De novo assembly and annotation of the North American bison (Bison bison) reference genome and subsequent variant identification.

Genomic tools have improved the ability to manage bison populations and enhanced efforts to conserve this iconic species. These tools have been particularly useful for detecting introgression of cattle genome within bison herds but are limited by the need to use the cattle genome as a surrogate for mapping reads. This complicates efforts to distinguish the species of origin of chromosomal segments in individual bison at the genomic level. An assembly (Bison_UMD1.0) based on 75X genome coverage by Illumina and 454 reads was generated using the MaSuRCA assembler, generating a 2.81 Gigbases de novo reference genome from American bison. Comparison of bison and domestic cattle references identified 28 443 364 single nucleotide variants and 2 627 645 insertions/deletions distinguishing the species. Sequence alignment of an additional 12 modern bison samples and two historic bison samples to domestic cattle and bison references provides a dataset of genomic variants defining the different species and within-species variation. This first annotated draft assembly represents a resource for the management and conservation of bison, as well as a means to study the effects on the genome of interspecies hybridization. The comparisons of historical bison sequences with the new bison reference identified genomic differences between modern and pre-population bottleneck bison. The results support the application of genomics to enhance future research on disease, the establishment of satellite conservation herds and insight into bison and cattle speciation. The first genome assembly for bison and dataset provides a foundation that can be built upon as genetic technologies improve over the years.

Dobson LK ，Zimin A ，Bayles D ，Fritz-Waters E ，Alt D ，Olsen S ，Blanchong J ，Reecy J ，Smith TPL ，Derr JN ... -  《-》

Conservation genomics: disequilibrium mapping of domestic cattle chromosomal segments in North American bison populations.

Introgressive hybridization is one of the major threats to species conservation, and is often induced by human influence on the natural habitat of wildlife species. The ability to accurately identify introgression is critical to understanding its importance in evolution and effective conservation management of species. Hybridization between North American bison (Bison bison) and domestic cattle (Bos taurus) as a result of human activities has been recorded for over 100 years, and domestic cattle mitochondrial DNA was previously detected in bison populations. In this study, linked microsatellite markers were used to identify domestic cattle chromosomal segments in 14 genomic regions from 14 bison populations. Cattle nuclear introgression was identified in five populations, with an average frequency per population ranging from 0.56% to 1.80%. This study represents the first use of linked molecular markers to examine introgression between mammalian species and the first demonstration of domestic cattle nuclear introgression in bison. To date, six public bison populations have been identified with no evidence of mitochondrial or nuclear domestic cattle introgression, providing information critical to the future management of bison genetic resources. The ability to identify even low levels of introgression resulting from historic hybridization events suggests that the use of linked molecular markers to identify introgression is a significant development in the study of introgressive hybridization across a broad range of taxa.

Halbert ND ，Ward TJ ，Schnabel RD ，Taylor JF ，Derr JN ... -  《MOLECULAR ECOLOGY》

Genomic evaluation of hybridization in historic and modern North American Bison (Bison bison).

During the late nineteenth century North American bison underwent a significant population bottleneck resulting in a reduction in population size of over 99% and a species-level near-extinction event. Factors responsible for this destruction included indiscriminate killing, loss of access to suitable habitat, and diseases. At the nadir of this population crash, very few wild plains bison survived and were restricted to Yellowstone National Park, USA and a small number of wild wood bison remained in Wood Buffalo National Park, Canada. However, most surviving bison in the late 1800's were maintained by cattle ranchers in private herds where hybridization between bison with various breeds of domestic cattle was often encouraged. Over the last 20 years, the legacy of this introgression has been identified using mitochondrial DNA and limited nuclear microsatellite analyses. However, no genome-wide assessment has been performed, and some herds were believed to be free of introgression based on current genetic testing strategies. Herein, we report detailed analyses using whole genome sequencing from nineteen modern and six historical bison, chosen to represent the major lineages of bison, to identify and quantitate signatures of nuclear introgression in their recent (within 200 years) history. Both low and high coverage genomes provided evidence for recent introgression, including animals from Yellowstone, Wind Cave, and Elk Island National Parks which were previously thought to be free from hybridization with domestic cattle. We employed multiple approaches, including one developed for this work, to identify putative cattle haplotypes in each bison genome. These regions vary greatly in size and frequency by sample and herd, though we detected domestic cattle introgression in all bison genomes tested. Since our sampling strategy spanned across the diversity of modern bison populations, these finding are best explained by multiple historical hybridization events between these two species with significant genetic recombination over the last 200 years. Our results demonstrate that whole genome sequencing approaches are required to accurately quantitate cattle introgression in bison.

Stroupe S ，Forgacs D ，Harris A ，Derr JN ，Davis BW ... -  《Scientific Reports》

A Reference Genome Assembly of American Bison, Bison bison bison.

Bison are an icon of the American West and an ecologically, commercially, and culturally important species. Despite numbering in the hundreds of thousands today, conservation concerns remain for the species, including the impact on genetic diversity of a severe bottleneck around the turn of the 20th century and genetic introgression from domestic cattle. Genetic diversity and admixture are best evaluated at genome-wide scale, for which a high-quality reference is necessary. Here, we use trio binning of long reads from a bison-Simmental cattle (Bos taurus taurus) male F1 hybrid to sequence and assemble the genome of the American plains bison (Bison bison bison). The male haplotype genome is chromosome-scale, with a total length of 2.65 Gb across 775 scaffolds (839 contigs) and a scaffold N50 of 87.8 Mb. Our bison genome is ~13× more contiguous overall and ~3400× more contiguous at the contig level than the current bison reference genome. The bison genome sequence presented here (ARS-UCSC_bison1.0) will enable new research into the evolutionary history of this iconic megafauna species and provide a new tool for the management of bison populations in federal and commercial herds.

Oppenheimer J ，Rosen BD ，Heaton MP ，Vander Ley BL ，Shafer WR ，Schuetze FT ，Stroud B ，Kuehn LA ，McClure JC ，Barfield JP ，Blackburn HD ，Kalbfleisch TS ，Bickhart DM ，Davenport KM ，Kuhn KL ，Green RE ，Shapiro B ，Smith TPL ... -  《-》

Lessons for livestock genomics from genome and transcriptome sequencing in cattle and other mammals.

Decreasing sequencing costs and development of new protocols for characterizing global methylation, gene expression patterns and regulatory regions have stimulated the generation of large livestock datasets. Here, we discuss experiences in the analysis of whole-genome and transcriptome sequence data. We analyzed whole-genome sequence (WGS) data from 132 individuals from five canid species (Canis familiaris, C. latrans, C. dingo, C. aureus and C. lupus) and 61 breeds, three bison (Bison bison), 64 water buffalo (Bubalus bubalis) and 297 bovines from 17 breeds. By individual, data vary in extent of reference genome depth of coverage from 4.9X to 64.0X. We have also analyzed RNA-seq data for 580 samples representing 159 Bos taurus and Rattus norvegicus animals and 98 tissues. By aligning reads to a reference assembly and calling variants, we assessed effects of average depth of coverage on the actual coverage and on the number of called variants. We examined the identity of unmapped reads by assembling them and querying produced contigs against the non-redundant nucleic acids database. By imputing high-density single nucleotide polymorphism data on 4010 US registered Angus animals to WGS using Run4 of the 1000 Bull Genomes Project and assessing the accuracy of imputation, we identified misassembled reference sequence regions. We estimate that a 24X depth of coverage is required to achieve 99.5 % coverage of the reference assembly and identify 95 % of the variants within an individual's genome. Genomes sequenced to low average coverage (e.g., <10X) may fail to cover 10 % of the reference genome and identify <75 % of variants. About 10 % of genomic DNA or transcriptome sequence reads fail to align to the reference assembly. These reads include loci missing from the reference assembly and misassembled genes and interesting symbionts, commensal and pathogenic organisms. Assembly errors and a lack of annotation of functional elements significantly limit the utility of the current draft livestock reference assemblies. The Functional Annotation of Animal Genomes initiative seeks to annotate functional elements, while a 70X Pac-Bio assembly for cow is underway and may result in a significantly improved reference assembly.

Taylor JF ，Whitacre LK ，Hoff JL ，Tizioto PC ，Kim J ，Decker JE ，Schnabel RD ... -  《-》