Placentation in the garter snake, Thamnophis sirtalis

The structure and polysaccharide constitution of the jelly capsule of the egg of Rana pipiens is described. Microscopic examination of the jelly capsule revealed the presence of five discrete jelly layers that differed clearly in their response to selected cytochemical tests. These layers were classified as M1-through M5 from the inner to the outermost layer. A sixth layer occasionally could be observed between M3 and M4. All layers contain neutral mucopolysaccharides. In addition layers M1 and M3 contain sulphated mucopolysaccharides, M2 and M4 contain non-sulphated acid mucopolysaccharides, and layer M5 contains both sulphated and non-sulphated acid mucopolysaccharides. M2 may also contain a small quantity of sulphated mucopolysaccharides. The layer that occasionally appears between M3 and M4 is probably an area in which free acidic groups are in higher concentration than in adjacent areas rather than being a discrete jelly layer. Neither hyaluronic acid nor sialic acid was localized by the methods employed. The possible significance of some of these constituents is discussed.     

Pulmonary carbonic anhydrase in the garter snake, Thamnophis sirtalis

This study examined whether the snake lung possesses intravascular carbonic anhydrase (CA). Lungs were perfused with control salines and with salines containing CA inhibitors. Perfusion with control salines resulted in a stable CO(2) excretion, whereas CA inhibitors significantly reduced pulmonary CO(2) excretion. Membrane-permeable and membrane-impermeable CA inhibitors produced comparable decreases in CO(2) excretion, suggesting that extracellular, intravascular CA participated in the pulmonary CO(2)-HCO3(-)-H(+) reactions. Treatment of lungs with phosphatidylinositol specific-phospholipase C (PI-PLC) significantly decreased CO(2) excretion, indicating that CA was connected to the luminal endothelial cell membrane by a phosphatidylinositol glycan linkage. Taken together, these results are the first to demonstrate the presence of membrane-bound, intravascular CA (CA IV) in the snake lung.     

Thermal biology of the common garter snake Thamnophis sirtalis (L.)

Summary The thermoregulatory significance of a striped-melanic colour polymorphism in the common garter snake, Thamnophis sirtalis, was assessed through a combination of labortory experimentation and field study. In experiments with living snakes the melanic morph maintained a higher body temperature than the striped morph, when exposed to natural insolation. Experiments with excised skin showed that this thermal advantage is attributable to some integumental difference between the two morphs. Body temperatures of snakes in the field revealed that, during the colder part of the active season, melanics were able to stay warmer than striped snakes by an amount (1.24 C°) approximating the difference observed in the laboratory. Some evidence and argument is presented to suggest that melanism also may confer protection against overheating in warm periods.     

A proposal to sequence the genome of a garter snake (Thamnophis sirtalis)

Here we develop an argument in support of sequencing a garter snake (Thamnophis sirtalis) genome, and outline a plan to accomplish this. This snake is a common, widespread, nonvenomous North American species that has served as a model for diverse studies in evolutionary biology, physiology, genomics, behavior and coevolution. The anole lizard is currently the only genome sequence available for a non-avian reptile. Thus, the garter snake at this time would be the first available snake genome sequence and as such would provide much needed comparative representation of non-avian reptilian genomes, and would also allow critical new insights for vertebrate comparative genomic studies. We outline the major areas of discovery that the availability of the garter snake genome would enable, and describe a plan for whole-genome sequencing.     

The mechanism of venom secretion from Duvernoy's gland of the snake Thamnophis sirtalis

The venom glands of snakes of the families Elapidae and Viperidae are thought to have evolved from Duvernoy's gland of colubrid ancestors. In highly venomous snakes elements of the external adductor musculature of the jaw insert fibers directly onto the capsule of the venom gland. These muscles, upon contraction, cause release of contents by increasing intraglandular pressure. In Thamnophis sirtalis, a colubrid, there is no direct connection between Duvernoy's gland and the adductor musculature. The anatomical arrangement of the gland, skull, adductor muscles, and the integument is such that contraction of the muscles may facilitate emptying of the gland. This hypothesis was tested by electrical stimulation of the muscles, which resulted in significantly greater release of secretion than elicited by controls. The results suggest a possible early step in the evolution of a more intimate association between venom glands and adductor musculature in highly venomous snakes.     

Behavioural and hormonal responses to capture stress in the male red-sided garter snake, Thamnophis sirtalis parietalis

We measured the behavioural and hormonal responses to capture stress in male red-sided garter snakes. Four hours of capture stress resulted in no suppression of mating behaviour relative to control individuals. In contrast, the same stress resulted in a significant increase in plasma levels of corticosterone and a significant decrease in plasma levels of testosterone. There was a significant negative correlation between plasma levels of corticosterone and testosterone in both control and capture-stress groups, suggesting that the increase in corticosterone directly drives the decrease in testosterone. While there was no relation between body size and initial plasma levels of the two steroids, longer individuals had a significantly greater increase in corticosterone following capture stress than did shorter individuals. Snakes display indeterminate growth, suggesting that older individuals have decreased sensitivity to negative feedback in the hypothalamic-pituitary-adrenal axis and thus hypersecrete glucocorticoids. These results suggest that male red-sided garter snakes have uncoupled their behavioural stress response from their hormonal stress response to maximize reproductive opportunities. Copyright 2000 The Association for the Study of Animal Behaviour.     

Population size and survivorship of the common garter snake, Thamnophis sirtalis, near the northern limit of its distribution

The common garter snake, Thamnophis sirtalis . has frequently been studied, but never in the far north where climatic influences on distribution and abundance might be expected to be severe. We examined the structure and dynamics of a communal den population at the northern limit of the species' range. Snakes were sampled at the hibernaculum from spring 1983 to spring 1987. Males were more easily caught than females, and few inferences could be made about the latter. Population estimates, though possessing wide standard errors, seemed to indicate that the denning population of 500–600 snakes, mostly adults, was stable. Annual survivorship of large males (≥400 mm SVL) was high (0.68–0.98) and was not correlated with body size. Thirty-four snakes that were first marked in 1983 were recaptured in the spring of 1987, indicating that they had survived at least six years, assuming they were a minimum of two years old when first marked. Recruitment to the denning population consisted of an influx of 'new' individuals (450–550 mm SVL) each autumn. It is not known where these snakes spend the first few years of their existence. The relative Stability of numbers and high overwinter survivorship observed over the course of this study contrast sharply with the only previous study of T. sirtalis in cold climates.     

Ontogenetic changes in the feeding system of the red-sided garter snake, Thamnophis sirtalis parietalis. I. Allometric analysis

The ontogenetic growth pattern of selected components of the skeleton, muscle mass, and muscle lever arms within the head of the red-sided garter snake, Thamnophis sirtalis parietalis , were investigated. The results of this analysis appear to indicate an ontogenetic shift from an early emphasis upon prey manipulation to a later emphasis upon striking. The ecological, morphological and phylogenetic evidence for this shift is described and specific testable hypotheses are proposed.     

Hematology and plasma biochemistry values for the giant garter snake (Thamnophis gigas) and valley garter snake (Thamnophis sirtalis fitchi) in the Central Valley of California

Hematology and plasma biochemistry parameters are useful in the assessment and management of threatened and endangered species. Although reference ranges are readily available for many mammalian species, reference ranges for snakes are lacking for most species. We determined hematology and plasma biochemistry reference ranges for giant garter snakes (Thamnophis gigas) and valley garter snakes (Thamnophis sirtalis fitchi) living in four management areas in the Central Valley of California. White blood cell, heterophil, lymphocyte, and azurophil counts in giant garter snakes were approximately twice the values of valley garter snakes. Statistically significant differences in aspartate aminotransferase, globulin, and potassium between the two species did not appear clinically significant. No significant differences were found in the measured parameters between male and female giant garter snakes. Some differences were found among collection sites. These reference ranges provide baseline data for comparisons over time and between collection sites.     

The photoreceptors and visual pigments of the garter snake (Thamnophis sirtalis): a microspectrophotometric, scanning electron microscopic and immunocytochemical study

Scanning electron microscopy, immunocytochemistry, and single cell microspectrophotometry were employed to characterize the photoreceptors and visual pigments in the retina of the garter snake, Thamnophis sirtalis. The photoreceptor population was found to be comprised entirely of cones, of which four distinct types were identified. About 45.5% of the photoreceptors are double cones consisting of a large principal member joined near the outer segment with a much smaller accessory member. About 40% of the photoreceptors are large single cones, and about 14.5% are small single cones forming two subtypes. The outer segments of the large single cones and both the principal and accessory members of the doubles contain the same visual pigment, one with peak absorbance near 554 nm. The small single cones contain either a visual pigment with peak absorbance near 482 nm or one with peak absorbance near 360 nm. Two classes of small single cones could be distinguished also by immunocytochemistry and scanning electron microscopy. The small single cones with the 360-nm pigment provide the garter snake with selective sensitivity to light in the near ultraviolet region of the spectrum. This ultraviolet sensitivity might be important in localization of pheromone trails. Accepted: 10 March 1997     

Kinematics of swimming garter snakes (Thamnophis sirtalis)

We investigate the kinematics of swimming garter snakes (Thamnophis sirtalis) using a novel nonlinear regression-based digitization method to establish quantitative statistical support for non-constant wavelengths in the undulatory pattern exhibited by swimming snakes. We find that in swimming snakes, the growth of the amplitude of the propulsive wave head-to-tail is strongly correlated (p < 0.005) with the head-to-tail growth in the wavelength. We investigate correlations between kinematic parameters and steady swimming speed, and find a very strong positive correlation between swimming speed and undulation frequency. We furthermore find a statistically well-supported positive correlation between swimming speed and both the initial amplitude of the propulsive wave at the head and the degree of amplitude growth from head to tail.     

Comparison of plasma and testicular testosterone levels during the active season in the common garter snake, Thamnophis sirtalis (L)

Plasma and testicular testosterone levels were determined during three periods (spring, summer and autumn) of the active season in the common garter snake, Thamnophis sirtalis. Plasma testosterone levels were highest in spring and lowest in summer. Testicular testosterone levels were higher in spring than autumn but not significantly different in spring than summer or in summer than autumn. This study presents further evidence that in reptiles, plasma and testicular androgen cycles are not necessarily parallel.     

lntracortical Connections in the Snakes Natrix sipedon and Thamnophis sirtalis

The association and commissural connections between the four cortical areas in water (Natrix sipedon) and garter (Thamnophis sirtalis) snakes were studied by placing lesions on the cortical surface and studying the resulting degeneration in Fink-Heimer preparations. Lateral cortex projects to the outer one third of layer 1 of ipsilateral medial cortex. Dorsal cortex projects to the middle third of layer 1 of ipsilateral medial cortex. Dorsomedial cortex projects bilaterally to the inner third of layer 1 and to layer 3 of me dial cortex. It also projects to layer 1 of contralateral dorsomedial cortex. Medial cortex projects ipsilaterally to each of the other cortical areas. With the apparent exception of the projection of medial cortex to lateral cortex, each projection is organized such that each rostrocaudal segment of a cortical area projects to all segments of the target area lying at the same or more caudal levels.     

Kinematics of swimming garter snakes (Thamnophis sirtalis).

We investigate the kinematics of swimming garter snakes (Thamnophis sirtalis) using a novel nonlinear regression-based digitization method to establish quantitative statistical support for non-constant wavelengths in the undulatory pattern exhibited by swimming snakes. We find that in swimming snakes, the growth of the amplitude of the propulsive wave head-to-tail is strongly correlated (p < 0.005) with the head-to-tail growth in the wavelength. We investigate correlations between kinematic parameters and steady swimming speed, and find a very strong positive correlation between swimming speed and undulation frequency. We furthermore find a statistically well-supported positive correlation between swimming speed and both the initial amplitude of the propulsive wave at the head and the degree of amplitude growth from head to tail.