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    Direct and indirect impacts of the Tuberolachnus salignus (Hemiptera: Aphididae) invasion in New Zealand and management alternatives
    (Published by Oxford University Press on behalf of Entomological Society of America, 2022) Tun KM; Minor M; Jones T; Clavijo-McCormick AC; Joyce A
    Invasive insects are a serious problem in New Zealand, and their introduction and successful establishment are predicted to increase with global commerce and climate change. A recent introduction to New Zealand is Tuberolachnus salignus (Gmelin), a large aphid that attacks mainly willows but also other plants such as poplars, apples, and pears. It was first reported in 2013 but has since then spread rapidly throughout the country. We conducted a 2-yr study exploring the direct (on the host plant) and indirect (on other organisms) impacts of the aphid, in a field setting including 15 willow clones selected to represent the variety of species and hybrids present in New Zealand. Our research revealed great variation in the level of resistance/susceptibility of different clones and suggested a trade-off between reproduction, growth, and defense. We investigated the indirect effects of the aphid on honeydew foragers and on the soil ecosystem, through honeydew production and deposition, revealing complex cascading effects involving multiple trophic levels. We also explore and discuss management alternatives including the replacement of willows for native species or resistant varieties, the use of biological control agents, and the feasibility of chemical control. This work is one of few studies on the complex ecological effects of invasive phytophagous insects and could serve as a model for future research and to inform pest management. To conclude, we identify gaps in the knowledge and highlight aspects requiring further research.
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    Viability and dormancy of the Clematis vitalba aerial seed bank.
    (John Wiley & Sons, Inc on behalf of German Society for Plant Sciences, Royal Botanical Society of the Netherlands., 2024-04-01) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW; Bentsink L
    Old man's beard (Clematis vitalba L.) is a liana species that has become invasive in many areas of its introduced range. Seeds are produced in abundance and are both physiologically and morphologically dormant upon maturity. To understand the importance of seeds to its invasiveness, changes in viability and dormancy of the aerial seed bank were tracked throughout the after-ripening period and during storage. Seeds collected every second month for 2 years were subjected to germination tests. Other seeds stored in outdoor ambient conditions or in a dry, chilled state were dissected before, during, and after imbibition, as well as during incubation, to measure embryo size. Less than 72% of seeds on the mother plant were viable. Viable seeds remained completely morpho-physiologically dormant throughout autumn, even when treated with nitrate. Physiological dormancy declined in response to seasonal changes, yet morphological dormancy did not change until seeds had been exposed to appropriate germination conditions for several days. Fully dormant autumn seeds decayed at higher rates during incubation than partially or fully after-ripened seeds, which were also more germinable and less dormant. Furthermore, seeds incubated in complete darkness were more likely to decay or remain dormant than those exposed to light. This study demonstrates that fewer than three-quarters of seeds produced are viable and further decay occurs after dispersal, yet total fertility is still very high, with enormous propagule pressure from seeds alone. Viable seeds are protected with two forms of dormancy; morphological dormancy requires additional germination cues in order to break after seasonal changes break physiological dormancy.
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    Population genetics and genomics of a marsupial species : analysis of native and invasive brushtail possum populations (Trichosurus vulpecula) : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Conservation Biology, Massey University, Manawatū Campus, New Zealand
    (Masey University, 2024-04-15) Pattabiraman, Nimeshika
    One of the leading causes of global biodiversity decline is the introduction of invasive pest species that destroy native flora and compete with native fauna for food and other resources. Aotearoa New Zealand is one of the foremost countries in the world that has focussed on eradicating pest species and in particular exotic mammals from the archipelago, which lacks native, terrestrial mammals. The New Zealand Government recently set in train the ambitious task of removing all mustelids, rats, and possums from the terrestrial landscape by the year 2050. Brushtail possums (Trichosurus vulpecula) were introduced to Aotearoa New Zealand from Australia in the mid-1800s, after which they were translocated across the country and have become widespread, destroying indigenous habitat, eating native birds and invertebrates, and spreading bovine TB. Control efforts have seen possum numbers decline in the last two decades from close to 75 million in 2002 to 40 million in 2020. There is, however, a gap in the scientific understanding of possum populations with respect to their genetic composition and population structure across the country, and this knowledge could help us develop effective and dynamic management strategies to eradicate possums on a nationwide scale. In this thesis, I focus on three aspects of population structure and diversity of brushtail possums. First, I investigated a small geographical study area - The Kenepuru Peninsula - where I sought evidence of genetic correlations with geography, time and fur colour. I used two types of genetic markers that target the nuclear and mitochondrial regions of possum DNA with large population samples. In every case, it was determined that the possums comprised one freely interbreeding population at this scale. In particular I demonstrated that colour morphs associated with distinct subspecies in Australia, freely interbreed in New Zealand. I then increased the scale of sampling to include representation of populations across New Zealand and Australia, with the same genetic markers. This threw light on the heterogenous nature of possum diversity in New Zealand, and showed that even after ~110 generations, possums retained genetic separation among spatial groups. Additionally, the data showed evidence of multiple possum lineages across New Zealand that are derived from several Australian populations. High haplotype diversity in New Zealand suggests that the rapidly expanding population has retained novel haplotypes and the data thus far indicated a non-homogenous (metapopulation) distribution of possums without geographical concordance. As the project progressed, I was able to apply high-throughput genotyping-by-sequencing to generate a large genomic dataset. This dataset provided much more detail of the genotypic distribution of possums in Australia and among invasive metapopulations in New Zealand, as well as informing us of the relationship between them. This large, robust database of possum population structure and genetic diversity throughout Aotearoa New Zealand will support future studies in providing informed management decisions to eradicate brushtail possums.
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    Effects of Two Invasive Weeds on Arthropod Community Structure on the Central Plateau of New Zealand
    (MDPI (Basel, Switzerland), 20/07/2020) Effah E; Barrett DP; Peterson PG; Potter MA; Holopainen JK; Clavijo McCormick A
    Heather (Calluna vulgaris) and broom (Cytisus scoparius), originally from Europe, are the main invasive plants on New Zealand's North Island Central Plateau, where they threaten native flora and fauna. Given the strong link between arthropod communities and plants, we explored the impact of these invasive weeds on the diversity and composition of associated arthropod assemblages in this area. The arthropods in heather-invaded areas, broom-invaded areas, and areas dominated by the native species mānuka (Leptospermum scoparium) and Dracohyllum (Dracophyllum subulatum) were collected and identified to order. During summer and autumn, arthropods were collected using beating trays, flight intercept traps and pitfall traps. Diversity indices (Richness, Shannon's index and Simpson's index) were calculated at the order level, and permutational multivariate analysis (PERMANOVA) was used to explore differences in order-level community composition. Our results show a significant variation in community composition for all trapping methods in both seasons, whereas invasive plants did not profoundly impact arthropod order richness. The presence of broom increased arthropod abundance, while heather was linked to a reduction. Under all possible plant pairings between heather, broom, mānuka, and Dracophylum, the impact of neighbouring plant identity on arthropod community composition was further explored for the samples collected using beating trays. The results suggest that during plant invasion, arthropod communities are affected by neighbouring plant identity and that impacts vary between arthropod sampling methods and seasons.
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    Evolutionary history of rat-borne Bartonella: the importance of commensal rats in the dissemination of bacterial infections globally
    (John Wiley & Sons, 2013) Hayman DTS; McDonald KD; Kosoy MY
    Emerging pathogens that originate from invasive species have caused numerous significant epidemics. Some bacteria of genus Bartonella are rodent-borne pathogens that can cause disease in humans and animals alike. We analyzed gltA sequences of 191 strains of rat-associated bartonellae from 29 rodent species from 17 countries to test the hypotheses that this bacterial complex evolved and diversified in Southeast Asia before being disseminated by commensal rats Rattus rattus (black rat) and Rattus norvegicus (Norway rat) to other parts of the globe. The analysis suggests that there have been numerous dispersal events within Asia and introductions from Asia to other regions, with six major clades containing Southeast Asian isolates that appear to have been dispersed globally. Phylogeographic analyses support the hypotheses that these bacteria originated in Southeast Asia and commensal rodents (R. rattus and R. norvegicus) play key roles in the evolution and dissemination of this Bartonella complex throughout the world.
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    Natural Variation in Volatile Emissions of the Invasive Weed Calluna vulgaris in New Zealand
    (MDPI (Basel, Switzerland), 21/02/2020) Effah E; Barrett DP; Peterson PG; Godfrey AJR; Potter MA; Holopainen JK; Clavijo McCormick A
    Invasive plants pose a threat to natural ecosystems, changing the community composition and ecological dynamics. One aspect that has received little attention is the production and emission of volatile organic compounds (VOCs) by invasive plants. Investigating VOCs is important because they are involved in vital ecological interactions such as pollination, herbivory and plant competition. Heather, Calluna vulgaris, is a major invasive weed in New Zealand, especially on the Central Plateau, where it has spread rapidly since its introduction in 1912, outcompeting native species. However, the chemical behaviour of heather in its invaded ranges is poorly understood. We aimed to explore the natural variation in volatile emissions of heather and the biotic and abiotic factors influencing them on the Central Plateau of New Zealand. To this end, foliar volatiles produced by heather at four different sites were collected and analysed using gas chromatography coupled to mass spectrometry. Soil properties, herbivory and other environmental data were also collected at each site to investigate their effects on VOC emissions using generalised linear models (GLMs). Our results reveal significant differences in VOC emissions between sites and suggest that soil nutrients are the main factor accounting for these differences. Herbivory and temperature had only a minor effect, while soil water content had no impact. Further studies are needed to investigate how these variations in the invasive plant's foliar volatiles influence native species.