Widespread dispersal of progeny is expected to result in enough gene flow to maintain genetic homogeneity over large areas. Surveys of genetic markers in species with planktonic larvae have mostly confirmed this expectation. However, genetic structure has occasionally been found at small spatiotemporal scales and interpreted as evidence of restricted dispersal, natal homing, sweepstakes reproductive success, or natural selection. We investigated genetic population structure in blue crabs from the Atlantic and Gulf of Mexico coasts of North America. Sampling was most intensive from five estuaries along the coast of Louisiana, with megalopae, juveniles and adults sampled from 2010 to 2016. 1446 individuals were genotyped at 2486 SNPs in 1363 putative protein-coding loci. Levels of differentiation between locations were consistently low, but significant differentiation was found among locations and among years. No evidence was found for chaotic genetic patchiness or sweepstakes reproductive success: no genetic differentiation was detected among collections of megalopae and none of the sampled individuals were closely related. Our results indicate that gene flow in blue crabs maintains near genetic homogeneity from the northern Gulf of Mexico through the Atlantic coast of North America.

The Arctic pelagic environment is expected to strongly alter due to global climate change. As a consequence, modification of the unicellular plankton species composition and biomass, with consequences to biogeochemical cycling and pelagic food web, is expected. In this study we used meta-barcoding of the V4 region of the 18S rRNA gene to profile eukaryotic microbial communities exported to deeper water layers at the Long-Term Ecological Research Site HAUSGARTEN in the northeastern Fram Strait. We collected sinking particles at ca. 80 to 300 m depths using long-term deployed sediment traps and analyzed selected samples of spring and summer periods from 2000-2011. Acknowledging the limitations and biases of currently used 18S rRNA gene meta-barcoding primers in detecting certain taxa especially from environmental samples, we developed new primer sets and compared them with those already in use. Using the information generated by three different primer sets, the results of our study suggest decreasing trends in the abundances of large-cell phytoplankton (i.e., diatoms) and increasing pico-phytoplankton (Micromonas sp. and haptophytes) during the warm anomaly of 2005-2007. Phylogenetic analyses further revealed the displacement of cold-adapted with warm-adapted phylotypes of Micromonas and haptophytes, which could be related to the warming event. Ecotype-level changes observed in this study do not only suggest changing structures in community composition and ecosystem functioning but also in the biogeography and distribution of some species. These data provided new insights and information on the potential diversity changes and species displacement brought about by the environmental changes occurring in the Arctic Ocean.

Persian oak decline is a syndrome within the oak decline complex in Iran. Profuse stem bleed-ing and larval galleries of the native buprestid, Agrilus hastulifer characterize the disease. A systematic study comparing healthy with diseased trees was undertaken. This work reports the result of isolations from healthy trees and diseased tissue in affected trees, at eight sites in Iran. Culturable bacterial communities were identified using the 16S rDNA sequencing. A significantly higher proportion of symptomatic tissue pieces from diseased trees (Disease In-dex=5) yielded bacterial growth than other disease indexes (83.78%). Significantly higher yields were also obtained from bulk and rhizosphere compared with the root, leaf, and stem. Overall bacterial communities compositions varied at each site, but significant similarities were evident in diseased tissues at all sites. Enterobacteriaceae were dominated in diseased trees whereas Bacilluceae and Moraxellaceae were remarkable more abundant in healthy trees. Sig-nificant associations occurred between diseased tissues and certain bacterial species, implying that the cause of tissue necrosis was not due to random microbiota. Brenneria goodwinii, Ser-ratia marecescence, and Dickeya chrysanthemi were key species consistently isolated from diseased tissue; Campylobacter jejuni and an un-named Clostridium taxon were also frequent-ly isolated from both healthy and diseased trees. It was concluded that there was a shift in the cultivatable bacterial microbiome of diseased trees, with Enterobacteriaceae strongly repre-sented in symptomatic but not healthy tissues. No single dominated species was isolated from diseased tissues, so tissue degradation in oak likely have a polymicrobial cause.

Single-nucleotide polymorphisms (SNPs) have numerous advantages over microsatellites, including greater power to infer population structure and history and to detect loci undergoing selection. Here, we conduct the first continental-level SNP study of polar bears (Ursus maritimus) using genotypes from an array of 5441 SNP loci genotyped in 16–30 polar bears sampled in each of 16 geographic regions in Canada and West Greenland. Our study aimed to assess population history and genetic structure and to identify evidence of adaptive loci. Using these data, we confirmed the existence of four broad-scale genetic clusters in North America (FCT = 0.035) and identified nine fine-scale subclusters using more powerful spatial methods. An assessment of historical patterns of migration suggests that polar bears migrated into North America from the Beaufort Sea after the last glacial maximum. Using a conservative approach, we identified 17 loci that may represent adaptive variation, including one SNP in the 3’ untranslated region of PDLIM5 (PDZ And LIM Domain 5), a gene involved in cardiovascular function, which has undergone substantial selection in polar bears since their divergence from brown bears. Outlier loci differentiated the Norwegian Bay genetic cluster more strongly from remaining clusters than did our complete dataset, suggesting possible adaptive differences in the High Arctic. Through careful consideration of SNP loci, sample inclusion, and analytical approaches, we provide a comprehensive picture of polar bear population structure at a continental level. This study provides a model for the analysis of wide-ranging species that can contribute to their conservation and management.

The biodiverse Neotropical ecoregion remains insufficiently assessed, poorly managed, and threatened by unregulated human activities. Novel, rapid and cost-effective DNA-based approaches are valuable to improve understanding of the biological communities and for biomonitoring in remote areas. Here, we evaluate the potential of environmental DNA (eDNA) metabarcoding for assessing the structure and distribution of fish communities by analysing sediments and water from 11 locations along the Jequitinhonha River catchment (Brazil). Each site was sampled twice, before and after a major rain event in a five-week period and fish diversity was estimated using high-through-put sequencing of 12S rRNA amplicons. In total, 252 Molecular Operational Taxonomic Units (MOTUs) and 34 fish species were recovered, including endemic, introduced, and previously unrecorded species for this basin. Spatio-temporal variation of fish assemblages was detected, richness during the first campaign was nearly twice as high as in the second sampling round; though peaks of diversity were primarily associated with only four locations. No correlation between β-diversity and longitudinal distance or presence of dams was detected, but low species richness observed at sites located near dams indicates that these anthropogenic barriers might have an impact on local fish diversity. Unexpectedly high α-diversity levels recorded at the river mouth suggest that these sections should be further evaluated as putative “eDNA reservoirs” for rapid monitoring. By uncovering spatio-temporal changes, unrecorded biodiversity components, and putative anthropogenic impacts on fish assemblages, we further strengthen the potential of eDNA metabarcoding as a biomonitoring tool, especially in regions often neglected or difficult to access.