PhD project: Population drivers, demographics and disease in wild snake populations

Reptile populations around the world are declining due to a number of threats such as habitat loss, climate change and, increasingly, disease. It is crucial to understand how such threats influence the dynamics of populations of all wildlife (not only reptiles) as counts are a standard method for assessing the conservation status of a species. 

To date, there has been a limited number of studies looking at the population dynamics of reptiles in the UK, which is worrying, particularly after the recent confirmation that snake fungal disease (Ophidiomyces ophiodiicola) is present in wild UK snake populations. Currently we don’t know how the disease affects European snake species, but if we look to the US, where snake fungal disease has been better studied, then the potential impacts are startling. 

This research project will focus on investigating the population dynamics of barred grass snakes (Natrix helvetica) at a population where snake fungal disease has recently been identified. The snakes will be surveyed over a number of seasons using artificial cover objects combined with legacy data to help understand how the population functions. Some of the factors that will be investigated are population demographics, transience and survivability, which are important to establish before trying to assess the potential effects of snake fungal disease. 

These surveys will involve capturing and photographing each individual in order to develop a capture history. At the same time as monitoring the snakes, each individual will be examined for the visual signs of disease and swab samples will be taken for later analysis when appropriate. 

Grass snakes have a unique ventral belly scale pattern (like a tiger’s striped) which is the foundation of the method used to identify individuals through time and space. It is hoped that this may cast a light on the spatial ecology of the barred grass snakes at the field site. 

Steven Allain is a member of the Durrell Institute of Conservation and Ecology.  


Professor Richard Griffiths
Dr Becki Lawson (Zoological Society of London)
Dr Dave Leech (British Trust for Ornithology)


NERC EnvEast PhD Scholarship



  • Smales, L., Allain, S., Wilkinson, J. and Harris, E. (2020). A new species of Pseudoacanthocephalus (Acanthocephala: Echinorhynchidae) from the guttural toad, Sclerophrys gutturalis (Bufonidae), introduced into Mauritius, with comments on the implications of the introductions of toads and their parasites into the UK. Journal of Helminthology [Online] 94. Available at: https://www.cambridge.org/core/journals/journal-of-helminthology.
    Pseudoacanthocephalus goodmani n. sp. is described from faecal pellets collected from Sclerophrys gutturalis (Power, 1927), the guttural toad. The species is characterized by a suite of characters, including a proboscis armature of 14–18 longitudinal rows of 4–6 hooks with simple roots, lemnisci longer than the proboscis receptacle, equatorial testes, a cluster of elongated cement glands and eggs without polar prolongations of the middle membrane 72.6–85.8 long. The toad had been accidentally translocated from Mauritius to the UK in a tourist's luggage and survived a washing machine cycle. The guttural toad was introduced into Mauritius from South Africa in 1922 and the cane toad, Rhinella marina (Linneaus, 1758), from South America, between 1936 and 1938. It seems most likely, therefore, that P. goodmani was introduced, with the guttural toad, from South Africa. The cane toad is host to the similar species, Pseudoacanthocephalus lutzi, from the Americas, but P. lutzi has not been recorded from places where the cane toad has been introduced elsewhere. Clearly, the guttural toad is a hardy and adaptable species, although it seems unlikely that it could become established in Northern Europe. Nevertheless, any accidental translocation of hosts poses the potential risk of introducing unwanted pathogens into the environment and should be guarded against.
  • Allain, S. and Duffus, A. (2019). Emerging infectious disease threats to European herpetofauna. The Herpetological Journal [Online] 29:189-206. Available at: https://www.thebhs.org/publications/the-herpetological-journal/volume-29-number-4-october-2019.
    In the past decade, infectious disease threats to European herpetofauna have become better understood. Since the 1990s, three major emerging infections in amphibians have been identified (Batrachochytrium dendrobatidis, B. salamandrivorans, and ranaviruses) as well as at least one of unknown status (herpesviruses), while two major emerging infections of reptiles (Ophidiomyces ophiodiicola and ranaviruses) have been identified in wild European populations. The effects of emerging infections on populations have ranged from non-existent to local extirpation. In this article, we review these major infectious disease threats to European herpetofauna, including descriptions of key mortality and/or morbidity events in Europe of their emergence, and address both the distribution and the host diversity of the agent. Additionally, we direct the reader to newly developed resources that facilitate the study of infectious agents in herpetofauna and again stress the importance of an interdisciplinary approach to examining these infectious diseases.
  • Saucedo, B., Garner, T., Kruithof, N., Allain, S., Goodman, M., Cranfield, R., Sergeant, C., Vergara, D., Kik, M., Forzán, M., van Beurden, S. and Gröne, A. (2019). Common midwife toad ranaviruses replicate first in the oral cavity of smooth newts (Lissotriton vulgaris) and show distinct strain-associated pathogenicity. Scientific Reports [Online] 9:4453. Available at: https://doi.org/10.1038/s41598-019-41214-0.
    Ranavirus is the second most common infectious cause of amphibian mortality. These viruses affect caudates, an order in which information regarding Ranavirus pathogenesis is scarce. In the Netherlands, two strains (CMTV-NL I and III) were suspected to possess distinct pathogenicity based on field data. To investigate susceptibility and disease progression in urodeles and determine differences in pathogenicity between strains, 45 adult smooth newts (Lissotriton vulgaris) were challenged via bath exposure with these ranaviruses and their detection in organs and feces followed over time by PCR, immunohistochemistry and in situ hybridization. Ranavirus was first detected at 3 days post infection (p.i.) in the oral cavity and upper respiratory mucosa. At 6 days p.i, virus was found in connective tissues and vasculature of the gastrointestinal tract. Finally, from 9 days p.i onwards there was widespread Ranavirus disease in various organs including skin, kidneys and gonads. Higher pathogenicity of the CMTV-NL I strain was confirmed by higher correlation coefficient of experimental group and mortality of challenged animals. Ranavirus-exposed smooth newts shed virus in feces intermittently and infection was seen in the absence of lesions or clinical signs, indicating that this species can harbor subclinical infections and potentially serve as disease reservoirs.
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