Meiosis of newly formed allopolyploids frequently encounter perturbations induced by the merging of divergent and hybridizable genomes. However, to date, the meiotic properties of allopolyploids with dysploid parental karyotypes have not been studied in detail. The allotetraploid Cucumis ×hytivus (HHCC, 2n = 38) was obtained from interspecific hybridization between C. sativus (CC, 2n = 14) and C. hystrix (HH, 2n = 24) followed by chromosome doubling. The results of this study thus offer an excellent opportunity to explore the meiotic properties of allopolyploids with dysploid parental karyotypes.
Biﬁdobacteria are among the most prevalent gut commensals in mammals, playing crucial functional roles that start from their early colonization of the infant gastrointestinal tract and last throughout the life span of their host. Metagenomic approaches have been employed to unveil the genetic features of biﬁdobacteria in order to understand how they participate in the correct development of a healthy microbiome. Nevertheless, their low relative abundance in many environmental samples may represent a major limitation for metagenomics approaches. To overcome this restriction, we applied an enrichment method that allows ampliﬁcation of biﬁdobacterial DNA obtained from human or animal fecal samples for up to 26,500-fold, resulting in the metagenomic reconstruction of genomes belonging to biﬁdobacterial strains, present at very low abundance in collected samples. Functional predictions of the genes from these reconstructed genomes allows us to identify unique signatures among members of the same biﬁdobacterial species, highlighting genes correlated with the uptake of nutrients and adhesion to the intestinal mucosa.
Pomfret fishes of the genus Pampus are commercially important in the Indo-Pacific region, yet the phylogenetic relationships and taxonomy of Pampus remain contentious. Here, we sampled 151 specimens, representing all known species of the genus, as well as two outgroup species (two families). We collected sequences from 17,292 single-copy nuclear coding loci using target-gene enrichment and Illumina sequencing for a subset samples of P. echinogaster, P. argenteus, P. cinereus, P. liuorum, P. chinensis, P. minor, and P. punctatissimus, which were carefully examined according to their species descriptions. Concatenated gene tree and species tree analyses resulted in identical and highly supported phylogenies, in which P. argenteus was sister to P. minor in one clade and P. cinereus sister to P. chinensis and P. punctatissimus in the other clade. Phylogenetic reconstruction using sequences of cytochrome c oxidase subunit I (COI) collected by us and those retrieved from NCBI suggests extensive misidentification of Pampus species in the NCBI database. We also measured morphological characters of each species as well as observed their osteological structure using micro-CT. Both molecular and morphological results suggest that P. echinogaster is a synonym of P. argenteus, and P. liuorum is a synonym of P. cinereus. Pampus cinereus from China, Bangladesh and an uncertain origin were grouped into three clades according to their sampling localities, but we could not find decisive morphological characters to describe the “cryptic species” of P. cinereus. Finally, based on the results of the molecular analyses and morphological reexamination, we created an identification key for the genus of Pampus.
Australasia harbors very high squamate diversity and is a center of endemicity for a number of major lineages. However, despite this diversity, the diplodactyloid geckos of Australia, New Caledonia, and New Zealand (comprised of three endemic families and >200 species) are the only extant squamates with unequivocal Mesozoic origins in the region. Diplodactyloid geckos also exhibit notable phenotypic and ecological diversity, most strikingly illustrated by the functionally limbless pygopods. Here, we present the first phylogenomic analyses of the pattern and timing of diplodactyloid evolution, based on a dataset of more than 4000 ultraconserved elements (UCEs) from 180 species. These analyses fully resolve nearly all nodes, including a number of intergeneric relationships that have proven problematic in previous studies. The hypothesis that New Caledonia and New Zealand clades represent independent post-KT boundary colonization events of Tasmantis from Australian ancestors is confirmed. Phylogenetic relationships recovered here further highlight contrasting patterns of diversity, most strikingly between insular and/or morphologically highly derived clades that have diversified rapidly, as opposed to other species poor and phylogenetically divergent relictual lineages on mainland Australia. Our new timetree suggests slightly older branching times than previous analyses and does not find a mass extinction event in the early Cenozoic. Finally, our new phylogeny highlights caudal variation across the clade. Most strikingly, the distinctive leaf-tail morphology shown by one family may in fact be plesiomorphic.
A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American sedimentary sequences at the onset of the Younger Dryas (YD) event (~12,800 cal yr BP), consistent with the YD Impact Hypothesis. We report high-resolution analyses of a 1-meter section of a lake core from White Pond, South Carolina, USA. After developing a Bayesian age-depth model that brackets the late Pleistocene through early Holocene, we analyzed and quantified the following: (1) Pt and palladium (Pd) abundance, (2) geochemistry of 58 elements, (3) coprophilous spores, (4) sedimentary organic matter (OC and sedaDNA), (5) stable isotopes of C (δ13C) and N (δ15N), (6) soot, (7) aciniform carbon, (8) cryptotephra, (9) mercury (Hg), and (10) magnetic susceptibility. We identified large Pt and Pt/Pd anomalies within a 2-cm section dated to the YD onset (12,785 ± 58 cal yr BP). These anomalies precede a decline in coprophilous spores and correlate with an abrupt peak in soot and C/OC ratios, indicative of large-scale regional biomass burning. We also observed a relatively large excursion in δ15N values, indicating rapid climatic and environmental/hydrological changes at the YD onset. Our results are consistent with the YD Impact Hypothesis and impact-related environmental and ecological changes.
Abstract The evolution of cetaceans, from their early transition to an aquatic lifestyle to their subsequent diversification, has been the subject of numerous studies. However, while the higher-level relationships among cetacean families have been largely settled, several aspects of the systematics within these groups remain unresolved. Problematic clades include the oceanic dolphins (37 spp.), which have experienced a recent rapid radiation, and the beaked whales (22 spp.), which have not been investigated in detail using nuclear loci. The combined application of high-throughput sequencing with techniques that target specific genomic sequences provide a powerful means of rapidly generating large volumes of orthologous sequence data for use in phylogenomic studies. To elucidate the phylogenetic relationships within the Cetacea, we combined sequence capture with Illumina sequencing to generate data for ∼3200 protein-coding genes for 68 cetacean species and their close relatives including the pygmy hippopotamus. By combining data from >38,000 exons with existing sequences from 11 cetaceans and seven outgroup taxa, we produced the first comprehensive comparative genomic dataset for cetaceans, spanning 6,527,596 aligned base pairs and 89 taxa. Phylogenetic trees reconstructed with maximum likelihood and Bayesian inference of concatenated loci, as well as with coalescence analyses of individual gene trees, produced mostly concordant and well-supported trees. Our results completely resolve the relationships among beaked whales as well as the contentious relationships among oceanic dolphins, especially the problematic subfamily Delphininae. We carried out Bayesian estimation of species divergence times using MCMCTree, and compared our complete dataset to a subset of clocklike genes. Analyses using the complete dataset consistently showed less variance in divergence times than the reduced dataset. In addition, integration of new fossils (e.g., Mystacodon selenensis) indicate that the diversification of Crown Cetacea began before the Late Eocene and the divergence of Crown Delphinidae as early as the Middle Miocene.
The identification and association of the nucleotide sequences encoding antibiotic resistance elements is critical to improve surveillance and monitor trends in antibiotic resistance. Current methods to study antibiotic resistance in various environments rely on extensive deep sequencing or laborious culturing of fastidious organisms, which are both heavily time-consuming operations. An accurate and sensitive method to identify both rare and common resistance elements in complex metagenomic samples is needed. Referencing the Comprehensive Antibiotic Resistance Database, we designed a set of 37,826 probes to specifically target over 2000 nucleotide sequences associated with antibiotic resistance in clinically relevant bacteria. Testing of this probeset on DNA libraries generated from multi-drug resistant bacteria to selectively capture resistance genes reproducibly produced higher reads on-target at greater length of coverage when compared to shotgun sequencing. We also identified additional resistance gene sequences from human gut microbiome samples that sequencing alone was not able to detect. Our method to capture the resistome enables sensitive gene detection in diverse environments where antibiotic resistance represents less than 0.1% of the metagenome.
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