School of BioSciences - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 3 of 3
  • Item
    Thumbnail Image
    Conservation of freshwater macroinvertebrates through molecular methods
    Tsyrlin, Edward ( 2023-09)
    Freshwater macroinvertebrates are a diverse group of aquatic animals that lack backbones, including insects, worms, crustaceans, and molluscs, with sizes larger than one-third of a millimetre. For over a century, this group has primarily served as an indicator of stream health, and for practical reasons, have been typically identified at the family level. While potentially suitable for generic ‘waterway health’ assessments, the recent evidence of the biodiversity loss within freshwater ecosystems globally, requires reliable methods that go beyond the family level to more accurately measure biodiversity, including species richness and composition within this group. To address this need, in Chapter 2, Marxan conservation planning software was used to analyse a dataset collected from 140 sites in Greater Melbourne, Australia, spanning from 1993 to 2009. Our analysis demonstrated the inadequacy of the family-level data analysis in assessing species-level diversity. Specifically, the minimum number of sites required to observe all families or all species in Greater Melbourne was compared to show that the use of family-level data leads to an insufficient sampling effort for the purpose of biodiversity assessments. Furthermore, the selection of 17% and 50% of optimal conservation sites using family-level data versus species-level data revealed that the use of family-level data would result in important omissions, jeopardizing the conservation of rare species in the Melbourne area. The adoption of DNA metabarcoding as a routine species identification method is advocated for biomonitoring, including biodiversity assessments. This approach offers greater insights into local and regional biodiversity values, facilitates the detection of subtle changes in site community composition, and reinvigorates the study of species-level taxonomy among freshwater macroinvertebrates. Subsequent studies in this thesis focus on employing molecular techniques to enhance our understanding of the biodiversity and taxonomy of critically endangered and poorly known freshwater macroinvertebrates. Chapter 3 aimed to improve our knowledge of the distribution of two endangered amphipod species, Austrogammarus australis and Austrogammarus haasei, also known as Dandenong and Sherbrooke amphipods, within the Dandenong Ranges, Victoria, Australia. While the previous delineation of A. haasei was well supported by the DNA analyses, A. australis was separated into six distinct genetic lineages. Three other genetically distinct groups were found outside of the Dandenong Ranges. Further research is required to taxonomically classify these lineages, potentially leading to changes in the conservation status and management priorities for these groups. This study highlights the value of DNA barcoding techniques for detecting cryptic species, particularly when these species already hold conservation significance. In Chapter 4, DNA barcoding was also employed to detect environmental DNA (eDNA) of another critically endangered freshwater invertebrate, the Mount Donna Buang wingless stonefly (Riekoperla darlingtoni), to potentially identify new populations outside its known range. The survey revealed two new localities located 2.5 km west of previously known populations, expanding the extent of occurrence to 0.37 square km, across a total of five localities. A significant decline in the abundance of the main population correlated with climate warming. This study demonstrated that eDNA survey methods are sensitive and reliable for detecting freshwater invertebrate species occurring at low densities and difficult to sample habitats, compared to conventional methods. These results provided the necessary data for a submission to list the species under the Australian federal Environment Protection and Biodiversity Conservation Act (EPBC) 1999. The study also contributed to a case to protect the species from a proposed development within its range and attracted international recognition to this unique and vulnerable species through the IUCN. Chapter 5 addresses the common challenge of associating aquatic juvenile and terrestrial adult life stages. DNA barcoding has the advantage of reducing the need for rearing juvenile stages by associating both stages through their DNA. Additionally, DNA data facilitated the examination of relationship among the species in this study. This approach was applied to associate larval stages with previously described adults and to redescribe the larval stage of the diving beetle Chostonectes nebulosus. An identification key to all known Chostonectes was constructed using morphological characters. The increasingly pivotal role of DNA methods in detecting and discovering freshwater macroinvertebrate species is highlighted throughout the manuscript. These methods are expected to greatly improve the assessment and management of invertebrate diversity, laying a solid foundation for making well-informed decisions in conservation management and shaping evidence-based environmental policies.
  • Item
    No Preview Available
    Towards Strategies for the Control of Invasive Liriomyza Pests in Australia: Dispersal Pathways, Parasitoid Wasps and Endosymbionts
    Xu, Xuefen ( 2022)
    The Agromyzidae are a family of small, morphologically similar flies whose larvae feed internally on living plant tissue, often as stem and leaf-miners. The genus Liriomyza is the most well-known and more than 20 species are recorded as pests or potential pests of crops worldwide. They are highly polyphagous and have a strong propensity to colonize new plant hosts. Among them, three polyphagous Liriomyza species - Liriomyza sativae, L. huidobrensis, and L. trifolii - are recognized as the most damaging leafmining pests that have spread to many new areas in the world including Australia, imposing additional financial burdens to the agricultural and horticultural industries. Unfortunately, systematic strategies for the management of Liriomyza pests in Australia have been largely unexplored. Therefore, this thesis focuses on the identification of leafmining species, the dispersal pathway of one of the exotic Liriomyza species, and an exploration of biological control methods that can help control the outbreak of Liriomyza in Australia. Firstly, molecular methods based on cytochrome c oxidase subunit 1 (COI) DNA barcodes were deployed to character 13 dipteran leafminer species collected from Australia and overseas. In Australia, there already exist some leafmining species that look similar to exotic Liriomyza pests but with little economic importance. The taxonomy of leafmining flies is often challenging due to the complicated morphological keys as well as putative cryptic species. We here provide a baseline for DNA-based identification of pest Liriomyza incursions spreading across the Australian east coast and other species already present in Australia. Secondly, genome-wide single nucleotide polymorphisms (SNPs) were generated by double-digest restriction-site associated DNA sequencing (ddRAD-seq) to reveal the potential origin(s) of Liriomyza sativae into Australia and contribute to reconstruct its global invasion history, showing that the Torres Strait population is the source of the mainland population and highlighting the mixed origins of the Torres Strait population. Thirdly, 13 dipteran leaf-mining species were examined for Wolbachia infections and the potential for this endosymbiont in biocontrol. The comparison of Wolbachia relatedness relied on the wsp/MLST genes. A colony of Liriomyza brassicae was established and treated with tetracycline for reciprocal crosses and cytoplasmic incompatibility was demonstrated. These findings highlight the potential of Wolbachia to impact the Liriomyza pests based on approaches such as the incompatible insect technique. Fourthly, natural enemies like parasitoid wasps are recognized as effective biological agents worldwide to suppress the outbreak of polyphagous leafmining pests. However, the parasitoid complexes in Australia are poorly studied due to their small body size and challenging morphological diagnostic characteristics. To address the knowledge gap of parasitoid wasps in Australia, molecular methods based on cytochrome c oxidase subunit 1 (COI) DNA barcodes as well as traditional morphological approaches were employed to identify 13 parasitoid species. The status of endosymbionts was also checked in these parasitoid wasps given the limited information available in the literature, and two endosymbionts were identified. These findings provide the foundation for employing parasitoid wasps as biological agents for the management of exotic leafmining pests in the future. Fifthly, thelytokous parasitoid wasps are preferred for mass rearing due to an absence of male wastage, and the possible existence of thelytoky locally was explored. In Japan and China, Neochrysocharis formosa infected with Rickettsia are thelytokous and are suggested to be effective to control the polyphagous Liriomyza pests. In Australia, Neochrysocharis specimens have only been identified to genus but not formally identified. Using five DNA barcodes, we identified N. formosa from Australia and established the presence of Proacrias, a genus of leafminer parasitoid not previously detected in Australia. 16S rRNA sequencing indicated that both species were infected with a Rickettsia bacterium. These findings expand records of parasitoids to attack leafminers in Australia and highlight the potential of applying endosymbionts to produce thelytokous strains to increase the efficiency of biocontrol.
  • Item
    Thumbnail Image
    The diversity and behaviour of Dermaptera (earwigs) in the southern Australian grain belt
    Stuart, Oliver ( 2018)
    Dermaptera (earwigs) are a cosmopolitan order of insects that have recently come to the attention of the Australian grain industry. Researchers have been sampling Dermapteran diversity and abundance across the southern Australian grain belt, but resolution of the sample is stifled by taxonomic impediment, particularly for specimens of the morphologically uniform Anisolabididae family. Molecular methods can provide much needed resolution to the study of Australian Dermaptera. I barcoded known Dermaptera species from across the southern Australian states to assess the utility of barcoding for Dermapteran biodiversity research. I also assessed the diversity of the Anisolabididae by combining morphological identification and DNA barcodes. I then estimated their phylogeny with a larger molecular dataset comprised of two mitochondrial and two nuclear gene fragments under a maximum-likelihood framework. Anisolabididae males were divided into seven morphospecies based on the shape of the forceps and parameres (a male genital structure), and these morphospecies were corroborated by barcodes (low within versus between-species genetic distance). Paramere shape distinguished two putative genera, Anisolabis Fieber and Gonolabis Burr. The molecular phylogeny did not support the monophyly of the genera, rather forming clades distinguished by the shape of the forceps. The evolutionary significance of paramere versus forceps morphology in Dermapteran taxonomy is discussed. Anisolabididae were only found in Western and South Australia and showed apparent endemism. Extending the study of Australian Anisolabididae beyond grains-producing regions may reveal a diverse endemic fauna, almost entirely unexplored heretofore.