Invasion success of exotic vines in Australia : the importance of life-history, introduction-history and ecological attributes

University of Technology, Sydney. Faculty of Science.Exotic plants that become widespread and abundant (i.e. invasive) in their new range are becoming a worldwide environmental problem. Invasive plants are responsible for a number of ecological problems such as losses in biodiversity, alterations in ecosystem function and species extinctions. One of the most important steps for the successful management of invasive plants is the identification of factors that enable an introduced exotic species to become invasive. Importantly, not all introduced plants become invasive and by comparing exotic, non-invasive species to species that are invasive, it is possible to determine the suite of traits common to invasive plants that distinguishes them from non-invasive exotics. The identification of the characteristics of highly invasive species provides a greater understanding of factors contributing to their invasion success and thus contributes to the effective management of invasive plants. In Australia, the invasion of a particular group of exotic plants, vines, is now recognised as a major threat to native biodiversity. The destructive potential of exotic vines in natural ecosystems has been recognised through the determination of invasion by exotic vines as a key threatening process by the New South Wales Scientific Committee. Yet despite the acknowledgment of the invasive potential of exotic vines, there is a paucity of information about the factors contributing to their invasion success. Thus, understanding the factors behind the invasion success of exotic vines is a research and management priority. The primary aim of this thesis was to investigate the role that life-history, introduction-history and ecological traits play in the invasion success of exotic vines across Australia. My research examined relationships between invasion success of exotic vines and these traits at local, regional and continental spatial scales. To do this, I employed a comparative, target-area approach to distinguish differences between the attributes of non-invasive and invasive exotic vines. Given the depauperate knowledge surrounding almost all aspects of the ecology of exotic vines in Australia, I first constructed an inventory of exotic vine species present in Australia. This important first step then enabled the process of identifying attributes related to the invasion success of exotic vines in Australia to take place. A total of 179 species of exotic vines were identified as having established self-sustaining populations in Australia. I then performed a desktop study that focused on introduction-history attributes. I focused specifically on residence time (i.e. the length of time that each species has been present in Australia), continent of origin and reason for introduction. Minimum residence time was a significant predictor of the invasion success of exotic vines at a continental scale. That is, exotic vine species that, on average, have been present in Australia for a longer period of time were significantly more abundant than those species that had been introduced more recently. The continent of origin and reason for introduction were not significant predictors of invasion success, meaning that neither the geographic origin nor mode of introduction of exotic vine species are of consequence - in the context of these two traits, all species have the same likelihood of becoming invasive. I then investigated relationships between life-history traits and invasion success of exotic vines across Australia. Six life-history traits were examined: seed volume, longevity, propagation, dispersal mechanism, leaf length and leaf shape. These traits were selected because they represent important aspects (or were surrogates) of a plant's life-history that have been shown to influence the invasion success of exotic plants in other ecosystems. In addition to cross-species analyses, phylogenetic regressions were performed to identify any traits that demonstrated correlated evolution with the capacity for invasion success throughout their phylogeny. I found that, in addition to residence time, annual life form, reproduction via seeds and animal dispersed seeds were traits that were positively related to the abundance of exotic vines in Australia. No phylogenetic relationships were detected between species traits and exotic vine abundance. Local and regional scale data were collected in three littoral rainforest communities located in northern New South Wales (NSW), Australia. Littoral rainforest is an ecologically endangered community in NSW and is often found as a highly fragmented and disturbed ecosystem. As a result, littoral rainforest is vulnerable to invasion by exotic species and consequently invasive vines pose a significant threat to the health of littoral rainforest ecosystems. At the regional scale, three study regions were sampled by establishing 40 randomly allocated quadrats (each 20 x 20 m) in each study area, with an entire region representing one sampling unit, or replicate. The presence of all exotic vine species in each quadrat was recorded. At the local scale, 20 of these quadrats were sampled in more detail, with individual quadrats representing sampling units. Here, the canopy cover of each exotic vine species was recorded. The way in which exotic vine communities are assembled may also reveal important insights into differences between non-invasive and invasive exotic vines. To explore patterns of association between exotic vine species at the regional scale, I constructed presence-absence matrices for the presence of each exotic vine species in every quadrat for each study region. I found that exotic vine species occurred together more often than would be expected by chance alone. There are several explanatory mechanisms behind these positive associations. A candidate explanation for the observed pattern is that facilitative mechanisms are operating amongst exotic vines, enabling a greater number of species to coexist. Notably, negative patterns of association (i.e. species being found together less than expected in a randomly assembled community) were never observed which adds further credence to the facilitation hypothesis. Life-history traits were then measured at local and regional spatial scales in order to investigate how these attributes may differ among non-invasive and invasive exotic vines. For each species, I measured specific leaf area (SLA), seed mass, reproductive allocation, flowering duration and fruiting duration every season over the course of one year. Not all species produced seeds during the sampling period and therefore three species were targeted for seed trait analysis. In addition to plant life-history traits, I measured soil nitrogen, phosphorus and pH at each quadrat to explore the relationships between exotic vine abundance and soil characteristics at the local scale. Different patterns and relationships between the traits measured and exotic vine invasion success emerged across different spatial scales, highlighting the importance of accounting for the scale at which plant traits are measured. Flowering and fruiting duration emerged as being the most consistent predictors of exotic vine abundance at both local and regional scales. Invasive species had longer flowering and fruiting times than non-invasive exotic species. A negative relationship between SLA was found as predicting exotic vine invasiveness, especially at local scales, with invasive vines having significantly lower SLA than non-invasive exotics. Furthermore, negative relationships between exotic vine invasiveness and the concentration of soil phosphorous and nitrogen were also observed. These negative relationships between low soil nutrients, low SLA and invasion success are likely to be interrelated, with low soil concentrations favouring species with low SLA due to the longer leaf longevity of low SLA species, which enables vines to retain nutrients for a longer period of time than co-occurring vines with higher SLA. In addition to measuring these traits, I also measured variation, or phenotypic plasticity, to explore the role that plasticity in a trait may have in explaining exotic vine abundance. Specifically, I measured the variance in SLA and seed mass within exotic vine species at both local and regional scales. I found that variation within SLA was a significant predictor of the abundance of some exotic vine species, yet was not related to the abundance of the most invasive species. This suggests that while trait plasticity does affect exotic vine abundances, it is not strongly related to their invasion success. The enemy release hypothesis is a common theory proposed to explain invasion success of introduced species, whereby introduced species may increase their abundance due to a lack of natural predators in their introduced range. Field observations at my study sites identified that some species appeared to suffer greater leaf damage than others. This observation led to further field investigations of the role that insect herbivory and leaf traits may play in predicting the invasion success of invasive exotic species in comparison to those that do not achieve the same level of abundance. I predicted that, according to the enemy release hypothesis, invasive plants would have significantly less insect herbivory than non-invasive exotic vines and that leaf traits would explain these decreased herbivory rates. I measured a number of attributes including the percent of leaf damage from insect attack, type of leaf damage, leaf toughness, SLA and leaf nitrogen content. There was no relationship found between the amount of herbivore damage and invasion success of exotic vines, thus not supporting the enemy release hypothesis. I also found that, whilst there were significant differences in the leaf attributes measured, specifically leaf toughness, SLA and nitrogen content among species, they were not related to the abundance of any exotic vines in littoral rainforest. These results suggest that a reduction in herbivore damage does not explain the invasion success of exotic vines. Indeed increased herbivory for one type of insect damage was associated with species that had high abundances. The findings of this thesis depart considerably from many other studies on plant species invasion, with unique findings between invasiveness and attributes such as low SLA, large seed mass and low soil nutrients. These differences highlight that exotic vines are unlike other groups of exotic plants in many ways, which may have important consequences for the ecosystems they invade. I suggest that these dissimilarities are primarily a function of the structural differences of vines to other plant functional groups, providing invasive vines with a number of ecological advantages

Recombination events among virulence genes in malaria parasites are associated with G-quadruplex-forming DNA motifs

Background Malaria parasites of the genus Plasmodium possess large hyper-variable families of antigen-encoding genes. These are often variantly-expressed and are major virulence factors for immune evasion and the maintenance of chronic infections. Recombination and diversification of these gene families occurs readily, and may be promoted by G-quadruplex (G4) DNA motifs within and close to the variant genes. G4s have been shown to cause replication fork stalling, DNA breakage and recombination in model systems, but these motifs remain largely unstudied in Plasmodium. Results We examined the nature and distribution of putative G4-forming sequences in multiple Plasmodium genomes, finding that their co-distribution with variant gene families is conserved across different Plasmodium species that have different types of variant gene families. In P. falciparum, where a large set of recombination events that occurred over time in cultured parasites has been mapped, we found a strong spatial association between these recombination events and putative G4-forming sequences. Finally, we searched Plasmodium genomes for the three classes of helicase that can unwind G4s: Plasmodium spp. have no identifiable homologue of the highly efficient G4 helicase PIF1, but they do encode two putative RecQ helicases and one homologue of the RAD3-family helicase FANCJ. Conclusions Our analyses, conducted at the whole-genome level in multiple species of Plasmodium, support the concept that G4s are likely to be involved in recombination and diversification of antigen-encoding gene families in this important protozoan pathogen

Support vector recurrent neurofuzzy networks in modeling nonlinear systems with correlated noise

Good generalization results are obtained from neurofuzzy networks if its structure is suitably chosen. To select the structure of neurofuzzy networks, the authors proposed a construction algorithm that is derived from the Support Vector Regression. However, the modeling errors are assumed to be uncorrelated. In this paper, systems with correlated modeling errors are considered. The correlated noise is modeled separately by a recurrent network. The overall network is referred to as the support vector recurrent neurofuzzy networks. The prediction error method is used to train the networks, where the derivatives are computed by a sensitivity model. The performance of proposed networks is illustrated by an example involving a nonlinear dynamic system corrupted by correlated noise.published_or_final_versio

Mammary Stem Cells: Premise, Properties, and Perspectives

Adult mammary stem cells (MaSCs) drive postnatal organogenesis and remodeling in the mammary gland, and their longevity and potential have important implications for breast cancer. However, despite intense investigation the identity, location, and differentiation potential of MaSCs remain subject to deliberation. The application of genetic lineage-tracing models, combined with quantitative 3D imaging and biophysical methods, has provided new insights into the mammary epithelial hierarchy that challenge classical definitions of MaSC potency and behaviors. We review here recent advances - discussing fundamental unresolved properties of MaSC potency, dynamics, and plasticity - and point to evolving technologies that promise to shed new light on this intractable debate. Elucidation of the physiological mammary differentiation hierarchy is paramount to understanding the complex heterogeneous breast cancer landscape.his work was supported by the Medical Research Council ( MR/J001023/1 to C.J.W. and B.L-L.), the Wellcome Trust ( 105377/Z/14/Z to O.B.H.), the National Health and Medical Research Council ( 1071074 to F.M.D.), and a University of Queensland Early Career Researcher Grant ( UQECR1718865 to F.M.D.)

Direct and indirect effects of rotavirus vaccination: Comparing predictions from transmission dynamic models

Early observations from countries that have introduced rotavirus vaccination suggest that there may be indirect protection for unvaccinated individuals, but it is unclear whether these benefits will extend to the long term. Transmission dynamic models have attempted to quantify the indirect protection that might be expected from rotavirus vaccination in developed countries, but results have varied. To better understand the magnitude and sources of variability in model projections, we undertook a comparative analysis of transmission dynamic models for rotavirus. We fit five models to reported rotavirus gastroenteritis (RVGE) data from England and Wales, and evaluated outcomes for short- and long-term vaccination effects. All of our models reproduced the important features of rotavirus epidemics in England and Wales. Models predicted that during the initial year after vaccine introduction, incidence of severe RVGE would be reduced 1.8-2.9 times more than expected from the direct effects of the vaccine alone (28-50% at 90% coverage), but over a 5-year period following vaccine introduction severe RVGE would be reduced only by 1.1-1.7 times more than expected from the direct effects (54-90% at 90% coverage). Projections for the long-term reduction of severe RVGE ranged from a 55% reduction at full coverage to elimination with at least 80% coverage. Our models predicted short-term reductions in the incidence of RVGE that exceeded estimates of the direct effects, consistent with observations from the United States and other countries. Some of the models predicted that the short-term indirect benefits may be offset by a partial shifting of the burden of RVGE to older unvaccinated individuals. Nonetheless, even when such a shift occurs, the overall reduction in severe RVGE is considerable. Discrepancies among model predictions reflect uncertainties about age variation in the risk and reporting of RVGE, and the duration of natural and vaccine-induced immunity, highlighting important questions for future research

Single-cell lineage tracing in the mammary gland reveals stochastic clonal dispersion of stem/progenitor cell progeny.

The mammary gland undergoes cycles of growth and regeneration throughout reproductive life, a process that requires mammary stem cells (MaSCs). Whilst recent genetic fate-mapping studies using lineage-specific promoters have provided valuable insights into the mammary epithelial hierarchy, the true differentiation potential of adult MaSCs remains unclear. To address this, herein we utilize a stochastic genetic-labelling strategy to indelibly mark a single cell and its progeny in situ, combined with tissue clearing and 3D imaging. Using this approach, clones arising from a single parent cell could be visualized in their entirety. We reveal that clonal progeny contribute exclusively to either luminal or basal lineages and are distributed sporadically to branching ducts or alveoli. Quantitative analyses suggest that pools of unipotent stem/progenitor cells contribute to adult mammary gland development. Our results highlight the utility of tracing a single cell and reveal that progeny of a single proliferative MaSC/progenitor are dispersed throughout the epithelium.This work was supported by a grant from the Medical Research Council programme grant no. MR/J001023/1 (B.L-L. and C.J.W). F.M.D. was funded by a National Health and Medical Research Council CJ Martin Biomedical Fellowship (GNT1071074). O.B.H. was funded by a Wellcome Trust PhD studentship (105377/Z/14/Z)

Non-passive behavior of equivalent circuit components in AC powder electroluminescence (ACPEL) lamps

For the first time, the voltage and frequency characteristics of a single layer AC powder electroluminescent lamp have been examined in detail to reveal the individual contributions of the material components involved. Statistical modelling has been employed to refine the equivalent circuit description of the lamp. DC-blocked resistance-capacitance networks can be reduced to a single effective resistance and capacitance in series. The frequency dependence of these two quantities in the range 4–1600 Hz has been used to unravel the behavior of the different underlying resistance and capacitance components at different voltage amplitudes in the range 25–150 V. The resistive contribution, R, of the activated ZnS phosphor is shown to be non-passive, and obeys the form: R(V,f) = R0(V).f−1/3.e−T.f, where V is the applied voltage, f is the frequency and T is a time constant, at all voltages. For both ZnS and BaTiO3, other characteristics indicate the presence of a thinner, non-polarized region within each semiconducting particle located within the particle's crust. A marked change in the characteristics of the different component values occurs between 25 and 50 V, consistent with the onset of light emission, after which smooth changes in all values are observed up to 150 V.We are grateful to the Technology Strategy Board (TSB) (UK) for substantial financial funding in the form of TSB Technology programs for the PLACES, FAB3D, ACTIVEL, SHAPEL, and BEDS programs and to our many industrial collaborators on these programs

G-quadruplex DNA motifs in the malaria parasite Plasmodium falciparum and their potential as novel antimalarial drug targets

G-quadruplexes are DNA or RNA secondary structures that can be formed from guanine-rich nucleic acids. These four-stranded structures, composed of stacked quartets of guanine bases, can be highly stable and have been demonstrated to occur in vivo in the DNA of human cells and other systems, where they play important biological roles, influencing processes such as telomere maintenance, DNA replication and transcription, or, in the case of RNA G-quadruplexes, RNA translation and processing. We report for the first time that DNA G-quadruplexes can be detected in the nuclei of the malaria parasite Plasmodium falciparum, which has one of the most A/T-biased genomes sequenced and therefore possesses few guanine-rich sequences with the potential to form G-quadruplexes. We show that despite this paucity of putative G-quadruplex-forming sequences, P. falciparum parasites are sensitive to several G-quadruplex-stabilizing drugs, including quarfloxin, which previously reached phase 2 clinical trials as an anticancer drug. Quarfloxin has a rapid initial rate of kill and is active against ring stages as well as replicative stages of intraerythrocytic development. We show that several G-quadruplex-stabilizing drugs, including quarfloxin, can suppress the transcription of a G-quadruplex-containing reporter gene in P. falciparum but that quarfloxin does not appear to disrupt the transcription of rRNAs, which was proposed as its mode of action in both human cells and trypanosomes. These data suggest that quarfloxin has potential for repositioning as an antimalarial with a novel mode of action. Furthermore, G-quadruplex biology in P. falciparum may present a target for development of other new antimalarial drugs