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Fragmentation of natural vegetation creates one of the largest threats to plant-pollinator interactions. Although fragmentation impacts on plant populations have been explored in many, mainly herbaceous, species, the response of wild mass-flowering species is poorly known. Here, we studied 28 heathland patches dominated by the mass-flowering shrub Rhododendron ferrugineum, each presenting different R. ferrugineum floral display sizes (total inflorescence number per patch) and patch isolation (median distance to the three nearest patches). We assessed the impacts of these two factors on (i) heathland patch visitor assemblage (considering R. ferrugineum versus surrounding community) and (ii) R. ferrugineum flower visitation rate and pollen transfer limitation (comparing seed set from emasculated to pollen-supplemented flowers). We found that diversity and abundance of bees visiting R. ferrugineum in heathland patches significantly decreased with decreasing R. ferrugineum floral display, while overall visitor density per patch and flower visitation rate increased. Moreover, a decrease in massive floral display and increase in patch isolation resulted in reduced visitor density in the surrounding community. Even in patches with few individuals, we found disproportionate visitor abundance in R. ferrugineum compared to the surrounding community. Finally, pollen transfer limitation in R. ferrugineum was neither affected by visitation rate nor by patch attributes. By disproportionally attracting pollinators from co-flowering species, and probably promoting geitonogamous pollen transfer, the mass-flowering trait appears adequate to compensate, in terms of conspecific pollen transfer, for the decrease in visitor diversity and abundance and in mate availability, which usually result from population fragmentation.

Parents and progenies genetic diversity, and male and female contributions to the seed crop were assessed in three experimental Prunus avium seed orchards. Collected data were used to compare different effective population sizes, based on phenological, seed crop and paternity analysis. Our results did not show any difference of genetic diversity between parents and progenies. A limited pollen pollution was detected. We showed that distance and coflowering among clones had a significant effect on effective pollination, and a significant effect of the production of flowers was revealed in one of the seed orchards. Our study also revealed a quite low number of effective size of fathers per mother, but high effective sizes of mothers, fathers and parents at the level of the seed orchard. Finally, the calculation of effective size of mothers, fathers and parents was not highly modified when having the complete information based on the paternity analysis., La diversité génétique des parents et de leurs descendants, ainsi que les contributions mâle et femelle à la récolte de graines ont été estimées dans trois vergers à graines expérimentaux de Prunus avium. Les données collectées ont été utilisées pour comparer différentes tailles de population efficace, en se basant sur l'analyse de la phénologie, de la récolte de graines et de la paternité. Nos résultats n'ont pas montré de différence de diversité génétique entre les parents et les descendants. Une pollution pollinique limitée a été mise en évidence. Nous avons montré un effet significatif de la distance et de la cofloraison entre clones sur la pollinisation efficace, ainsi qu'un effet significatif de la production de fleurs dans l'un des vergers à graines. Notre étude a aussi révélé un faible nombre efficace de pères à l'échelle de chaque mère, et un nombre efficace de mères, de pères et de parents important à l'échelle du verger à graines. Enfin, le calcul des tailles efficaces de pères et de parents à l'échelle du verger à graines n'a pas été fortement influencé par le fait d'avoir l'information totale de contribution donnée par l'analyse de paternité.

L’organisation de la diversité génétique a été décrite dans le cas d’un peuplement mélangé de chêne sessile et pédonculé constitué de 355 arbres adultes répartis sur une surface de 6 ha. La diversité a été appréhendée à l’aide de 6 loci microsatellites manifestant un polymorphisme très élevé (de 15 à 32 allèles par locus). L'organisation a été décrite à l’aide de deux paramètres : la différenciation (Fst) entre différentes subdivisions spatiales de la parcelle étudiée et l’autocorrélation spatiale (I) entre les génotypes présents sur la parcelle. Les deux espèces se caractérisent par une différenciation génétique faible mais significative, quelle que soit la taille des subdivisions spatiales considérées (à l’exception des faibles tailles < 10 m chez le chêne pédonculé). L’autocorrélation est significative aux faibles distances chez le chêne sessile alors qu’une structuration plus faible apparaît chez le chêne pédonculé. Ces valeurs sont interprétées en fonction des flux de gènes chez les deux espèces, dont des indications sont données pour les flux de pollen. En effet des recherches de paternité à l’aide des données multilocus sur les microsatellites ont permis d’identifier les parents pollinisateurs de treize descendances récoltées dans la parcelle. Ces résultats suggèrent que les flux de pollen cumulent une dispersion à courte distance et des transports à longue distance. La faible structuration spatiale est interprétée comme le résultat de l’asymétrie de flux entre graines et pollen. La structure mise en place par la dispersion réduite des graines est érodée par les flux de pollen à longue distance., The spatial genetic structure was analysed in a 6 ha mixed stand of 355 adult oaks trees (Quercus petraea (Matt.) Liebl. and Quercus robur L.). The genetic diversity was investigated with six highly polymorphic microsatellite loci (15 to 32 alleles per locus). Two parameters of the spatial genetic structure were used: the genetic differentiation (Fst), for different spatial scales within the stand, and the spatial autocorrelation (7) between the genotypes in the stand. Both species are characterised by a low but significant genetic differentiation, whatever the spatial scale of observation (except for the smallest scale of < 10 m for Quercus robur). The autocorrelation values are significant for the smallest scales for Quercus petraea and the spatial structure appears weaker for Quercus robur. Results are interpreted in terms of gene flow for both species. Paternity analysis based on multilocus microsatellite data made it possible to identify the paternal parents of progenies collected on 13 mother trees in the stand. Results of the paternity analysis indicate that pollen flow combines dispersion at short distances and transport at long distances. As a result, the spatial structure observed is seen as the consequence of the asymmetry of pollen versus seed flow. Restricted seed movement is likely to build up spatial structures that are disrupted by long distance pollen movements.

International audience; Concerns have been raised in Europe about the efficiency, sustainability, and environmental impact of the first genetically modified crops. The committees and regulators in charge of approving procedures have encouraged a field trial approach for safety assessment studies under current agronomic conditions. We describe the gene flow from sugar beet (Beta vulgaris L.) in a multi-year and multi-crop monitoring study on farmers' fields at two locations that has been carried out since 1995. We analyzed two sugar beet lines that have been genetically transformed for herbicide resistance. One sugar beet has resistance to glufosinate and the other to glyphosate. Large differences among lines, years and locations were observed. These differences provided a broad range of situations to estimate the risks. Sugar beet bolters produced the majority (86%) of the herbicide-resistant seeds harvested in the field. Direct pollen flow from sugar beet bolters to weed beets that were growing within the same field as well as in a neighboring field that was left fallow accounted for only 0.4% of the resistant seeds released over the years and locations. Descendants of the hybrids between the sugar beet and the weed beet produced the remaining 13.6% of resistant seeds. Herbicide-resistant seeds from the progeny of the weed beet were recorded up to 112 m away from the closest transgenic pollen donor. Indications were observed of non-randomness of the weed beet producing resistant progeny. We also analyzed pollen flow to male-sterile bait plants located within and outside of the sugar beet field. Herbicide-resistant pollen flow was recorded up to 277 m, and fitted with an inverse power regression. Using sugar beet varieties with no, or very low, sensitivity to bolting and destroying bolters are two necessary measures that could delay gene flow.