Semi-aquatic Snakes Research Articles

Demographic effects of prolonged drought on a nascent introduction of a semi-aquatic snake

Faced with a nascent introduction of a non-native species, conservationists need to quickly determine how a population performs in its new environment. Although correlative models can predict environmental suitability at a coarse scale, they often neglect short-term climatic variability, instead relying on long-term averages. Accurately projecting the fate of any particular introduction requires demographic data on how a population responds to a novel environment. The recent introduction of watersnakes (genus Nerodia) poses a risk to California’s already imperiled aquatic vertebrate fauna. Despite inhabiting a seemingly suitable climate, a non-native Nerodia sipedon population in central California is likely to have been affected by a prolonged extreme drought from 2012 to 2015. We studied the only known population of N. sipedon in California for 3 years from 2013 to 2015, and estimated its abundance and annual survival. Its abundance declined from a peak of 218 (95% Credible Interval 149–313) in August 2013 to 97 (80–119) in July 2015. Annual survival of N. sipedon from 2013 to 2014 (0.23, 0.13–0.39) and from 2014 to 2015 (0.29, 0.18–0.41) was lower than survival estimates reported from native populations. Snake body condition, the abundance of large adult females, and prey availability all declined throughout the study. We conclude that the population of N. sipedon declined from 2013 to 2015, likely due to decreasing habitat and prey availability from the prolonged regional drought. This study highlights the importance of the effect of climatic extremes on the trajectory of introduced populations in a novel environment.

New Distributional Record and Intra-Specific Variation Of Cerberus schneiderii In Iyam River, Lucena City, Quezon, Philippines

Cerberus is a genus of semi-aquatic snakes that inhabit a wide range of aquatic habitats including estuarine environments. There are two species belonging to this genus known to occur in the Philippines. However, its distributional record is still not well established since only limited areas are surveyed despite of its wide distributional range in the coastal habitats of the country. This study primarily aims to document the occurrence of Cerberus in Iyam River, Lucena City. The scalation patterns and metric characters were also described to determine the range of individual variability among the species. Samples were collected from different habitat types in the sampling area by systematic transect walking. By close examination, it was revealed that the samples exhibit the established morphological description of Cerberus schneiderii. Moreover, population exhibit high variability in scalation pattern such as anal plate, anterior chin shield, lower labials at the first chin shield, type of scale, prefrontal plate, upper labials at loreal, and ocular ring; and metric characters such as total length, tail length, snout-vent length (SVL) and Tail:SVL ratio (H’ = 0.67-1.0). Statistical analysis further showed a strong significant correlation (P = <0.01) between total length and SVL, total length and weight, SVL and weight, and total length and tail length. The occurrence of different morphotypes is very important in understanding the extent of intra-specific variation within Cerberus schneiderii and the possible role of local adaptations and habitat use.

An Overview of Reptile Fungal Pathogens in the Genera Nannizziopsis, Paranannizziopsis, and Ophidiomyces

Abstract Two recent molecular analyses of morphologically similar fungal isolates formerly grouped under the appellation “Chrysosporium anamorph of Nannizziopsis vriesii (CANV) complex” led to major taxonomic revisions and revealed new insights into the biology of these reptile pathogens. All CANV-complex isolates differed from N. vriesii and were assigned to 16 species, either within Nannizziopsis or within the new genera Paranannizziopsis and Ophidiomyces, and 14 of these species were newly described. From these revisions, a trend in host specificity clearly emerged that was not previously apparent. Nannizziopsis now includes nine species associated with chamaeleonid, gekkonid, cordylid, teiid, agamid, and iguanid lizards; crocodiles; and human hosts. Paranannizziopsis includes four species that infect squamates and tuataras. Ophidiomyces, with the single species Ophidiomyces ophiodiicola (formerly Chrysosporium ophiodiicola), is only associated with terrestrial or semiaquatic snakes. Nannizziopsi guarr...

CHARACTERIZATION OF CHROMOSOME OF STRIPPED KEELBACK Xenochrophis vittattus (Linnaeus, 1758) FROM PIYUNGAN, BANTUL, DAERAH ISTIMEWA YOGYAKARTA

<p>Indonesia is a tropical country which has varies of habitat types that are dispersed into thousands islands. The diversity and its tropical climate, makes Indonesia as a suitable place as a natural habitat for herpetofauna, especially Sub Order Serpentes. Xenochrophis vittattus (Linnaeus, 1578), called stripped keelback snakes, is a semi-aquatic snakes spread in Indonesia, especially in Java, Sumatra, Bangka, and Manado, and commonly used as pet. Since there are few reports on genetic studies, especially in the field of karyology, this study aims to characterize the chromosomes of stripped keelback from Piyungan population, Bantul, Yogyakarta. This study used a brief splash of blood cultures method. This has been known as the first stripped keelback cytological study in Indonesia. The results showed that striped keelback has a diploid chromosome (2n) = 34, consists of metacentric chromosome (number 1, 2, 3, 4, 19, 20, 21, 22, 23, 24, 25, and 26); submetacentric chromosome (number 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18). Whereas the chromosome number 27, 28, 29, 30, 31, 32, 33, and 34 were micro chromosomes. Striped keelback karyotype formula was 2n = 2x = 34 = 12 m 14 sm 8 micro chromosomes. The longest chromosome of stripped keelback was 2.9335 ± 0.1772 um, whereas the shortest one was 0.5088 ± 0.013 um, and the R value was 5.9106 ± 1.1265.</p><p><br /><strong>Keywords</strong>: Xenochrophis vittattus, Stripped keelback, chromosome characterization, karyotype</p>

Visual Detection of Speckles in the Fish Xenotoca variata by the Predatory Snake Thamnophis melanogaster in Water of Different Turbidity.

Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Thamnophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vulnerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior displayed by the snake T. melanogaster. We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number of, or many speckles). The results showed that in a pool with high or zero turbidity, the number of speckles is not a determining factor in the deployment of the predatory behavior of the snake T. melanogaster toward X. variata. Our findings suggest that snakes can view the fish at intermediate percentages of turbidity, but the number of speckles in male X. variata is irrelevant as an interspecific visual signal in environments with insufficient luminosity. The successful capture of aquatic prey is influenced by integration between chemical and visual signals, according to environmental factors that may influence the recognition of individual traits.

Direct and Indirect Interactions between an Invasive Alien Fish (Perccottus glenii) and Two Native Semi-aquatic Snakes

The ecological links of aquatic invasive fish and native reptiles are rarely studied. Thus, we analyzed the diet and helminth composition of a recently introduced invasive alien fish (the Rotan, Perccottus glenii) and of two native semi-aquatic snakes (the Dice Snake Natrix tessellata, the Grass Snake N. natrix) in Cranberry Lake, Russia. We also studied diet and helminthes of water frogs (Pelophylax spp.) as a potential mechanism of transmission of parasites. We identified 19 prey taxa and four helminthes for P. glenii, 21 and 24 for Pelophylax spp., and two and 16 for the snakes. The piscivorous N. tessellata has been feeding on P. glenii since its introduction and the subsequent elimination of native fish. Although we did not find P. glenii in the diet of the mainly frog-eating N. natrix, helminth analysis indicated that this snake may prey upon this fish. Both studied snakes contracted the parasitic tapeworm Ophiotaenia europaea from P. glenii. Therefore, the invasive fish and the native snakes demons...

Phylogeography of the Mekong mud snake (Enhydris subtaeniata): the biogeographic importance of dynamic river drainages and fluctuating sea levels for semiaquatic taxa in Indochina

During the Cenozoic, Southeast Asia was profoundly affected by plate tectonic events, dynamic river systems, fluctuating sea levels, shifting coastlines, and climatic variation, which have influenced the ecological and evolutionary trajectories of the Southeast Asian flora and fauna. We examined the role of these paleogeographic factors on shaping phylogeographic patterns focusing on a species of semiaquatic snake, Enhydris subtaeniata (Serpentes: Homalopsidae) using sequence data from three mitochondrial fragments (cytochrome b, ND4, and ATPase—2785 bp). We sampled E. subtaeniata from seven locations in three river drainage basins that encompassed most of this species’ range. Genetic diversities were typically low within locations but high across locations. Moreover, each location had a unique suite of haplotypes not shared among locations, and pairwise φST values (0.713–0.998) were highly significant between all location pairs. Relationships among phylogroups were well resolved and analysis of molecular variance (AMOVA) revealed strong geographical partitioning of genetic variance among the three river drainage basins surveyed. The genetic differences observed among the populations of E. subtaeniata were likely shaped by the Quaternary landscapes of Indochina and the Sunda Shelf. Historically, the middle and lower Mekong consisted of strongly dissected river valleys separated by low mountain ranges and much of the Sunda Shelf consisted of lowland river valleys that served to connect faunas associated with major regional rivers. It is thus likely that the contemporary genetic patterns observed among populations of E. subtaeniata are the result of their histories in a complex terrain that created abundant opportunities for genetic isolation and divergence yet also provided lowland connections across now drowned river valleys.

Warming up for cold water: influence of habitat type on thermoregulatory tactics in a semi-aquatic snake

AbstractIn ectotherms, thermal acclimation and behavioural thermoregulation have evolved to match organismal performance with local or temporary thermal conditions. In semi-aquatic species, however, this matching encompasses a trade-off: organisms that thermoregulate close to optimal muscle function on land will inevitably depart from that optimum when entering water, a medium that may differ drastically in temperature. With regard to predator evasion and foraging success, how do semi-aquatic ectotherms deal with such a challenge? We experimentally raised young semi-aquatic Tiger snakes in either terrestrial or semi-aquatic environments over 11 months. When tested in a standardised enclosure, young snakes raised in a semi-aquatic environment selected slightly, but significantly higher mean body temperatures than their terrestrially raised siblings (respectively 30.3°C versus 29.5°C). The former allowed their body temperature to remain higher than 32°C for twice as long as the latter group (4.4 hours vs 2.1 hours). Locomotor performances (swimming speed) were, unsurprisingly, strongly linked to body temperature. Entering water with a higher body temperature (30°C versus 19°C) delayed a sharp drop in locomotor performances, and thus lengthened maximum performance time. We hypothesise that young snakes, by allowing their body temperature to reach above their usual optimum body temperature, may delay the drop in locomotor efficiency in case of foraging opportunity or in order to escape a predator.

Reproductive and Trophic Ecology of an Assemblage of Aquatic and Semi-Aquatic Snakes in Tonle Sap, Cambodia

was variation in both the frequency of feeding and the prey size and type among species, with the homalopsids more similar to one another than to the other non-homalopsid species. The prey to predator mass ratio ranged from 0.04 to 0.1 in the homalopsids, compared to 0.15 to 0.17 in the non-homalopsids. There was also variation in the feeding frequency between the sexes that differed between species and six species continued to feed while gravid. These detailed life history analyses can help provide a basis for assessing conservation options for these heavily exploited species.

Empirical Tests of Biased Body Size Distributions in Aquatic Snake Captures

Abstract Ecologists often rely on a suite of demographic parameters—such as age structure, body size distributions, population density, and sex ratios—to understand life history patterns, population dynamics, and community structure of snakes. Unfortunately, in many cases little consideration is given to how sampling techniques may influence the outcome of demographic studies. Herein, we use a combination of field capture techniques, an extensive database of field-captured snakes, and laboratory and field experiments to evaluate how capture methods may influence demographic assessments of several North American semi-aquatic snake species, including Agkistrodon piscivorus, Farancia abacura, Nerodia fasciata, N. floridana, N. rhombifer, N. taxispilota, Regina rigida, Seminatrix pygaea, and Thamnophis sauritus. We found that commercially available aquatic funnel traps (i.e., minnow traps) generally yielded biased assessments of population demography, but that the nature and magnitude of these biases varied p...

Variation in pupil diameter in North American Gartersnakes ( Thamnophis) is regulated by immersion in water, not by light intensity

A variable pupil generally regulates the amount of incoming light available for image formation on the retina. However, some of the semi-aquatic snakes (North American Gartersnakes, Thamnophis) that forage in relatively low light conditions reduce the pupil aperture in response to submergence underwater at the expense incoming light. Given that these snakes have all-cone retinas, reduction of incoming light because of pupillary constriction upon immersion seems counterintuitive. To test the effect of light and water on pupil aperture, three species of North American Gartersnakes ( T. atratus, T. hammondii, and T. sirtalis) were exposed to nine light intensities in air and water. There was no effect of light on relative pupil aperture for any species. However, all three species showed a significant reduction in pupil aperture upon submergence underwater. The lack of a light response is surprising, and may be related to the method of accommodation in snakes. Snakes lack a ciliary muscle, and move the lens by constricting the pupil, which increases pressure in the posterior chamber and pushes the lens forward. Upon submergence, the snakes may be attempting to overcome the change in refractive index and defocus imposed by the water, by constricting the pupil. Thus, having the iris muscle involved in accommodation may preclude it from much of a light regulating function.

Funnel Traps May Be Inappropriate for Many Studies of Semi-Aquatic Snakes

ABSTRACT We conducted a study to test whether funnel traps anchored to brush piles constructed at the edge of aquatic habitats largely devoid of cover would increase the catchability of semi-aquatic snakes in these systems. Brush pile traps captured significantly more snakes and potential snake prey than traps placed in the water along pond banks in 2000, but not in 2001. Changes in pond hydrology during 2001 may explain these disparate results. Additionally, we used quantitative and anecdotal data from our study as well as others in the literature to provide a critical and broad overview of funnel trapping for snakes in aquatic habitats. We conclude that trap design and deployment must address snake mortality and caution against using funnel traps in studies of diet, habitat use, activity, and growth as snakes may actively seek out and forage on prey sequestered in traps.

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.

The Status Of Tanquaanomala (Von Linstow, 1904 (Nematoda: Gnathostomatoidea)

Tanqua anomala (von Linstow, 1904) is redescribed from specimens collected from the intestine of the semi-aquatic snake Acrochordus javanicus Hornstedt, 1787 from south Sumatra. The morphological features given in the redescription allow the confirmation of T. anomala as a valid species, and distinguish it from other members of the genus. Tanqua ophidis Johnston & Mawson, 1948 is re-examined and placed in synonymy with T. anomala.

Effects of flood suppression on natricine snake diet and prey overlap

Organisms may become adapted to disturbances when these disturbances occur periodically and at intermediate intensity. To investigate the effects of flood suppression, this study compared diet and competition of semi-aquatic snakes during flood (2000–2001) and no flood (2003–2005) years. Three natricine species, Nerodia erythrogaster (Forster in Bossu, 1771), Nerodia fasciata (L., 1766), and Thamnophis proximus (Say in James, 1823), were palpated for prey items in an east Texas floodplain under both conditions. Prey items were classified as crayfish, salamanders, anurans, or fish. Simpson’s diversity index of prey, frequency of consumed prey type, and prey importance values were compared between flood and no flood years. Pianka’s index of niche overlap was used to compare changes in diet overlap between species in the years with floods and those without. In the absence of floods, the number of prey types consumed by N. erythrogaster and T. proximus decreased. The frequency of prey types consumed during flood years was significantly different from the period of flood suppression for all three species. The order of prey importance also changed in the absence of floods for all three snake species. Without floods, diet overlap decreased between N. erythrogaster and the other two species; however, overlap between N. fasciata and T. proximus doubled.

Comparing Filippi and Luiselli's (2000) method with a cartographic approach to assess the conservation status of secretive species: the case of the Iberian snake-fauna

Abstract The conservation status of the snake fauna of a given region or territory is often hard to estimate due the secretive habits of these animals, as well as of the lack of long-term demographic studies and generally low population densities. We examined the conservation status of the snakes from the Iberian Peninsula by applying two complementary methods. The first method, created by Filippi and Luiselli for a study of the Italian snakes conservation status, takes into account the ecological and non-ecological attributes which make species vulnerable to extinction. The second is a cartographic analysis which consists of calculating two indexes derived from the comparison of old and recent citations in UTM 10 × 10 km squares of Iberian snakes by means of extensive database sets. For each species, we calculated the percentage of recent citations, and the percentage of squares with both old and recent citations. Species with low proportion of recent citations and new squares appeared to be in decline. We found considerable coincidence between the two methods in the identification of the most threatened snake species: Vipera latastei, Coronella girondica, and Natrix natrix. We suspect that the ecological specialisation and the low reproductive output make C. girondica and V. latastei prone to extinction when faced with environmental changes (i.e. habitat loss). For N. natrix, we argue that this semi-aquatic snake experiences suboptimal environmental conditions in Mediterranean habitats. A combination of both methods proved adequate to detect vulnerability to extinction of snake species, hence revealing an effective tool for establishing conservation strategies in snakes and other secretive faunas.

Post-drought responses of semi-aquatic snakes inhabiting an isolated wetland: Insights on different strategies for persistence in a dynamic habitat

Most aquatic habitats are temporally dynamic, and selection has favored diverse strategies to persist in the face of fluctuating environmental conditions. Isolated wetlands in the southeastern United States harbor high diversities of aquatic and semi-aquatic organisms. However, drought may render these wetlands temporarily unsuitable for many species, sometimes for years at a time. We studied the movement patterns and demography of seven species of semi-aquatic snakes at Ellenton Bay, an isolated 10-ha freshwater wetland in the Upper Coastal Plain of South Carolina, following complete drying of the bay during a drought from 2000 to 2003. Behavioral and population responses varied markedly among species. Cottonmouths (Agkistrodon piscivorus) migrated to and from the wetland annually, fared well, and reproduced during the drought. Banded watersnakes (Nerodia fasciata) suffered a dramatic population decline and apparently did not reproduce, while eastern green watersnakes (N. floridand) were locally extirpated. Black swamp snakes (Seminatrix pygaea) aestivated within the wetland and were less affected by the drought than Nerodia. Interspecific differences in response to drought demonstrate that conservation measures may affect species differently and highlight the importance of terrestrial habitat around wetlands for semi-aquatic reptiles.

Influence of sex and reproductive condition on terrestrial and aquatic locomotor performance in the semi‐aquatic snake Seminatrix pygaea

1 Most life-history models assume a trade-off between reproductive investment and parental survival. Several studies have documented reproductive costs in terms of reduced locomotor performance in terrestrial habitats. However, few studies have determined the reproductive costs of pregnancy in aquatic environments, or compared pregnancy-induced locomotor costs among habitats. This knowledge gap is important because many organisms rely on multiple habitat types during pregnancy. 2 We compared sexual differences in maximum locomotor velocity and the relative impacts of pregnancy on locomotor performance in aquatic and terrestrial environments for a semi-aquatic snake (Seminatrix pygaea). In addition, because most life-history models predict a direct trade-off between reproductive investment and reproductive costs, we quantified the relationship between reproductive investment and postpartum increase in velocity for both habitat types. 3 Both males and non-pregnant females always swam faster than they crawled, but males were significantly faster for their size than were non-pregnant females. These results mirror sexual differences known to exist in other snakes, but differ in that the degree of sexual divergence in velocity does not vary with habitat for S. pygaea. 4 Pregnancy significantly reduced both crawling and swimming velocity. Moreover, pregnancy impaired crawling velocity significantly more than swimming velocity. The mean (± 1 SE) percentage increases in crawling and swimming velocity after parturition were 72·8 ± 21·6 and 59·4 ± 12·8%, respectively. There was a direct trade-off between reproductive investment and aquatic locomotor impairment: snakes that invested more in offspring experienced larger decreases in swimming velocity. However, evidence for such a trade-off in the terrestrial habitat was weaker. 5 Our results demonstrate that the cost of reproduction for semi-aquatic organisms may differ between aquatic and terrestrial habitats in complex ways. Swimming may be more effective than crawling for escaping predators during pregnancy, because swimming results in faster velocities and is less impaired by pregnancy. However, the assumption of a direct trade-off between reproductive investment and locomotor impairment may be stronger for swimming performance compared with crawling performance.

Individual reproductive success and clutch-size of a population of the semi-aquatic snake Natrix tessellata from central Italy : are smaller males and larger females advantaged ?

Succès reproducteur individuel et taille de ponte dans une population de la couleuvre semi-aquatique Natrix tessellata en Italie centrale : les plus petits mâles et les plus grandes femelles sont-ils avantagés ? — Le succès de la formation des couples et de la reproduction de Natrix tessellata, serpent semi-aquatique, a été étudié dans le centre de l’Italie. Le succès des appariements a été établi en suivant par radiopistage 10 mâles et 12 femelles durant la période d’accouplement et en comptant combien chaque individu avait de partenaires sexuels en fonction de sa taille corporelle (longueur museauanus). Les femelles étaient significativement plus grandes que les mâles. Deux patrons opposés de succès individuel ont été mis en évidence dans la population : un succès d’appariement plus grand pour les plus petits mâles et pour les plus grandes femelles. De fait, chez les mâles, il y avait une relation significative entre la taille du mâle et le nombre de femelles avec lesquelles il s’accouplait tandis que les plus grandes femelles étaient courtisées et s’accouplaient avec un plus grand nombre de mâles. La taille maternelle était positivement liée au nombre d’oeufs pondus.

Intraspecific differences in thermal tolerance of the diamondback watersnake ( Nerodia rhombifer): effects of ontogeny, latitude, and sex

Ontogenetic shifts in microhabitat use are widespread among taxa and can result in drastic shifts in thermal habitat among age classes. Likewise, geographic variation in climate along latitudinal gradients can cause differences in thermal environments among populations of a species. Using a common garden design, we examined four populations of a single species of semi-aquatic snake, Nerodia rhombifer, to determine whether ontogenetic shifts in habitat use (and/or body size) and latitudinal differences in ambient temperature have resulted in evolutionary changes in thermal tolerance. We found ontogenetic differences in thermal tolerance for all populations, with neonates tolerating temperatures 2 °C higher than adults, a pattern that is consistent with ontogenetic shifts in body size and microhabitat use in this species. There were differences in thermal tolerance among latitudes in neonates, suggesting genetic differences among populations, but adults showed no latitudinal differences. In combination, the increased thermal tolerance of neonates and the age-specific response to latitude suggest individuals may be most sensitive to selection on thermal tolerance as neonates. Although latitudinal differences exist in neonates, their tolerances were not ranked according to latitude, suggesting the effects of some other local factor (e.g., microclimate) may be important. Lastly, among neonates, females tolerate higher temperatures than males.