Species Of Water Snakes Research Articles

Investigating relationships among stress, reproduction, and immunity in three species of watersnake

Energy is a finite resource required for all physiological processes and must be allocated efficiently among essential activities to ensure fitness and survival. During the active season, adult organisms are expected to prioritize investment in reproduction over other energetically expensive processes, such as responding to immunological challenges. Furthermore, when encountering a stressor, the balance between reproduction and immunity might be disrupted in order to fuel the stress response. Because of the distinct differences in life histories across species, watersnakes provide a unique group of study in which to examine these tradeoffs. Over a two-year period, we captured three watersnake species throughout Northeast Arkansas. Animals were subjected to restraint stress and blood samples were collected throughout the acute stress response. Blood samples were used to assess innate immunity and steroid hormone concentrations. We found the peak in corticosterone concentration is season-specific, potentially because energetic reserves fluctuate with reproductive activities. We also found body condition was positively related to acute stress and negatively related to immunity. Watersnakes evidently prioritize reproduction over immunity, especially during the energetically intensive process of vitellogenesis. Energetic tradeoffs between reproduction, immunity, and the stress response are complex, and this study contributes to our understanding of energetic shifts in free-living organisms in the context of stress.

Divergent Genital Morphologies and Female-Male Covariation in Watersnakes.

Genital evolution can be driven by diverse selective pressures. Across taxa we see evidence of covariation between males and females, as well as divergent genital morphologies between closely related species. Quantitative analyses of morphological changes in coevolving male and female genitalia have not yet been shown in vertebrates. This study uses 2D and 3D geometric morphometrics to quantitatively compare the complex shapes of vaginal pouches and hemipenes across three species of watersnakes (the sister taxa Nerodia fasciata, N. sipedon, and a close relative N. rhombifer) to address the relationship between genital morphology and divergence time in a system where sexual conflict may have driven sexually antagonistic coevolution of genital traits. Our pairwise comparisons of shape differences across species show that the sister species have male and female genitalia that are significantly different from each other, but more similar to each other than to N. rhombifer. We also determine that the main axes of shape variation are the same for males and females, with changes that relate to deeper bilobation of the vaginal pouch and hemipenes. In males, the protrusion of the region of spines at the base of the hemipene trades off with the degree of bilobation, suggesting amelioration of sexual conflict, perhaps driven by changes in the relative size of the entrance of the vaginal pouch that could have made spines less effective.

Corticosterone in three species of free-ranging watersnakes: Testing for reproductive suppression and an association with body condition

The potentially suppressive effects of the hypothalamic-pituitary-adrenal (HPA) axis on the hypothalamic-pituitary-gonadal (HPG) axis revolve around the central role that glucocorticoids play in mobilizing energy. As an individual's energy balance becomes negative, the HPA axis helps mobilize energy and shifts energy expenditure away from reproduction toward maintenance and survival. While there is evidence in support of these relationships, substantial species variability exists. Studies in a greater diversity of species promise to enhance our understanding of the interactions between these axes. In this field study we tested for relationships among body condition, corticosterone, and sex steroid concentrations in three species of closely related watersnakes: the common watersnake (Nerodia sipedon), the diamondback watersnake (Nerodia rhombifer) and the queen snake (Regina septemvittata). Snakes were sampled before and after a 30 min acute confinement stressor and body condition was estimated using the scaled mass index. All three species exhibited robust elevations of corticosterone in response to acute stress, but only plasma progesterone was elevated by the acute stressor in queen snakes. There was no evidence for a suppression of sex steroid concentrations in any of the species. Body condition was negatively associated with baseline corticosterone in queen snakes and with post-stressor corticosterone in both queen and common watersnakes. Overall we found fairly strong support for the proposed link between corticosterone and energetics in two of the three watersnake species, but no support for the hypothesis that acute stressors are associated with reproductive suppression, at least as measured by steroid concentrations.

A new oviparous species of Helicops Wagler, 1828 (Serpentes, Xenodontinae) from Brazilian Amazonia with reflections on the evolution of viviparity among hydropsine watersnakes

We describe a new watersnake species of the genus Helicops from the left bank of the upper Madeira River, southwestern Amazonia, Brazil. Due to its spotted dorsal pattern, it resembles the sympatric species H. hagmanni, H. leopardinus, and H. polylepis, but a combination of features including, scale counts, prominence of dorsal keels, and hemipenial morphology allows its unequivocal recognition. The new species also exhibits oviparous reproduction, representing the fourth egg-laying lineage reported in the genus. The evolution of viviparity among the lineages of Helicops comprises an important debate in the field of the natural history of reptiles, especially regarding the highly unlikely possibilities of reversals from viviparity to oviparity due to constraints of genetic, ecological, and physiological nature. Based on such premises, we reconstructed the reproductive modes within the genus using a preconceived topology and discussed hypothetical scenarios for the emergence of viviparity depending on three possible positions of the new taxon. Finally, we also provide considerations on the apparent restriction of this snake to the left bank of the upper Madeira in the light of classic biogeographic evidence that points to the potential role of this major river as a vicariant element between faunas on its opposite margins.

Multi-decadal trends in mercury and methylmercury concentrations in the brown watersnake (Nerodia taxispilota).

Mercury (Hg) is an environmental contaminant that poses a threat to aquatic systems globally. Temporal evaluations of Hg contamination have increased in recent years, with studies focusing on how anthropogenic activities impact Hg bioavailability in a variety of aquatic systems. While it is common for these studies and ecological risk assessments to evaluate Hg bioaccumulation and effects in wildlife, there is a paucity of information regarding Hg dynamics in reptiles. The goal of this study was to investigate temporal patterns in total mercury (THg) and methylmercury (MeHg) concentrations across a 36-year period, as well as evaluate relationships among and between destructive (kidney, liver, muscle) and non-destructive (blood, tail) tissue types in a common watersnake species. To accomplish this, we measured THg and MeHg concentrations in multiple tissues from brown watersnakes (Nerodia taxispilota) collected from Steel Creek on the Savannah River Site (SRS; Aiken, SC, USA) from two time periods (1983-1986 and 2019). We found significant and positive relationships between tail tips and destructive tissues. In both time periods, THg concentrations varied significantly by tissue type, and destructive tissues exhibited higher but predictable THg values relative to tail tissue. Methylmercury concentrations did not differ among tissues from the 1980s but was significantly higher in muscle compared to other tissues from snakes collected in 2019. Percent MeHg of THg in N.taxispilota tissues mirrored patterns reported in other reptiles, although the range of % MeHg in liver and kidney differed between time periods. Both THg and MeHg concentrations in N.taxispilota declined significantly from the 1980s to 2019, with average values 1.6 to 4-fold lower in contemporary samples. Overall, our data add further evidence to the utility of watersnakes to monitor Hg pollution in aquatic environments and suggest attenuation of this contaminant in watersnakes in our study system.

Long known, brand new, and possibly threatened: a new species of watersnake of the genus Helicops Wagler, 1828 (Serpentes; Xenodontinae) from the Tocantins-Araguaia River Basin, Brazil.

We describe a new species of watersnake of the genus Helicops from the Tocantins-Araguaia River Basin based on characters of coloration and hemipenial morphology, also corroborated by a molecular phylogenetic analysis including 18 terminals of 10 additional congeners. The new species superficially resembles the spotted-patterned He. leopardinus, but differs from it in exhibiting dorsal spots fused into irregular bands, and a unique hemipenial structure with two pairs of distinctly enlarged basal spines. In addition, despite the superficial resemblance of color pattern, our genetic evidence indicates that the new species does not belong to the He. leopardinus radiation, representing the sister group of a component including terminals of this species, He. modestus, and He. infrataeniatus. Finally, we discuss the apparent restriction of the new species to the Tocantins-Araguaia Basin with focus on vicariant processes that may have promoted its differentiation, as well as on the conservation challenges in an area severely affected by anthropic impacts associated with the rapid expansion of hydroelectric and agricultural sectors in the Brazilian Cerrado.

Brown watersnakes (Nerodia taxispilota) as bioindicators of mercury contamination in a riverine system

Mercury (Hg) is a contaminant that enters the environment through natural or anthropogenic means. Ecological risk assessments have examined Hg bioaccumulation and effects in many taxa, but little is known about Hg dynamics in reptiles, or their potential use as bioindicator species for monitoring Hg in aquatic systems. Numerous snake species, like North American watersnakes (Nerodia spp.), are piscivorous and are exposed to Hg through their diet. The purpose of this study was to identify factors associated with Hg accumulation in a common watersnake species and compare Hg concentrations of the snakes to those in fish occupying the same habitats. To this end, we sampled brown watersnakes (Nerodia taxispilota) from the Savannah River, a major river system in the southeastern U.S., and compared N. taxispilota Hg accumulation trends to those of bass (Micropterus salmoides), catfish (Ictalurus and Ameiurus spp.), and panfish (Lepomis and Pomoxis spp.) collected from the same reach. Total Hg (THg) in N. taxispilota tail tips ranged from 0.020 to 0.431 mg/kg (wet weight; mean: 0.104 ± 0.008). Snake tail THg was significantly correlated with blood THg, which ranged from 0.003 to 1.140 mg/kg (0.154 ± 0.019). Snake size and site of capture were significantly associated with tail THg. Snake tail THg increased at sites along and downstream of the area of historic Hg pollution, consistent with fish THg. Snake muscle THg was predicted based on tail THg and ranged from 0.095 to 1.160 (0.352 ± 0.022). To gauge Hg biomagnification in N. taxispilota, we compared predicted snake muscle THg concentrations to THg in fish of consumable size. Average biomagnification factors for THg in N. taxispilota were 3.1 (panfish) and 5.4 (catfish), demonstrating N. taxispilota likely biomagnify Hg through their diet. These results reveal N. taxispilota to be an effective bioindicator species for monitoring Hg in aquatic environments.

Intraspecific dietary variation in niche partitioning within a community of ecologically similar snakes

Niche partitioning is an important mechanism for allowing ecologically similar species to coexist, contributing to biodiversity and the functioning of ecological communities. Species partition niches by taking advantage of environmental heterogeneity. However, niche partitioning and species coexistence investigations often do not include intraspecific variation or individual differences like sex and body size even though these factors can have important ecological consequences. Such intrapopulation factors can reduce the number of individuals among species that overlap in resource use and potentially facilitate coexistence. Using stable isotopes (δ13C and δ15N), we quantified dietary differences among three ecologically similar, sympatric watersnake species: Nerodia erythrogaster, N. rhombifer and N. sipedon. Additionally for each species, we determined intraspecific dietary patterns and determined how those within-species patterns may contribute to dietary niche partitioning among species. Nerodia erythrogaster fed more on terrestrial prey, while N. rhombifer fed at higher trophic levels. Females across species fed at higher trophic levels than did males, and isotopic variance differed between the sexes in N. sipedon. Larger watersnakes foraged at higher trophic levels and fed more on terrestrial prey. Each watersnake species had a distinct diet that overlapped to some degree with the other species’ diets, but these diets varied both between sexes and among size groups within species. This inter- and intraspecific dietary variation can facilitate species coexistence by reducing the number of individuals from all species that use the same resources. Intraspecific variation can add important and nuanced layers to the evolution of species coexistence, and research on interspecific niche relationships needs to increasingly consider the effects of these intraspecific variations.

Chance, luck and a fortunate finding: a new species of watersnake ofthe genus Helicops Wagler, 1828 (Serpentes: Xenodontinae), from the Brazilian Pantanal wetlands.

We describe a new watersnake of the genus Helicops based on a single specimen found in the northern limit of the Brazilian Pantanal. Immediately after collection, the unique features of color pattern and head proportions prevented us to attribute this specimen to any other congener. Further comparisons revealed that the combination of entire nasal scales, a distinctively acuminate snout, high dorsal and supralabial counts, as well as a dorsal pattern with chain-like spot rows and a venter with vivid and peculiar orange markings confirmed that the specimen represented a new species. Molecular data supported our morphological conclusion recovering the new species deeply nested within Helicops terminals, sister to a clade composed by H. carinicaudus and H. nentur. Our discovery represents a rare instance of a snake species restricted to the Brazilian Pantanal, but we refrain from considering it a Pantanal endemic until further records allow more considerations on distributional patterns.

Traditional trapping methods outperform eDNA sampling for introduced semi-aquatic snakes.

Given limited resources for managing invasive species, traditional survey methods may not be feasible to implement at a regional scale. Environmental DNA (eDNA) sampling has proven to be an effective method for detecting some invasive species, but comparisons between the detection probability of eDNA and traditional survey methods using modern occupancy modeling methods are rare. We developed a qPCR assay to detect two species of watersnake (Nerodia fasciata and Nerodia sipedon) introduced to California, USA, and we compared the efficacy of eDNA and aquatic trapping. We tested 3–9 water samples each from 30 sites near the known range of N. fasciata, and 61 sites near the known range of N. sipedon. We also deployed aquatic funnel traps at a subset of sites for each species. We detected N. fasciata eDNA in three of nine water samples from just one site, but captured N. fasciata in traps at three of ten sites. We detected N. sipedon eDNA in five of six water samples from one site, which was also the only site of nine at which this species was captured in traps. Traditional trapping surveys had a higher probability of detecting watersnakes than eDNA surveys, and both survey methods had higher detection probability for N. sipedon than N. fasciata. Occupancy models that integrated both trapping and eDNA surveys estimated that 5 sites (95% Credible Interval: 4–10) of 91 were occupied by watersnakes (both species combined), although snakes were only detected at four sites (three for N. fasciata, one for N. sipedon). Our study shows that despite the many successes of eDNA surveys, traditional sampling methods can have higher detection probability for some species. We recommend those tasked with managing species invasions explicitly compare eDNA and traditional survey methods in an occupancy framework to inform their choice of the best method for detecting nascent populations.

Watersnakes Prey on Invasive Fishes in an Urban Canal in Southern Florida

Abstract Canals in southern Florida are populated by a variety of invasive fish species, but interactions between these invasive fishes and native species are poorly understood. Watersnakes are documented predators of fishes and are well studied in many portions of their range; however, few studies have addressed their ecology and life history in the expansive southern Florida canal system. I captured individuals of 2 watersnake species in a canal in a residential southern Florida neighborhood to determine which fish species were preyed upon. I recovered 4 prey items, all of which were invasive fishes.

Diet Composition and Foraging Habitat Use by Three Species of Water Snakes,HelicopsWagler, 1830, (Serpentes: Dipsadidae) in Eastern Brazilian Amazonia

Abstract Water snakes of the genus Helicops have different uses of food resources that can facilitate species coexistence. To assess diet and foraging habitat of water snakes in eastern Brazilian Amazonia, we used prey consumed by Helicops angulatus, Helicops hagmanni, and Helicops polylepis deposited in scientific collections to analyze variations in composition, breadth, and niche overlap on a regional scale. Among these prey, we used fish (main item) to calculate ecomorphological attributes that might indicate fish habitat and, consequently, the foraging habitat used by snakes. Our analyses indicate these three snake species have similar diet compositions but differ in the proportion in which each item is consumed. Helicops angulatus had the most generalized diet and H. hagmanni had the most specialized diet. Food niche overlap among the three species was moderate. All three species forage in the medium and upper strata of the water column in the lentic zone; however, H. polylepis feeds on prey with va...

The relationship of head morphology and diet among three sympatric watersnake species

Abstract Investigating dietary resource utilization and head morphology of gape-limited predators can provide a basis for understanding interspecific competition and species coexistence. For sympatric species, convergence of head morphology can indicate similar prey or foraging strategies while divergence can suggest competition, resource partitioning or expansion into new habitats. Sexual dimorphism can further complicate the head morphology-diet relationship by potentially reducing intraspecific competition. To understand the relationship between head morphology and diet, we studied three sympatric species, the plain-bellied (Nerodia erythrogaster), diamondback (N. rhombifer), and northern (N. sipedon) watersnakes in western Kentucky. All three species inhabit similar wetlands and feed on amphibians and fishes. The anurophagous plain-bellied watersnakes had longer, narrower heads that likely allow snakes to capture anuran metamorphs and froglets while facilitating movement through dense vegetation. The piscivorous diamondback watersnake had a wider head, which would enhance contact with prey in this open-mouth forager, and smaller interocular distance, resulting in dorsally placed eyes that facilitate seeing fish prey from below. The mostly piscivorous northern watersnake had an intermediate, generalized head shape, which may reflect the typically wide diet range of this species. Head shape did not differ between snake sexes but diamondback and northern females had larger heads than males and fed more frequently on fishes. The relationship between head morphology and diet highlights potential interspecific and intersexual competition and aids in the understanding of species coexistence patterns.

Intraspecific and interspecific variation of female genitalia in two species of watersnake

The morphological differences in female genitalia within and between species are little studied and poorly understood, yet understanding patterns of variation in female genitalia can provide insights into mechanisms of genital evolution. The present study aimed to explore the patterns of intraspecific and interspecific variation in female genitalia in two sister taxa of watersnake (Nerodia sipedon and Nerodia fasciata) that have similar genital shape. We used a geometric morphometric (GM) approach to study variation in shape of the vagina between and within two sister species. We examined genital shape in female watersnakes ranging from small, sexually immature females to large reproductive females that had recently given birth. We found that shape variation of genitalia is strongly correlated with body size, where larger but not smaller females have a bifurcation in the vagina. However, we also found significant shape variation in the structure of the vagina between the two species, where N. fasciata has narrower genitalia with more prominent bifurcation, whereas N.sipedon has wider genitalia with less marked bifurcation. Using GM allowed us to detect significant differences in genital shape that were not apparent upon visual examination alone, suggesting that shape variation in female genitalia may be greater than previously assumed. Additional study of morphological differences in male reproductive organs for these species would help to determine whether there has been genital co-evolution, and potentially mechanical reproductive isolation, in these two closely-related and occasionally sympatric species. © 2013 The Linnean Society of London.

Comparative immunolocalization of Na+/K+‐ATPase and Na+/K+/2Cl− cotransporter in the kidneys of freshwater and marine snakes

In contrast with the marine sea snakes, watersnakes in the genus Nerodia are not known to have functional salt glands. Despite this physiological difference, at least two species of watersnake are known to inhabit marine environments; the remaining members of this genus occupy freshwater habitats. The mechanism by which marine watersnakes regulate ion balance without functional salt glands is unknown. In this study, we compared the cellular anatomy of kidneys from two species of watersnake, Nerodia fasciata (freshwater) and N. clarkii (marine), and one species of sea snake, Laticauda semifasciata (marine). Specifically, we examined the localization of Na+/K+‐ATPase (NKA) and Na+/K+/2Cl− cotransporter (NKCC), two proteins that are known to regulate membrane potential and drive salt secretion in all vertebrate secretory cells examined to date. Using histology and immunohistochemistry, we localized NKA and NKCC to the basolateral membranes of the distal tubules in all three species of snake. These results are consistent with the localization of these proteins in other secretory tissues such as the gills of teleost fishes and the salt glands of marine elasmobranchs, birds, and reptiles, and suggest a potential role for ion regulation at the level of the kidney. This research was funded by the National Geographic Society (8058‐06 to HBL) and the National Science Foundation (IOB‐0519579 to DHE).

Transcontinental Introductions of Watersnakes (Nerodia) into California

Author(s): Balfour, Peter S.; Stitt, Eric W. | Abstract: The watersnakes (Nerodia) are a group of semi-aquatic snakes native to North America, primarily east of the Rocky Mountains. Five populations of 3 watersnake species have become established in California. In the northern Sacramento area, more than 100 southern watersnakes (N. fasciata), including numerous gravid females, have been captured since their discovery in 1992. Thus far, this population is known from two tributaries of the American River. In southern California, another southern watersnake population is known from Harbor Park Lake, a semi-isolated urban lake in Los Angeles County. A population of northern watersnakes (N. sipedon) has become established in Roseville, CA, and until the mid-1990s a dense population of diamondbacked watersnakes (N. rhombifer) flourished at Lafayette Reservoir in Contra Costa County. These are potentially worrisome introductions because watersnakes share numerous traits with other invasive aquatic species, including a wide breadth of physiological tolerances, large native distributional ranges, and they occur in many different freshwater types. Watersnakes can be highly fecund, are viviparous, and readily disperse. They are generalist predators that coevolved with many of the aquatic vertebrates now inhabiting western waters. As such, introduced Nerodia pose potential threats to native wildlife, including special status species such as the federally-listed threatened giant gartersnake. To address issues surrounding the management, eradication, or control of Nerodia populations in the western states, concerned biologists formed the multi-agency Nerodia Working Group. Short-term goals of the group include experimental eradication/control of the southern California population, listing Nerodia as a restricted genus under Section 671 of Title 14 of California’s Code of Regulations, and conducting outreach to the pet trade and other groups to raise awareness about these potentially invasive species.

STATUS AND DISTRIBUTION OF THE GREY-HEADED FISH-EAGLE (ICHTHYOPHAGA ICHTHYAETUS) IN THE PREK TOAL CORE AREA OF TONLE SAP LAKE, CAMBODIA

ABSTRACT The regional population of the Grey-headed Fish-Eagle (Ichthyophaga ichthyaetus) in Southeast Asia is thought to be in recent decline and its conservation status under threat. We undertook a systematic survey in a flooded swamp forest at the Tonle Sap Lake in Cambodia and recorded 32 pairs of eagles in an area of approximately 80 km2. Three species of water snakes were identified as eagle prey items, previously unrecorded for this species. We suggest that this eagle population has significant regional importance and discuss potential anthropogenic threats to population stability, such as water snake harvesting and construction of upstream hydropower dams.

Beyond the wetland border: Estimating the impact of roads for two species of water snakes

We used models integrating road maps, traffic volume, and snake movements to examine the potential for roads to contribute to mortality in two species of water snakes that differ in their vagility, use of terrestrial habitats, and conservation status. Road networks and traffic volumes typical of three regions in Indiana, USA, may account for mortality of 14–21% of the population per year in the more vagile, terrestrial, and imperiled copperbelly water snake ( Nerodia erythrogaster neglecta) but only 3–5% mortality in the more sedentary, aquatic, and common northern water snake ( Nerodia sipedon). The majority (>91%) of road crossings and associated mortality are predicted to occur during overland migrations to other wetlands, suggesting roads bisecting travel routes between wetlands may function as mortality sinks. Our models highlight the proportionately greater risk of mortality for the more vagile and imperiled species, N. e. neglecta, and suggest current wetland conservation strategies that focus on the wetland alone are unlikely to adequately protect wetland biodiversity from certain types of anthropogenic habitat modification. What is needed is a landscape approach to wetland conservation that considers not only the quality of wetlands and nearby terrestrial habitats, but also ensures that terrestrial corridors between wetlands remain permeable and offer safe passage for wildlife.

Habitat Separation among Three Species of Water Snakes in Northwestern Kentucky

Historical records and recent studies indicate that populations of the Copperbellied Watersnake (Nerodia erythrogaster neglecta) are in decline. Reduction in range and fragmentation of populations are largely based on human activities, primarily through alteration of shallow wetlands. We conducted a comparative study of habitat use to determine why N. e neglecta may be more vulnerable to human-induced changes than sympatric congeners. Nerodia erythrogaster neglecta were observed primarily along shorelines with gentle slopes near very shallow water and often used herbaceous vegetation, logs, grasses, and sedges substrate categories. Nerodia sipedon pleuralis used habitat most similar to N. e. neglecta. Although N. s. pleuralis were observed to be more aquatic and were more often found in open water, they showed the same close association with shorelines and basking substrates as N. e. neglecta. Nerodia rhombifer is the least selective in habitat use of the three species and is the least similar in habitat use to N. e. neglecta in this study. As a whole, the results of this study support previous research that suggests N. e. neglecta is a seasonal habitat specialist. The extensive destruction of seasonal wetlands in the Midwest may thus have a greater impact on N. e. neglecta than their sympatric congeners.

Organochlorine residue levels in Mississippi River water snakes in southern Louisiana.

This study was designed to determine the usefulness of water snakes in pollution monitoring. This was accomplished by assessing the organochlorine load in tissues of snakes inhabiting three sites along the Mississippi River near Baton Rouge, Louisiana. Two species of water snakes, Nerodia rhombifera and Nerodia cyclopion, were chosen for analysis of chlorinated hydrocarbons. Fishes account for 95.2 and 98.4%, respectively, of the total volume of food consumed by N. rhombifera and N. cyclopion. Thus, the organochlorine load of both species should reflect considerable biomagnification relative to water column levels.