The dynamics of litterfall in eucalypt woodland surrounding pine plantations

University of Technology, Sydney. Faculty of Science.Biological invasions pose one of the greatest threats to global biodiversity and frequently result in the widespread loss of flora and fauna. Biological invasions have become a major focus of ecology in recent decades, and in particular, the invasive species radiata pine (Pinus radiata D. Don) is of considerable concern. Radiata pine has a very limited distribution in the northern hemisphere in its natural range. Its utility in the timber and manufacturing industries, however, has lead to widespread planting, especially in the southern hemisphere, where over 4 million hectares of plantations have been established. In fact, radiata pine is now the most commonly cultivated conifer in the world. A growing body of evidence from studies in the southern hemisphere has shown that pines are spreading invasively beyond the confines of plantations, displacing native species and becoming the dominant species in a number of vegetation types. The negative ecological impacts associated with pine plantations now extend well beyond plantation boundaries. While a number of studies have examined the invasion of individual pines (wildings) from plantations into surrounding vegetation, very few studies have considered the impacts of pine plantations and pine litter on surrounding native plant communities. Pine litter is defined here as structures shed from pines; primarily needles and pollen cones, but also seeds and twigs. In New South Wales (Australia), pine plantations are frequently bordered by native vegetation, providing ideal conditions for pine-litter intrusion to occur. Nevertheless, rates of pine-litter intrusion have never been quantified. Furthermore, the responses of an ecosystem to an influx of pine litter are largely unknown. The aims of this thesis are first to quantify the intrusion of pine litter into native vegetation adjacent to pine plantations and second to determine the impacts of pine litter intrusion on the structure and function of native woodland communities. Fieldwork was conducted at two geographically disparate locations in the Central Tablelands of New South Wales (Australia): Jenolan Caves Karst Conservation Reserve and Gurnang State Forest. At both sites, pine plantations and native woodland are separated by a narrow fire trail that is only a few metres wide. A comparative framework is used, whereby sites in eucalypt woodland that were adjacent to pine plantations (adjacent sites) were compared with sites in eucalypt woodland that were not adjacent to plantations but rather adjacent to eucalypt woodland (reference sites). As the effect of plantations is expected to decrease with increasing distance into native vegetation, sampling plots located at distances of 0, 5, 15, 25 and 50 m from the edge of the native vegetation were established at reference and adjacent sites. This enabled testing of both the impact of plantations on native vegetation, and also the spatial extent of this impact on native vegetation. The first and crucial step in examining the intrusive effects of pine plantations was to quantify the amount of native and exotic litterfall at reference and adjacent sites. At each sampling plot, I measured the amount of native and exotic litterfall (i.e. pine litter intrusion) every 4 weeks for 1 year at Gurnang State Forest and for 2 years at Jenolan Caves Karst Conservation Reserve. Pine needles and pollen cones were found to be a significant component of litterfall in woodlands adjacent to pine plantations. Exotic and native litterfall varied both seasonally and annually. Interestingly, peak needlefall from pines occurred in autumn and winter, which coincided with the minimum native leaffall. Conversely, pine needlefall was at a minimum during summer, during which native leaffall was high. The comparison of two separate woodlands adjacent to plantations revealed similar patterns of pine-litter intrusion although the absolute quantity of pine-litter intrusion was greater at Jenolan compared to Gurnang. Comparison of the carbon (C) and nitrogen (N) content of litterfall revealed subtle yet significant differences between pine and native litterfall. Pine litter generally had a lower N content than native leaffall at Jenolan, but a higher N content than native litter at Gurnang. At both locations, the pine litterfall is additional to native litterfall and as such, pine-litter intrusion is adding additional resources to woodlands adjacent to the plantation. Having determined the rates of pine-litter intrusion, the next step was to determine the fate of pine litter once it had intruded into woodland vegetation. In the absence of fire, plant litter is ultimately broken down through the decomposition process. A three-by-three experimental design was employed, where 3 litter types (pine, native and a 50:50 mix of pine and native litter) were placed under 3 different conditions (‘reference sites’, ‘adjacent sites’, and sites within pine plantations). Litterbags were constructed and filled with a known mass of litter before being placed in the field. Every 8 weeks, for 18 months, litterbags were collected and destructively sampled. Decomposition was measured as a function of weight loss through time, while the corresponding nitrogen and carbon contents were determined. While decomposition was quite slow overall, rates of decomposition were generally faster for native litter than for pine litter. Throughout the experiment, the N concentration of litter increased in all litter types although it was higher in native litter than in pine litter. An important consequence of the slower rate of decomposition of pine litter is likely to be the accumulation of pine litter in woodlands adjacent to plantations. This may have severe implications for the structure and composition of plant communities adjacent to plantations. To test this, I examined the seasonal and spatial patterns of plant community structure of eucalypt woodlands surrounding pine plantations at Jenolan and Gurnang. Eucalypt woodland at Gurnang showed only a minor change in the structure and composition of understorey vegetation at sites nearest the plantation. In contrast, eucalypt woodland at Jenolan showed a much stronger response to plantations, with significantly lower total species richness at adjacent sites compared with reference sites. This resulted in a pronounced ‘edge effect’ up to 15 m into eucalypt woodland adjacent to pine plantations. Canonical correspondence analysis was used to examine the relationship between environmental variables and plant community structure. Pine litterfall explained a significant portion of the variation in plant community structure at reference and adjacent sites at Jenolan, where large quantities of pine litter intrude into native vegetation. At Gurnang, where smaller quantities of pine litter intrude into eucalypt woodland, pine litter intrusion explained a lower portion of the variance between reference and adjacent sites. The plantation at Jenolan consists of large, mature pines that have formed a dense closed canopy, while at Gurnang, the plantation has been established more recently and the pines are not as large, and have not formed a closed canopy. The plantations at Jenolan are therefore a greater source of litter and are also likely to have more pronounced influence on the microclimate compared with the plantations at Gurnang. Lower diversity of flora at Gurnang also may limit the ability to detect differences in plant communities between reference and adjacent sites. Finally, I investigated the impact of pine litter on plant community structure by testing the hypothesis that pine litter facilitates the germination and growth of radiata pine seeds. Using a manipulative glasshouse experiment, radiata pine seeds were sown in pots and exposed to varying quantities of different litter treatments (pine litter, native litter and a 50-50 mix of pine and native litter). The germination and subsequent growth and survival of pines were measured over a period of 2 months. Litter depth but not litter type was found to be an important determinant of pine seedling establishment. With the exception of treatments that were covered by a small layer of litter (i.e. 1 cm) increases in litter depth resulted in delayed and lower rates of seedling emergence. Although pine and native leaves are different shapes (i.e. needle vs. broadleaf) and form very differently structured litter layers (dense mat vs. loosely structured), both litters appear to cause similar physical resistance to seedling establishment. These results indicate that litter accumulation resulting from pine intrusion can alter the establishment of pine seedlings. Given the invasive nature of radiata pine, it is highly likely that increased litter depth resulting from pine-litter intrusion will influence the establishment of many native species. In summary, significant quantities of pine litter were found to intrude into native woodland adjacent to pine plantations, which in turn, appears to be responsible for observed shifts in ecosystem structure and function. This is of particular concern in instances where pine plantations are situated adjacent to native vegetation that has been set aside specifically for conservation purposes. I therefore suggest the provision of a buffer zone around plantations in order to minimise intrusive impacts of plantations on native biodiversity. Whilst this can be achieved using a number of techniques, careful consideration of the structure of native vegetation is needed when selecting the appropriate technique. Having an inappropriate buffer may have an undesirable influence on native vegetation

Neural crest migration is driven by a few trailblazer cells with a unique molecular signature narrowly confined to the invasive front

Neural crest (NC) cell migration is crucial to the formation of peripheral tissues during vertebrate development. However, how NC cells respond to different microenvironments to maintain persistence of direction and cohesion in multicellular streams remains unclear. To address this, we profiled eight subregions of a typical cranial NC cell migratory stream. Hierarchical clustering showed significant differences in the expression profiles of the lead three subregions compared with newly emerged cells. Multiplexed imaging of mRNA expression using fluorescent hybridization chain reaction (HCR) quantitatively confirmed the expression profiles of lead cells. Computational modeling predicted that a small fraction of lead cells that detect directional information is optimal for successful stream migration. Single-cell profiling then revealed a unique molecular signature that is consistent and stable over time in a subset of lead cells within the most advanced portion of the migratory front, which we term trailblazers. Model simulations that forced a lead cell behavior in the trailing subpopulation predicted cell bunching near the migratory domain entrance. Misexpression of the trailblazer molecular signature by perturbation of two upstream transcription factors agreed with the in silico prediction and showed alterations to NC cell migration distance and stream shape. These data are the first to characterize the molecular diversity within an NC cell migratory stream and offer insights into how molecular patterns are transduced into cell behaviors

Towards designer organelles by subverting the peroxisomal import pathway

The development of ‘designer’ organelles could be a key strategy to enable foreign pathways to be efficiently controlled within eukaryotic biotechnology. A fundamental component of any such system will be the implementation of a bespoke protein import pathway that can selectively deliver constituent proteins to the new compartment in the presence of existing endogenous trafficking systems. Here we show that the protein–protein interactions that control the peroxisomal protein import pathway can be manipulated to create a pair of interacting partners that still support protein import in moss cells, but are orthogonal to the naturally occurring pathways. In addition to providing a valuable experimental tool to give new insights into peroxisomal protein import, the variant receptor-signal sequence pair forms the basis of a system in which normal peroxisomal function is downregulated and replaced with an alternative pathway, an essential first step in the creation of a designer organelle

In vitro and in vivo evaluation of human adenovirus type 49 as a vector for therapeutic applications

The human adenovirus phylogenetic tree is split across seven species (A–G). Species D adenoviruses offer potential advantages for gene therapy applications, with low rates of pre-exist-ing immunity detected across screened populations. However, many aspects of the basic virology of species D—such as their cellular tropism, receptor usage, and in vivo biodistribution profile— remain unknown. Here, we have characterized human adenovirus type 49 (HAdV-D49)—a rela-tively understudied species D member. We report that HAdV-D49 does not appear to use a single pathway to gain cell entry, but appears able to interact with various surface molecules for entry. As such, HAdV-D49 can transduce a broad range of cell types in vitro, with variable engagement of blood coagulation FX. Interestingly, when comparing in vivo biodistribution to adenovirus type 5, HAdV-D49 vectors show reduced liver targeting, whilst maintaining transduction of lung and spleen. Overall, this presents HAdV-D49 as a robust viral vector platform for ex vivo manipulation of human cells, and for in vivo applications where the therapeutic goal is to target the lung or gain access to immune cells in the spleen, whilst avoiding liver interactions, such as intravascular vaccine applications

A citizen science based survey method for estimating the density of urban carnivores

Globally there are many examples of synanthropic carnivores exploiting growth in urbanisation. As carnivores can come into conflict with humans and are potential vectors of zoonotic disease, assessing densities in suburban areas and identifying factors that influence them are necessary to aid management and mitigation. However, fragmented, privately owned land restricts the use of conventional carnivore surveying techniques in these areas, requiring development of novel methods. We present a method that combines questionnaire distribution to residents with field surveys and GIS, to determine relative density of two urban carnivores in England, Great Britain. We determined the density of: red fox (Vulpes vulpes) social groups in 14, approximately 1km2 suburban areas in 8 different towns and cities; and Eurasian badger (Meles meles) social groups in three suburban areas of one city. Average relative fox group density (FGD) was 3.72 km-2, which was double the estimates for cities with resident foxes in the 1980’s. Density was comparable to an alternative estimate derived from trapping and GPS-tracking, indicating the validity of the method. However, FGD did not correlate with a national dataset based on fox sightings, indicating unreliability of the national data to determine actual densities or to extrapolate a national population estimate. Using species-specific clustering units that reflect social organisation, the method was additionally applied to suburban badgers to derive relative badger group density (BGD) for one city (Brighton, 2.41 km-2). We demonstrate that citizen science approaches can effectively obtain data to assess suburban carnivore density, however publicly derived national data sets need to be locally validated before extrapolations can be undertaken. The method we present for assessing densities of foxes and badgers in British towns and cities is also adaptable to other urban carnivores elsewhere. However this transferability is contingent on species traits meeting particular criteria, and on resident responsiveness

Assessment of a novel, capsid-modified adenovirus with an improved vascular gene transfer profile

<p>Background: Cardiovascular disorders, including coronary artery bypass graft failure and in-stent restenosis remain significant opportunities for the advancement of novel therapeutics that target neointimal hyperplasia, a characteristic of both pathologies. Gene therapy may provide a successful approach to improve the clinical outcome of these conditions, but would benefit from the development of more efficient vectors for vascular gene delivery. The aim of this study was to assess whether a novel genetically engineered Adenovirus could be utilised to produce enhanced levels of vascular gene expression.</p> <p>Methods: Vascular transduction capacity was assessed in primary human saphenous vein smooth muscle and endothelial cells using vectors expressing the LacZ reporter gene. The therapeutic capacity of the vectors was compared by measuring smooth muscle cell metabolic activity and migration following infection with vectors that over-express the candidate therapeutic gene tissue inhibitor of matrix metalloproteinase-3 (TIMP-3).</p> <p>Results: Compared to Adenovirus serotype 5 (Ad5), the novel vector Ad5T*F35++ demonstrated improved binding and transduction of human vascular cells. Ad5T*F35++ mediated expression of TIMP-3 reduced smooth muscle cell metabolic activity and migration in vitro. We also demonstrated that in human serum samples pre-existing neutralising antibodies to Ad5T*F35++ were less prevalent than Ad5 neutralising antibodies.</p> <p>Conclusions: We have developed a novel vector with improved vascular transduction and improved resistance to human serum neutralisation. This may provide a novel vector platform for human vascular gene transfer.</p&gt

Genetic Background Can Result in a Marked or Minimal Effect of Gene Knockout (GPR55 and CB2 Receptor) in Experimental Autoimmune Encephalomyelitis Models of Multiple Sclerosis

PMCID: PMC379391