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Phylogeography and Molecular Ecology of Selected Invasive Species in the Hawaiian Islands

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Title:Phylogeography and Molecular Ecology of Selected Invasive Species in the Hawaiian Islands
Authors:Le Roux, Johannes J.
Date Issued:2007
Abstract:Most alien (non-native) species which become naturalized are not disruptive to natural ecosystems. However, the small fraction that do spread and become invasive can have severe environmental and economic impacts. These impacts are often irreversible as control efforts normally only start after species are widespread. Molecular ecology renders a new approach to better understand invasions and can help in their management by resolving taxonomic issues, elucidating geographical source(s), detecting hybridization and introgression, and tracking dispersal and spread. Using a molecular ecological approach, some of these phenomena were investigated in this dissertation research for three different plant invaders in Hawaii. Molecular markers were developed for Pennisetum setaceum (fountaingrass), Miconia calvescens (velvet tree) and Senecio madagascariensis (fireweed) to answer ecological and management related questions.
Molecular and quantitative genetic variation indicated that fountaingrass is monoclonal throughout Hawaii and furthermore, that this clone or “super-genotype” is shared globally among invasive and native ranges. This indicates phenotypic plasticity as the sole mechanism behind fountaingrass’ invasive success. Fountaingrass is unlikely to evolve resistance against successful control mechanisms. Subsequent herbicide trails indicated that grass-selective herbicides are ineffective against fountaingrass. Phylogenetic and population genetic structure showed that fireweed introduced to Hawaii originated from eastern South Africa. Effective and host-specific biological control agents against fireweed are most likely to be found in this region. The high genetic diversity found in fireweed is indicative of multiple introductions. Genetic spatial autocorrelation revealed a diffusive dispersal pattern in the Hawaiian Islands.
Genetic structure indicated that bottlenecked populations of velvet tree are highly inbred in Hawaii and southern Pacific Islands. The data further suggested that invasive populations throughout northern and southern Pacific islands are genetically similar despite differential invasive success. These results indicate that invasions in both hemispheres are potentially fi-om similar geographic origin and/or that Hawaiian infestations are the result of a secondary introduction directly from Tahiti. The introduction of genotypes pre-adapted for various morphological, physiological and life history traits facilitate invasion success of velvet tree. Climatological similarities between the Society and the Hawaiian Islands indicate that Hawaiian infestations of velvet tree have not yet reached an optimum. Biological control would be the only effective control method against velvet tree with most productive control agents likely to be found in Mexico.
Appears in Collections: Ph.D. - Horticulture

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