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Microplastics are plastic fragments with a size less than 5 mm in length. In addition to a threat to the marine environments where these are abundantly present, these have also started polluting freshwater ecosystems. However, the uptake of microplastics by living organisms differs depending on their habitats and feeding behaviors. We investigated the presence, size, type, and color of microplastics in the gastrointestinal tract contents of two water snakes, namely Natrix natrix and Natrix tessellata. The snakes were collected from different regions of Turkey and preserved as museum materials. Our results showed that fibers constituted the predominant polymer type in both snake species (94.7% for N. natrix and 87.9% for N. tessellata), whose dimensions ranged from 250 to 3750 µm. We did not find any significant difference in the number of microplastics ingested between the two species. In addition, the uptake of microplastics did not relate to the size and weight of snakes. Microplastics were not consistently present all years, and similarly, these were not detected in all samples within the distribution area. These results could be attributed to the environment and diet of two snake species.

When captured by a predator, the prey’s options for escape decrease dramatically; however, some species, such as dice snakes, display a wide variety of behaviours in order to escape. We explored how factors such as locality, body temperature, body size, sex, reproductive status (i.e. gravid vs. non-gravid), presence and state of injuries, and the presence of food affect the occurrence of behavioural displays in a capture situation within and among four free-ranging populations of dice snakes, Natrix tessellata (Colubridae). Our study shows that dice snakes regularly hiss, discharge their cloacal glands, and coat themselves in musk when captured, while other behaviours were displayed only occasionally. Our study corroborates previous findings of local differentiation in snake behaviour, especially the case of supposed Batesian mimicry in dice snakes. In three of four localities where the dice snake lives in proximity or in sympatry with nose-horned vipers, they display fake striking, with additional head flattening as opposed to the viper-free locality. Larger snakes exhibit a wider array of antipredator behaviours, which commonly include musking and hissing. Expectedly, warmer snakes were more likely to display vigorous antipredator behaviours such as struggling and striking. Injured snakes (a possible measure of a previous exposure to predation) displayed fewer behaviours and musked and hissed less. We call into question the analysis of isolated antipredator behavioural displays, and encourage using entire behavioural sequences in order to understand the complexity of antipredator behaviour.Significance statementA wrong decision when facing off a predator will likely result in death, which makes predation a major shaping force behind prey behaviour. Prey animals usually try to avoid being captured as escape becomes difficult, but some species, such as dice snakes, have a large arsenal of antipredator capture behaviours at their disposal. We examined nine different capture behaviours in dice snakes across four different localities. Our study corroborates previous findings that local adaptations, injuries, sex, size, body temperature, food, and reproductive status significantly influence antipredator behaviour on capture. However, our results also suggest that the entire sequence of capture behaviours displayed might be equally important as the occurrence of each behaviour. Therefore, future studies should avoid analysis of isolated antipredator behavioural displays and instead use entire behavioural sequences to understand the complexity of antipredator behaviour.

The widespread relationship between salt excreting structures (e.g., salt glands) and marine life strongly suggests that the ability to regulate salt balance has been crucial during the transition to marine life in tetrapods. Elevated natremia (plasma sodium) recorded in several marine snakes species suggests that the development of a tolerance toward hypernatremia, in addition to salt gland development, has been a critical feature in the evolution of marine snakes. However, data from intermediate stage (species lacking salt glands but occasionally using salty environments) are lacking to draw a comprehensive picture of the evolution of an euryhaline physiology in these organisms. In this study, we assessed natremia of free-ranging Dice snakes (Natrix tessellata, a predominantly fresh water natricine lacking salt glands) from a coastal population in Bulgaria. Our results show that coastal N. tessellata can display hypernatremia (up to 195.5 mmol.l-1) without any apparent effect on several physiological and behavioural traits (e.g., hematocrit, body condition, foraging). More generally, a review of natremia in species situated along a continuum of habitat use between fresh- and seawater shows that snake species display a concomitant tolerance toward hypernatremia, even in species lacking salt glands. Collectively, these data suggest that a physiological tolerance toward hypernatremia has been critical during the evolution of an euryhaline physiology, and may well have preceded the evolution of salt glands.

Ophidiomycosis is an emerging infectious disease caused by the fungus Ophidiomyces ophidiicola (Oo). To date, Oo presence or associated disease condition has been recorded in wild and/or captive snakes from North America, Europe, Asia and Australia, but the data is still scarce outside the Nearctic. Although Italy is a country with a high snake biodiversity in the European panorama, and animals with clinical signs compatible with Oo infection have been documented, to date no investigations have reported the disease in the wild. Therefore, a pilot survey for the Italian territory was performed in conjunction with setting up a complete diagnostic workflow including SYBR Green-based real-time PCR assay for the detection of Oo genomic and mitochondrial DNA combined with histopathology of scale clips. Oo presence was investigated in 17 wild snake specimens from four different species. Four snakes were sampled in a targeted location where the mycosis was suspected via citizen science communications (i.e. North of the Lake Garda), whereas other ophidians were collected following opportunistic sampling. Oo genomic and mitochondrial DNA were detected and sequenced from all four Lake Garda Natrix tessellata, including three juveniles with macroscopic signs such as discolouration and skin crusts. From histopathological examination of scale clips, the three young positive individuals exhibited ulceration, inflammation and intralesional hyphae consistent with Oo infection, and two of them also showed the presence of arthroconidial tufts and solitary cylindrical arthrospores, allowing “Ophidiomycosis and Oo shedder” categorisation. For the remaining snake samples, the real-time PCR tested negative for Oo. This pilot survey permitted to localise for the first time Oo infection in free-ranging ophidians from Italy. Ophidiomycosis from Lake Garda highlights the need to increase sampling efforts in this area as well as in other northern Italian lakes to assess the occurrence of the pathogen, possible risk factors of the infection, its impact on host population fitness and the disease ecology of Oo in European snakes.

Context Human-induced landscape modification, such as urbanization, creates new environments that can have adverse effects on flora and fauna, posing threats to biodiversity. Understanding how reptiles respond to urbanization is crucial, especially in light of their ongoing population declines. Objectives We examined the influence of landscape-scale and local-scale urbanization features on the abundance of an aquatic snake species. Our investigation focused on dice snakes ( Natrix tessellata ) inhabiting a lake with a heavily urbanized shoreline. Methods We conducted visual encounter surveys at 25 study sites during the activity period of dice snakes around Lake Balaton in Hungary. We measured both landscape-scale and local-scale variables, including urban land use cover, vegetation cover, road cover, distance of main roads and city size, emergent vegetation cover and the area of artificial rock and concrete shoreline protection structures. We analysed snake survey data using N-mixture models to estimate abundance and examine relationships with landscape-scale and local-scale variables. Results Urban land use cover, road cover, the proximity of main roads and the extent of artificial rock and concrete shoreline protection structures positively affected the abundance of snakes. These findings imply that urban habitats may offer new ecological opportunities for dice snakes. Conclusions The findings of this study indicate that both landscape-scale and local-scale human-induced landscape modifications may have a positive impact on the abundance of urban snakes. Taken together, our findings suggest that urbanization is a complex phenomenon, affecting species at different levels and with subtle effects.

Abstract The Western Palearctic harbours a diverse snake fauna, including numerous endemic species and yet unnamed clades, identified through molecular analyses. However, morphological characteristics of these clades, even of common species, often remain relatively unexplored. In this study, we provide an examination of the morphology and cranial anatomy of the semi-aquatic snake species Natrix tessellata (Laurenti, 1768), with a focus on populations of the so-called ‘Europe’ and ‘Greece’ clades. Utilising both museum collections and field data, we first morphologically examined 541 individuals of N. tessellata , categorising them according to previously established clades and lineages that resulted in relatively low morphometric and meristic variation across the species’ range. When assessing the 448 specimens from the ‘Europe’ and the ‘Greece’ clades separately, we similarly observed little variation in meristic characteristics. On the other hand, individuals of the ‘Greece’ clade displayed smaller and more slender body and head proportions compared to those of the ‘Europe’ clade and the pigmentation of the labial scales is distinctively paler in the ‘Greece’ clade, whereas the overall body colouration remains largely similar between the two. Our osteological analysis of 47 N. tessellata skulls also indicated slight differences in the frontoparietal portion of the braincase between the ‘Europe’ and the ‘Greece’ clades, warranting further examination with a larger dataset and extending to other skull components. These findings hold significance for ongoing enquiries into the species’ biogeography, morphology and ecological adaptations. In summary, the integration of morphological and osteological data with genetic information offers a promising avenue for potential taxonomic revisions of N. tessellata in the future.

ABSTRACT Ophiotaenia tessellata sp. n. (Proteocephalidea: Proteocephalinae) is described from the intestine of the dice water snake Natrix tessellata (Laurenti, 1768) (Serpentes: Colubridae) collected from El Faiyoum Governorate, Egypt. Standard methods of collection of the snakes and examination of the cestode tapeworms for taxonomic studies were used. Ophiotaenia tessellata sp. n. was identified and being separable from Ophiotaenia species found in African snakes as well as those from colubrid snakes based on many morphological characteristics. Analysis of a dataset based on 473 bp of its 18S rRNA gene regions was carried out to determine the phylogenetic position of the new species among other proteocephalideans. Ophiotaenia tessellata sp. n. shows a close relationship to O. lapata Rambeloson, Ranaivoson and de Chambrier, 2012 parasite of the endemic snake Madagascarophis colubrinus from Madagascar; both infect African colubrid snakes.

Marginal populations of animals are highly susceptible to environmental pressures associated with climatic changes. Understanding their distribution and ecological requirements is, thus, essential for the development of efficient conservation strategies. The dice snake, Natrix tessellata , is listed as critically endangered in the Czech Republic. In certain regions (Bohemia and Silesia), its populations are located beyond the northern border of the continuous range of the species, while the south Moravian populations are connected to it. Based on the statewide database of the Czech Nature Conservation Agency, we created a predictive model and determined key factors influencing the species distribution. The most relevant factors were: watercourses and bodies, average annual temperatures, altitude, slope inclination and precipitation seasonality. The model fits the presence records well and is applicable in both theory and practice of the species conservation – for example, focusing faunistic research to certain areas, critical analysis of controversial presence reports and as an input for species management in the form of repatriation and introduction.

We examined morphological differences in cranium size and shape between closely related snake species, Natrix natrix and Natrix tessellata (Natricinae, Colubroidea), as well as variation within species. These two snake species have similar ecology and habitat preferences but differ in feeding strategies. Our hypothesis was that divergence in size and shape of cranial elements between species depends on their functional role and anatomical relationships. To analyse complex, kinetic crania, we applied computed microtomography and 3D geometric morphometrics. We analysed size and shape of six cranial elements separately. We selected two “non-trophic” structures (akinetic braincase and mobile nasals) and four movable “trophic” skeletal elements (maxillae, quadrates, pterygoids and compound bones) which are involved in prey capture and swallowing. Our results showed that N. natrix and N. tessellata significantly differ in size and shape of all analysed cranial elements. In both species, cranium is significantly larger in females than in males. To account for possible differences in shape due to differences in size, we estimated allometric and non-allometric component of shape variation. For all elements, except nasals, allometry accounted for a significant proportion of the variance in shape. The analysis of non-allometric component of shape variation revealed significant dimorphism in shape of the braincase and maxilla between N. tessellata females and males, and marginally significant sexual dimorphism in shape of maxilla in N. natrix . These results indicated that sexual dimorphism in skull shape is species specific and not entirely caused by selection for larger size in females.

An ecological analysis of the helminth fauna of the dice snake Natrix tessellata from different habitats of Astrakhan oblast was carried out in 2004, 2005, and 2008. The helminth community of the reptile included 21 species of parasitic worms: 11 trematodes, 1 cestode, 8 nematodes, and 1 acanthocephalan. Of these, 11 species were found in all the studied localities and form the bulk of N. tessellata helminth fauna. Dominant and subdominant helminth species were found in snakes in all habitats as a result of the implementation of its main trophic relationships. A comparison of the helminth composition from different study sites showed a relatively high degree of similarity. Differences in the helminth fauna of the dice snake from different habitats were insignificant and related to rare and accidental parasite species. Significant differences in the infection level of snakes with certain species of helminths were revealed. Most of the helminth species that parasitise the dice snake have a complex life cycle. The helminth infection of reptiles was determined to a large extent by biotic factors: fauna and the number of invertebrates (intermediate hosts of helminths) and vertebrates (paratenic and final hosts) in the biocenosis.