Nuclear and Chloroplast Microsatellites Show Multiple Introductions in the Worldwide Invasion History of Common Ragweed, Ambrosia artemisiifolia

BACKGROUND: Ambrosia artemisiifolia is a North American native that has become one of the most problematic invasive plants in Europe and Asia. We studied its worldwide population genetic structure, using both nuclear and chloroplast microsatellite markers and an unprecedented large population sampling. Our goals were (i) to identify the sources of the invasive populations; (ii) to assess whether all invasive populations were founded by multiple introductions, as previously found in France; (iii) to examine how the introductions have affected the amount and structure of genetic variation in Europe; (iv) to document how the colonization of Europe proceeded; (v) to check whether populations exhibit significant heterozygote deficiencies, as previously observed. PRINCIPAL FINDINGS: We found evidence for multiple introductions of A. artemisiifolia, within regions but also within populations in most parts of its invasive range, leading to high levels of diversity. In Europe, introductions probably stem from two different regions of the native area: populations established in Central Europe appear to have originated from eastern North America, and Eastern European populations from more western North America. This may result from differential commercial exchanges between these geographic regions. Our results indicate that the expansion in Europe mostly occurred through long-distance dispersal, explaining the absence of isolation by distance and the weak influence of geography on the genetic structure in this area in contrast to the native range. Last, we detected significant heterozygote deficiencies in most populations. This may be explained by partial selfing, biparental inbreeding and/or a Wahlund effect and further investigation is warranted. CONCLUSIONS: This insight into the sources and pathways of common ragweed expansion may help to better understand its invasion success and provides baseline data for future studies on the evolutionary processes involved during range expansion in novel environments

Invasive species of Heracleum in Europe: an insight into genetic relationships and invasion history

Several species of the genus Heracleum (Umbelliferae) were introduced into Europe from south-west Asia in the 19th century and are now widespread in many countries. At least three invasive taxa with unresolved relationships to one another are thought to occur in Europe: Heracleum mantegazzianum Sommier & Levier, H. sosnowskyi Manden, and H. persicum Desf. ex Fischer. They are tall plants forming extensive stands with a high cover. To elucidate genetic relationships between the species, and gain insight into their invasion history, samples were collected from native ranges in Asia and invaded ranges of the three species in Europe and analysed using amplified fragment length polymorphism. Five other Heracleum species were also studied and in total, 189 samples from 72 populations were analysed. The results confirmed that there are three distinct tall Heracleum species invading in Europe. Within each of the three species, plants collected in the invaded range are genetically close to those from their native ranges. A close genetic relationship between the three invasive Heracleum species in Europe was also found. A high overall genetic variability detected in the invaded range suggests that the majority of invading populations were not affected by a genetic bottleneck and that rapid evolution, drift, or hybridization played a role in genetic structuring of invading populations. For H. mantegazzianum, genetic distance of populations in the native range significantly decreased with geographical distance, but not in the invaded range. It is likely that the current pattern of genetic diversity in Europe resulted from multiple introductions of all three species

High levels of genetic diversity in Salix viminalis of the Czech Republic as revealed by microsatellite markers

Willows (Salix spp.) grown as short rotation coppice are recognised as an important bioenergy crop, and breeding programmes are underway in several countries, including the Czech Republic. The basket willow Salix viminalis is one of the few willow species that is widespread in the Czech Republic and thus a potential source of diversity, but the most extensive germplasm collection available shows evidence of redundancy. To investigate levels of variation in natural populations of this species for use in crop improvement programmes, a set of 38 microsatellite markers was used to assess genetic diversity and population structure among 84 S. viminalis individuals collected from seven Czech rivers (the Odra, Bečva, Morava, Dyje, Jihlava, Sázava and Vltava), covering a wide geographic distribution. The markers detected 6.95 alleles per locus on average with 92 % of the sampled individuals having a unique multilocus genotype giving a high clonal richness measure among all samples (R = 0.952). Three sets of putative clones (with identical genotypes as determined by the markers used here) were also identified. Significant levels of genetic diversity were revealed within all sampling sites. With the exception of sites on the Odra and Morava, pairwise F ST (0.02–0.1) values indicated moderate differentiation between sites. Principal coordinates analysis revealed some separation of the Dyje individuals from all others. This was in agreement with the population structure results derived from Bayesian analyses using STRUCTURE software. These results provide the first evidence that potentially useful levels of genotypic variation are present within natural S. viminalis populations in the Czech Republic

A set of primers for plastid indels and nuclear microsatellites in the invasive plant Heracleum mantegazzianum (Apiaceae) and their transferability to Heracleum sphondylium

This study reports the isolation and polymorphism characterization of four plastid indels and six nuclear microsatellite loci in the invasive plant Heracleum mantegazzianum. These markers were tested in 27 individuals from two distant H. mantegazzianum populations. Plastid indels revealed the presence of five chlorotypes while five nuclear microsatellite loci rendered polymorphism. Applications of these markers include population genetics and phylogeography of H. mantegazzianum. A very good transferability of markers to Heracleum sphondylium was demonstrated

Getting the most out of fluorescent amplified fragment length polymorphism

Amplified fragment length polymorphism (AFLP (TM)) is one of the most widely applied molecular marker detection systems used today. Among the reasons for its popularity are its reproducibility, capacity to generate large numbers of data points in a single assay, and "off-the-shelf" universal applicability. The original AFLP protocol was developed using radioactive detection. The transfer of this technique to fluorescent detection on automated DNA fragment analysers not only removed the undesirable requirement for radioactivity but also provided the possibility for increased effectiveness and detection throughput. Unfortunately, a number of problems are frequently encountered with fluorescent AFLPs, particularly failure to amplify high molecular-weight fragments and generation of nonuniform peak distributions. Here, we describe an improved generic protocol for fluorescent AFLPs achieved mainly thorough optimization of the multiplexed selective amplification reaction. This improved protocol gives increased production of valuable high molecular-weight markers and uniform peak intensities, facilitating unambiguous scoring. The protocol has been successfully applied, without further optimization, to species of Salix and Populus (Salicaceae), Melampsora (Melampsoraceae, rust fungi) and Heracleum (Apiaceae), as well as sugar beet (Beta vulgaris L. subsp. vulgaris, Amaranthaceae), the endangered species Ranunculus kadzunensis Makino (Ranunculaceae), and to Aphidius ervi Haliday (Braconidae), a parasitoid wasp

THGEM based photon detector for Cherenkov imaging applications

We are developing a single photon detector for Cherenkov imaging counters. This detector is based on the use of THGEM electron multipliers in a multilayer design. The major goals of our project are ion feedback suppression down to a few per cent, large gain, fast response, insensitivity to magnetic fields, and a large detector size. We report about the project status and perspectives. In particular, we present a systematic study of the THGEM response as a function of geometrical parameters, production techniques and the gas mixture composition. The first figures obtained from measuring the response of a CsI coated THGEM to single photons are presented

THGEM based photon detector for Cherenkov imaging applications

We are developing a single photon detector for Cherenkov imaging counters. This detector is based on the use of THGEM electron multipliers in a multilayer design. The major goals of our project are ion feedback suppression down to a few per cent, large gain, fast response, insensitivity to magnetic fields, and a large detector size. We report about the project status and perspectives. In particular, we present a systematic study of the THGEM response as a function of geometrical parameters, production techniques and the gas mixture composition. The first figures obtained from measuring the response of a CsI coated THGEM to single photons are presented