Invasive and endangered: Population genetics of plant species at both extremes: Japanese knotweed and eastern silvery aster.

摘要

Populations of invasive and endangered species experience genetic changes due to extreme conditions such as bottlenecks or fragmentation. Japanese knotweed is a destructive herbaceous invasive perennial weed that ranks among the world's worst invasive species. Studies in Europe have uncovered interesting features of its reproduction including the presence of a single female clone and hybridization with congeners. In the past there has been little emphasis on the contribution of sexual reproduction to its spread. As a result of apparent sexual reproduction in and the lack of genetic information about U.S. populations, a detailed genetic analysis of knotweed was initiated. Novel SSR markers were cloned for Japanese knotweed. We examined the genetic composition of Massachusetts populations, measured the relative amounts of sexual and asexual reproduction, discovered a nuclear marker specific to Giant knotweed and used this for hybrid detection. We surveyed knotweed from across the U.S., tallied multi-locus genotypes, hybrids, samples matching the female "British clone", and chloroplast haplotypes. An additional genetic study was carried out to analyze the reproduction and breeding system of knotweed and to determine the origin of seeds on males. We confirmed that U.S. populations are not purely clonal, are sexually reproducing and generating genetic variation---mostly through hybridization and backcrossing, and that seed dispersal is responsible for establishing some patches in MA. The pattern observed is consistent with sexual reproduction rather than multiple introductions of diverse material. Seed is not apomictic and data supports a subdioecious breeding system. These are the first detailed genetic studies of Japanese knotweed in the U.S.;Eastern Silvery Aster is a perennial forb whose populations are endangered at its northern range on Nantucket, MA. Three Nantucket and three NC populations were genetically analyzed using ITS and four nuclear intron-flanking loci. Populations were compared and it was found that more alleles were found in North Carolina compared to Nantucket populations, but standardizing sample sizes with rarefaction showed similar levels of allelic richness and number of private alleles. This data indicated that small endangered Nantucket populations of Eastern Silvery Aster are not currently exhibiting any obvious population genetic effects of fragmentation.