Author Identifiers

Bridget Duncan

https://orcid.org/0000-0001-8203-4295

Date of Award

2021

Degree Type

Thesis

Degree Name

Bachelor of Science (Biological Science)

School

School of Science

First Advisor

Annette Koenders

Second Advisor

Quinton Burnham

Third Advisor

Michael Lohr

Abstract

Human-wildlife interactions have developed since the agricultural revolution that occurred 10,000 years ago, and the expansion of commensal species’ geographical distribution led to conflicts that prompted humans to adopt a wide range of control methods for pest species (Horvitz, Wang, Wan, & Nathan, 2017; Riyahi et al., 2013; Saraswat, Sinha, & Radhakrishna, 2015). The order Rodentia is characterised by a high number of successful invaders, which humans have attempted to manage with the use of anticoagulant rodenticides (ARs) since the 1940s (Capizzi, Bertolino, & Mortelliti, 2014; Ruiz-Suárez et al., 2014). The rise and spread of a genetic mutation that infers AR resistance among mice and rats led to the production of stronger second generation compounds, which are characterised by higher toxicity and longer persistence in the liver tissue (Lohr & Davis, 2018; Ruiz-Suárez et al., 2014). These traits have led to AR residues being detected in a variety of non-target organisms from both terrestrial and aquatic environments (Kotthoff et al., 2018; López-Perea, Camarero, Sánchez-Barbudo, & Mateo, 2019; Rattner, Lazarus, Elliott, Shore, & Van Den Brink, 2014a). Additionally, the impact of ARs on non-target species is exacerbated when rodents are resistant to the poison as they become capable of transmitting high doses to their predators.

To reduce negative effects on the ecosystem, rodent eradication requires information on the presence of resistance within populations; this has been intensely studied in Europe through laboratory feeding trials, blood clotting response tests and genetic screening of the Vkorc1 gene (Goulois, Lambert, Legros, Benoit, & Lattard, 2016; Grandemange, Lasseur, Longin-Sauvageon, Benoit, & Berny, 2010; Mayumi Ishizuka et al., 2007; Pelz et al., 2012). In Australia, the only available information on resistance of rodent populations comes from a study in 1975 on black rats from Sydney, and another study on Mus musculus of Lord Howe Island, New South Wales (Billing, 2000; Saunders, 1978; Wheeler et al., 2018).

Since the house mouse (Mus musculus) exhibits a degree of natural tolerance to rodenticides (Cowan et al., 2017), and its eradication has higher failure rate compared to rats (Howald et al., 2007), it is vital to know whether particular populations possess mutations that may infer resistance, and how common the mutations are within the population. The aim of this study was to produce the first data showing whether Vkorc1 mutations that may provide anticoagulant resistance in house mouse are present in Western Australia by sampling populations from the Perth metropolitan area, which is continuously exposed to ARs, and from Browse Island, which has no history of exposure. Additionally, the mitochondrial D-loop of house mice was sequenced to investigate population genetic structure, identify the origin of Western Australian mice, and to elucidate whether resistance was linked to certain haplotypes.

No resistance-related Vkorc1 mutations have been detected in either house mouse populations. A genetic introgression in the intronic sequence of the Vkorc1 gene of Browse Island house mouse was detected and it is thought to have originated through hybridisation with the Algerian mouse (Mus spretus). Analysis of the mitochondrial D-loop reported two haplotypes in the house mouse population of Perth, and two haplotypes in the population of Browse Island.

The findings suggest that both house mouse populations exhibit no genetic resistance to ARs, and therefore less strong rodenticides can be employed in pest control and eradication attempts, which will result in a less negative impact on nontarget species. Biosecurity measures must be in place to avoid potentially resistant house mice to enter Western Australia, and to prevent the introduction of new house mouse subspecies on mainland, such as the one found on Browse Island.

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