Amphibian disease risks and the anthropogenic dispersal of invasive Litoria species : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Albany, New Zealand
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Date
2021
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Massey University
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Abstract
The scope of this research is to provide a broad outline of the interaction between anthropogenic disease spread, risk of an invasive amphibian species establishing into the New Zealand environs, and prevalence of amphibian chytrid in wild introduced amphibian populations. The objective of this overview is to identify risk pathways that could threaten New Zealand’s four endemic Leiopelma species of frogs.
Worldwide amphibian populations are in decline with an estimated 32.5% of amphibians globally threatened (IUCN 2008). New Zealand’s four endemic amphibians Leiopelma spp. are high on the ICUN list of critically endangered animals, further, two of the three introduced tree frogs (Litoria spp..) are listed endangered and vulnerable in their native home. Disease has been one factor implicated in the worldwide amphibian decline in particular the two diseases Chytridiomycosis and Ranavirus. Although Chytridiomycosis has had the most profound effect on the decline of amphibian species. The spread of such diseases is, at least in part, human-mediated through media such as the bait trade, food industry, and possibly the pet trade. To date, there have been no reports of Ranavirus in New Zealand amphibians. Conversely, amphibians chytrid fungus is widespread and has been implicated in the decline of the endemic Leiopelma archeyi. This makes amphibian chytrid an ideal disease to model disease transmission with particular reference to the anthropogenic movement of amphibians.
The two main goals of this Ph.D. were to investigate specific anthropogenic mediated risks of spreading disease using the pathogen Batrachochytrium dendrobatidis (Bd), which is responsible for amphibian chytrid fungus, as a modality to model this. Included in this will be the enquiry into how Bd entered New Zealand and how it spread so quickly via the movement of Litoria spp.. Furthermore, to look at invasive amphibian species incursion risks by evaluating previous border seizures.
Currently, it is unknown how the amphibian chytrid entered New Zealand and whether New Zealand’s borders are a high-risk entry pathway for amphibian disease. Examining the anthropogenic dispersal of Litoria in New Zealand and developing systems that reduce the risk of introducing disease into naive populations is an important role in ensuring the long-term survival of New Zealand’s endangered Leiopelma spp. frogs. The presence of Bd in New Zealand has been recorded but the prevalence of the pathogen in populations is unknown. Identifying the prevalence of infection within populations will provide insight into how populations of Litoria spp. are surviving Bd infection. Furthermore, this Ph.D. project will assess the risk of invasive exotic amphibians entering New Zealand and becoming naturalised.
Education is one of the important areas that will greatly help the plight of New Zealand’s frogs. For education to be successful it needs to be targeted, therefore assessing risk areas of amphibian disease is imperative. Furthermore, understanding the public’s knowledge of frogs in New Zealand will further help in the development of resource material and targeting the main groups where education is needed.
Key findings of this research are that the three species of Litoria frogs are moved around New Zealand in large numbers via the pet trade. The spread of amphibian chytrid has most likely been so rapid due to the frequency and volume of tadpoles and frogs being bought and sold. The pet trade thereby effectively and inadvertently is a major means of the unregulated translocation of Litoria amphibians throughout New Zealand. Results of this research also show there is a gap in the knowledge about amphibians in areas of husbandry, disease, species identification, and legal responsibilities in the ownership and containment of amphibians in New Zealand. Additionally, the introduction of a new disease is more likely to occur than the risk of an invasive species becoming established. Finally, the wild populations of Litoria frogs were surviving with a high prevalence of amphibian chytrid fungus in two of the three study sites in this research, the third site which had the presence of a reservoir species had low numbers of frogs present.
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Litoria, Diseases, Dispersal, Batrachochytrium dendrobatidis, New Zealand