Department of Botany and Zoology

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Browsing Department of Botany and Zoology by Subject "Acacia pycnantha"

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    Human usage in the native range may determine future genetic structure of an invasion : insights from Acacia pycnantha
    (BioMed Central, 2013-10) Le Roux, Johannes J.; Richardson, David M.; Wilson, John R. U.; Ndlovu, Joice
    Background: The influence of introduction history and post-introduction dynamics on genetic diversity and structure has been a major research focus in invasion biology. However, genetic diversity and structure in the invasive range can also be affected by human-mediated processes in the native range prior to species introductions, an aspect often neglected in invasion biology. Here we aim to trace the native provenance of the invasive tree Acacia pycnantha by comparing the genetic diversity and structure between populations in the native Australian range and the invasive range in South Africa. This approach also allowed us to explore how human actions altered genetic structure before and after the introduction of A. pycnantha into South Africa. We hypothesized that extensive movement and replanting in A. pycnantha’s Australian range prior to its introduction to South Africa might result in highly admixed genotypes in the introduced range, comparable genetic diversity in both ranges, and therefore preclude an accurate determination of native provenance(s) of invasive populations. Results: In the native range Bayesian assignment tests identified three genetic clusters with substantial admixture and could not clearly differentiate previously identified genetic entities, corroborating admixture as a result of replantings within Australia. Assignment tests that included invasive populations from South Africa indicated similar levels of admixture compared to Australian populations and a lack of genetic structure. Invasive populations of A. pycnantha in South Africa are as genetically diverse as native populations, and could not be assigned to particular native range regions. Conclusions: Our results indicate that the genetic structure of A. pycnantha in Australia has been greatly altered through various planting initiatives. Specifically, there is little geographic structure and high levels of admixture. While numerous introduction history scenarios may explain the levels of admixture observed in South Africa, planting records of A. pycnantha in Australia suggest that populations were probably already admixed before propagules were introduced to South Africa. These findings have important implications for the management of invasive A. pycnantha populations in South Africa, especially for classical biological control, and more broadly, for studies that aim to understand the evolutionary dynamics of the invasion process.
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    The invasion ecology of Acacia pycnantha : a genetic approach
    (Stellenbosch : Stellenbosch University, 2013-12) Ndlovu, Joice; Richardson, D. M.; Le Roux, J. J.; Wilson, J. R. U.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Australian Acacia species are an important group of invaders and are known to form dense monospecific cultures in invaded habitats. Despite the ecological and economic importance of invasive acacias, little is known about their invasive biology both from an ecological and evolutionary perspective. Molecular genetic methods have increasingly become important in identifying source populations for invasive species and determining the population genetic structure of these populations. This thesis applied molecular tools to understand the invasion ecology of Acacia pycnantha and its rhizobial symbionts as a model system of Australian Acacia introductions. Specific objectives were to: reconstruct the molecular phylogeny of invasive and native populations of populations of Acacia pycnantha and identify the native provenance of A. pycnantha; identify microsatellite markers for Acacia pycnantha and other invasive Australian acacias based on transferring microsatellite markers developed for A. mangium, A. saligna, Paraserianthes lophantha and universal chloroplast microsatellites developed from tobacco; assess the introduction dynamics of Acacia pycnantha in South Africa and identify the source populations in the species’ native range ; and determine which nitrogen fixing symbionts nodulate A. pycnantha and determine whether A. pycnantha brought its symbionts along from its native range or acquired them in the invasive range. Nuclear and chloroplast DNA sequence data were used to reconstruct phylogeographic relationships between native and invasive A. pycnantha populations. The chloroplast phylogeny showed that Australian populations of A. pycnantha are geographically structured into two previously informally recognized lineages (representing wetland and dry land forms). Habitat fragmentation is probably the result of cycles of aridity and abundant rainfall during the Pleistocene0. The invasive population in Portugal was found to be the wetland form while South African populations were found to be predominantly wetland form although some dryland forms were identified. Thirty microsatellites out of the forty nine tested microsatellites successfully amplified across all species tested (A. implexa, A. longifolia, A. melanoxylon, A. pycnantha and A. podalyriifolia). High Transfer rates varied between 85% for microsatellites developed for A. mangium to 50% for those developed in A. saligna. Although transfer rates were high only twelve microsatellites (24%) out of the fifty tested were polymorphic while the chloroplast microsatellites showed no polymorphism. The low level of polymorphic loci calls for development of more microsatellites in this genus especially for species that have high commodity value. Nuclear microsatellites revealed three genetic groupings with substantial admixture in the native range (1. wetland Victoria and South Australia populations; 2. dryland Victoria and Flinders Range population; and 3. New South Wales). Admixture in the native range may have occurred as a result of reforestation exercises. Acacia pycnantha has been widely used in rea forestation projects in Australia because of its fast growth rate and ease of germination. Admixed populations were most - likely introduced to South Africa thus establishment of A. pycnantha may have been facilitated by already admixed propagules in the invasive range. Extensive admixture in the native range made it difficult to identify source populations of invasive A. pycnantha found in South Africa. The rhizobial symbionts of A. pycnantha were identified, showing that this species utilizes a wider suite of symbionts in its invasive range than its native range and there is support for both the co-introduction and host jumping hypotheses. This creates substantial opportunities for horizontal gene transfer between previously allopatric bacterial lineages, with as yet unknown consequences for plant and bacterial invasions.
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    The invasion ecology of Acacia pycnantha : a genetic approach
    (Stellenbosch : Stellenbosch University, 2013-12) Ndlovu, Joice; Richardson, D. M.; Le Roux, J. J.; Wilson, J. R. U.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    Australian Acacia species are an important group of invaders and are known to form dense monospecific cultures in invaded habitats. Despite the ecological and economic importance of invasive acacias, little is known about their invasive biology both from an ecological and evolutionary perspective. Molecular genetic methods have increasingly become important in identifying source populations for invasive species and determining the population genetic structure of these populations. This thesis applied molecular tools to understand the invasion ecology of Acacia pycnantha and its rhizobial symbionts as a model system of Australian Acacia introductions. Specific objectives were to: reconstruct the molecular phylogeny of invasive and native populations of populations of Acacia pycnantha and identify the native provenance of A. pycnantha; identify microsatellite markers for Acacia pycnantha and other invasive Australian acacias based on transferring microsatellite markers developed for A. mangium, A. saligna, Paraserianthes lophantha and universal chloroplast microsatellites developed from tobacco; assess the introduction dynamics of Acacia pycnantha in South Africa and identify the source populations in the species’ native range; and determine which nitrogen fixing symbionts nodulate A. pycnantha and determine whether A. pycnantha brought its symbionts along from its native range or acquired them in the invasive range. Nuclear and chloroplast DNA sequence data were used to reconstruct phylogeographic relationships between native and invasive A. pycnantha populations. The chloroplast phylogeny showed that Australian populations of A. pycnantha are geographically structured into two previously informally recognized lineages (representing wetland and dry land forms). Habitat fragmentation is probably the result of cycles of aridity and abundant rainfall during the Pleistocene0. The invasive population in Portugal was found to be the wetland form while South African populations were found to be predominantly wetland form although some dryland forms were identified. Thirty microsatellites out of the forty nine tested microsatellites successfully amplified across all species tested (A. implexa, A. longifolia, A. melanoxylon, A. pycnantha and A. podalyriifolia). High Transfer rates varied between 85% for microsatellites developed for A. mangium to 50% for those developed in A. saligna. Although transfer rates were high only twelve microsatellites (24%) out of the fifty tested were polymorphic while the chloroplast microsatellites showed no polymorphism. The low level of polymorphic loci calls for development of more microsatellites in this genus especially for species that have high commodity value. Nuclear microsatellites revealed three genetic groupings with substantial admixture in the native range (1. wetland Victoria and South Australia populations; 2. dryland Victoria and Flinders Range population; and 3. New South Wales). Admixture in the native range may have occurred as a result of reforestation exercises. Acacia pycnantha has been widely used in real forestation projects in Australia because of its fast growth rate and ease of germination. Admixed populations were most - likely introduced to South Africa thus establishment of A. pycnantha may have been facilitated by already admixed propagules in the invasive range. Extensive admixture in the native range made it difficult to identify source populations of invasive A. pycnantha found in South Africa. The rhizobial symbionts of A. pycnantha were identified, showing that this species utilizes a wider suite of symbionts in its invasive range than its native range and there is support for both the co-introduction and host jumping hypotheses. This creates substantial opportunities for horizontal gene transfer between previously allopatric bacterial lineages, with as yet unknown consequences for plant and bacterial invasions.