Complete mitochondrial DNA sequence analysis of Bison bison and bison-cattle hybrids: function and phylogeny

Chromosome-level reference genome for North American bison (Bison bison) and variant database aids in identifying albino mutation

We developed a highly contiguous chromosome-level reference genome for North American bison to provide a platform to evaluate the conservation, ecological, evolutionary, and population genomics of this species. Generated from a F1 hybrid between a North American bison dam and a domestic cattle bull, completeness and contiguity exceed that of other published bison genome assemblies. To demonstrate the utility for genome-wide variant frequency estimation, we compiled a genomic variant database consisting of 3 true albino bison and 44 wild-type pelage color bison. Through the examination of genomic variants fixed in the albino cohort and absent in the controls, we identified a nonsynonymous single nucleotide polymorphism (SNP) mutation on chromosome 29 in exon 3 of the tyrosinase gene (c.1114C>T). A TaqMan SNP Genotyping Assay was developed to genotype this SNP in a total of 283 animals across 29 herds. This assay confirmed the absence of homozygous variants in all animals except 7 true albino bison included in this study. In addition, the only heterozygous animals identified were 2 wild-type pelage color dams of albino offspring. Therefore, we propose that this new high-quality bison genome assembly and incipient variant database provides a highly robust and informative resource for genomics investigations for this iconic North American species.

Mitogenomes revealed the history of bison colonization of Northern Plains after the Last Glacial Maximum

American bison demonstrated differential patterns of extinction, survival, and expansion since the terminal Pleistocene. We determined population dynamics of the Northern Great Plains bison using 40 mitochondrial genomes from radiocarbon dated remains with the age ranging from 12,226 to 167 calibrated years before present. Population dynamics correlated with environmental and anthropogenic factors and was characterized by three primary periods: terminal Pleistocene population growth starting 14,000 years ago, mid Holocene demographic stability between 6700 and 2700 years ago, and late Holocene population decline in the last 2700 years. Most diversification of mtDNA haplotypes occurred in the early Holocene when bison colonized new territories opened by retreating ice sheets. Holocene mtDNA lineages were not found in modern bison and lacked association with archaeological sites and morphological forms.

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.

Genetic variation of the mitochondrial DNA control region across plains bison herds in USA and Canada

Once numbering in the tens of millions, bison (Bison bison) have faced a broad range of challenges over the past century, including genetic impacts from the population bottleneck in the 1800s, and significant loss and fragmentation of habitat resulting in little opportunity for population growth on remaining small, geographically isolated reserves. To identify best practices for bison stewardship against this backdrop, managers must understand the genetic composition of existing conservation herds. This study characterized 14 plains bison (Bison bison bison) herds managed by the U.S. Department of Interior and Parks Canada Agency based on complete mtDNA control region sequences. Among 209 bison, we detected 11 major mtDNA control region haplotypes based on nucleotide substitutions and 23 sub-haplotypes where indels are considered. We determined matrilineal relationships between the herds and compared our genetic findings to historic records. The recent common ancestry of modern bison deriving from small, scattered groups combined with gene flow through foundation and translocation events between herds during the last 100 years, is reflected in Fst value (0.21), haplotype (0.48 ± 0.04) and nucleotide (0.004 ± 0.002) diversities, and mean number of pairwise differences (3.38 ± 1.74). Genetic diversity was distributed unevenly among herds, with 21.41% of genetic variation observed between herds. Median joining network, together with trends in the Tajima’s D and Fs tests, revealed two patterns in the recent evolution of mtDNA sequences in bison: mutational process has generated diversity with a Hap 1 haplotype epicenter, and missed mtDNA haplotypes exist in the network due to bottleneck, loss through management practices, or incomplete sampling of specimens across conservation herds. This work significantly expands characterization of the genetic diversity among bison conservation herds, providing additional decision support for managers considering restoring gene flow to achieve long-term species viability.

Mitonuclear incompatibility as a hidden driver behind the genome ancestry of African admixed cattle

Background

Africa is an important watershed in the genetic history of domestic cattle, as two lineages of modern cattle, Bos taurus and B. indicus, form distinct admixed cattle populations. Despite the predominant B. indicus nuclear ancestry of African admixed cattle, B. indicus mitochondria have not been found on the continent. This discrepancy between the mitochondrial and nuclear genomes has been previously hypothesized to be driven by male-biased introgression of Asian B. indicus into ancestral African B. taurus. Given that this hypothesis mandates extreme demographic assumptions relying on random genetic drift, we propose a novel hypothesis of selection induced by mitonuclear incompatibility and assess these hypotheses with regard to the current genomic status of African admixed cattle.

Results

By analyzing 494 mitochondrial and 235 nuclear genome sequences, we first confirmed the genotype discrepancy between mitochondrial and nuclear genome in African admixed cattle: the absence of B. indicus mitochondria and the predominant B. indicus autosomal ancestry. We applied approximate Bayesian computation (ABC) to assess the posterior probabilities of two selection hypotheses given this observation. The results of ABC indicated that the model assuming both male-biased B. indicus introgression and selection induced by mitonuclear incompatibility explains the current genomic discrepancy most accurately. Subsequently, we identified selection signatures at autosomal loci interacting with mitochondria that are responsible for integrity of the cellular respiration system. By contrast with B. indicus-enriched genome ancestry of African admixed cattle, local ancestries at these selection signatures were enriched with B. taurus alleles, concurring with the key expectation of selection induced by mitonuclear incompatibility.

Conclusions

Our findings support the current genome status of African admixed cattle as a potential outcome of male-biased B. indicus introgression, where mitonuclear incompatibility exerted selection pressure against B. indicus mitochondria. This study provides a novel perspective on African cattle demography and supports the role of mitonuclear incompatibility in the hybridization of mammalian species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01206-x.

A Behavioral Index for Assessing Bison Stress Level during Handling and Demographic Predictors of Stress Response

There are an estimated half-a-million Plains Bison (Bison bison) present in North America in commercial and conservation herds. Most bison are rounded up and "worked" annually for parasite control, veterinarian attention, and processing, making it important to understand the impacts of these operations. Research indicates bison generally experience higher levels of stress than cattle during similar handling processes. However, most methods for assessing stress-level during working are invasive, increase handling time, and paradoxically increase stress levels. We designed a behavioral index to assess bison stress level during handling and used it to evaluate various predictors of stress response in a semi-wild bison herd. We examined how sex, age, herd of origin, previous experience, calf rearing, and body condition influenced bison stress response during working operations from 2015 to 2017. Our results indicate that stress level decreased with age and previous experience being worked through a particular facility. Additionally, herd of origin influenced stress level, indicating that stress response may have a genetic or epigenetic component. Our study provides an easily applicable tool for monitoring bison stress levels.

Diversity and Paleodemography of the Addax (Addax nasomaculatus), a Saharan Antelope on the Verge of Extinction

Since the 19th century, the addax (Addax nasomaculatus) has lost approximately 99% of its former range. Along with its close relatives, the blue antelope (Hippotragus leucophaeus) and the scimitar-horned oryx (Oryx dammah), the addax may be the third large African mammal species to go extinct in the wild in recent times. Despite this, the evolutionary history of this critically endangered species remains virtually unknown. To gain insight into the population history of the addax, we used hybridization capture to generate ten complete mitochondrial genomes from historical samples and assembled a nuclear genome. We found that both mitochondrial and nuclear diversity are low compared to other African bovids. Analysis of mitochondrial genomes revealed a most recent common ancestor ~32 kya (95% CI 11–58 kya) and weak phylogeographic structure, indicating that the addax likely existed as a highly mobile, panmictic population across its Sahelo–Saharan range in the past. PSMC analysis revealed a continuous decline in effective population size since ~2 Ma, with short intermediate increases at ~500 and ~44 kya. Our results suggest that the addax went through a major bottleneck in the Late Pleistocene, remaining at low population size prior to the human disturbances of the last few centuries.

The complete mitochondrial genome and phylogenetic analysis of Yanglong yak (Bos grunniens)

In this study, we assembled the complete mitochondrial genome of Yanglong yak (Bos grunniens) from Illumina sequencing reads. The mitochondrial genome is 16,323 bp long with an A + T-biased nucleotide composition, and encodes 13 protein-coding, 22 tRNA, and two rRNA genes along with a noncoding control region. In addition, its gene order is identical to those of the previously published mitochondrial genomes of its congeners. Phylogenetic analysis indicates that this breed is closely related to Datong yak, Pamir yak, Tianjun yak, polled yak, Seron yak, Sunnan yak, a series of Domestic Yak and wild yak, followed by Jinchuan yak and Gannan yak, and slightly far away from Bison and Bos taurus.

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.

Sequencing and annotation of the endangered wild buffalo (Bubalus arnee) mitogenome for taxonomic assessment

The wild water buffalo (Bubalus arnee) is one of the most endangered and least studied large bovid in the Indian subcontinent. India retains 90% of the estimated global population of >4000 individuals as two fragmented populations in Assam and Chhattisgarh, both threatened by habitat loss and degradation, hunting, disease from livestock, and hybridization with the domestic buffalos. Small, fragmented population size and potential hybridisation pressures from co-occurring domestic buffalos are the major conservation challenges. For the first time, we sequenced the 16,357 bp long mitogenome of three opportunistically collected wild water buffalo samples from Assam (n = 1) and Chhattishgarh (n = 2). The annotated sequence has a base composition of 26.4% T, 26.6% C, 33.1% A and 13.9% G depicting an AT-rich mitogenome composition, including 13 protein-coding genes (11,361 bp), 22 transfer RNA (tRNA) (1514 bp), two ribosomal genes (2525 bp), and a non-coding control region (928 bp). The gene order is conserved with other bovid species. Comparative mitogenome analyses showed both populations are genetically similar but significantly different from domestic buffalo. We also identified structural differences in seven tRNA secondary structures between both species. The genetic distance between wild buffalo and other bovids varied between 0.103 and 0.122. Multiple Bayesian phylogenetic trees showed that both wild and domestic water buffalo formed sister clades which were paraphyletic to other potentially sympatric species of genus Bos. This study provides baseline information on wild buffalo mitogenome for further research on phylogeny, phylogeography and hybrid assessment and help conserving this endangered species.

Identifying the true number of specimens of the extinct blue antelope (Hippotragus leucophaeus)

Native to southern Africa, the blue antelope (Hippotragus leucophaeus) is the only large African mammal species known to have become extinct in historical times. However, it was poorly documented prior to its extinction ~ 1800 AD, and many of the small number of museum specimens attributed to it are taxonomically contentious. This places limitations on our understanding of its morphology, ecology, and the mechanisms responsible for its demise. We retrieved genetic information from ten of the sixteen putative blue antelope museum specimens using both shotgun sequencing and mitochondrial genome target capture in an attempt to resolve the uncertainty surrounding the identification of these specimens. We found that only four of the ten investigated specimens, and not a single skull, represent the blue antelope. This indicates that the true number of historical museum specimens of the blue antelope is even smaller than previously thought, and therefore hardly any reference material is available for morphometric, comparative and genetic studies. Our study highlights how genetics can be used to identify rare species in natural history collections where other methods may fail or when records are scarce. Additionally, we present an improved mitochondrial reference genome for the blue antelope as well as one complete and two partial mitochondrial genomes. A first analysis of these mitochondrial genomes indicates low levels of maternal genetic diversity in the ‘museum population’, possibly confirming previous results that blue antelope population size was already low at the time of the European colonization of South Africa.

Characterization of the complete mitogenome of the Hongyuan Yak Bos grunniens (Artiodactyla: Bovidae) and its phylogenetic analysis

The Hongyuan breed Yak (Bos grunniens) belongs to a member of t the subfamily Bovinae. We provide a complete mitogenome of B. grunniens and analyze its phylogenetic relationship with other related species. Its mitogenome is a circular molecule with 16,322 bp in size, including 13 protein coding genes, 22 tRNA genes, 2 rRNA genes, and a non-coding control region (D-loop, CR) that are conserved in most Bovidae mitogenomes. The total base composition of the B. grunniens mitogenome is 33.67% A, 27.29% T, 25.84% C, and 13.20% G. The gene composition, structure and the arrangement for B. grunniens are similar to those of most other Bovidae species. Phylogenetic analysis of mitochondrial genomes of 30 close species with Bayesian inference and maximum likelihood based on 13 protein-coding genes indicated that B. grunniens breed Hongyuan is more closely related to B. grunniens breed Qinghai Plateau than to B. grunniens breed Xuedong and B. grunniens breed Maiwa. The complete mitogenome of B. grunniens breed Hongyuan provides a potentially useful resource for further exploration of the taxonomic status and phylogenetic relationships of Bovinae and related species.

Characterization of the complete mitochondrial genome of the Meiren yak (Bos grunniens)

In this study, high-throughput Illumina sequencing was employed to assemble the complete mitochondrial genome of the Meiren yak (Bos grunniens), a local yak breed from Gansu Province, China. The mitochondrial genome is 16,321 bp long with an A + T-biased nucleotide composition and harbors 13 protein-coding, 22 Trna, and 2 rRNA genes, and a noncoding control region. The mitogenomic organization and codon usage are highly similar to those of previously published congeneric mitochondrial genomes. Bayesian phylogenetic analysis indicates that Meiren yak is most closely related to nine other yak breeds (incl. Datong, Huanhu, Pali, Pamir, Polled, Qilian, Seron, Sunan, and Tianjun yaks).

Characterization of the complete mitochondrial genome of the Tianjun yak (Bos grunniens)

Tianjun yak (Bos grunniens) is a yak breed with strong adaptation to the high-elevation, cold and anoxic environments. Its complete mitochondrial genome is 16,323 bp long with an asymmetric base composition, and harbors the 37 typical mitochondrial genes and one noncoding control region. The PCGs are initiated with the typical ATA or ATG codons, and are terminated with TAA, TAG or the incomplete stop codon T--. Phylogenetic analysis suggests that Tianjun yak is most closely related to the polled yak.

Characterization of the complete mitochondrial genome of the Pamir yak (Bos grunniens)

Pamir yak (Bos grunniens) is a yak breed from Pamir Plateau with strong adaptation to the high-elevation, cold and anoxic environments. Its complete mitochondrial genome was determined to be 16,323 bp long with a moderately asymmetric nucleotide composition, and harbors the typical set of 37 mitochondrial genes and the noncoding control region. The PCGs start with the typical ATA or ATG codons, and end with TAA, TAG or the incomplete termination codon T. Phylogenetic analysis suggests that Pamir yak is most closely related to six other yak breeds (i.e. Datong, Pali, polled, Qilian, Seron and Sunan yaks).

Complete mitochondrial genome of two Thitarodes species (Lepidoptera, Hepialidae), the host moths of Ophiocordyceps sinensis and phylogenetic implications

Thitarodes (Lepidoptera, Hepialidae) is the only genus that hosts to the Ophiocordyceps sinensis, a traditional Chinese medicine considered as a powerful medicinal supplement. In this study, the complete mitochondrial genomes (mitogenomes) of two species, T. damxungensis and T. pui, have been sequenced, which are 15,928 bp and 15,362 bp in size respectively, and both contain 13 protein-coding genes (PCGs), 2 rRNAs, 22 tRNAs and an AT-rich region. Like other hepialoids, the gene arrangement of the mitogenomes of T. damxungensis and T. pui is identical to the ancestral arrangement but differs from those of other lepidopteran species on account of the different arrangements of trnM, trnI, and trnQ. The size of AT-rich region is 545 bp in T. damxungensis and 1030 bp in T. pui. Tandem repetition in the AT-rich region is responsible for the length difference of the A + T-rich region in both species. In Hepialidae, the phylogenetic study based on the dataset of the sequences that combined the protein-coding genes and RNA genes suggested that the species T. yunnanensis should still belong to the genus Thitarodes rather than Ahamns, which is different from the results based on the traditional phylogeny.

Characterization of the complete mitochondrial genome of the Seron yak (Bos grunniens)

In this study, we assembled the mitochondrial genome for Seron yak (Bos grunniens), a local yak breed with strong adaptation to marshy grasslands. The resultant mitochondrial genome is 16,325 bp long with an A + T-biased base composition (61.0% A + T) and harbours the typical set of 37 mitochondrial genes and 1 non-coding control region. The PCGs start with the typical ATA or ATG codons and are terminated with TAA, TAG or the incomplete stop codon T. Phylogenetic analysis supports the inclusion of Bison within the genus Bos, and suggests that Seron yak is most closely related to Datong yak and polled yak.

The complete mitochondrial genome of the hybrid of Jersey cattle (Bos taurus; ♂) × Gannan yak (Bos grunniens; ♀)

In this study, we reconstructed the complete mitochondrial genome of the hybrid of Jersey cattle (Bos taurus; ♂) × Gannan yak (Bos grunniens; ♀) from Illumina sequencing reads. The mitochondrial genome is 16,322 bp in length with an A + T-biased nucleotide composition, and encodes 13 protein-coding genes, 22 tRNAs, and 2 rRNAs along with a noncoding control region. In addition, its gene order is identical to those of previously published mitochondrial genomes of the genera Bison and Bos. Phylogenetic analysis indicates that this hybrid is most closely related to Gannan yak and Jinchuan yak.

Fossil and genomic evidence constrains the timing of bison arrival in North America

The arrival of bison in North America marks one of the most successful large-mammal dispersals from Asia within the last million years, yet the timing and nature of this event remain poorly determined. Here, we used a combined paleontological and paleogenomic approach to provide a robust timeline for the entry and subsequent evolution of bison within North America. We characterized two fossil-rich localities in Canada's Yukon and identified the oldest well-constrained bison fossil in North America, a 130,000-y-old steppe bison, Bison cf. priscus We extracted and sequenced mitochondrial genomes from both this bison and from the remains of a recently discovered, ∼120,000-y-old giant long-horned bison, Bison latifrons, from Snowmass, Colorado. We analyzed these and 44 other bison mitogenomes with ages that span the Late Pleistocene, and identified two waves of bison dispersal into North America from Asia, the earliest of which occurred ∼195-135 thousand y ago and preceded the morphological diversification of North American bison, and the second of which occurred during the Late Pleistocene, ∼45-21 thousand y ago. This chronological arc establishes that bison first entered North America during the sea level lowstand accompanying marine isotope stage 6, rejecting earlier records of bison in North America. After their invasion, bison rapidly colonized North America during the last interglaciation, spreading from Alaska through continental North America; they have been continuously resident since then.

Mitochondrial Genome Analysis Reveals Historical Lineages in Yellowstone Bison

Yellowstone National Park is home to one of the only plains bison populations that have continuously existed on their present landscape since prehistoric times without evidence of domestic cattle introgression. Previous studies characterized the relatively high levels of nuclear genetic diversity in these bison, but little is known about their mitochondrial haplotype diversity. This study assessed mitochondrial genomes from 25 randomly selected Yellowstone bison and found 10 different mitochondrial haplotypes with a haplotype diversity of 0.78 (± 0.06). Spatial analysis of these mitochondrial DNA (mtDNA) haplotypes did not detect geographic population subdivision (F_ST = -0.06, p = 0.76). However, we identified two independent and historically important lineages in Yellowstone bison by combining data from 65 bison (defined by 120 polymorphic sites) from across North America representing a total of 30 different mitochondrial DNA haplotypes. Mitochondrial DNA haplotypes from one of the Yellowstone lineages represent descendants of the 22 indigenous bison remaining in central Yellowstone in 1902. The other mitochondrial DNA lineage represents descendants of the 18 females introduced from northern Montana in 1902 to supplement the indigenous bison population and develop a new breeding herd in the northern region of the park. Comparing modern and historical mitochondrial DNA diversity in Yellowstone bison helps uncover a historical context of park restoration efforts during the early 1900s, provides evidence against a hypothesized mitochondrial disease in bison, and reveals the signature of recent hybridization between American plains bison (Bison bison bison) and Canadian wood bison (B. b. athabascae). Our study demonstrates how mitochondrial DNA can be applied to delineate the history of wildlife species and inform future conservation actions.

Complete mitogenome sequencing and phylogenetic analysis of PaLi yak (Bos grunniens)

PaLi yak is a very important local breed in China; as a year-round grazing animal, it plays a very important role for the economic and native herdsmen. The PaLi yak complete mitochondrial DNA is sequenced in this study, the total length is 16,324 bp, containing 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region (D-loop region). The order and composition are similar to most of the other vertebrates. The base contents are: 33.72% A, 25.80% C, 13.21% G and 27.27% T; A + T (60.99%) was higher than G + C (39.01%). The phylogenetic relationships were analyzed using the complete mitogenome sequence, results showed that the genetic relationship between yak and cattle is distinct. These information provides useful data for further study on protection of genetic resources and the taxonomy of Bovinae.

The complete mitochondrial genome of the Qinghai Plateau yak Bos grunniens (Cetartiodactyla: Bovidae)

The Qinghai Plateau yak Bos grunniens (Cetartiodactyla: Bovidae) is an important primitive local breed in the Qinghai-Tibetan Plateau and adjacent regions. In this study, its complete mitochondrial genome sequence has been assembled and characterized from high-throughput Illumina sequencing data. This genome is 16 322 bp in length, and contains 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a non-coding D-loop or control region. The nucleotide composition is asymmetric (33.73% A, 25.79% C, 13.19% G, and 27.29% T) with an overall A + T content of 61.02%. The gene arrangement and the composition are similar to most other vertebrates. These data would contribute to our better understanding its population genetics and evolutionary history.

Hunting the Extinct Steppe Bison (Bison priscus) Mitochondrial Genome in the Trois-Frères Paleolithic Painted Cave

Despite the abundance of fossil remains for the extinct steppe bison (Bison priscus), an animal that was painted and engraved in numerous European Paleolithic caves, a complete mitochondrial genome sequence has never been obtained for this species. In the present study we collected bone samples from a sector of the Trois-Frères Paleolithic cave (Ariège, France) that formerly functioned as a pitfall and was sealed before the end of the Pleistocene. Screening the DNA content of the samples collected from the ground surface revealed their contamination by Bos DNA. However, a 19,000-year-old rib collected on a rock apart the pathway delineated for modern visitors was devoid of such contaminants and reproducibly yielded Bison priscus DNA. High-throughput shotgun sequencing combined with conventional PCR analysis of the rib DNA extract enabled to reconstruct a complete mitochondrial genome sequence of 16,318 bp for the extinct steppe bison with a 10.4-fold coverage. Phylogenetic analyses robustly established the position of the Bison priscus mitochondrial genome as basal to the clade delineated by the genomes of the modern American Bison bison. The extinct steppe bison sequence, which exhibits 93 specific polymorphisms as compared to the published Bison bison mitochondrial genomes, provides an additional resource for the study of Bovinae specimens. Moreover this study of ancient DNA delineates a new research pathway for the analysis of the Magdalenian Trois-Frères cave.

Evolutionary neutrality of mtDNA introgression: evidence from complete mitogenome analysis in roe deer

Introgressive hybridization offers a unique platform for studying the molecular basis of natural selection acting on mitogenomes. Most of the mtDNA protein-coding genes are extremely conserved; however, some of the observed variations have potentially adaptive significance. Here, we evaluated whether the evolution of mtDNA in closely related roe deer species affected by widespread mtDNA introgression is neutral or adaptive. We characterized and compared 16 complete mitogenomes of European (Capreolus capreolus) and Siberian (C. pygargus) roe deer, including four of Siberian origin introgressed into European species. The average sequence divergence of species-specific lineages was estimated at 2.8% and varied across gene classes. Only 21 of 315 fixed differences identified in protein-coding genes represented nonsynonymous changes. Only three of them were determined to have arisen in the C. pygargus lineage since the time to the most recent common ancestor (TMRCA) of both Capreolus species, reflecting a decelerated evolutionary ratio. The almost four-fold higher dN /dS ratio described for the European roe deer lineage is constrained by overall purifying selection, especially pronounced in the ND4 and ND5 genes. We suggest that the highly divergent C. capreolus lineage could have maintained a capability for genomic incorporation of the well-preserved and almost ancestral type of mtDNA present in C. pygargus. Our analyses did not indicate any signs of positive selection for Siberian roe deer mtDNA, suggesting that the present widespread introgression is evolutionarily neutral.

The complete sequence of mitochondrial genome of Wuyi Black pig (Sus Scrofa)

Wuyi Black pig is a native breed of Fujian province in China. It is the first time that the complete mitochondrial genome sequence of Wuyi Black pig is reported in this work, which is determined through the PCR-based method. The total length of the mitognome is 16,709 bp, which contains 2 ribosomal RNA genes, 22 tRNA genes, 13 PCGs and 1 control region (D-loop region). The total base composition of Wuyi Black pig mitochondrial genome is 34.67% for A, 26.20% for C, 25.81% for T and 13.33% for G, in the order A > C > T > G. The complete mitochondrial genome of Wuyi Black pig provides an important data in genetic mechanism and the evolution genomes.

Complete mitochondrial genome of the Yakow (Bos primigenius taurus × Bos grunniens) in China

The Chinese Yakow, Bos primigenius taurus × Bos grunniens, is a large and commercially important hybrid in family Bovidae. We first determined and annotated its complete mitochondrial genome. The mitogenome is 16,322 bp in length, consisting of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes and a control region. As in other mammals, most mitochondrial genes are encoded on the heavy strand, except for ND6 and eight tRNA genes, which are encoded on the light strand. Its overall base composition is A: 33.7%, T: 27.3%, C: 25.8% and G: 13.2%. The complete mitogenome of Yakow (B. p. taurus × B. grunniens) could provide an important data to further explore the taxonomic status of Yakow (B. p. taurus × B. grunniens) in B. grunniens and enrich the genetic information or evolutionary history of the Bovidae.

Complete mitochondrial genome of the a rare subspecies of genus Bos, Tianzhu white yak from Tibetan area in China

The population of domestic yak, Tianzhu white yak, from Tibetan area in China is considered as a rare Bos grunniens species. We first determined and annotated its complete mitochondrial genome. The mitogenome is 16,319 bp in length, consisting of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes and a control region. As in other mammals, most mitochondrial genes are encoded on the heavy strand, except for ND6 and eight tRNA genes, which are encoded on the light strand. Its overall base composition is A: 33.7%, T: 27.2%, C: 25.8% and G: 13.2%. The complete mitogenome of the new subspecies of Bos grunniens could provide an important data to further explore the taxonomic status of the subspecies.

The complete sequence of mitochondrial genome of Laiwu Black pig (Sus Scrofa)

In the present study, the ear tissue of an adult Laiwu Black pig is from the Shandong province of China. The complete mitochondrial genome of Laiwu Black pig was determined by polymerase chain reaction (PCR). The complete mitochondrial genome is 16,710 bp, and it contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, a control region (D-loop), with the genome organization and gene order being identical to that of the typical vertebrates.

Jumping and gliding rodents: mitogenomic affinities of Pedetidae and Anomaluridae deduced from an RNA-Seq approach

An RNA-Seq strategy was used to obtain the complete set of protein-coding mitochondrial genes from two rodent taxa. Thanks to the next generation sequencing (NGS) 454 approach, we determined the complete mitochondrial DNA genome from Graphiurus kelleni (Mammalia: Rodentia: Gliridae) and partial mitogenome from Pedetes capensis (Pedetidae), and compared them with published rodent and outgroup mitogenomes. We finished the mitogenome sequencing by a series of amplicons using conserved PCR primers to fill the gaps corresponding to tRNA, rRNA and control regions. Phylogenetic analyses of the mitogenomes suggest a well-supported rodent phylogeny in agreement with nuclear gene trees. Pedetes groups with Anomalurus into the clade Anomaluromorpha, while Graphiurus branches within the squirrel-related clade. Moreover, Pedetes+Anomalurus branch with Castor into the mouse-related clade. Our study demonstrates the utility of NGS for obtaining new mitochondrial genomes as well as the importance of choosing adequate models of sequence evolution to infer the phylogeny of rodents.

Genetic variation and differentiation of bison (Bison bison) subspecies and cattle (Bos taurus) breeds and subspecies

The genetic relationship of American plains bison (Bison bison bison) and wood bison (Bison bison athabascae) was quantified and compared with that among breeds and subspecies of cattle. Plains bison from 9 herds (N = 136), wood bison from 3 herds (N = 65), taurine cattle (Bos taurus taurus) from 14 breeds (N = 244), and indicine cattle (Bos taurus indicus) from 2 breeds (N = 53) were genotyped for 29 polymorphic microsatellite loci. Bayesian cluster analyses indicate 3 groups, 2 of which are plains bison and 1 of which is wood bison with some admixture, and genetic distances do not show plains bison and wood bison as distinct groups. Differentiation of wood bison and plains bison is also significantly less than that of cattle breeds and subspecies. These and other genetic data and historical interbreeding of bison do not support recognition of extant plains bison and wood bison as phylogenetically distinct subspecies.

Phenotypic effects of cattle mitochondrial DNA in American bison

Hybridization between endangered species and more common species is a significant problem in conservation biology because it may result in extinction or loss of adaptation. The historical reduction in abundance and geographic distribution of the American plains bison (Bison bison bison) and their recovery over the last 125 years is well documented. However, introgression from domestic cattle (Bos taurus) into the few remaining bison populations that existed in the late 1800s has now been identified in many modern bison herds. We examined the phenotypic effect of this ancestry by comparing weight and height of bison with cattle or bison mitochondrial DNA (mtDNA) from Santa Catalina Island, California (U.S.A.), a nutritionally stressful environment for bison, and of a group of age-matched feedlot bison males in Montana, a nutritionally rich environment. The environmental and nutritional differences between these 2 bison populations were very different and demonstrated the phenotypic effect of domestic cattle mtDNA in bison over a broad range of conditions. For example, the average weight of feedlot males that were 2 years of age was 2.54 times greater than that of males from Santa Catalina Island. In both environments, bison with cattle mtDNA had lower weight compared with bison with bison mtDNA, and on Santa Catalina Island, the height of bison with cattle mtDNA was lower than the height of bison with bison mtDNA. These data support the hypothesis that body size is smaller and height is lower in bison with domestic cattle mtDNA and that genomic integrity is important for the conservation of the American plains bison.

Origin and spread of Bos taurus: new clues from mitochondrial genomes belonging to haplogroup T1

Background

Most genetic studies on modern cattle have established a common origin for all taurine breeds in the Near East, during the Neolithic transition about 10 thousand years (ka) ago. Yet, the possibility of independent and/or secondary domestication events is still debated and is fostered by the finding of rare mitochondrial DNA (mtDNA) haplogroups like P, Q and R. Haplogroup T1, because of its geographic distribution, has been the subject of several investigations pointing to a possible independent domestication event in Africa and suggesting a genetic contribution of African cattle to the formation of Iberian and Creole cattle. Whole mitochondrial genome sequence analysis, with its proven effectiveness in improving the resolution of phylogeographic studies, is the most appropriate tool to investigate the origin and structure of haplogroup T1.

Methodology

A survey of >2200 bovine mtDNA control regions representing 28 breeds (15 European, 10 African, 3 American) identified 281 subjects belonging to haplogroup T1. Fifty-four were selected for whole mtDNA genome sequencing, and combined with ten T1 complete sequences from previous studies into the most detailed T1 phylogenetic tree available to date.

Conclusions

Phylogenetic analysis of the 64 T1 mitochondrial complete genomes revealed six distinct sub-haplogroups (T1a–T1f). Our data support the overall scenario of a Near Eastern origin of the T1 sub-haplogroups from as much as eight founding T1 haplotypes. However, the possibility that one sub-haplogroup (T1d) arose in North Africa, in domesticated stocks, shortly after their arrival from the Near East, can not be ruled out. Finally, the previously identified “African-derived American" (AA) haplotype turned out to be a sub-clade of T1c (T1c1a1). This haplotype was found here for the first time in Africa (Egypt), indicating that it probably originated in North Africa, reached the Iberian Peninsula and sailed to America, with the first European settlers.

Characterization of the complete mitochondrial genome sequence of Spirometra erinaceieuropaei (Cestoda: Diphyllobothriidae) from China

Sparganosis, caused by the plerocercoid larvae of members of the genus Spirometra, can cause significant public health problem and considerable economic losses. In the present study, the complete mitochondrial DNA (mtDNA) sequence of Spirometra erinaceieuropaei from China was determined, characterized and compared with that of S. erinaceieuropaei from Japan. The gene arrangement in the mt genome sequences of S. erinaceieuropaei from China and Japan is identical. The identity of the mt genomes was 99.1% between S. erinaceieuropaei from China and Japan, and the complete mtDNA sequence of S. erinaceieuropaei from China is slightly shorter (2 bp) than that from Japan. Phylogenetic analysis of S. erinaceieuropaei with other representative cestodes using two different computational algorithms [Bayesian inference (BI) and maximum likelihood (ML)] based on concatenated amino acid sequences of 12 protein-coding genes, revealed that S. erinaceieuropaei is closely related to Diphyllobothrium spp., supporting classification based on morphological features. The present study determined the complete mtDNA sequences of S. erinaceieuropaei from China that provides novel genetic markers for studying the population genetics and molecular epidemiology of S. erinaceieuropaei in humans and animals.

Deep sequencing the transcriptome reveals seasonal adaptive mechanisms in a hibernating mammal

Mammalian hibernation is a complex phenotype involving metabolic rate reduction, bradycardia, profound hypothermia, and a reliance on stored fat that allows the animal to survive for months without food in a state of suspended animation. To determine the genes responsible for this phenotype in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) we used the Roche 454 platform to sequence mRNA isolated at six points throughout the year from three key tissues: heart, skeletal muscle, and white adipose tissue (WAT). Deep sequencing generated approximately 3.7 million cDNA reads from 18 samples (6 time points ×3 tissues) with a mean read length of 335 bases. Of these, 3,125,337 reads were assembled into 140,703 contigs. Approximately 90% of all sequences were matched to proteins in the human UniProt database. The total number of distinct human proteins matched by ground squirrel transcripts was 13,637 for heart, 12,496 for skeletal muscle, and 14,351 for WAT. Extensive mitochondrial RNA sequences enabled a novel approach of using the transcriptome to construct the complete mitochondrial genome for I. tridecemlineatus. Seasonal and activity-specific changes in mRNA levels that met our stringent false discovery rate cutoff (1.0 × 10(-11)) were used to identify patterns of gene expression involving various aspects of the hibernation phenotype. Among these patterns are differentially expressed genes encoding heart proteins AT1A1, NAC1 and RYR2 controlling ion transport required for contraction and relaxation at low body temperatures. Abundant RNAs in skeletal muscle coding ubiquitin pathway proteins ASB2, UBC and DDB1 peak in October, suggesting an increase in muscle proteolysis. Finally, genes in WAT that encode proteins involved in lipogenesis (ACOD, FABP4) are highly expressed in August, but gradually decline in expression during the seasonal transition to lipolysis.