Investigating the presence of the amphibian chytrid fungus in a non-native species

In 2015 we were able to confirm the presence of a population of the non-native common midwife toad (Alytes obstetricans) in central Cambridge. The population has persisted for at least a decade and we have developed a novel method to be able to locate the toads. The toads are currently restricted to the back gardens of a row or parallel Victorian-aged terraced houses. Their dispersal is limited due to the fact that the population is surrounded by walls and roads – isolating them unless somebody decides to move them. We’ve actively networked with the local community to be able to gain access to the gardens the toads inhabit, when the conditions are right to survey. This has led to a small level of community engagement which we hope to build on in future years. Since the early months of 2017, the project has grown with leaps and bounds with more residents allowing us access to their gardens to survey for midwife toads. This is something that we didn’t expect!

Figure 1. A male midwife toad carrying fertilised eggs on its hindlegs, this characteristic behaviour is where the species derives its common name. Photo credit Steven Allain

As a non-native species it’s not known what threats the species poses to our native amphibians, this is an area of research which needs to be explored more. Due to the nature of their vastly different life history it is unlikely they’ll pose a problem in terms of competition with the local amphibian species. We’ve found them happily living and breeding alongside Bufo bufo, Rana temporaria, Lissotriton helveticus and L. vulgaris. The only threat we feel the midwife toads may pose to the native and naive amphibian populations is as a disease vector. Since 2016, we’ve been actively swabbing the midwife toads in an effort to screen them for the amphibian chytrid fungus (Batrachochytrium dendrobatidis). Preventing the spread of disease to native species may be impossible as A. obstetricans are the most numerous amphibian species within the study area. This may be due to the fact that they are able to exploit the opportunities better and due to their cryptic nature are less likely to be predated on by cats or other predators.

One of the main aims of the project is to develop a baseline population estimate of A. obstetricans as we are currently unaware as to how big the population is, although our current estimates are between 50-100 sexually mature individuals. The initial method of introduction or the size of the founding population is still not known and is another area we wish to investigate further once we’ve screened more individuals. So far from a limited number of samples we’ve had analysed the results have been negative for B. dendrobatidis. This is encouraging news but a larger sample size is needed to be sure that the toads are not acting as a vector of disease. We’d like to thank the Amphibian and Reptile Groups UK for supporting the analysis of the initial batch through their 100% Fund.

Figure 2. A individual being swapped for later examination of presence or absence of B. dendrobatidis. Photo credit Steven Allain

We’ve also been working to collect morphometric data on the midwife toads to gain a better understanding of their population dynamics. Each individual encountered has also been photographed in order to create a reference database of the population. This method has been used before to re-identify Alytes tadpoles and it’s hoped we will be able to use this method to count repeat encounters, therefore creating a more accurate prediction of the population size. For the first time this season we were able to identify one of breeding ponds and locate midwife toad tadpoles of differing age classes. We plan to swab the tadpoles in the coming months as it’s likely now that they will overwinter in the pond.

Currently we are trying to fund the next stage of the project through crowdfunding, as it is being increasingly difficult to find grants that are willing to support such a project. This may be due to the uncertain and uneasy global political and economic climate we are currently experiencing, or it may just be bad timing on our part. Our aim is to raise $1500 which will pay for analysis of all samples taken in 2017 and all of the ones we aim to take in 2018 as well. We would appreciate it if you could donate or help to spread the word regarding the project.

Thank you.

Steven Allain
About Steven Allain 5 Articles
Steve is a zoology graduate from Anglia Ruskin, Cambridge. He is the current chairman of the Cambridgeshire and Peterborough Amphibian & Reptile Group (CPARG) and helps to organise and coordinate a number of amphibian and reptile surveys around the county to map the distribution of amphibians within Cambridgeshire. Steve has been a blogger for The Wandering Herpetologist and an intern for IUCN SSC Amphibian Red List Authority since last summer. He has recently joined the SAVE THE FROGS! Task Force and is currently carrying out an amphibian based research project in Malaysia. Check out Steve on Twitter (@stevoallain) and find more of his work on ResearchGate.

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