Multiple introductions boosted genetic diversity in the invasive range of black cherry (Prunus serotina; Rosaceae)

Background and Aims Black cherry (Prunus serotina) is a North American tree that is rapidly invading European forests. This species was introduced first as an ornamental plant then it was massively planted by foresters in many countries but its origins and the process of invasion remain poorly documented. Based on a genetic survey of both native and invasive ranges, the invasion history of black cherry was investigated by identifying putative source populations and then assessing the importance of multiple introductions on the maintenance of gene diversity. Methods Genetic variability and structure of 23 populations from the invasive range and 22 populations from the native range were analysed using eight nuclear microsatellite loci and five chloroplast DNA regions. Key Results Chloroplast DNA diversity suggests there were multiple introductions from a single geographic region (the north-eastern United States). A low reduction of genetic diversity was observed in the invasive range for both nuclear and plastid genomes. High propagule pressure including both the size and number of introductions shaped the genetic structure in Europe and boosted genetic diversity. Populations from Denmark, The Netherlands, Belgium and Germany showed high genetic diversity and low differentiation among populations, supporting the hypothesis that numerous introduction events, including multiple individuals and exchanges between sites, have taken place during two centuries of plantation. Conclusions This study postulates that the invasive black cherry has originated from east of the Appalachian Mountains (mainly the Allegheny plateau) and its invasiveness in north-western Europe is mainly due to multiple introductions containing high numbers of individual

Quantification of short and long asbestos fibers to assess asbestos exposure: a review of fiber size toxicity.

International audienceThe fibrogenicity and carcinogenicity of asbestos fibers are dependent on several fiber parameters including fiber dimensions. Based on the WHO (World Health Organization) definition, the current regulations focalise on long asbestos fibers (LAF) (Length: L ≥ 5 μm, Diameter: D  3). However air samples contain short asbestos fibers (SAF) (L < 5 μm). In a recent study we found that several air samples collected in buildings with asbestos containing materials (ACM) were composed only of SAF, sometimes in a concentration of ≥10 fibers.L-1. This exhaustive review focuses on available information from peer-review publications on the size-dependent pathogenetic effects of asbestos fibers reported in experimental in vivo and in vitro studies. In the literature, the findings that SAF are less pathogenic than LAF are based on experiments where a cut-off of 5 μm was generally made to differentiate short from long asbestos fibers. Nevertheless, the value of 5 μm as the limit for length is not based on scientific evidence, but is a limit for comparative analyses. From this review, it is clear that the pathogenicity of SAF cannot be completely ruled out, especially in high exposure situations. Therefore, the presence of SAF in air samples appears as an indicator of the degradation of ACM and inclusion of their systematic search should be considered in the regulation. Measurement of these fibers in air samples will then make it possible to identify pollution and anticipate health risk

Ecology and population genetics of an invasive forest tree species : Prunus serotina Ehrh

Within the general context of plant invasions, we chose to study the biological characteristics of one of the most invasive forest tree species in Europe: black cherry (Prunus serotina Ehrh.). The objectives of this thesis were twofold: describe the reproductive traits and dispersal characteristics of the species and disentangle its introduction patterns, using both ecological and genetic tools. First introduced in Europe for ornamental purposes then to serve different objectives in forests, this North American species rapidly spread around plantations to invade several types of woodlands and open habitats. Preliminary analyses were carried out to characterize the polyploid nature of the species and to find functional polymorphic microsatellite markers. In order to answer the first objective, the reproductive cycle was studied in the understory of an invaded pine plantation and a spatially-explicit-individual-based model was fit on genetic and demographic data collected at a landscape scale. Results suggested that despite a low fruit set (0.03), a high number of seeds fell (611 seeds.m-2) and germinated (19 seeds.m-2) each year on the forest floor. Thorough analysis of seed dispersal patterns showed that the bulk of the seed crop falls near the maternal parent as 95% of the seeds were found to disperse up to 5 m. Model output for longer dispersal distances suggested that successful establishment of seedlings after long distance dispersal events is more frequent than previously thought. Thirty one percent of the seedlings were indeed established further than 100 m away from their maternal parent. Twenty five populations were then sampled across Europe to describe the species introduction patterns. Two introduction scenarios, mainly differing by the number of individuals introduced and the putative number of independent sources from the native range, were postulated to explain the observed genetic patterns. The methods and models used in this work could be useful in a wide range of dispersal and ecological studies. / Dans le contexte général des invasions biologiques, nous avons choisi d'étudier les caractéristiques biologiques d'une des espèces forestières les plus envahissantes en Europe: le cerisier tardif (Prunus serotina Ehrh.). Les objectifs de cette thèse étaient doubles : décrire les caractéristiques de reproduction et de dispersion de l'espèce et comprendre les patrons de son introduction, en utilisant à la fois des outils écologiques et génétiques. Initialement introduite en Europe comme ornementale puis utilisée à différentes fins en forêts, cette espèce native de l'Amérique du Nord s'est rapidement échappée des plantations pour coloniser les bois et les habitats ouverts environnants. Des analyses préliminaires ont du être menées pour caractériser la nature polyploïde de l'espèce et déterminer des marqueurs microsatellites fonctionnels sur l'espèce. Dans le but de répondre au premier objectif, le cycle de reproduction a été étudié en sous étage d'une plantation de pins envahie et un modèle spatialement explicite prenant en compte l'individu a été calibré à l'aide de données génétiques et démographiques récoltées à l'échelle du paysage. Les résultats ont suggéré que malgré un faible taux de fructification (0.03), un nombre important de graines tombaient (611 graines.m-2) et germaient (19 graines.m-2) chaque année sur le sol forestier. Une analyse fine des patrons de dispersion des graines a montré que la majeure partie de celles-ci tombait près du parent maternel. Ainsi, 95% des graines ont été échantillonnées dans des distances allant de 0 à 5 m du pied de l'arbre. Les résultats du modèle ont suggéré que l'établissement des plantules après des évènements de dispersion à longue distance était plus fréquent qu'initialement postulé. Trente et un pourcent des plantules se sont en effet établies à des distances supérieures à 100 m de leur parent maternel. Vingt-cinq populations ont ensuite été échantillonnées à travers l'Europe pour décrire les patrons d'introduction de l'espèce. Deux scénarios d'introduction, différant principalement par le nombre d'individus introduits et le nombre de sources d'introductions indépendantes en provenance de l'aire d'origine, ont été suggérés pour expliquer les patrons génétiques observés. Les méthodes et modèles utilisés dans ce travail pourraient être appliqués à une grande variété d'études écologiques et de dispersion.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3) -- UCL, 200

Disomic segregation of microsatellites in the tetraploid Prunus serotina Ehrh. (Rosaceae)

Tetraploid black cherry (Prunus serotina) is the only Prunus L. species that has commercial importance as a timber tree in North America and is well known in Europe for its invasive behavior. Inheritance studies have never been performed and it is not known whether the species is allo or autotetraploid. Six microsatellite nuclear markers were used to test the inheritance in progenies of controlled crosses. Inheritance was proven to be disomic at all loci and a typical diploid mendelian inheritance was found at two loci. A first screening of a population in the invasive range showed high number of alleles per locus (ranging from 6 to 16) and high level of observed heterozygosity (0.75 to 1). Knowing that inheritance is disomic at six microsatellite loci and that at least two of them can be treated as codominant, diploid markers will be beneficial for future genetic studies

Modeling seed dispersal of black cherry, an invasive forest tree: how microsatellites may help?

We used empirical models and three dispersal functions (Weibull, lognormal and 2Dt) to model seed distributions derived from the black cherry (Prunus serotina Ehrh.) understorey of a pine-dominated stand. Two different approaches were used to disentangle the overlapping seed shadows: the traditional inverse modeling approach and the genetic approach that uses microsatellite markers to assign a dispersed seed to its maternal parent. The distinction was made between the seeds passively dispersed by gravity (fruits with mesocarp) and those dispersed by birds (fruits without mesocarp). Our main objectives were to compare the three dispersal functions and assess the differences between the two approaches used. The functions performed equally well, but the lognormal function often showed a better data correlation. The best dispersal curves obtained by both traditional and genetic approaches were quite similar for the seeds dispersed by gravity, and 95% of these seeds were predicted to fall 5 and 3 m away from the parent tree for the traditional and genetic approaches, respectively. Differences were more important for the seeds dispersed by birds. The traditional approach predicted a lower number of seeds near the parent plant and a higher dispersal distance. Microsatellites provided accurate information on individual dispersal events and led to a better insight into the dispersal process