A genetic approach for house mouse management on islands: rodenticide resistance, phylogeography and diet metabarcoding

Invasive house mice (Mus musculus ssp.) pose a significant threat to island ecosystems. This thesis employs a genetic approach to investigate three key aspects of house mouse management: rodenticide resistance, phylogeography of house mouse populations on islands, and their dietary habits. Anticoagulant rodenticide (AR) resistance was examined through the analysis of VKORC1 single nucleotide polymorphisms (SNPs) in 11 islands in Italy and 6 locations in Aotearoa/New Zealand, two areas with very different biogeographic history but both with managed house mouse populations. The study found a widespread presence of missense mutations in Italian islands, while they are less common in Aotearoa/New Zealand. Among the SNPs found in this study, the well-known resistance-giving mutation Tyr139Cys is the only one found both in Italy and Aotearoa/New Zealand. The increased frequency of Tyr139Cys on Ventotene Island after a four-year rat eradication campaign, and its high prevalence in the only location with prolonged AR use (Auckland Zoo) in Aotearoa/New Zealand, suggests that persistent AR use may have exerted selective pressure on resistant genotypes. Therefore, AR should be used for the shortest time possible and resistance screening should always be the first step of AR-based eradication campaigns. Phylogeographic analyses using mitochondrial DNA focused on the central Mediterranean basin. Sicily appears to be the centre of genetic diversity in the area with five different haplogroups. Surprisingly, the small island of Ventotene shows two different haplogroups not even represented in mainland Italy. The origin of this diversity is likely due to the importance of central Mediterranean in marine traffic since the Iron Age, which allowed the arrival of different haplogroups mediated by the different civilizations that colonized the islands. Conversely, other small islands show a single haplogroup each with a high similarity to some found in mainland Italy, suggesting more recent single founder events. This study provides the first insights into the feeding behaviour of mice on Mediterranean islands. DNA metabarcoding of gut and intestinal content showed a diverse diet based on arthropods (mainly lepidopterans) and large-seeded plants. Therefore, in the case of house mouse eradication, invertebrates should be given greater consideration, given their predominance in the diet of mice. By integrating these three aspects, this thesis enhances our understanding of invasive house mice on islands and provides valuable data for effective conservation strategies that should address both genetic and ecological dimensions.