The Origin, Genetic Diversity and Taxonomy of the Invasive Diatom Didymosphenia geminata (Bacilliariophyceae) in New Zealand

摘要

This thesis describes an investigation of the origin, genetic diversity andtaxonomy of Didymosphenia geminata, in New Zealand. D. geminata,commonly known as Didymo or Rock Snot , is a freshwater diatom, aphotosynthetic alga with a silica shell. It attaches to rocks and plants by itsmucilaginous stalks, its large blooms often covering all availablesubstrates and causing shifts in community structure. Although it washistorically associated with high altitude, oligotrophic waters, it is nowshowing increased ecological tolerance. It has been increasing inabundance and range in Europe and North America and has beenintroduced into new areas including New Zealand, Iran and India. Sincethe first discovery of D. geminata in New Zealand in October 2004, it hasspread rapidly across the South Island.I have conducted a phylogeographic study of D. geminata samples fromEurope, Asia, North America and New Zealand, using D. geminata-specificprimers to amplify the internal transcribed spacer (ITS) region. Ihave also used these primers to amplify the small nuclear ribosomal DNA(nrDNA) subunit 18S to investigate the taxonomic placement of D.geminata within the pennate diatoms.Results from this investigation indicate that D. geminata may belong to theFamily Cymbellaceae. It appears that D. geminata may have beenintroduced though several different introduction events to North Americafrom Europe and then to New Zealand from North America. These resultscan be used to inform strategies regarding the control and management ofthis invasive species, including lending support for continuation of theBiosecurity New Zealand program aimed at improving public, andespecially freshwater users', awareness and responsibility regarding D.geminata in New Zealand. This program is especially important asdispersal appears to be human-mediated. Limiting the number and sourceof introductions to an area can reduce the potential for increased geneticvariation and thus adaptation to new environments.