during gestation. Females tend more toward cryptic behavior during pregnancy than after. These observations are consistent with behavioral shifts observed in lizards during periods of reduced locomotor ability.

Feeding habits and diet overlap of three species of garter snakes (Thamnophis) on Vancouver Island

Closely related, sympatrtc species of organisms often show resource partitioning. In this study, diet partitioning is examined in three sympalric species of garter snakes (Thamnophis) on Vancouver Island. Thamnophis sirtalis feeds mainly on amphibians and earthworms, Thamnophis ordinoides on earthworms and slugs, and Thamnophis elegans on slugs, fish, and small mammals. Thamnophis sirtalis and T. ordinoides, which are mote widely distributed on Vancouver Island than is T. elegans, have not been shown to modify their diets in the absence of T. elegans, but it is suggested that this lack of niche shift may be due to variations in prey availability. Neither innate differences in food preferences among the species nor interspecific competition for food have been shown to explain the observed differences in diet among the three species. Certain types of prey appear more likely than others to turn up in large numbers in stomach samples and it is suggested that this may be due to variations in ease of capture and (or) abundance. Possible explanations of the observed diets are discussed.

The cranial nerves of the colubrid snakes Elaphe and Thamnophis

AbstractThe cranial nerves of adult Elaphe obsoleta quadrivittata and late embryonic Thamnophis ordinoides, were studied, respectively, by dissection and by microscopic examination of serial sections. There are 11 cranial nerves in these snakes; the spinal accessory (XI) cannot be identified. In general, the nerves are similar to those of lizards. Certain nerves usually combine into a trunk: the oculomotor (III), trochlear (IV), ophthalmic division (V1) and abducens (VI), form the ocular trunk, whereas the glossopharyngeal (IX), vagus (X), and hypoglossal (XII), compose the craniocervical trunk. No terminal nerve is found. The first nerve exists as the independent vomeronasal and olfactory proper nerves. There is a large lagenar (auditory) part of the eighth nerve. The three main divisions of the trigeminal nerve (V) have the widest distribution in the head. In addition, there is a pterygoid division (V4) in snakes, innervating the muscles of the upper jaw series of bones. The V4 is best developed in snakes among all vertebrates. A chorda tympani of VII is present. The glossopharyngeal is a small nerve. The vagus comprises a large laryngeal branch and a larger visceral nerve to the trunk. The hypoglossal heavily innervates the tongue musculature.There are four cephalic parasympathetic ganglia: ciliary, preorbital, infraorbital, and inferior alveolar. Several of the ganglia may also include sympathetic cell bodies. The ciliary ganglion innervates intraocular smooth muscle, whereas the other ganglia supply the various cephalic glands. No distinct superior cervical sympathetic ganglion is recognized. Sympathetics distribute in the head through the craniocervical trunk and its communications with the facial and trigeminal nerves.

Further Remarks concerning Thamnophis ordinoides and Its Relatives

Further Remarks concerning Thamnophis ordinoides and Its Relatives

Geographic Variation in Garter Snakes of the Species Thamnophis sirtalis in the Pacific Coast Region of North America

Investigation of the western forms of garter snakes of the species Thamnophis sirtalis was begun after the completion of an extensive systematic study (Fitch, 1940) of the Thamnophis ordinoides group in the same area. The ordinoides complex is represented by eleven forms, which show a remarkable degree of divergence in different directions, not only in structural characters, but in habits and habitats as well.