School of BioSciences - Research Publications
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ItemNo Preview AvailableCharacterization of the first Wolbachia from the genus Scaptodrosophila, a male-killer from the rainforest species S.claytoni(WILEY, 2022-10)The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution and a predominance of species in Australia, but there is little information on the presence and impacts of Wolbachia endosymbionts in this group. Here we describe the first Wolbachia infection from this group, wClay isolated from Scaptodrosophila claytoni (van Klinken), a species from the east coast of Australia. The infection is polymorphic in natural populations, occurring at a frequency of around 6%-10%. wClay causes male killing, producing female-biased lines; most lines showed 100% male killing, though in 1 line it was <80%. The lines need to be maintained through the introduction of males unless the infection is removed by tetracycline treatment. wClay is transmitted at a high fidelity (98.6%) through the maternal lineage and has been stable in 2 laboratory lines across 24 generations, suggesting it is likely to persist in populations. The infection has not been previously described but is closely related to the male-killing Wolbachia recently described from Drosophila pandora based on multilocus sequence typing and the wsp gene. Male-killing Wolbachia are likely to be common in drosophilids but remain difficult to detect because the infections can often be at a low frequency.
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ItemWarmer temperatures reduce chemical tolerance in the redlegged earth mite (Halotydeus destructor), an invasive winter-active pest(JOHN WILEY & SONS LTD, 2022-07)
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ItemThe mitogenome of Halotydeus destructor (Tucker) and its relationships with other trombidiform mites as inferred from nucleotide sequences and gene arrangements(WILEY, 2021-10)The redlegged earth mite, Halotydeus destructor (Tucker, 1925: Trombidiformes, Eupodoidea, Penthaleidae), is an invasive mite species. In Australia, this mite has become a pest of winter pastures and grain crops. We report the complete mitogenome for H. destructor, the first to represent the family Penthaleidae, superfamily Eupodoidea. The mitogenome of H. destructor is 14,691 bp in size, and has a GC content of 27.87%, 13 protein-coding genes, two rRNA genes, and 22 tRNA genes. We explored evolutionary relationships of H. destructor with other members of the Trombidiformes using phylogenetic analyses of nucleotide sequences and the order of protein-coding and rRNA genes. We found strong, consistent support for the superfamily Tydeoidea being the sister taxon to the superfamily Eupodoidea based on nucleotide sequences and gene arrangements. Moreover, the gene arrangements of Eupodoidea and Tydeoidea are not only identical to each other but also identical to that of the hypothesized arthropod ancestor, showing a high level of conservatism in the mitogenomic structure of these mite superfamilies. Our study illustrates the utility of gene arrangements for providing complementary information to nucleotide sequences with respect to inferring the evolutionary relationships of species within the order Trombidiformes. The mitogenome of H. destructor provides a valuable resource for further population genetic studies of this important agricultural pest. Given the co-occurrence of closely related, morphologically similar Penthaleidae mites with H. destructor in the field, a complete mitogenome provides new opportunities to develop metabarcoding tools to study mite diversity in agro-ecosystems. Moreover, the H. destructor mitogenome fills an important taxonomic gap that will facilitate further study of trombidiform mite evolution.
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ItemEmpowering Australian insecticide resistance research with genetic information: the road ahead(WILEY, 2021-02)Abstract Insecticides are important for chemical control of arthropod pests in agricultural systems but select for resistance as an adaptive trait. Identifying the genetic mechanism(s) underpinning resistance can facilitate development of genetic markers, which can be used in monitoring programs. Moreover, understanding of genetic mechanisms in a broader population genetic context can be used to infer the origins of resistance, predict the dynamics of resistance evolution and evaluate the efficacy of different management strategies. Transitioning genetic information successfully into practical solutions requires overcoming two major hurdles. Firstly, genetic mechanisms must be identified to develop genetic markers. Secondly, routine use of genetic markers is required to build substantial spatio‐temporal data on the distribution and frequency of resistance alleles. In this study, we demonstrate large knowledge gaps on the genetic mechanisms of insecticide resistances in Australia using eight established arthropod pests important to the grains industry: Bemisia tabaci (silverleaf whitefly), Frankliniella occidentalis (western flower thrips), Halotydeus destructor (redlegged earth mite), Helicoverpa armigera (cotton bollworm), Myzus persicae (green peach aphid), Plutella xylostella (diamondback moth), Tetranychus urticae (two‐spotted spider mite) and Thrips tabaci (onion thrips). Many resistances have not been characterised at the genetic level in most pests, even for chemical MoA groups with a long history of use in Australia. Moreover, monitoring of resistance is spatio‐temporally patchy, which precludes examination of long‐term trends or predictive modelling. We suggest that leveraging cumulative global knowledge of resistances to develop a priori candidate genes, and incorporation of genomic approaches, can help overcome the hurdles of embracing genetic information in resistance management. We highlight the recently invasive Spodoptera frugiperda (fall armyworm) as a case study where genetic markers and genomic approaches should prove useful in rapidly assessing the risk of this species to the Australian grains industry and other agricultural commodities. The uptake of genetic information into management can only occur once its benefit to empower insecticide resistance research is fully realised. Ultimately, the road ahead requires amalgamation of multifaceted data (genes, environment and spatio‐temporal replication) to better understand and predict the dynamics of resistance evolution.
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ItemRelated plants tend to share pollinators and herbivores, but strength of phylogenetic signal varies among plant families(WILEY, 2020-05)Related plants are often hypothesized to interact with similar sets of pollinators and herbivores, but this idea has only mixed empirical support. This may be because plant families vary in their tendency to share interaction partners. We quantify overlap of interaction partners for all pairs of plants in 59 pollination and 11 herbivory networks based on the numbers of shared and unshared interaction partners (thereby capturing both proportional and absolute overlap). We test for relationships between phylogenetic distance and partner overlap within each network; whether these relationships varied with the composition of the plant community; and whether well-represented plant families showed different relationships. Across all networks, more closely related plants tended to have greater overlap. The strength of this relationship within a network was unrelated to the composition of the network's plant component, but, when considered separately, different plant families showed different relationships between phylogenetic distance and overlap of interaction partners. The variety of relationships between phylogenetic distance and partner overlap in different plant families probably reflects a comparable variety of ecological and evolutionary processes. Considering factors affecting particular species-rich groups within a community could be the key to understanding the distribution of interactions at the network level.
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ItemReady on arrival: Standing variation at a chromosomal inversion contributes to rapid adaptation in an invasive marine crab(WILEY, 2022-01)In this issue of Molecular Ecology, Tepolt et al. (2021) illustrate how the genetic architecture of adaptation and life history influence invasive success. A marvel of many invasive species is that they are incredibly successful despite evolutionary expectations that they will have low adaptive potential and suffer inbreeding depression due to initially small founding population sizes. Determining the combinations of ecoevolutionary factors that permit this apparent "genetic paradox of invasions" is an ongoing endeavour of invasive species research. Tepolt et al. (2021) study the European green crab in its invasive range on the North American west coast. Following a single introduction into California, this crab quickly spread across a wide latitude gradient, despite low diversity in the original founding population. Adaptation of this crab to clinal variation in temperature appeared largely driven by an inferred chromosomal inversion. This inversion exists as a balanced polymorphism in the European home range of green crabs and is associated with thermal tolerance. Tepolt et al. (2021) therefore demonstrate that adaptive evolution post introduction need not be impeded by bottlenecks if variation at key parts of the genome is available and can be maintained in introduced populations. Moreover, Tepolt et al. (2021) show how chromosomal inversions acting as large-effect loci might facilitate rapid responses to selection in introduced populations.
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ItemGlobal connections with some genomic differentiation occur between Indo-Pacific and Atlantic Ocean wahoo, a large circumtropical pelagic fish(WILEY, 2021-08)Abstract Aim Globally distributed pelagic fishes are typified by very low to negligible genetic differentiation at oceanic scales arising from high gene flow and (or) large population sizes. However, genomic approaches employing thousands of loci to characterise genetic variation can illuminate subtle patterns of genetic structure and facilitate demographic inference, such that effects arising from gene flow and population size can be partially decoupled. We used a population genomics approach to identify putative stocks in a circumtropical pelagic fish, wahoo, and to assess global connectivity in this species. Location Indo‐Pacific and Atlantic Oceans. Taxon Wahoo, Acanthocybium solandri (Cuvier, 1832). Methods Globally distributed wahoo samples from 11 locations (representing a total of 296 individuals) were sequenced using a pool‐seq ezRAD approach to obtain 1289–9825 genome‐wide SNP loci per population pair for analyses of genetic structure at a minor allele frequency (MAF) >0.05. Demographic inference using a diffusion approximation method (∂a∂i) was performed using 11,495–12,812 SNPs per population pair at a MAF >0.02. Results Genetic structure, measured as FST, was overall low, suggesting very little heterogeneity amongst sample pairs (pairwise FST ≤ 0.021). However, there was a clear signal of regional genetic structuring between ocean basins. A principal coordinate analysis separated samples from the Indo‐Pacific with those from the Atlantic and an analysis of molecular variance suggested that ~77% of variation in genetic structure was amongst regions. Our demographic analyses found greater support for models including migration over simple models of isolation. Main conclusions Our study provides the most thorough genetic investigation of wahoo to date. We provide evidence for global connectivity of wahoo populations over their evolutionary history, but we also provide the first indication of subtle regional structure between the Indo‐Pacific and Atlantic Oceans, which occurs against a background of high gene flow. The identification of regional stocks will inform new management strategies and guide future investigations in wahoo, an increasingly important species in global fisheries.
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ItemGenetic and phenotypic variation exhibit both predictable and stochastic patterns across an intertidal fish metapopulation(WILEY, 2021-09)Interactions among selection, gene flow, and drift affect the trajectory of adaptive evolution. In natural populations, the direction and magnitude of these processes can be variable across different spatial, temporal, or ontogenetic scales. Consequently, variability in evolutionary processes affects the predictability or stochasticity of microevolutionary outcomes. We studied an intertidal fish, Bathygobius cocosensis (Bleeker, 1854), to understand how space, time, and life stage structure genetic and phenotypic variation in a species with potentially extensive dispersal and a complex life cycle (larval dispersal preceding benthic recruitment). We sampled juvenile and adult life stages, at three sites, over three years. Genome-wide SNPs uncovered a pattern of chaotic genetic patchiness, that is, weak-but-significant patchy spatial genetic structure that was variable through time and between life stages. Outlier locus analyses suggested that targets of spatially divergent selection were mostly temporally variable, though a significant number of spatial outlier loci were shared between life stages. Head shape, a putatively ecologically responsive (adaptive) phenotype in B. cocosensis also exhibited high temporal variability within sites. However, consistent spatial relationships between sites indicated that environmental similarities among sites may generate predictable phenotype distributions across space. Our study highlights the complex microevolutionary dynamics of marine systems, where consideration of multiple ecological dimensions can reveal both predictable and stochastic patterns in the distributions of genetic and phenotypic variation. Such considerations probably apply to species that possess short, complex life cycles, have large dispersal potential and fecundities, and that inhabit heterogeneous environments.