Genomes reveal selective sweeps in kiang and donkey for high-altitude adaptation

Chromosome-scale assembly of Artemia tibetiana genome, first aquatic invertebrate genome from Tibet Plateau

Genomic-level studies on the adaptive evolution of animals in the Qinghai-Tibet Plateau have been rapidly increasing. However, most studies are concentrated on vertebrates, and there are few reports on invertebrates. Here, we report the chromosome-level genome assembly for the brine shrimp Artemia tibetiana from Kyêbxang Co, a high-altitude (4620 m above sea level) salt lake on the plateau, based on the combination of Illumina, Nanopore long-reads and Hi-C sequencing data. The assembled genome is 1.69 Gb, and 94.83% of the assembled sequences are anchored to 21 pseudo-chromosomes. Approximately 75% of the genome was identified as repetitive sequences, which is higher than most crustaceans documented so far. A total of 17,988 protein-coding genes were identified, among them 14,388 were functionally annotated. This genomic resource provides the foundation for whole-genome level investigation on the genetic adaptation of Artemia to the harsh conditions in the Qinghai-Tibet Plateau.

Potential Genetic Markers Associated with Environmental Adaptability in Herbivorous Livestock

Herbivorous livestock, such as cattle, sheep, goats, horses, and donkeys, play a crucial role in agricultural production and possess remarkable resilience to extreme environmental conditions, driven by complex genetic mechanisms. Recent advancements in high-throughput sequencing, genome assembly, and environmental data integration have enabled a deeper understanding of the genetic basis of their environmental adaptation. This review identifies key genes associated with high-altitude, heat, cold, and drought adaptation, providing insights into the molecular mechanisms underlying these traits. By elucidating these genetic adaptations, our study aims to support conservation efforts, inform selective breeding programs, and enhance agricultural productivity, ultimately contributing to sustainable livestock farming and economic benefits for farmers.

Unraveling the genetic and physiological potential of donkeys: insights from genomics, proteomics, and metabolomics approaches

Donkeys (Equus asinus) have played a vital role in agriculture, transportation, and companionship, particularly in developing regions where they are indispensable working animals. The domestication of donkeys marked a significant turning point in human history, as they became essential for transportation, agriculture, and trade, especially in arid and semi-arid areas where their resilience and endurance were highly valued. In modern society, donkeys are indispensable due to their diversified applications, including meat, dairy, medicine, and functional bioproducts, supporting economic, cultural, and medical industries. Despite their critical importance, research on donkeys has historically been overshadowed with studies on horses. However, recent advancements in high-throughput sequencing and bioinformatics have significantly deepened our understanding of the molecular landscape of donkey genome, uncovering their unique adaptations, genetic diversity, and potential therapeutic applications. Microsatellite and mitochondrial DNA (mtDNA) markers have proven effective in assessing the genetic diversity of donkeys across various regions of the world. Additionally, significant strides have been made in characterizing differentially abundant genes, proteins, and metabolic profiles in donkey milk, meat, and skin, and in identifying specific genes/proteins/metabolites associated with sperm quality, motility, and reproduction. Advanced genomic technologies, such as genome-wide association studies and the identification of selection signatures, have also been instrumental in delineating genomic regions associated with phenotypic and adaptive traits. This review integrates data from diverse studies, including those on genetic diversity, transcriptomics, whole genome sequencing, protein analysis, and metabolic profiling, to provide a comprehensive overview of donkey biology. It underscores the unique characteristics of donkeys and emphasizes the importance of continued research to improve their genetic management, conservation, and agricultural use, ensuring their ongoing contribution to human societies.

Equus mitochondrial pangenome reveals independent domestication imprints in donkeys and horses

Mitochondria are semi-autonomous organelles that play a crucial role in the energy budget of animal cells and are closely related to the locomotor abilities of animals. Equidae is renowned for including two domesticated species with distinct purposes: the endurance-oriented donkey and the power-driven horse, making it an ideal system for studying the relationship between mitochondria and locomotor abilities. In this study, to cover the genetic diversity of donkeys, we sequenced and assembled six new mitochondrial genomes from China. Meanwhile, we downloaded the published mitochondrial genomes of all species within Equus and conducted a comprehensive pan-mitochondrial genome analysis. We found that the mitochondrial genomes of Equus are highly conserved, each encoding 37 genes, including 13 protein-coding genes (PCGs). Phylogenetic analysis based on mitochondrial genomes supports previous research, indicating that the extant species in Equus are divided into three main branches: horses, donkeys, and zebras. Specifically, 761 genetic variants were identified between donkeys and horses, 68 of which were non-synonymous mutations in PCGs, potentially linked to their different locomotor abilities. Structural protein modeling indicated that despite genetic differences, the overall protein structures between donkeys and horses remain similar. This study revealed the mitochondrial genome variation patterns of domesticated animals, offering novelty perspectives on domestication imprints. Additionally, it provides reliable candidate molecular markers for the identification of donkeys and horses.

Study on intestinal microbial communities of three different cattle populations on Qinghai-Tibet Plateau

The Tibetan cattle, indispensable·animals on the Qinghai-Tibet Plateau, have become a focal point for the region's economic development. As such, the hybridization of these cattle has been recognized as a pivotal strategy to enhance the local cattle industry. However, research on the gut microbiota of Tibetan hybrid cattle remains scarce. Based on this, we conducted a comparative analysis of the gut microbiota and its functional implications across three distinct cattle populations: two the hybrid cattle populations (Tibetan local cattle × Holstein cattle, TH and Tibetan local cattle × Jersey cattle, TJ) and one the Tibetan locoal cattle population (BL). Bacteroidetes and Firmicutes dominate the gut microbiota across all populations at the phylum level. In addition, the predominant phyla in BL cattle were found to be Cyanobacteria, Verrucomicrobiota, and Actinobacteria, which may be one of the important reasons for the adaptability of Tibetan local cattle to the high-altitude environment of the Qinghai-Tibet Plateau. Further analysis identified specific biomarkers associated with the immune systems of BL cattle, including Bacteroidales_RF16, Coriobacterium, and Muribaculaceae. In contrast, TH cattle are primarily dominated by Oscillospiraceae and Clostridia_UCG_014, and TJ cattle are mainly dominated by Christensenellaceae and Gammaproteobacteria. KEGG enrichment analysis revealed that BL and TH cattle showed significant enrichment in the immune system, energy metabolism, and amino acid metabolism-related pathways compared with TJ cattle. Overall, these results suggest that BL and TH cattle demonstrate enhanced adaptability compared to TJ cattle, and indicate that intestinal microbiota of cattle at different altitudes and breeds have diverse structures and functions. Our study presents a new perspective on the role of the microbiome in the hybridization and enhancement of Tibetan cattle.

Non-targeted LC-MS metabolomics reveals serum metabolites for high-altitude adaptation in Tibetan donkeys

Tibetan donkeys inhabit the harsh environment of the Qinghai-Tibet Plateau. Research on serum metabolites related to their high-altitude adaptation is limited compared to other livestock. We used liquid chromatography-mass spectrometry (LC-MS) to analyze serum samples from healthy adult donkeys in Shigatse, Changdu, and Dezhou to evaluate the effects of high altitudes on serum metabolites. Metabolomics analysis identified 443 differential metabolites (DMs) across the three groups, meeting criteria of VIP ≥ 1, p-value < 0.05, and Fold-Change ≥ 1.2 or ≤ 0.5. Significant upregulation was observed in deoxycholic acid, vitamin A, vitamin C, flavin mononucleotide, n-acetylserotonin, N'-formyl-kynurenine, calcidiol, and adenosine monophosphate in the high-altitude group compared to the low-altitude control group. The DMs were involved in processes such as bile secretion, vitamin digestion and absorption, tryptophan metabolism, and parathyroid hormone synthesis, secretion, and action. All these are crucial for nutrient metabolism, immune function, and antioxidant stress response. This study constructed a metabolomics dataset of Tibetan donkey serum and revealed differential metabolites among donkeys from different geographic regions and environments. The results offer crucial insights into the adaptive regulatory mechanisms.

Chromosome-level genome assembly of the kiang (Equus kiang) illuminates genomic basis for its high-altitude adaptation

The kiang (Equus kiang) can only be observed in the Qinghai-Tibet Plateau (QTP). The kiang displayed excellent athletic performance in the high-altitude environment, which attracted wide interest in the investigation of the potential adaptive mechanisms to the extreme environment. Here, we assembled a chromosome-level genome of the kiang based on Hi-C sequencing technology. A total of 324.14 Gb clean data were generated, and the chromosome-level genome with 26 chromosomes (25 + X) and scaffold N50 of 101.77 Mb was obtained for the kiang. The genomic synteny analysis revealed large-scale chromosomal rearrangement during the evolution process of Equus species. Phylogenetic and divergence analyses revealed that the kiang was the sister branch to the ass and diverged from a common ancestor at approximately 13.5 Mya. The expanded gene families were mainly related to the hypoxia response, metabolism, and immunity. The kiang suffered a significant loss of olfaction-related genes, which might indicate decreased olfactory sensibility. Positively selected genes (PSGs) detected in the kiang were mainly associated with hypoxia response. Especially, there were two species-specific missense amino acid mutations in the PSG STAT3 annotated in the hypoxia-inducible factor 1 signal pathway, which may play an important role in the high-altitude adaptation of the kiang. Moreover, structure variations in the kiang genome were also identified, which possibly contributed to the high-altitude adaptation of the kiang. Comparative analysis revealed a lot of species-specific insertions and deletions in the kiang genome, such as PIK3CB and AKT with 3258 and 189 bp insertions in the intron region, respectively, possibly affecting the expression and regulation of hypoxia-related downstream pathways. This study provided valuable genomic resources, and our findings help a better understanding of the underlying adaptive strategies to the high-altitude environment in the kiang.

A review of genetic resources and trends of omics applications in donkey research: focus on China

Omics methodologies, such as genomics, transcriptomics, proteomics, metabolomics, lipidomics and microbiomics, have revolutionized biological research by allowing comprehensive molecular analysis in livestock animals. However, despite being widely used in various animal species, research on donkeys has been notably scarce. China, renowned for its rich history in donkey husbandry, plays a pivotal role in their conservation and utilization. China boasts 24 distinct donkey breeds, necessitating conservation efforts, especially for smaller breeds facing extinction threats. So far, omics approaches have been employed in studies of donkey milk and meat, shedding light on their composition and quality. Similarly, omics methods have been utilized to explore the molecular basis associated with donkey growth, meat production, and quality traits. Omics analysis has also unraveled the critical role of donkey microbiota in health and nutrition, with gut microbiome studies revealing associations with factors such as pregnancy, age, transportation stress, and altitude. Furthermore, omics applications have addressed donkey health issues, including infectious diseases and reproductive problems. In addition, these applications have also provided insights into the improvement of donkey reproductive efficiency research. In conclusion, omics methodologies are essential for advancing knowledge about donkeys, their genetic diversity, and their applications across various domains. However, omics research in donkeys is still in its infancy, and there is a need for continued research to enhance donkey breeding, production, and welfare in China and beyond.

Factors affecting the quality and nutritional value of donkey meat: a comprehensive review

Donkey meat is characterized by a high content of proteins, essential amino acids, and unsaturated fatty acids and is low in fat, cholesterol, and calories. Thus, it is considered a high-quality source of meat. Based on the data from PubMed and Web of science within past 10 years, this review summarizes the factors affecting the quality of donkey meat and its nutritional value, including breed, genetics, gender, age, muscle type, feeding regimen, storage and processing conditions. Breed, gender, age, and feeding regimen mainly affect the quality of donkey meat by influencing its intramuscular fat content and carcass quality. Meanwhile, the tenderness and flavor of donkey meat depend on the muscle type, storage and processing conditions. Genetics, on the other hand, fundamentally affect donkey meat quality by influencing the polymorphism of genes. These findings provide valuable insights and guidance for producers, consumers, and decision-makers in the donkey meat industry, promoting the development of more effective marketing strategies and the improvement of meat quality, thereby enabling the expansion and progress of the entire industry.

Oxygen stress on age-stage, two-sex life tables and transcriptomic response of diamondback moth (Plutella xylostella)

Elucidating the genetic basis of local adaption is one of the important tasks in evolutionary biology. The Qinghai-Tibet Plateau has the highest biodiversity for an extreme environment worldwide, and provides an ideal natural laboratory to study adaptive evolution. The diamondback moth (DBM), Plutella xylostella, is one of the most devastating pests of the global Brassica industry. A highly heterozygous genome of this pest has facilitated its adaptation to a variety of complex environments, and so provides an ideal model to study fast adaptation. We conducted a pilot study combining RNA-seq with an age-stage, two-sex life table to study the effects of oxygen deprivation on DBM. The developmental periods of all instars were significantly shorter in the hypoxic environment. We compared the transcriptomes of DBM from Fuzhou, Fujian (low-altitude) and Lhasa, Tibet (high-altitude) under hypoxia treatment in a hypoxic chamber. Some DEGs are enriched in pathways associated with DNA replication, such as DNA repair, nucleotide excision repair, base excision repair, mismatch repair and homologous recombination. The pathways with significant changes were associated with metabolism process and cell development. Thus, we assumed that insects could adapt to different environments by regulating their metabolism. Our findings indicated that although adaptive mechanisms to hypoxia in different DBM strains could be similar, DBM individuals from Tibet had superior tolerance to hypoxia compared with those of Fuzhou. Local adaptation of the Tibetan colony was assumed to be responsible for this difference. Our research suggests novel mechanisms of insect responses to hypoxia stress.

Population genomic analysis provides evidence of the past success and future potential of South China tiger captive conservation

BACKGROUND

Among six extant tiger subspecies, the South China tiger (Panthera tigris amoyensis) once was widely distributed but is now the rarest one and extinct in the wild. All living South China tigers are descendants of only two male and four female wild-caught tigers and they survive solely in zoos after 60 years of effective conservation efforts. Inbreeding depression and hybridization with other tiger subspecies were believed to have occurred within the small, captive South China tiger population. It is therefore urgently needed to examine the genomic landscape of existing genetic variation among the South China tigers.

RESULTS

In this study, we assembled a high-quality chromosome-level genome using long-read sequences and re-sequenced 29 high-depth genomes of the South China tigers. By combining and comparing our data with the other 40 genomes of six tiger subspecies, we identified two significantly differentiated genomic lineages among the South China tigers, which harbored some rare genetic variants introgressed from other tiger subspecies and thus maintained a moderate genetic diversity. We noticed that the South China tiger had higher F_ROH values for longer runs of homozygosity (ROH > 1 Mb), an indication of recent inbreeding/founder events. We also observed that the South China tiger had the least frequent homozygous genotypes of both high- and moderate-impact deleterious mutations, and lower mutation loads than both Amur and Sumatran tigers. Altogether, our analyses indicated an effective genetic purging of deleterious mutations in homozygous states from the South China tiger, following its population contraction with a controlled increase in inbreeding based on its pedigree records.

CONCLUSIONS

The identification of two unique founder/genomic lineages coupled with active genetic purging of deleterious mutations in homozygous states and the genomic resources generated in our study pave the way for a genomics-informed conservation, following the real-time monitoring and rational exchange of reproductive South China tigers among zoos.

Genome-wide analysis reveals selection signatures for body size and drought adaptation in Liangzhou donkey

Liangzhou donkey is a domestic animal breed distributed on the edge of the Tengger Desert in Gansu Province of China. It has small body size and strong adaptability to dry environments. Here, we sequenced 10 Liangzhou donkey genomes and compared them to the 55 genomes of 8 representative donkey breeds worldwide. The population structure analysis revealed that Liangzhou donkey harboured the ancestry with the Asian domestic donkeys (0.863) and European domestic donkeys (0.137). Three methods (nucleotide diversity, linkage disequilibrium decay and runs of homozygosity) implied the genetic diversity in Liangzhou donkey. In addition, we analyzed the genetic basis of the small body size and drought adaptation of Liangzhou donkey by using F_st, θπ-ratio, XP-EHH, CLR and θπ methods. We found that the NCAPG-LCORL on chromosome 3 may be a candidate region for small body size trait of Liangzhou donkey. The CYP4A11 gene located on chromosome 5 showed strong sign of selection sweep. CYP4A11 can convert arachidonic acid into 19(S)-HETE, which can promote water reabsorption in renal tubule and enhance the ability of Liangzhou donkey to adapt to dry environment. These results contribute to a better understanding of the underlying population structure of Liangzhou donkeys and provides a valuable resource for future research on donkey breeding in response to climate change.

Origin, Evolution, and Research Development of Donkeys

Lack of archaeological and whole-genome diversity data has restricted current knowledge of the evolutionary history of donkeys. With the advancement of science and technology, the discovery of archaeological evidence, the development of molecular genetics, and the improvement of whole-genome sequencing technology, the in-depth understanding of the origin and domestication of donkeys has been enhanced, however. Given the lack of systematic research, the present study carefully screened and collected multiple academic papers and books, journals, and literature on donkeys over the past 15 years. The origin and domestication of donkeys are reviewed in this paper from the aspects of basic information, cultural origin, bioarcheology, mitochondrial and chromosomal microsatellite sequences, and whole-genome sequence comparison. It also highlights and reviews genome assembly technology, by assembling the genome of an individual organism and comparing it with related sample genomes, which can be used to produce more accurate results through big data statistics, analysis, and computational correlation models. Background: The donkey industry in the world and especially in China is developing rapidly, and donkey farming is transforming gradually from the family farming model to large-scale, intensive, and integrated industrial operations, which could ensure the stability of product quality and quantity. However, theoretical research on donkey breeding and its technical development lags far behind that of other livestock, thereby limiting its industrial development. This review provides holistic information for the donkey industry and researchers, that could promote theoretical research, genomic selection (GS), and reproductive management of the donkey population.

The genomic history and global expansion of domestic donkeys

Donkeys transformed human history as essential beasts of burden for long-distance movement, especially across semi-arid and upland environments. They remain insufficiently studied despite globally expanding and providing key support to low- to middle-income communities. To elucidate their domestication history, we constructed a comprehensive genome panel of 207 modern and 31 ancient donkeys, as well as 15 wild equids. We found a strong phylogeographic structure in modern donkeys that supports a single domestication in Africa ~5000 BCE, followed by further expansions in this continent and Eurasia and ultimately returning to Africa. We uncover a previously unknown genetic lineage in the Levant ~200 BCE, which contributed increasing ancestry toward Asia. Donkey management involved inbreeding and the production of giant bloodlines at a time when mules were essential to the Roman economy and military.

Consequences of Hybridization in Mammals: A Systematic Review

Hybridization, defined as breeding between two distinct taxonomic units, can have an important effect on the evolutionary patterns in cross-breeding taxa. Although interspecific hybridization has frequently been considered as a maladaptive process, which threatens species genetic integrity and survival via genetic swamping and outbreeding depression, in some cases hybridization can introduce novel adaptive variation and increase fitness. Most studies to date focused on documenting hybridization events and analyzing their causes, while relatively little is known about the consequences of hybridization and its impact on the parental species. To address this knowledge gap, we conducted a systematic review of studies on hybridization in mammals published in 2010-2021, and identified 115 relevant studies. Of 13 categories of hybridization consequences described in these studies, the most common negative consequence (21% of studies) was genetic swamping and the most common positive consequence (8%) was the gain of novel adaptive variation. The total frequency of negative consequences (49%) was higher than positive (13%) and neutral (38%) consequences. These frequencies are biased by the detection possibilities of microsatellite loci, the most common genetic markers used in the papers assessed. As negative outcomes are typically easier to demonstrate than positive ones (e.g., extinction vs hybrid speciation), they may be over-represented in publications. Transition towards genomic studies involving both neutral and adaptive variation will provide a better insight into the real impacts of hybridization.

Genome-Wide Selective Signatures Reveal Candidate Genes Associated with Hair Follicle Development and Wool Shedding in Sheep

Hair follicle development and wool shedding in sheep are poorly understood. This study investigated the population structures and genetic differences between sheep with different wool types to identify candidate genes related to these traits. We used Illumina ovine SNP 50K chip genotyping data of 795 sheep populations comprising 27 breeds with two wool types, measuring the population differentiation index (Fst), nucleotide diversity (θπ ratio), and extended haplotype homozygosity among populations (XP-EHH) to detect the selective signatures of hair sheep and fine-wool sheep. The top 5% of the Fst and θπ ratio values, and values of XP-EHH < −2 were considered strongly selected SNP sites. Annotation showed that the PRX, SOX18, TGM3, and TCF3 genes related to hair follicle development and wool shedding were strongly selected. Our results indicated that these methods identified important genes related to hair follicle formation, epidermal differentiation, and hair follicle stem cell development, and provide a meaningful reference for further study on the molecular mechanisms of economically important traits in sheep.