Population genetic analyses of species inhabiting fragmented landscapes are essential tools for conservation. Occasionally, analyses of fragmented populations find no evidence of isolation, even though a barrier to dispersal is apparent. In some cases, not enough time may have passed to observe divergence due to genetic drift, a problem particularly relevant for long‐lived species with overlapping generations. Failing to consider this quality during population structure analyses could result in incorrect conclusions about the impact of fragmentation on the species. We designed a model to explore how lifespan and population size influence perceived population structure of isolated populations over time. This iterative model tracked how simulated populations of variable lifespan and population size were affected by drift alone, using a freshwater mussel, Quadrula quadrula (mapleleaf), as a model system. In addition to exhibiting dramatic lifespan variability among species, mussels are also highly imperiled and exhibit fragmentation by dams throughout the range of many species. Results indicated that, unless population size was small (<50 individuals) or lifespan short (<22 years), observing genetic divergence among populations was unlikely. Even if wild populations are isolated, observing population structure in long‐lived mussels from modern damming practices is unlikely because it takes longer for population structure to develop in these species than most North American dams have existed. Larger population sizes and longer lifespans increase the time needed for significant divergence to occur. This study helps illuminate the factors that influence genetic responses by populations to isolation and provides a useful model for conservation‐oriented research.

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DNMT3B is known as a de novo DNA methyltransferase. However, its preferential target sites for DNA methylation are largely unknown. Our analysis on ChIP-seq experiment in human embryonic stem cells (hESC) revealed that DNMT3B, mCA and H3K36me3 share the same genomic distribution profile. Deletion of DNMT3B or its histone-interacting domain (PWWP) demolished mCA in hESCs, suggesting that PWWP domain of DNMT3B directs the formation of mCA landscape. In contrast to the common presumption that PWWP guides DNMT3B-mediated mCG deposition, we found that deleting PWWP does not affect the mCG landscape. Nonetheless, DNMT3B knockout led to the formation of 2985 de novo hypomethylated regions at annotated promoter sites. Upon knockout, most of these promoters gain the bivalent marks, H3K4me3 and H3K27me3. We call them spurious bivalent promoters. Gene ontology analysis associated spurious bivalent promoters with development and cell differentiation. Overall, we found the importance of DNMT3B for shaping the mCA landscape and for maintaining the fidelity of the bivalent promoters in hESCs.

In this study we demonstrate the utility of whole genome shotgun (WGS) metagenomics in study organisms with small genomes to improve upon amplicon-based estimates of biodiversity and microbial diversity in environmental samples for the purpose of understanding ecological and evolutionary processes. We generated a database of full-length and near-full-length ribosomal DNA sequence complexes from 273 lichenized fungal species and used this database to facilitate fungal species identification in the southern Appalachian Mountains using low coverage WGS at higher resolution and without the biases of amplicon-based approaches. Using this new database and methods herein developed, we detected between 2.8 and 11 times as many species from lichen fungal propagules by aligning reads from WGS-sequenced environmental samples compared to a traditional amplicon-based approach. We then conducted complete taxonomic diversity inventories of the lichens in each one-hectare plot to assess overlap between standing taxonomic diversity and diversity detected based on propagules present in environmental samples (i.e., the "potential" of diversity). From the environmental samples, we detected 94 species not observed in organism-level sampling in these ecosystems with high confidence using both WGS and amplicon-based methods. This study highlights the utility of WGS sequence-based approaches in detecting hidden species diversity and demonstrates that amplicon-based methods likely miss important components of fungal diversity. We suggest that the adoption of this method will not only improve understanding of biotic constraints on the distributions of biodiversity but will also help to inform important environmental policy.

Alterations to watercourses affect connectivity in aquatic systems and can influence dispersal of aquatic biota. Dams fragment populations and act as isolating barriers, but canals create connections between waterbodies that can be used as corridors for dispersal by opportunistic invaders. The Niagara Peninsula of Ontario, Canada, has a 200-y history of canal operation, resulting in major modification of the watercourses in the region. This modification allowed numerous invasive species to enter the upper Great Lakes (e.g., sea lamprey) and probably has facilitated dispersal in native species. The purpose of our study was to explore the effects of canal and dam construction on the genetic structure of Mapleleaf (Quadrula quadrula), a widespread and relatively common species in the central Great Lakes that has been found only recently in several western Lake Ontario harbors. Establishment of Q. quadrula in Lake Ontario may have been a recent event, facilitated by the Niagara Peninsula's history of canal operation. We used analyses of microsatellite DNA genotypes to examine the effect of canals on the genetic structure of mussel populations. Structure analysis revealed a pattern of gene flow between lakes that cannot be explained by watercourse connections prior to the creation of the Welland Canal. Evidence suggestive of historical bottlenecks at some Lake Ontario sites may indicate that these populations became established after canal creation. After considering genetic structure, hydrogeography and isolation-by-distance (IBD) analysis, the first iteration of the canal (1829-1833) is most supported as the configuration that facilitated colonization. However, weak IBD signals across canal models may signify continued gene flow across configurations. Our study demonstrates the connective effect of canals on freshwater mussel populations and has the potential to improve conservation strategies for this and other unionid species at risk.