The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Multiple introductions of divergent genetic lineages in an invasive fungal pathogen, Cryphonectria parasitica, in France

The occurrence of multiple introductions may be a crucial factor in the successful establishment of invasive species, but few studies focus on the introduction of fungal pathogens, despite their significant effect on invaded habitats. Although Cryphonectria parasitica, the chestnut blight fungus introduced in North America and Europe from Asia during the 20th century, caused dramatic changes in its new range, the history of its introduction is not well retraced in Europe. Using 10 microsatellite loci, we investigated the genetic diversity of 583 isolates in France, where several introductions have been hypothesized. Our analyses showed that the seven most frequent multilocus genotypes belonged to three genetic lineages, which had a different and geographically limited distribution. These results suggest that different introduction events occurred in France. Genetic recombination was low among these lineages, despite the presence of the two mating types in each chestnut stand analysed. The spatial distribution of lineages suggests that the history of introductions in France associated with the slow expansion of the disease has contributed to the low observed rate of recombination among the divergent lineages. However, we discuss the possibility that environmental conditions or viral interactions could locally reduce recombination among genotypes

Rapid identification of polymorphic sequences in non-model fungal species: the PHYLORPH method tested in Armillaria species

Development of molecular markers for phylogenetic, population genetics and phylogeographic studies remains arduous in non-model species with low or no genomic resources. Sequencing the whole or a large part of the genome of the target species using next-generation sequencing technologies is considered a promising method, although it still needs a large investment in bioinformatics. To quickly find polymorphic markers in fungal species, we tested an alternative method, named PHYLORPH. This method allows users to quickly target polymorphic regions of single copy genes in fungi using public databases. We applied this method to Armillaria species, which are important fungal pathogens and saprophytes playing a central role in the dynamics of forest ecosystems worldwide. We isolated 32 single copy genes with numerous single nucleotide polymorphism (SNP) sites. A genetic analysis of two French populations validated the polymorphism of 80 among 92 SNPs tested, and seven of these sequences exactly reconstructed the known phylogenetic tree of four tested Armillaria species. These results confirmed that the PHYLORPH method is efficient to identify various markers at both the intra- and interspecific levels for fungal species with no or few previous genetic markers

Data from: What was old is new again: thermal adaptation within clonal lineages during range expansion in a fungal pathogen

Range-expanding species are expected to gain an increasing importance in the context of global change. They provide a great opportunity to study contemporary evolutionary changes and to unravel the mechanisms of evolution. Cryphonectria parasitica, the causal agent of chestnut blight, originating from Asia, has been spread since the beginning of the 20th century into different continents. We took advantage of the C. parasitica recent emergence in northern France to study the changes in population genetic structure and in phenotypic traits along this colonization and climatic gradient. Four hundred twenty-seven C. parasitica isolates were sampled in 47 chestnut sites in northern France. The C. parasitica outbreak in the north was found to be due to the expansion of five dominant clonal groups from southern France and to the emergence of a few rare recombined genotypes. The evolutionary changes during C. parasitica range expansion were studied by analyzing phenotypic changes in isolates from the same clonal lineage, with or without a geographic shift. Growth rates were assessed in vitro, at four temperatures. The northern isolates grew faster at 12 and 15°C and more slowly at 28 and 32°C than the southern isolates. These results strongly suggest local adaptation to low temperatures in C. parasitica, with a trade-off of slower growth at high temperatures. They also reflect the high evolutionary potential of C. parasitica along a colonization gradient and show that clonal evolution is not a limitation for the rapid thermal adaptation of this invasive fungal species

Genetic and phenotypic changes in Cryphonectria parasitica populations along a colonisation gradient

National audienc

Early detection of Cryphonectria parasitica by real-time PCR

The development and validation of a real-time PCR method for the detection of Cryphonectria parasitica in bark tissues is described. The selected region in the genome was a fragment of the internal transcribed spacer region. The DNA extraction and PCR conditions were optimized to be routinely applicable to fresh and dried bark. The sensitivity of the assay allowed the detection of 2 fg of genomic DNA, equivalent to one spore of the pathogen. There was no cross-reaction with closely related Cryphonectria species. The use of droplet digital PCR (ddPCR) confirmed the high sensitivity of the real-time PCR method, and its capacity to be used as an early detection method. A survey was conducted in Belgium on chestnut trees displaying cankers using isolation and the real-time PCR method. Both methods provided the same results for 83% of the samples (either negative or positive results). For the remaining samples, C. parasitica was not isolated, while amplifications close to the end of the PCR run (resulting in late Cycle threshold (Ct) values) were observed with the real-time PCR. Some of these samples were collected in stands where C. parasitica had already been detected on other chestnut trees, or in sites close to the infected stands. The application of this method may help plant protection services to detect new introductions of the pathogen within areas still free of chestnut blight and to prevent its establishment. It may also be useful for scientists involved in the epidemiology of the disease