Thamnophis Sirtalis Research Articles

Snakes on a lane: Road type and edge habitat predict hotspots of snake road mortality

Roads constitute just 1% of the total land in the US, but their impacts on wildlife are significant and far-reaching. Snakes are particularly susceptible to road mortality because many species do not avoid crossing roads, may use the road’s surface to thermoregulate, or freeze when approached by a vehicle. We conducted opportunistic surveys to collect road mortality points for snakes in southeastern Ohio over 15 years (2003–2018). We used logistic regression to predict roadkill hotspots and evaluate variables that influence road mortality. The species most frequently found dead on roads were Black Ratsnakes (Pantherophis spiloides), Northern Black Racers (Coluber constrictor), Eastern Gartersnakes (Thamnophis sirtalis), and Rough Greensnakes (Opheodrys aestivus). Across the 14 snake species we recorded dead on roads, percent pasture within a 100 m buffer of the roadkill point, township route, county route, and state route were all negative predictors of road mortality. All surveys started in Athens, Ohio, and distance to roadkill locations was a positive predictor for road mortality. These results indicate that high-traffic roads pose a risk to snake populations, but that mortality also occurs on low-traffic roads as well. Our top model showed that low levels of pasture embedded in other land cover types was an important predictor of roadkill, suggesting that edge habitat contributes to snake road mortality. Because road mortality does not seem to be localized, road mortality mitigation structures such as underpasses and fences may have limited benefits for snake populations in our study area. The creation of edge habitat away from roads could provide snakes with necessary habitat without increasing their risk of mortality.

Current and time-lagged effects of climate on innate immunity in two sympatric snake species.

Changing environments result in alterations at all levels of biological organization, from genetics to physiology to demography. The increasing frequency of droughts worldwide is associated with higher temperatures and reduced precipitation that can impact population persistence via effects on individual immune function and survival.We examined the effects of annual climate variation on immunity in two sympatric species of garter snakes from four populations in California over a seven‐year period that included the record‐breaking drought.We examined three indices of innate immunity: bactericidal competence (BC), natural antibodies (NABs), and complement‐mediated lysis (CL).Precipitation was the only climatic variable explaining variation in immune function: spring precipitation of the current year was positively correlated to Thamnophis sirtalis BC and NABs, whereas spring precipitation of the previous year was positively correlated to T. elegans BC and NABs. This suggests that T. elegans experiences a physiological time‐lag in response to reduced precipitation, which may reflect lack of capital for investment in immunity in the year following a dry year.In general, our findings demonstrate compelling evidence that climate can influence wild populations through effects on physiological processes, suggesting that physiological indices such as these may offer valuable opportunities for monitoring the effects of climate.

Stable isotope analysis suggests that tetrodotoxin-resistant Common Gartersnakes (Thamnophis sirtalis) rarely feed on newts in the wild

Toxin-resistant predators may suffer costs from eating chemically defended prey and do not feed exclusively on toxic prey. Common Gartersnakes (Thamnophis sirtalis (Linnaeus, 1758)) have been considered the drivers of an evolutionary arms race with highly toxic newts (genus Taricha Gray, 1850), which they consume with few or no deleterious effects. However, how frequently newts are consumed in nature is less clear. To address this question, we investigated the diets of Th. sirtalis at a site in central Oregon where snakes have high levels of resistance and newts have high levels of tetrodotoxin in the skin. Because snake diets are difficult to quantify using traditional means, we used stable isotopes to estimate the proportion of Th. sirtalis diets made up of newts. Our estimate for the proportion of Th. sirtalis diet made up of Rough-skinned Newts (Taricha granulosa (Skilton, 1849)) at this site is 3.2%. Mole Salamanders (genus Ambystoma Tschudi, 1838) were predicted to be the most important prey, followed by slugs, chorus frogs, and mice, with a very minor role for earthworms. Our results demonstrate that even though Th. sirtalis are physiologically capable of consuming toxic prey, they do not often do so. Generalist predators can be exposed to very strong selection from, and exert reciprocal selection on even rarely eaten, chemically defended prey.

Importance of woodland patches as hibernacula for gartersnakes in a prairie river floodplain of central Nebraska

Gartersnakes are common inhabitants along prairie rivers in the Great Plains, but little information is known about hibernacula among diverse floodplain habitats. We radio-tracked Common Gartersnakes (Thamnophis sirtalis) and Plains Gartersnakes (Thamnophis radix) to hibernacula on islands in a braided river system subject to frequent environmental changes along the Platte River in central Nebraska. We further examined capture rates of gartersnakes in floodplain woodland patches from June to November to examine seasonal use of this habitat. In early and mid-September, movements of snakes with transmitters were in grasslands. From late September to mid-October, the farthest movements were documented, and snakes moved from grasslands into woodland patches. From late October to January, movements were minimal in and around hibernacula in wooded or formerly wooded habitats. Capture rates of gartersnakes in woodland trapping arrays also increased in October and November, further demonstrating woodland use during times when snakes travel to and reside at hibernacula. Although grasslands comprised most of the prairie islands at the study area, observations suggested that the limited woodlands on these islands are important for gartersnakes prior to and during hibernation along the Platte River in central Nebraska. Areas with large trees, such as Plains Cottonwoods (Populus deltoides), appeared to provide overwintering sites. In central Nebraska, riparian woodlands continue to be cleared to enhance habitat for endangered and threatened species such as Whooping Cranes (Grus americana), but some of these islands originally contained trees prior to European settlement. Conservation of at least some woodland habitats appears important for overwintering gartersnakes in central Nebraska.

Exogenous leptin promotes reproductive behavior during aphagia in red-sided garter snakes (Thamnophis sirtalis parietalis)

Despite the established dichotomy between investment in either reproduction or self-maintenance, a hormonal mechanism that influences an organism's decision to prioritize these behaviors remains elusive. The protein hormone leptin is a likely candidate because it is secreted from adipocytes in proportion to the amount of stored fat in numerous species. Although the majority of studies suggest that leptin stimulates reproduction, the actions of leptin can be context-dependent. Leptin increases sexual behavior in fed individuals, but inhibits sexual behavior in food-restricted individuals. We investigated if exogenous leptin influences sexual behavior in red-sided garter snakes (Thamnophis sirtalis parietalis) experiencing a predictable bout of aphagia during the mating season. We tested two doses of recombinant murine leptin injected for three days. Males were subjected to three mating trials, one on each day of injections, while females were subjected to one mating trial on the last day of injections. Leptin affects male and female snakes similarly by increasing both appetitive (i.e., mating behavior score) and consummatory (i.e., number of copulations, proportion of individuals copulated) sex behavior. We found no evidence to suggest that leptin influenced latency to copulate or duration of copulation. Because leptin promotes reproductive behavior in non-feeding garter snakes, these findings do not align with research on food-restricted mammals. Further investigations into how leptin affects sexual behavior in snakes exposed to food-restriction manipulations would clarify if the role of leptin is evolutionarily divergent.

Long-term monitoring of two snake species reveals immune-endocrine interactions and the importance of ecological context.

While there is huge promise in monitoring physiological parameters in free-living organisms, we also find high amounts of variability over time and space. This variation requires us to capitalize on long-term physiological monitoring to adequately address questions of population health, conservation status, or evolutionary trends as long-term sampling can examine ecoimmunological and endocrine interactions in wild populations while accounting for the variation that often makes ecophysiological field studies difficult to compare. In this study, we tested how immune efficacy and endocrinology interact while accounting for ecological context and environmental conditions in two snake species. Specifically, we measured bacterial killing ability, steroid hormones, and morphological characteristics in multiple populations of the Western Terrestrial Gartersnake (Thamnophis elegans) and Common Gartersnake (T. sirtalis) for multiple seasons over 6 years. Leveraging this long-term dataset, we tested how a broad immune measure and endocrine endpoints interact while accounting for individual traits, sampling date, and environmental conditions. Across both species, we found bacterial killing ability to be directly related to corticosterone(CORT) and temperature and greater overall in the spring compared to the fall. We found CORT and testosterone yielded relationships with individual sex, sampling temperature, and time of year. Wild populations can exhibit high amounts of variation in commonly collected physiological endpoints, highlighting the complexity and difficulty inherent in interpreting single endpoints without taking ecological and environmental conditions into account. Our study emphasizes the importance of reporting the environmental conditions under which the sampling occurred to allow for better contextualization and comparison between studies.

Energy Metrics of Red-Sided Garter Snakes (Thamnophis sirtalis parietalis) Vary with Sex but Not Life-History Stage

Because reproduction is energetically expensive, an organism's energy stores are likely involved in mediating transitions between reproductive and self-maintenance activities. We investigated whether body condition index, adipocyte follicle size, and liver glycogen differ with the life-history transition from reproduction to migration and foraging in red-sided garter snakes (Thamnophis sirtalis parietalis). Females primarily investing in mating behavior located at the den had a significantly higher body condition index than females migrating to summer feeding grounds. The body condition index of male snakes did not differ between snakes located at the den and those migrating to summer feeding grounds. Neither adipocyte follicle area nor liver glycogen stores differed significantly between snakes performing mating activities at the den and those migrating to summer feeding grounds. We did find a sexual dimorphism in that female red-sided garter snakes had significantly larger adipocyte follicles and higher liver glycogen compared with males. Our findings support the across-species phenomenon of females and males displaying a sexual dimorphism in stored energy substrates. Conversely, we did not find evidence to suggest that red-sided garter snakes primarily utilize fatty acids to fuel the initiation of migration, a finding that is not consistent with other long-distance migrators, such as birds. Because we did not find evidence to suggest that stored energy metrics influence the decision to migrate, a physiological mechanism that induces migration in red-sided garter snakes remains elusive.

Effects of intracoelomic alfaxalone–dexmedetomidine on righting reflex in common garter snakes (Thamnophis sirtalis): preliminary data

ObjectiveTo evaluate the effect of dexmedetomidine on alfaxalone immobilization in snakes. Study designNonblinded, crossover study. AnimalsA total of eight mature common garter snakes (Thamnophis sirtalis). MethodsSnakes were administered each of three treatments intracoelomically: alfaxalone (30 mg kg–1; treatment A), alfaxalone (30 mg kg–1) combined with dexmedetomidine (0.05 mg kg–1; treatment AD0.05); and alfaxalone (30 mg kg–1) combined with dexmedetomidine (0.10 mg kg–1; treatment AD0.10). A minimum of 10 days elapsed between experimental trials. Times to loss of righting reflex (LRR) and return of righting reflex (RRR) were recorded. Heart rate (HR) was recorded every 5 minutes throughout the period of LRR and averaged for each snake. Times to LRR and RRR, and mean HR in snakes that achieved LRR were reported. ResultsLRR occurred in eight (100%), five (63%) and three (38%) snakes in treatments A, AD0.05 and AD0.10, respectively. For all treatments, time to LRR ranged 3–20 minutes. Median (range) times to RRR were 39 (30–46), 89 (62–128) and 77 (30–185) minutes for treatments A, AD0.05 and AD0.10, respectively. In animals where righting reflex was lost, mean HR was lower in all dexmedetomidine treatments compared with treatment A. Conclusions and clinical relevanceIn this pilot study, alfaxalone resulted in reliable immobilization, whereas dexmedetomidine and alfaxalone combinations resulted in highly variable durations of immobilization with low HR in immobilized animals. For snakes that achieved LRR, the addition of dexmedetomidine (0.05 mg kg–1) to alfaxalone appeared to extend the period of immobilization compared with alfaxalone alone.

The geographic mosaic of arms race coevolution is closely matched to prey population structure.

Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co‐occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of “trait remixing” in the geographic mosaic theory, the process by which non‐adaptive forces dictate spatial variation in the interactions among species.

Sperm telomere length correlates with blood telomeres and body size in red‐sided garter snakes,Thamnophis sirtalis parietalis

AbstractTelomeres, tandem repeats of TTAGGG at the ends of chromosomes, are highly dynamic structures that shorten in response to a variety of factors, including organismal stress and tissue‐specific growth rates. Cell turnover rates are frequently linked to their functions, resource availability and telomere dynamics. Using male red‐sided garter snakes,Thamnophis sirtalis parietalis, as a model, we investigated the relationship between telomere length in sperm cells, blood cells telomere length and a growth proxy (age‐adjusted body length and mass). This relationship is interesting because snakes exhibit indeterminate growth and because these garter snakes have a dissociated reproductive cycle where spermatogenesis occurs months prior to the mating season. In this study, we determined sperm telomere length (STL) and male age using qPCR and skeletochronology, respectively. Sperm telomere length correlated positively with snout–vent length (SVL) and with age‐adjusted SVL as a proxy for growth rate (residuals of size against age regression, hereafter growth), but not with age. Although an individual’s STL is correlated with blood telomere length (BTL), sperm telomeres are 60% longer than blood telomeres. In previous work, we have shown that BTL is shorter in older males and unrelated to SVL or any growth rate proxies. We hypothesized that STL is related to growth and SVL because growth and sperm production both occur during summer when resources are most abundant and stress lowest. This study is the first to compare telomere dynamics between cell types in a snake and supports growing evidence that telomere dynamics may be highly tissue‐specific and driven by the life‐history strategy of an organism.

Combining genetic and demographic monitoring better informs conservation of an endangered urban snake.

Conversion and fragmentation of wildlife habitat often leads to smaller and isolated populations and can reduce a species' ability to disperse across the landscape. As a consequence, genetic drift can quickly lower genetic variation and increase vulnerability to extirpation. For species of conservation concern, quantification of population size and connectivity can clarify the influence of genetic drift in local populations and provides important information for conservation management and recovery strategies. Here, we used genome-wide single nucleotide polymorphism (SNP) data and capture-mark-recapture methods to evaluate the genetic diversity and demography within seven focal sites of the endangered San Francisco gartersnake (Thamnophis sirtalis tetrataenia), a species affected by alteration and isolation of wetland habitats throughout its distribution. The primary goals were to determine the population structure and degree of genetic isolation among T. s. tetrataenia populations and estimate effective size and population abundance within sites to better understand the present and future importance of genetic drift. We also used temporally sampled datasets to examine the magnitude of genetic change over time. We found moderate population genetic structure throughout the San Francisco Peninsula that partitions sites into northern and southern regional clusters. Point estimates of both effective size and population abundance were generally small (≤ 100) for a majority of the sites, and estimates were particularly low in the northern populations. Genetic analyses of temporal datasets indicated an increase in genetic differentiation, especially for the most geographically isolated sites, and decreased genetic diversity over time in at least one site (Pacifica). Our results suggest that drift-mediated processes as a function of small population size and reduced connectivity from neighboring populations may decrease diversity and increase differentiation. Improving genetic diversity and connectivity among T. s. tetrataenia populations could promote persistence of this endangered snake.

Captivity Affects Head Morphology and Allometry in Headstarted Garter Snakes, Thamnophis sirtalis.

In response to the growing number of amphibian and reptiles species in decline, many conservation managers have implemented captive breeding and headstarting programs in an effort to restore these populations. However, many of these programs suffer from low survival success, and it is often unclear as to why some individuals do not survive after reintroduction. Here I document changes to head morphology in the eastern garter snake, Thamnophis sirtalis, in response to time spent in captivity. Thamnophis raised on three diet treatments all differed in head size from wild individuals, and head size differed between the three treatments. Overall, head size was smaller in all three diet treatments than in wild snakes, potentially limiting the available prey for the captive garter snakes. Allometric patterns of growth in head size were also different for each diet treatment. Several potential implications of these changes in morphology are discussed, and what these changes may mean for other species that are part of headstarting and reintroduction programs.

Aggregation and social interaction in garter snakes (Thamnophis sirtalis sirtalis)

Previous research has shown that competition, familiarity, diet, and relatedness can all influence aggregation patterns in garter snakes. We controlled for these factors and examined social aggregation patterns in juvenile Eastern garter snakes (Thamnophis sirtalis sirtalis). We assayed snakes individually for consistent individual differences in boldness and sociability. We then placed snakes in groups of 10 in an enclosure with four shelters and observed their social interactions over a period of 8 days. We demonstrate that the snakes actively seek social interaction, prefer to remain with larger aggregates, and associate nonrandomly with specific individuals or groups. We show that their social interaction patterns are influenced by individual boldness, sociability, and age. The snakes’ social networks were perturbed twice a day by “shuffling” their locations. Despite these disturbances, the snakes eventually re-formed their preferred social environment. Aggregation and exploration patterns also varied across time, with most activity occurring later in the day. These results highlight the complexity of snake sociality and may have important implications for conservation efforts. Snakes are often considered nonsocial animals, but this is inaccurate. We used social network analyses to compare juvenile Eastern garter snakes’ group behaviors to their individual personalities. Our research demonstrates that these snakes actively seek out social interaction and prefer to join and remain with larger groups and that their social interaction patterns are influenced by consistent individual differences in boldness and sociability. Our work contributes to a sparse but growing body of literature on sociability in reptiles. This work is important for changing perceptions among the scientific community and the public as a whole. As a consequence, it may aid efforts in developing appropriate conservation techniques that consider sociability patterns in relocated reptiles.

The geographic mosaic in parallel: Matching patterns of newt tetrodotoxin levels and snake resistance in multiple predator-prey pairs.

The Geographic Mosaic Theory of Coevolution predicts that coevolutionary arms races will vary over time and space because of the diverse ecological settings and population histories of interacting species across the landscape. Thus, understanding coevolution may require investigating broad sets of populations sampled across the range of the interaction. In addition, comparing coevolutionary dynamics between similar systems may reveal the importance of specific factors that structure coevolution. Here, we examine geographic patterns of prey traits and predator traits in the relatively unstudied interaction between the Sierra garter snake (Thamnophis couchii) and sympatric prey, the rough-skinned newt (Taricha granulosa), Sierra newt (Ta. sierrae) and California newt (Ta. torosa). This system parallels, in space and phenotypes, a classic example of coevolution between predatory common garter snakes (Th. sirtalis) and their toxic newt prey exhibiting hotspots of newt tetrodotoxin (TTX) levels and matching snake TTX resistance. We quantified prey and predator traits from hundreds of individuals across their distributions, and functional trait matching at sympatric sites. We show strong regional patterns of trait covariation across the shared ranges of Th. couchii and newt prey. Traits differ significantly among localities, with lower newt TTX levels and snake TTX resistance at the northern latitudes, and higher TTX levels and snake resistance at southern latitudes. Newts and snakes in northern populations show the highest degree of functional trait matching despite possessing the least extreme traits. Conversely, newts and snakes in southern populations show the greatest mismatch despite possessing exaggerated traits, with some snakes so resistant to TTX they would be unaffected by any sympatric newt. Nevertheless, individual variation was substantial, and appears to offer the opportunity for continued reciprocal selection in most populations. Overall, the three species of newts appear to be engaged in a TTX-mediated arms race with Th. couchii. These patterns are congruent with those seen between newts and Th. sirtalis, including the same latitudinal gradient in trait covariation, and the potential 'escape' from the arms race by snake predators. Such concordance in broad scale patterns across two distinct systems suggests common phenomena might structure geographic mosaics in similar ways.

Sex linkage of the skeletal muscle sodium channel gene (SCN4A) explains apparent deviations from Hardy-Weinberg equilibrium of tetrodotoxin-resistance alleles in garter snakes (Thamnophis sirtalis).

The arms race between tetrodotoxin-bearing Pacific newts (Taricha) and their garter snake predators (Thamnophis) in western North America has become a classic example of coevolution, shedding light on predator-prey dynamics, the molecular basis of adaptation, and patterns of convergent evolution. Newts are defended by tetrodotoxin (TTX), a neurotoxin that binds to voltage-gated sodium channels (Nav proteins), arresting electrical activity in nerves and muscles and paralyzing would-be predators. However, populations of the common garter snake (T. sirtalis) have overcome this defense, largely through polymorphism at the locus SCN4A, which renders the encoded protein (Nav1.4) less vulnerable to TTX. Previous work suggests that SCN4A commonly shows extreme deviations from Hardy-Weinberg equilibrium (HWE) in these populations, which has been interpreted as the result of intense selection imposed by newts. Here we show that much of this apparent deviation can be attributed to sex linkage of SCN4A. Using genomic data and quantitative PCR, we show that SCN4A is on the Z chromosome in Thamnophis and other advanced snakes. Taking Z-linkage into account, we find that most apparent deviations from HWE can be explained by female hemizygosity rather than low heterozygosity. Sex linkage can affect mutation rates, selection, and drift, and our results suggest that Z-linkage of SCN4A may make significant contributions to the overall dynamics of the coevolutionary arms race between newts and snakes.

Responses of grassland snakes to tallgrass prairie restoration

Understanding faunal responses to habitat restoration is important in assessing restoration success. We investigated occupancy and abundance of snakes at Nachusa Grasslands, a large‐scale grassland restoration in the midwestern United States. Using artificial cover objects, we sampled within a chronosequence of 12 units converted from row‐crop agriculture 2–25 years before the start of our study. Recaptures of marked snakes revealed that movement distances differed among species in accordance with differences in body size, being least in Dekay's Brownsnakes, intermediate in the Plains Gartersnakes and Common Gartersnakes, and greatest in Eastern Foxsnakes. Consistent with this result, occupancy increased with restoration age in Dekay's Brownsnakes but was unrelated to restoration age in the three larger, more mobile species. Similarly, abundance increased with restoration age in Dekay's Brownsnake but was unrelated to restoration age in other species. The Smooth Greensnake, another small‐bodied snake with limited mobility, and an Illinois species of greatest conservation need, was not detected at Nachusa Grasslands. Given detection probabilities observed during a parallel study at a nearby large grassland‐dominated preserve, we infer that the Smooth Greensnake is truly absent from Nachusa Grasslands. Taken together, our results demonstrate that establishment of faunal components following restoration may be time‐dependent with more sedentary species colonizing only slowly (e.g. Dekay's Brownsnakes) or not at all (e.g. Smooth Greensnakes). These results emphasize the need to clearly identify faunal restoration goals and the means to achieve them.

Courtship in the male red-sided garter snake is dependent on neural aromatase activity during winter dormancy.

The red-sided garter snake exhibits a dissociated reproductive pattern, mating at a time when their gonads are quiescent and circulating sex steroids, initially reported to be low, have been found to be elevated during the breeding season. However, the only cue identified that initiates courtship behavior and mating in the red-sided garter snake is an extended period of low-temperature dormancy (LTD) followed by exposure to warm temperatures. In this study, we examined a possible association between winter dormancy, sex steroid hormone metabolism, and initiation of reproductive behavior in the male red-sided garter snake. Upon emergence from winter dormancy, courtship behavior was assessed using attractive females as stimuli. Animals receiving implants containing 1,4,6-androstatriene-3,17-dione (ATD), an aromatase inhibiter, showed little or no courtship behavior, while animals implanted with ATD + 17β estradiol (E2 ) or blank implants exhibited normal courtship. In addition, neurons in the pathways critical in the control of reproductive behavior were examined using the Golgi method. Examination of brains collected upon emergence revealed animals implanted with ATD had a significantly reduced number of dendritic spines compared to controls and animals treated with ATD + E2 . This study provides the first documentation that courtship behavior and mating in the male red-sided garter snake appears to be controlled not by LTD alone, but in conjunction with sex steroid hormones. Moreover, behavioral data suggest that the aromatization of androgens during LTD appears to be critical for the initiation of reproductive behavior in the male red-sided garter snakes.

CONSERVATION BIOLOGY OF A SOUTHWESTERN ENDEMIC, THE TEXAS GARTER SNAKE, THAMNOPHIS SIRTALIS ANNECTENS: AN INTEGRATIVE PERSPECTIVE

We investigate the taxonomic status of the Texas garter snake, Thamnophis sirtalis annectens, a species of greatest conservation need in Texas. We broadly test the hypothesis that an integrative approach to species conservation has greater utility than using only a single data type (e.g., molecular, morphological, behavioral, or ecological) by demonstrating how ecological niche modeling and molecular genetics can be used synergistically to resolve taxonomic classifications. Using a phylogenetic analysis based on molecular data, we found that some putative T. s. annectens specimens actually represent a co-occurring subspecies (the red-sided garter snake, Thamnophis sirtalis parietalis), which is not of conservation concern. However, both T. s. annectens and T. s. parietalis are genetically distinctive from another co-occurring subspecies, Thamnophis sirtalis sirtalis, and the ecological distinctness of T. s. annectens from T. s. parietalis suggests that T. s. annectens is, in fact, a distinct evolutionary subunit. Only when both genetic and ecological information were included was the distinctiveness of T. s. annectens apparent, thus highlighting the need for integrative approaches in conservation management regardless of the taxa in question.

Neuronal plasticity in the forebrain of the male red-sided garter snake: Effect of season, low temperature dormancy, and hormonal status on dendritic spine density

Numerous studies have reported seasonal variations in regional morphology in the brains of seasonally breeding vertebrates. These alterations of neuronal morphology and dendritic spine density appear to be an active process within specific brain nuclei that regulate seasonal behaviors. In many cases, this neural plasticity has been found to be in response to changes in circulating sex steroid hormone levels and occur within pathways essential for the control of reproductive behaviors. Male red-sided garter snakes (Thamnophis sirtalis parietalis) (RSGS) exhibit a dissociated reproductive pattern where mating is initiated at a time when the gonads and steroidogenesis are inactive. And, although circulating levels of sex steroid hormones are elevated at the initiation of courtship and mating, the only known cue found to initiate courtship behavior and mating, is an extended period of low temperature dormancy (LTD) followed by exposure to warm temperatures. This study was designed to examine the role of seasons, sex steroid hormones, and LTD on neuronal and dendritic spine density within the anterior hypothalamus-preoptic area (AHPOA), a region shown to be critical for the regulation of reproductive behaviors. In the male RSGS, the density of dendritic spines on neurons in the AHPOA was significantly greater in spring, actively courting animals, than summer or fall, non-courting animals. Animals maintained under conditions of LTD exhibited significantly increasing spine density as time maintained in LTD increased. Animals receiving either testosterone or estradiol had a significantly greater density of dendritic spines than control animals. This study offers evidence suggesting that the “set up” of the pathways controlling courtship behavior and mating in the male RSGS, is not due solely to an extended period of LTD, but that an extended period of LTD in conjunction with circulating sex steroid hormones are critical for the initiation of reproductive behavior.

Comparison of Body Temperatures across Physiological States in Syntopic Snake Species (Thamnophis sirtalis and Nerodia sipedon) from Pennsylvania

Physiological states in snakes, such as digestion, gestation, and ecdysis, have been associated with different body temperatures (BT), yet few studies have examined these associations in a comparative context for wild-caught animals. We collected body and environmental temperatures for 2 natricine snake species—Thamnophis sirtalis (Common Gartersnake) and Nerodia sipedon (Common Watersnake)—from 4 artificial wetlands at the Letterkenny Army Depot, Franklin County, PA. We measured thermal data and associated microclimates from snakes captured under tin cover boards during monthly searches from Spring to Fall of 2012 (April–October). From 47 Common Gartersnakes and 20 Common Watersnakes, we found that most individuals of both species had a BT between 20 and 30 °C, which is consistent with data from other populations. Inter- and intraspecific comparisons of snake BTs in different physiological states revealed that Common Gartersnakes operated at higher temperatures than Common Watersnakes. Common Watersnakes thermoregulated within a generally narrower range of temperatures than Common Gartersnakes. The wide-ranging thermal ecology of the Common Gartersnake may facilitate its flexibility to occupy many habitats across an extensive geographic distribution and perhaps predispose it to greater adaptability in a changing thermal environment. We summarize our data on snake BTs and their associations with relevant environmental temperatures, discuss snake BT ranges across distinct physiological groups, and compare our results to those of other snake populations. Our findings provide a baseline to understand the degree to which operating snake temperatures, and consequently physiological processes, will change because of future warming in the Northeast.