Genome sequence of ground tit Pseudopodoces humilis and its adaptation to high altitude

Divergent adaptation to highland and tropical environments in Bolivian Creole cattle

Bolivian Creole cattle populations evolved under low levels of breeding management and, during more than 500 years of natural selection, became adapted to various environments such as the contrasting highland and subtropical environments. Recently, highland Creole cattle were crossbred with Holstein to improve dairy production. The aim of this research was to evaluate the divergent adaptation through selection footprints of Bolivian Creole cattle from Andean highland and tropical lowlands, and to evaluate the effect of Holstein introgression in highland Creole. For this purpose, 130 Creole cattle (75 highland, 55 lowland) and 88 Holstein were genotyped using a microarray. The database was used to determine population structure and admixture and detect selection sweeps using FST, Rsb, XP-EHH, and ROH. Ancestry inference suggested that selection peaks were not due to Holstein introgression. The NCBI database was used to retrieve genes from the common regions and then perform gene ontology analysis. The most prominent selection peaks were on BTA20 and BTA23 and included the PRLR (slick phenotype) and Class I and IIa BoLA genes. Other windows contained candidate genes for hypoxia (ANXA2, NDUFA4L2), angiogenesis and haematological parameters (ANXA2, CPLANE1, NRP1, NRP2), immune response (IL7R, IL6ST, IL31RA, C6, C7, STAT6, NKG2A, IRAK4, KLR, CLEC), oxidative stress (GSTA, HSD17B6) and morphological traits (PLAG1, CHCHD7, CAP2, ARL15). GO analysis revealed enrichment terms and pathways related to immune response, glutathione and retinol metabolism and reported QTLs for coat characteristics, immune response and tick resistance. The results suggest the complex mechanism in the adaptation of Bolivian Creole cattle to the contrasting highland and subtropical environments.

Genomic Insights Into Genetic Basis of Evolutionary Conservatism and Innovation in Frogs

Examining closely related species evolving in similar environments offers valuable insights into the mechanisms driving phylogenetic conservatism and evolutionary lability. This can elucidate the intricate relationship between inheritance and environmental factors. Nonetheless, the precise genomic dynamics and molecular underpinnings of this process remain enigmatic. This study explores the evolutionary conservatism and adaptation exhibited by two closely related high-altitude frog species: Nanorana parkeri and N. pleskei. We assembled a high-quality genome for Tibetan N. pleskei and compared it to the genomes of N. parkeri and their lowland relatives. Our findings reveal that these two Tibetan frog species diverged approximately 16.6 million years ago, pointing to a possible ancestral colonization of high-elevation habitats. Following this colonization, significant adaptive evolution occurred in both coding and non-coding regions of the ancestral lineage. This evolution led to notable phenotypic alterations, as evidenced by the reduced body size. Also, due to purifying selection, most ancestral adaptive features persisted in descendant species, indicating a strong element of evolutionary conservatism. However, descendant species evolved novel adaptations to exacerbated environmental challenges in the Tibet Plateau, mainly related to hypoxia response. Furthermore, our analysis underscores the critical role of regulatory variations in descendant adaptive evolution. Notably, hub genes in networks, such as EGLN3, accumulated more variations in regulatory regions as they were transmitted from ancestors to descendants. In sum, our study sheds light on the profound and lasting impact of genetic heritage on species' adaptive evolution.

Putative climate adaptation in American pikas (Ochotona princeps) is associated with copy number variation across environmental gradients

Improved understanding of the genetic basis of adaptation to climate change is necessary for maintaining global biodiversity moving forward. Studies to date have largely focused on sequence variation, yet there is growing evidence that suggests that changes in genome structure may be an even more significant source of adaptive potential. The American pika (Ochotona princeps) is an alpine specialist that shows some evidence of adaptation to climate along elevational gradients, but previous work has been limited to single nucleotide polymorphism based analyses within a fraction of the species range. Here, we investigated the role of copy number variation underlying patterns of local adaptation in the American pika using genome-wide data previously collected across the entire species range. We identified 37-193 putative copy number variants (CNVs) associated with environmental variation (temperature, precipitation, solar radiation) within each of the six major American pika lineages, with patterns of divergence largely following elevational and latitudinal gradients. Genes associated (n = 158) with independent annotations across lineages, variables, and/or CNVs had functions related to mitochondrial structure/function, immune response, hypoxia, olfaction, and DNA repair. Some of these genes have been previously linked to putative high elevation and/or climate adaptation in other species, suggesting they may serve as important targets in future studies.

Genomic analysis of Tibetan ground tits identifies molecular adaptations associated with cooperative breeding

Cooperative breeding is a sophisticated altruistic social behavior that helps social animals to adapt to harsh environments. The Tibetan ground tit, Pseudopodoces humilis, is a high-altitude bird endemic to the Tibetan plateau. Recently, it has become an exciting system for studying the evolution of facultative cooperative breeding. To test for molecular adaptations associated with cooperative breeding, we resequenced the whole genome of ground tits from 6 wild populations that display remarkable variation in the frequency of cooperative breeding. Population structure analyses showed that the 6 populations were divided into 4 lineages, which is congruent with the major geographical distribution of the sampling sites. Using genome-wide selective sweep analysis, we identified putative positively selected genes (PSGs) in groups of tits that displayed high and low cooperative breeding rates. The total number of PSGs varied from 146 to 722 in high cooperative breeding rate populations, and from 272 to 752 in low cooperative breeding rate populations. Functional enrichment analysis of these PSGs identified several significantly enriched ontologies related to oxytocin signaling, estrogen signaling, and insulin secretion. PSGs involved in these functional ontologies suggest that molecular adaptations in hormonal regulation may have played important roles in shaping the evolution of cooperative breeding in the ground tit. Taken together, our study provides candidate genes and functional ontologies involved in molecular adaptations associated with cooperative breeding in Tibetan ground tits, and calls for a better understanding of the genetic roles in the evolution of cooperative breeding.

Varied hypoxia adaptation patterns of embryonic brain at different development stages between Tibetan and Dwarf laying chickens

BACKGROUND

Tibetan chickens (Gallus gallus; TBCs), an indigenous breed distributed in the Qinghai-Tibet Plateau, are well adapted to the hypoxic environment. Currently, the molecular genetic basis of hypoxia adaptation in TBCs remains unclear. This study investigated hypoxia adaptation patterns of embryonic brain at different development stages by integrating analysis of the transcriptome with our previously published metabolome data in TBCs and Dwarf Laying Chickens (DLCs), a lowland chicken breed.

RESULTS

During hypoxia, the results revealed that 1334, 578, and 417 differentially expressed genes (DEGs) (|log2 fold change|>1, p-value < 0.05) on days 8, 12, and 18 of development, respectively between TBCs and DLCs. Gene Ontology (GO) and pathway analyses revealed that DEGs are mainly related to metabolic pathways, vessel development, and immune response under hypoxia. This is consistent with our metabolome data that TBCs have higher energy metabolism than DLCs during hypoxia. Some vital DEGs between TBCs and DLCs, such as EPAS1, VEGFD, FBP1, FBLN5, LDHA, and IL-6 which are involved in the HIF pathway and hypoxia regulation.

CONCLUSION

These results suggest varied adaptation patterns between TBCs and DLCs under hypoxia. Our study provides a basis for uncovering the molecular regulation mechanism of hypoxia adaptation in TBCs and a potential application of hypoxia adaptation research for other animals living on the Qinghai-Tibet Plateau, and may even contribute to the study of brain diseases caused by hypoxia.

Recent Advances in Genetics and Genomics of Snub-Nosed Monkeys (Rhinopithecus) and Their Implications for Phylogeny, Conservation, and Adaptation

The snub-nosed monkey genus Rhinopithecus (Colobinae) comprises five species (Rhinopithecus roxellana, Rhinopithecus brelichi, Rhinopithecus bieti, Rhinopithecus strykeri, and Rhinopithecus avunculus). They are range-restricted species occurring only in small areas in China, Vietnam, and Myanmar. All extant species are listed as endangered or critically endangered by the International Union for Conservation of Nature (IUCN) Red List, all with decreasing populations. With the development of molecular genetics and the improvement and cost reduction in whole-genome sequencing, knowledge about evolutionary processes has improved largely in recent years. Here, we review recent major advances in snub-nosed monkey genetics and genomics and their impact on our understanding of the phylogeny, phylogeography, population genetic structure, landscape genetics, demographic history, and molecular mechanisms of adaptation to folivory and high altitudes in this primate genus. We further discuss future directions in this research field, in particular how genomic information can contribute to the conservation of snub-nosed monkeys.

Convergent Genomic Signatures of High-Altitude Adaptation among Six Independently Evolved Mammals

The species living in the Qinghai-Tibet Plateau provide an excellent model system for studying the relationship between molecular convergent evolution and adaptation. Distant species experiencing the same selection pressure (i.e., hypoxia, low temperature and strong ultraviolet radiation) are likely to evolve similar genetic adaptations independently. Here, we performed comparative genomics studies on six independently evolved high-altitude species. The results also showed that the convergent evolution of the six species was mainly reflected at the level of rapidly evolving genes, and the functions of these rapidly evolving genes were mainly related to hypoxia response and DNA damage repair. In addition, we found that high-altitude species had more gene family changes than their low-altitude relatives, except for the order Lagomorpha. The results also show that the convergence of the gene family contraction of high-altitude species is much greater than that of expansion, revealing a possible pattern of species in adapting to high-altitude. Furthermore, we detected a positive selection signature in four genes related to hypoxia response and ultraviolet radiation damage in these six species (FYCO1, ERBIN, SCAMP1 and CXCL10). Our study reveals that hypoxia response might play an important role in the adaptation of independently evolved species to a high-altitude environment, providing a basic perspective for further exploring the high-altitude adaptation mechanism of different related species in the future.

Genome of Laudakia sacra Provides New Insights into High-Altitude Adaptation of Ectotherms

Anan’s rock agama (Laudakia sacra) is a lizard species endemic to the harsh high-altitude environment of the Qinghai–Tibet Plateau, a region characterized by low oxygen tension and high ultraviolet (UV) radiation. To better understand the genetic mechanisms underlying highland adaptation of ectotherms, we assembled a 1.80-Gb L. sacra genome, which contained 284 contigs with an N50 of 20.19 Mb and a BUSCO score of 93.54%. Comparative genomic analysis indicated that mutations in certain genes, including HIF1A, TIE2, and NFAT family members and genes in the respiratory chain, may be common adaptations to hypoxia among high-altitude animals. Compared with lowland reptiles, MLIP showed a convergent mutation in L. sacra and the Tibetan hot-spring snake (Thermophis baileyi), which may affect their hypoxia adaptation. In L. sacra, several genes related to cardiovascular remodeling, erythropoiesis, oxidative phosphorylation, and DNA repair may also be tailored for adaptation to UV radiation and hypoxia. Of note, ERCC6 and MSH2, two genes associated with adaptation to UV radiation in T. baileyi, exhibited L. sacra-specific mutations that may affect peptide function. Thus, this study provides new insights into the potential mechanisms underpinning high-altitude adaptation in ectotherms and reveals certain genetic generalities for animals’ survival on the plateau.

De Novo Whole-Genome Sequencing and Assembly of the Yellow-Throated Bunting (Emberiza elegans) Provides Insights into Its Evolutionary Adaptation

Simple Summary

We report the genomic sequence of Emberiza elegans for understanding the evolutionary mechanisms of environmental adaptation and for studying a more effective genetic monitoring of this species. The E. elegans assembly was approximately 1.14 Gb, with a scaffold N50 of 28.94 Mb. About 15,868 protein-coding genes were predicted, and 16.62% of the genome was identified as having repetitive elements. Our genomic evolution analyses found considerable numbers of adaptive genes that may help the yellow-throated bunting cope with migratory behavior and environmental stressors of diseases. These results provide us with new insights into genomic evolution and adaptation, thus providing a valuable resource for further studies of population genetic diversity and genome evolution in this species.

Abstract

Yellow-throated bunting is a small migratory songbird unique to the Palearctic region. However, the genetic studies of this species remain limited, with no nuclear genomic sequence reported to date. In this study, the genomic DNA from the bird was sequenced in long reads using Nanopore sequencing technology. Combining short-read sequencing, the genome was well-assembled and annotated. The final length of the assembly is approximately 1.14 Gb, with a scaffold N50 of 28.94 Mb. About 15,868 protein-coding genes were predicted, and 16.62% of the genome was identified as having repetitive elements. Comparative genomic analysis showed numerous expanded gene families and positively selected genes significantly enriched in those KEGG pathways that are associated with migratory behavior adaptation and immune response. Here, this newly generated de novo genome of the yellow-throated bunting using long reads provide the research community with a valuable resource for further studies of population genetic diversity and genome evolution in this species.

Chromosome-level genome of Tibetan naked carp (Gymnocypris przewalskii) provides insights into Tibetan highland adaptation

Gymnocypris przewalskii, a cyprinid fish endemic to the Qinghai-Tibetan Plateau, has evolved unique morphological, physiological and genetic characteristics to adapt to the highland environment. Herein, we assembled a high-quality G. przewalskii tetraploid genome with a size of 2.03 Gb and scaffold N50 of 44.93 Mb, which was anchored onto 46 chromosomes. The comparative analysis suggested that gene families related to highland adaptation were significantly expanded in G. przewalskii. According to the G. przewalskii genome, we evaluated the phylogenetic relationship of 13 schizothoracine fishes, and inferred that the demographic history of G. przewalskii was strongly associated with geographic and eco-environmental alterations. We noticed that G. przewalskii experienced whole-genome duplication, and genes preserved post duplication were functionally associated with adaptation to high salinity and alkalinity. In conclusion, a chromosome-scale G. przewalskii genome provides an important genomic resource for teleost fish, and will particularly promote our understanding of the molecular evolution and speciation of fish in the highland environment.

Environmental cues from neural crest derivatives act as metastatic triggers in an embryonic neuroblastoma model

Embryonic malignant transformation is concomitant to organogenesis, often affecting multipotent and migratory progenitors. While lineage relationships between malignant cells and their physiological counterparts are extensively investigated, the contribution of exogenous embryonic signals is not fully known. Neuroblastoma (NB) is a childhood malignancy of the peripheral nervous system arising from the embryonic trunk neural crest (NC) and characterized by heterogeneous and interconvertible tumor cell identities. Here, using experimental models mimicking the embryonic context coupled to proteomic and transcriptomic analyses, we show that signals released by embryonic sympathetic ganglia, including Olfactomedin-1, induce NB cells to shift from a noradrenergic to mesenchymal identity, and to activate a gene program promoting NB metastatic onset and dissemination. From this gene program, we extract a core signature specifically shared by metastatic cancers with NC origin. This reveals non-cell autonomous embryonic contributions regulating the plasticity of NB identities and setting pro-dissemination gene programs common to NC-derived cancers.

A high-quality assembly reveals genomic characteristics, phylogenetic status, and causal genes for leucism plumage of Indian peafowl

BACKGROUND

The dazzling phenotypic characteristics of male Indian peafowl (Pavo cristatus) are attractive both to the female of the species and to humans. However, little is known about the evolution of the phenotype and phylogeny of these birds at the whole-genome level. So far, there are no reports regarding the genetic mechanism of the formation of leucism plumage in this variant of Indian peafowl.

RESULTS

A draft genome of Indian peafowl was assembled, with a genome size of 1.05 Gb (the sequencing depth is 362×), and contig and scaffold N50 were up to 6.2 and 11.4 Mb, respectively. Compared with other birds, Indian peafowl showed changes in terms of metabolism, immunity, and skeletal and feather development, which provided a novel insight into the phenotypic evolution of peafowl, such as the large body size and feather morphologies. Moreover, we determined that the phylogeny of Indian peafowl was more closely linked to turkey than chicken. Specifically, we first identified that PMEL was a potential causal gene leading to the formation of the leucism plumage variant in Indian peafowl.

CONCLUSIONS

This study provides an Indian peafowl genome of high quality, as well as a novel understanding of phenotypic evolution and phylogeny of Indian peafowl. These results provide a valuable reference for the study of avian genome evolution. Furthermore, the discovery of the genetic mechanism for the development of leucism plumage is both a breakthrough in the exploration of peafowl plumage and also offers clues and directions for further investigations of the avian plumage coloration and artificial breeding in peafowl.

Positive selection in noncoding genomic regions of vocal learning birds is associated with genes implicated in vocal learning and speech functions in humans

Vocal learning, the ability to imitate sounds from conspecifics and the environment, is a key component of human spoken language and learned song in three independently evolved avian groups—oscine songbirds, parrots, and hummingbirds. Humans and each of these three bird clades exhibit specialized behavioral, neuroanatomical, and brain gene expression convergence related to vocal learning, speech, and song. To understand the evolutionary basis of vocal learning gene specializations and convergence, we searched for and identified accelerated genomic regions (ARs), a marker of positive selection, specific to vocal learning birds. We found avian vocal learner-specific ARs, and they were enriched in noncoding regions near genes with known speech functions or brain gene expression specializations in humans and vocal learning birds, including FOXP2, NEUROD6, ZEB2, and MEF2C, and near genes with major neurodevelopmental functions, including NR2F1, NRP2, and BCL11B. We also found enrichment near the SFARI class S genes associated with syndromic vocal communication forms of autism spectrum disorders. These findings reveal strong candidate noncoding regions near genes for the evolutionary adaptations that distinguish vocal learning species from their close vocal nonlearning relatives and provide further evidence of molecular convergence between birdsong and human spoken language.

Genomic and functional evidence reveals convergent evolution in fishes on the Tibetan Plateau

High-altitude environments are strong drivers of adaptive evolution in endemic organisms. However, little is known about the genetic mechanisms of convergent adaptation among different lineages, especially in fishes. There are three independent fish groups on the Tibetan Plateau: Tibetan Loaches, Schizothoracine fishes and Glyptosternoid fishes; all are well adapted to the harsh environmental conditions. They represent an excellent example of convergent evolution but with an unclear genetic basis. We used comparative genomic analyses between Tibetan fishes and fishes from low altitudes and detected genomic signatures of convergent evolution in fishes on the Tibetan Plateau. The Tibetan fishes exhibited genome-wide accelerated evolution in comparison with a control set of fishes from low altitudes. A total of 368 positively selected genes were identified in Tibetan fishes, which were enriched in functional categories related to energy metabolism and hypoxia response. Widespread parallel amino acid substitutions were detected among the Tibetan fishes and a subset of these substitutions occurred in positively selected genes associated with high-altitude adaptation. Functional assays suggested that von Hippel-Lindau (VHL) tumour suppressor genes from Tibetan fishes enhance hypoxia-inducible factor (HIF) activity convergently under hypoxia compared to low-altitude fishes. The results provide genomic and functional evidence supporting convergent genetic mechanisms for high-altitude adaptation in fishes on the Tibetan Plateau.

Application of a novel haplotype-based scan for local adaptation to study high-altitude adaptation in rhesus macaques

When natural populations split and migrate to different environments, they may experience different selection pressures that can lead to local adaptation. To capture the genomic patterns of a local selective sweep, we develop XP-nSL, a genomic scan for local adaptation that compares haplotype patterns between two populations. We show that XP-nSL has power to detect ongoing and recently completed hard and soft sweeps, and we then apply this statistic to search for evidence of adaptation to high altitude in rhesus macaques. We analyze the whole genomes of 23 wild rhesus macaques captured at high altitude (mean altitude > 4000 m above sea level) to 22 wild rhesus macaques captured at low altitude (mean altitude < 500 m above sea level) and find evidence of local adaptation in the high-altitude population at or near 303 known genes and several unannotated regions. We find the strongest signal for adaptation at EGLN1, a classic target for convergent evolution in several species living in low oxygen environments. Furthermore, many of the 303 genes are involved in processes related to hypoxia, regulation of ROS, DNA damage repair, synaptic signaling, and metabolism. These results suggest that, beyond adapting via a beneficial mutation in one single gene, adaptation to high altitude in rhesus macaques is polygenic and spread across numerous important biological systems.

Evolution of the "world's only alpine parrot": Genomic adaptation or phenotypic plasticity, behaviour and ecology?

Climate warming, in particular in island environments, where opportunities for species to disperse are limited, may become a serious threat to cold adapted alpine species. In order to understand how alpine species may respond to a warming world, we need to understand the drivers that have shaped their habitat specialisation and the evolutionary adaptations that allow them to utilize alpine habitats. The endemic, endangered New Zealand kea (Nestor notabilis) is considered the only alpine parrot in the world. As a species commonly found in the alpine zone it may be highly susceptible to climate warming. But is it a true alpine specialist? Is its evolution driven by adaptation to the alpine zone, or is the kea an open habitat generalist that simply uses the alpine zone to, for example, avoid lower lying anthropogenic landscapes? We use whole genome data of the kea and its close, forest adapted sister species, the kākā (Nestor meridionalis) to reconstruct the evolutionary history of both species and identify the functional genomic differences that underlie their habitat specialisations. Our analyses do not identify major functional genomic differences between kea and kākā in pathways associated with high-altitude. Rather, we found evidence that selective pressures on adaptations commonly found in alpine species are present in both Nestor species, suggesting that selection for alpine adaptations has not driven their divergence. Strongly divergent demographic responses to past climate warming between the species nevertheless highlight potential future threats to kea survival in a warming world.

Elevation as a selective force on mitochondrial respiratory chain complexes of the Phrynocephalus lizards in the Tibetan plateau

Animals living in extremely high elevations have to adapt to low temperatures and low oxygen availability (hypoxia), but the underlying genetic mechanisms associated with these adaptations are still unclear. The mitochondrial respiratory chain can provide >95% of the ATP in animal cells, and its efficiency is influenced by temperature and oxygen availability. Therefore, the respiratory chain complexes (RCCs) could be important molecular targets for positive selection associated with respiratory adaptation in high-altitude environments. Here, we investigated positive selection in 5 RCCs and their assembly factors by analyzing sequences of 106 genes obtained through RNA-seq of all 15 Chinese Phrynocephalus lizard species, which are distributed from lowlands to the Tibetan plateau (average elevation >4,500 m). Our results indicate that evidence of positive selection on RCC genes is not significantly different from assembly factors, and we found no difference in selective pressures among the 5 complexes. We specifically looked for positive selection in lineages where changes in habitat elevation happened. The group of lineages evolving from low to high altitude show stronger signals of positive selection than lineages evolving from high to low elevations. Lineages evolving from low to high elevation also have more shared codons under positive selection, though the changes are not equivalent at the amino acid level. This study advances our understanding of the genetic basis of animal respiratory metabolism evolution in extreme high environments and provides candidate genes for further confirmation with functional analyses.

Genome-Wide Analyses Provide Insights into the Scavenging Lifestyle of the Striped Hyena (Hyaena hyaena)

Hyenas (family Hyaenidae) occupy a variety of different niches, of which the striped hyena (Hyaena hyaena) scavenges mainly on the carcasses of animals. We compared its genome with the genomes of nine other mammals, focusing on similarities and differences in chemoreception, detoxification, digestive, and immune systems. The results showed that the striped hyena's immune and digestive system-related gene families have significantly expanded, which was likely to be an adaptive response to its scavenging lifestyle. In addition, 88 and 26 positive selected genes (PSGs) were identified in the immune system and digestive system, respectively, which may be the molecular basis for immune defense system to effectively resist pathogen invasion. Functional enrichment analysis of PSGs revealed that most of them were involved in the immune regulation process. Among them, eight specific missense mutations were found in two PSGs (MHC class II antigen DOA and MHC class II antigen DOB), suggesting important reorganization of the immune system in the striped hyena. Moreover, we identified one cathelicidin gene and four defensin genes in the striped hyenas by genome mining, which have high-efficiency and broad-spectrum antimicrobial activity. Of particular interest, a striped hyena-specific missense mutation was found in the cathelicidin gene. PolyPhen-2 classified the missense mutation as a harmful mutation, which may have aided in immune adaptation to carrion feeding. Our genomic analyses on the striped hyena provided insights into its success in the adaptation to the scavenging lifestyle.

Genomic evidence sheds light on the genetic mechanisms of musk secretion in muskrats

Adult male muskrat (Ondatra zibethicus) has a pair of scent glands which secret musk to attract females during the breeding stage. The goal of the present study was to investigate the genetic mechanisms of musk secretion of muskrats at the whole genome level. Comparative genomics illustrated obvious expansion in 809 gene families, of which nine gene families played pivotal roles in steroid biosynthesis, possibly related to muskrat musk secretion. We identified 1112 positively selected genes (PSGs) in the muskrat, including estrogen receptor 1 (ER1), an important influencing factor to the weight and size of the scented glands of muskrats. HSD17B3, HSD17B4, CYP7B1 and CYP17B1, crucial to steroid hormone biosynthesis, were under strong positive selection in the muskrat, and phylogenetic analysis of HSD and CYP450 classes revealed high gene diversity. Functional enrichment revealed many pathways associated with musk secretion and/or growth and degeneration of scented gland significantly, such as peroxisome, PI3K-Akt signaling pathway, apoptosis, and prostate cancer. Two muskrat-specific missense mutations (Pro237Thr and Ser297Ile) were detected in LIPC, which were reported to be involved cholesterol metabolic process. More importantly, the missense mutations discovered in LIPC were classified as deleterious by PolyPhen-2, possibly affecting the musk secretion of muskrats.

Divergent selection and drift shape the genomes of two avian sister species spanning a saline-freshwater ecotone

The role of species divergence due to ecologically based divergent selection-or ecological speciation-in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms' adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline-freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here, we sequence 20 whole genomes of two avian sister species endemic to tidal marshes-the saltmarsh sparrow (Ammospiza caudacutus) and Nelson's sparrow (A. nelsoni)-to evaluate the influence of selective and demographic processes in shaping genome-wide patterns of divergence. Genome-wide divergence between these two recently diverged sister species was notably high (genome-wide F ST = 0.32). Against a background of high genome-wide divergence, regions of elevated divergence were widespread throughout the genome, as opposed to focused within islands of differentiation. These patterns may be the result of genetic drift resulting from past tidal march colonization events in conjunction with divergent selection to different environments. We identified several candidate genes that exhibited elevated divergence between saltmarsh and Nelson's sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism-all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.

A High-Quality Draft Genome Assembly of the Black-Necked Crane (Grus nigricollis) Based on Nanopore Sequencing

The black-necked crane (Grus nigricollis) which inhabits high-altitude areas has the largest body size of the world's 15 crane species, and is classified as threatened by the IUCN. To support further studies on population genetics and genomics, we present a high-quality genome assembly based on both Illumina and nanopore sequencing. In total, 54.59 Gb Illumina short reads and 116.5 Gb nanopore long reads were generated. The 1.23 Gb assembled genome has a high contig N50 of 17.89 Mb, and has a longest contig of 87.83 Mb. The completeness (97.7%) of the draft genome was evaluated with single-copy orthologous genes using BUSCO. We identified 17,789 genes and found that 8.11% of the genome is composed of repetitive elements. In total, 84 of the 2,272 one-to-one orthologous genes were under positive selection in the black-necked crane lineage. SNP-based inference indicated two bottlenecks in the recent demographic trajectories of the black-necked crane. The genome information will contribute to future study of crane evolutionary history and provide new insights into the potential adaptation mechanisms of the black-necked crane to its high-altitude habitat.

The Draft Genome of the Endangered Sichuan Partridge (Arborophila rufipectus) with Evolutionary Implications

The Sichuan partridge (Arborophila rufipectus, Phasianidae, Galliformes) is distributed in south-west China, and classified as endangered grade. To examine the evolution and genomic features of Sichuan partridge, we de novo assembled the Sichuan partridge reference genome. The final draft assembly consisted of approximately 1.09 Gb, and had a scaffold N50 of 4.57 Mb. About 1.94 million heterozygous single-nucleotide polymorphisms (SNPs) were detected, 17,519 protein-coding genes were predicted, and 9.29% of the genome was identified as repetitive elements. A total of 56 olfactory receptor (OR) genes were found in Sichuan partridge, and conserved motifs were detected. Comparisons between the Sichuan partridge genome and chicken genome revealed a conserved genome structure, and phylogenetic analysis demonstrated that Arborophila possessed a basal phylogenetic position within Phasianidae. Gene Ontology (GO) enrichment analysis of positively selected genes (PSGs) in Sichuan partridge showed over-represented GO functions related to environmental adaptation, such as energy metabolism and behavior. Pairwise sequentially Markovian coalescent analysis revealed the recent demographic trajectory for the Sichuan partridge. Our data and findings provide valuable genomic resources not only for studying the evolutionary adaptation, but also for facilitating the long-term conservation and genetic diversity for this endangered species.

Genome-wide analysis sheds light on the high-altitude adaptation of the buff-throated partridge (Tetraophasis szechenyii)

The buff-throated partridge (Tetraophasis szechenyii) is a hypoxia-tolerant bird living in an extremely inhospitable high-altitude environment, which has high ultraviolet (UV) radiation as well as a low oxygen supply when compared with low-altitude areas. To further understand the molecular genetic mechanisms of the high-altitude adaptation of the buff-throated partridges, we de novo assembled the complete genome of the buff-throated partridge. Comparative genomics revealed that positively selected hypoxia-related genes in the buff-throated partridge were distributed in the HIF-1 signaling pathway (map04066), response to hypoxia (GO:0001666), response to oxygen-containing compound (GO:1901700), ATP binding (GO:0005524), and angiogenesis (GO:0001525). Of these positively selected hypoxia-related genes, one positively selected gene (LONP1) had one buff-throated partridge-specific missense mutation which was classified as deleterious by PolyPhen-2. Moreover, positively selected genes in the buff-throated partridge were enriched in cellular response to DNA damage stimulus (corrected P value: 0.028006) and DNA repair (corrected P value: 0.044549), which was related to the increased exposure of the buff-throated partridge to UV radiation. Compared with other avian genomes, the buff-throated partridge showed expansion in genes associated with steroid hormone receptor activity and contractions in genes related to immune and olfactory perception. Furthermore, comparisons between the buff-throated partridge genome and red junglefowl genome revealed a conserved genome structure and provided strong evidence of the sibling relationship between Tetraophasis and Lophophorus. Our data and analysis contributed to the study of Phasianidae evolutionary history and provided new insights into the potential adaptation mechanisms to the high altitude employed by the buff-throated partridge.

Population Genomics Analysis Revealed Origin and High-altitude Adaptation of Tibetan Pigs

Tibetan pig is native to the Qinghai-Tibet Plateau and has adapted to the high-altitude environmental condition such as hypoxia. However, its origin and genetic mechanisms underlying high-altitude adaptation still remain controversial and enigmatic. Herein, we analyze 229 genomes of wild and domestic pigs from Eurasia, including 63 Tibetan pigs, and detect 49.6 million high-quality variants. Phylogenomic and structure analyses show that Tibetan pigs have a close relationship with low-land domestic pigs in China, implying a common domestication origin. Positively selected genes in Tibetan pigs involved in high-altitude physiology, such as hypoxia, cardiovascular systems, UV damage, DNA repair. Three of loci with strong signals of selection are associated with EPAS1, CYP4F2, and THSD7A genes, related to hypoxia and circulation. We validated four non-coding mutations nearby EPAS1 and CYP4F2 showing reduced transcriptional activity in Tibetan pigs. A high-frequency missense mutation is found in THSD7A (Lys561Arg) in Tibetan pigs. The selective sweeps in Tibetan pigs was found in association with selection against non-coding variants, indicating an important role of regulatory mutations in Tibetan pig evolution. This study is important in understanding the evolution of Tibetan pigs and advancing our knowledge on animal adaptation to high-altitude environments.

Evolutionary Rates of Bumblebee Genomes Are Faster at Lower Elevations

The importance of climate in determining biodiversity patterns has been well documented. However, the relationship between climate and rates of genetic evolution remains controversial. Latitude and elevation have been associated with rates of change in genetic markers such as cytochrome b. What is not known, however, is the strength of such associations and whether patterns found among these genes apply across entire genomes. Here, using bumblebee genetic data from seven subgenera of Bombus, we demonstrate that all species occupying warmer elevations have undergone faster genome-wide evolution than those in the same subgenera occupying cooler elevations. Our findings point to a critical biogeographic role in the relative rates of whole species evolution, potentially influencing global biodiversity patterns.

Genomic signatures of high-altitude adaptation in Ethiopian sheep populations

BACKGROUND

Ethiopian sheep populations such as Arsi-Bale, Horro and Adilo (long fat-tailed, LFT) inhabit mid to high-altitude areas; and Menz sheep (MZ, short fat-tailed) are adapted to cool sub-alpine environments. In contrast, Blackhead Somali sheep (BHS, fat-rumped) thrive well in arid and semi-arid areas characterized by high temperature and low precipitation. The genomic investigation of Ethiopian sheep populations may help to identify genes and biological pathways enable to adapt to the different ecological conditions.

OBJECTIVE

To uncover genomic regions and genes showing evidence of positive selection for altitude adaptation in Ethiopian sheep populations.

METHODS

A total of 72 animals inhabiting high-versus low-altitude environments were genotyped on an Ovine Infinium HD array (~ 600 K). Pairwise genetic differentiation (Fst) was calculated in sliding windows of 20 SNPs and the upper 1% smoothed Fst values were considered to represent positive selection signatures. Genes within < 25 kb of the most differentiated SNPs were considered as selection candidates.

RESULTS

Signatures of selection were detected in genes known to be associated high with altitude adaptation in MZ-BHS pair comparison (PPP1R12A, RELN, PARP2, and DNAH9) and in LFT-BHS pair comparison (VAV3, MSRB3,EIF2AK4, MET, and TACR1). The candidate genes (MITF, FGF5, MTOR, TRHDE, and TUBB3) associated with altitude adaptation and shared between the MZ-BHS and LTF-BHS pair comparisons were also detected as under selection. Further functional analyses reveal that the candidate genes were involved in biological processes and pathways relevant to adaptation under extreme altitudes, including respiratory system development and smoothened signaling pathway.

CONCLUSION

The results of the present study could aid in-depth understanding and exploitation of the underlying genetic mechanisms for sheep and other livestock species adaptation to high-altitude environments.

Complex Gene Loss and Duplication Events Have Facilitated the Evolution of Multiple Loricrin Genes in Diverse Bird Species

The evolution of a mechanically resilient epidermis was a key adaptation in the transition of amniotes to a fully terrestrial lifestyle. Skin appendages usually form via a specialized type of programmed cell death known as cornification which is characterized by the formation of an insoluble cornified envelope (CE). Many of the substrates of cornification are encoded by linked genes located at a conserved genetic locus known as the epidermal differentiation complex (EDC). Loricrin is the main protein component of the mammalian CE and is encoded for by a gene located within the EDC. Recently, genes resembling mammalian loricrin, along with several other proteins most likely involved in CE formation, have been identified within the EDC of birds and several reptiles. To better understand the evolution and function of loricrin in birds, we screened the genomes of 50 avian species and 3 crocodilians to characterize their EDC regions. We found that loricrin is present within the EDC of all species investigated, and that three loricrin genes were present in birds. Phylogenetic and molecular evolution analyses found evidence that gene deletions and duplications as well as concerted evolution has shaped the evolution of avian loricrins. Our results suggest a complex evolutionary history of avian loricrins which has accompanied the evolution of bird species with diverse morphologies and lifestyles.

New Approaches for Genome Assembly and Scaffolding

Affordable, high-throughput DNA sequencing has accelerated the pace of genome assembly over the past decade. Genome assemblies from high-throughput, short-read sequencing, however, are often not as contiguous as the first generation of genome assemblies. Whereas early genome assembly projects were often aided by clone maps or other mapping data, many current assembly projects forego these scaffolding data and only assemble genomes into smaller segments. Recently, new technologies have been invented that allow chromosome-scale assembly at a lower cost and faster speed than traditional methods. Here, we give an overview of the problem of chromosome-scale assembly and traditional methods for tackling this problem. We then review new technologies for chromosome-scale assembly and recent genome projects that used these technologies to create highly contiguous genome assemblies at low cost.

Sequence Characterization of DSG3 Gene to Know Its Role in High-Altitude Hypoxia Adaptation in the Chinese Cashmere Goat

The Tibetan cashmere goat is one of the main goat breeds used by people living in the plateau. It exhibits the distinct phenotypic characteristics observed in lowland goats, allowing them to adapt to the challenging conditions at high altitudes. It provides an ideal model for understanding the genetic mechanisms underlying high-altitude adaptation and hypoxia-related diseases. Our previous exome sequencing of five Chinese cashmere breeds revealed a candidate gene, DSG3 (Desmoglein 3), responsible for the high-altitude adaptation of the Tibetan goat. However, the whole DSG3 gene (44 kbp) consisting of 16 exons in the goat genome was not entirely covered by the exome sequencing. In this study, we resequenced all the 16 exons of the DSG3 gene in ten Chinese native goat populations. Twenty-seven SNP variants were found between the lowland and highland goat populations. The genetic distance (F_ST) of significant SNPs between the lowland and highland populations ranged from 0.42 to 0.58. By using correlation coefficient analysis, linkage disequilibrium, and haplotype network construction, we found three non-synonymous SNPs (R597E, T595I, and G572S) in exon 5 and two synonymous SNPs in exons 8 and 16 in DSG3. These mutations significantly segregated high- and low-altitude goats in two clusters, indicating the contribution of DSG3 to the high-altitude hypoxia adaptation in the Tibetan goat.

Whole-genome de novo sequencing reveals unique genes that contributed to the adaptive evolution of the Mikado pheasant

Background

The Mikado pheasant (Syrmaticus mikado) is a nearly endangered species indigenous to high-altitude regions of Taiwan. This pheasant provides an opportunity to investigate evolutionary processes following geographic isolation. Currently, the genetic background and adaptive evolution of the Mikado pheasant remain unclear.

Results

We present the draft genome of the Mikado pheasant, which consists of 1.04 Gb of DNA and 15,972 annotated protein-coding genes. The Mikado pheasant displays expansion and positive selection of genes related to features that contribute to its adaptive evolution, such as energy metabolism, oxygen transport, hemoglobin binding, radiation response, immune response, and DNA repair. To investigate the molecular evolution of the major histocompatibility complex (MHC) across several avian species, 39 putative genes spanning 227 kb on a contiguous region were annotated and manually curated. The MHC loci of the pheasant revealed a high level of synteny, several rapidly evolving genes, and inverse regions compared to the same loci in the chicken. The complete mitochondrial genome was also sequenced, assembled, and compared against four long-tailed pheasants. The results from molecular clock analysis suggest that ancestors of the Mikado pheasant migrated from the north to Taiwan about 3.47 million years ago.

Conclusions

This study provides a valuable genomic resource for the Mikado pheasant, insights into its adaptation to high altitude, and the evolutionary history of the genus Syrmaticus, which could potentially be useful for future studies that investigate molecular evolution, genomics, ecology, and immunogenetics.

Conservation genetics and genomics of threatened vertebrates in China

Conservation genetics and genomics are two independent disciplines that focus on using new techniques in genetics and genomics to solve problems in conservation biology. During the past two decades, conservation genetics and genomics have experienced rapid progress. Here, we summarize the research advances in the conservation genetics and genomics of threatened vertebrates (e.g., carnivorans, primates, ungulates, cetaceans, avians, amphibians and reptiles) in China. First, we introduce the concepts of conservation genetics and genomics and their development. Second, we review the recent advances in conservation genetics research, including noninvasive genetics and landscape genetics. Third, we summarize the progress in conservation genomics research, which mainly focuses on resolving genetic problems relevant to conservation such as genetic diversity, genetic structure, demographic history, and genomic evolution and adaptation. Finally, we discuss the future directions of conservation genetics and genomics.

Reconstruction of avian ancestral karyotypes reveals differences in the evolutionary history of macro- and microchromosomes

Background

Reconstruction of ancestral karyotypes is critical for our understanding of genome evolution, allowing for the identification of the gross changes that shaped extant genomes. The identification of such changes and their time of occurrence can shed light on the biology of each species, clade and their evolutionary history. However, this is impeded by both the fragmented nature of the majority of genome assemblies and the limitations of the available software to work with them. These limitations are particularly apparent in birds, with only 10 chromosome-level assemblies reported thus far. Algorithmic approaches applied to fragmented genome assemblies can nonetheless help define patterns of chromosomal change in defined taxonomic groups.

Results

Here, we make use of the DESCHRAMBLER algorithm to perform the first large-scale study of ancestral chromosome structure and evolution in birds. This algorithm allows us to reconstruct the overall genome structure of 14 key nodes of avian evolution from the Avian ancestor to the ancestor of the Estrildidae, Thraupidae and Fringillidae families.

Conclusions

Analysis of these reconstructions provides important insights into the variability of rearrangement rates during avian evolution and allows the detection of patterns related to the chromosome distribution of evolutionary breakpoint regions. Moreover, the inclusion of microchromosomes in our reconstructions allows us to provide novel insights into the evolution of these avian chromosomes, specifically.

Electronic supplementary material

The online version of this article (10.1186/s13059-018-1544-8) contains supplementary material, which is available to authorized users.

How to estimate kinship

The concept of kinship permeates many domains of fundamental and applied biology ranging from social evolution to conservation science to quantitative and human genetics. Until recently, pedigrees were the gold standard to infer kinship, but the advent of next‐generation sequencing and the availability of dense genetic markers in many species make it a good time to (re)evaluate the usefulness of genetic markers in this context. Using three published data sets where both pedigrees and markers are available, we evaluate two common and a new genetic estimator of kinship. We show discrepancies between pedigree values and marker estimates of kinship and explore via simulations the possible reasons for these. We find these discrepancies are attributable to two main sources: pedigree errors and heterogeneity in the origin of founders. We also show that our new marker‐based kinship estimator has very good statistical properties and behaviour and is particularly well suited for situations where the source population is of small size, as will often be the case in conservation biology, and where high levels of kinship are expected, as is typical in social evolution studies.

The first draft genome of Lophophorus: A step forward for Phasianidae genomic diversity and conservation

The monal genus (Lophophorus) is a branch of Phasianidae and its species inhabit the high-altitude mountains of the Qinghai-Tibet Plateau. The Chinese monal, L. lhuysii, is a threatened endemic bird of China that possesses high-altitude adaptability, diversity of plumage color and potentially low reproductive life history. This is the first study to describe the monal genome using next generation sequencing technology. The Chinese monal genome size is 1.01 Gb, with 16,940 protein-coding genes. Gene annotation yielded 100.93 Mb (9.97%) repeat elements, 785 ncRNA, 5,465,549 bp (0.54%) SSR and 15,550 (92%) genes in public databases. Compared to other birds and mammals, the genome evolution analysis showed numerous expanded gene families and positive selected genes involved in high-altitude adaptation, especially related to the adaptation of low temperature and hypoxia. Consequently, this gene data can be used to investigate the molecular evolution of high-altitude adaptation in future bird research. Our first published genome of the genus Lophophorus will be integral for the study of monal population genetic diversity and conservation, genomic evolution and Galliformes species differentiation in the Qinghai-Tibetan Plateau.

Genomic insights into natural selection in the common loon (Gavia immer): evidence for aquatic adaptation

Background

The common loon (Gavia immer) is one of five species that comprise the avian order Gaviiformes. Loons are specialized divers, reaching depths up to 60 m while staying submerged for intervals up to three minutes. In this study we used comparative genomics to investigate the genetic basis of the common loon adaptations to its ecological niche. We used Illumina short read DNA sequence data from a female bird to produce a draft assembly of the common loon (Gavia immer) genome.

Results

We identified 14,169 common loon genes, which based on well-resolved avian genomes, represent approximately 80.7% of common loon genes. Evolutionary analyses between common loon and Adelie penguin (Pygoscelis adeliae), red-throated loon (Gavia stellata), chicken (Gallus gallus), northern fulmar (Fulmarus glacialis), and rock pigeon (Columba livia) show 164 positively selected genes in common and red-throated loons. These genes were enriched for a number of protein classes, including those involved in muscle tissue development, immunoglobulin function, hemoglobin iron binding, G-protein coupled receptors, and ATP metabolism.

Conclusions

Signatures of positive selection in these areas suggest the genus Gavia may have adapted for underwater diving by modulating their oxidative and metabolic pathways. While more research is required, these adaptations likely result in (1) compensations in oxygen respiration and energetic metabolism, (2) low-light visual acuity, and (3) elevated solute exchange. This work represents the first effort to understand the genomic adaptations of the common loon as well as other Gavia and may have implications for subsequent studies that target particular genes for loon population genetic, ecological or conservation studies.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1181-6) contains supplementary material, which is available to authorized users.

New insights into the phylogenetics and population structure of the prairie falcon (Falco mexicanus)

Background

Management requires a robust understanding of between- and within-species genetic variability, however such data are still lacking in many species. For example, although multiple population genetics studies of the peregrine falcon (Falco peregrinus) have been conducted, no similar studies have been done of the closely-related prairie falcon (F. mexicanus) and it is unclear how much genetic variation and population structure exists across the species’ range. Furthermore, the phylogenetic relationship of F. mexicanus relative to other falcon species is contested. We utilized a genomics approach (i.e., genome sequencing and assembly followed by single nucleotide polymorphism genotyping) to rapidly address these gaps in knowledge.

Results

We sequenced the genome of a single female prairie falcon and generated a 1.17 Gb (gigabases) draft genome assembly. We generated maximum likelihood phylogenetic trees using complete mitochondrial genomes as well as nuclear protein-coding genes. This process provided evidence that F. mexicanus is an outgroup to the clade that includes the peregrine falcon and members of the subgenus Hierofalco. We annotated > 16,000 genes and almost 600,000 high-quality single nucleotide polymorphisms (SNPs) in the nuclear genome, providing the raw material for a SNP assay design featuring > 140 gene-associated markers and a molecular-sexing marker. We subsequently genotyped ~ 100 individuals from California (including the San Francisco East Bay Area, Pinnacles National Park and the Mojave Desert) and Idaho (Snake River Birds of Prey National Conservation Area). We tested for population structure and found evidence that individuals sampled in California and Idaho represent a single panmictic population.

Conclusions

Our study illustrates how genomic resources can rapidly shed light on genetic variability in understudied species and resolve phylogenetic relationships. Furthermore, we found evidence of a single, randomly mating population of prairie falcons across our sampling locations. Prairie falcons are highly mobile and relatively rare long-distance dispersal events may promote gene flow throughout the range. As such, California’s prairie falcons might be managed as a single population, indicating that management actions undertaken to benefit the species at the local level have the potential to influence the species as a whole.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4615-z) contains supplementary material, which is available to authorized users.

Genetic diversity and natural selection in wild fruit flies revealed by whole-genome resequencing

We characterized 26 wild fruit flies comparative population genomics from six different altitude and latitude locations by whole genome resequencing. Genetic diversity was relatively higher in Ganzi and Chongqing populations. We also found 13 genes showing selection signature between different altitude flies and variants related to hypoxia and temperature stimulus, were preferentially selected during the flies evolution. One of the most striking selective sweeps found in all high altitude flies occurred in the region harboring Hsp70Aa and Hsp70Ab on chromosome 3R. Interestingly, these two genes are involved in GO terms including response to hypoxia, unfolded protein, temperature stimulus, heat, oxygen levels. Mutation in HPH gene, a candidate gene in the hypoxia inducible factor pathway, might contributes to hypoxic high-altitude adaptation. Intriguingly, some of the selected genes, primarily utilized in humans, were involved in the response to hypoxia, which could imply a conserved molecular mechanisms underlying high-altitude adaptation between insects and humans.

Genome methylation and regulatory functions for hypoxic adaptation in Tibetan chicken embryos

Tibetan chickens have unique adaptations to the extreme high-altitude environment that they inhabit. Epigenetic DNA methylation affects many biological processes, including hypoxic adaptation; however, the regulatory genes for DNA methylation in hypoxic adaptation remain unknown. In this study, methylated DNA immunoprecipitation with high-throughput sequencing (MeDIP-seq) was used to provide an atlas of the DNA methylomes of the heart tissue of hypoxic highland Tibetan and lowland Chahua chicken embryos. A total of 31.2 gigabases of sequence data were generated from six MeDIP-seq libraries. We identified 1,049 differentially methylated regions (DMRs) and 695 related differentially methylated genes (DMGs) between the two chicken breeds. The DMGs are involved in vascular smooth muscle contraction, VEGF signaling pathway, calcium signaling pathway, and other hypoxia-related pathways. Five candidate genes that had low methylation (EDNRA, EDNRB2, BMPR1B, BMPRII, and ITGA2) might play key regulatory roles in the adaptation to hypoxia in Tibetan chicken embryos. Our study provides significant explanations for the functions of genes and their epigenetic regulation for hypoxic adaptation in Tibetan chickens.

Genome-wide identification of genes probably relevant to the adaptation of schizothoracins (Teleostei: Cypriniformes) to the uplift of the Qinghai-Tibet Plateau

BACKGROUND

Molecular adaptation to the severe environments present during the uplift of the Qinghai-Tibet Plateau has attracted the attention of researchers. The divergence of the three specialization groups of schizothoracins (Primitive, Specialized and Highly Specialized) may correspond to the three phases of plateau uplift. Based on the transcripts of representative species of the three specialized groups and an outgroup, genes in schizothoracins that may have played important roles during the adaptation to new environments were investigated.

RESULTS

The contigs of Gymnodiptychus dybowskii and Schizothorax pseudaksaiensis were compared with those of Gymnocypris przewalskii ganzihonensis and the outgroup Sinocyclocheilus angustiporus, and 5,894 ortholog groups with an alignment length longer than 90 nt after deleting gaps were retained. Evolutionary analyses indicated that the average evolutionary rate of the branch leading to the Specialized group was faster than that of the branch leading to the Highly Specialized group. Moreover, the numbers of gene categories in which more than half of the genes evolved faster than the average values of the genome were 117 and 15 along the branches leading to the Specialized and Highly Specialized groups, respectively. A total of 40, 36, and 55 genes were likely subject to positive selection along the branches leading to the Primitive, Specialized and Highly Specialized groups, respectively, and many of these genes are likely relevant to adaptation to the cold temperatures, low oxygen concentrations, and strong ultraviolet radiation that result from elevation.

CONCLUSIONS

By selecting representative species of the three groups of schizothoracins and applying next-generation sequencing technology, several candidate genes corresponding to adaptation to the three phases of plateau uplift were identified. Some of the genes identified in this report that were likely subject to positive selection are good candidates for subsequent evolutionary and functional analyses of adaptation to high altitude.

Genetic Adaptation of Schizothoracine Fish to the Phased Uplifting of the Qinghai-Tibetan Plateau

Many species of Schizothoracine, a subfamily of Cyprinidae, are highly endemic to the Qinghai–Tibetan Plateau (QTP). To characterize the adaptive changes associated with the Schizothoracine expansion at high altitudes, we sequenced tissue transcriptomes of two highland and two subhighland Schizothoracines and analyzed gene evolution patterns by comparing with lowland cyprinids. Phylogenetic tree reconstruction and divergence time estimation indicated that the common ancestor of Schizothoracine fish lived ∼32.7 million years ago (MYA), coinciding with the timing of the first phase of QTP uplifting. Both high- and subhigh-Schizothoracines demonstrated elevated dN/dS ratios in the protein-coding genes compared to lowland cyprinids, from which some biological processes implicated in altitude adaptation were commonly identified. On the other hand, the highland and subhighland lineages presented drastically divergent landscapes of positively selected genes (PSGs), enriched with very different gene ontology (GO) profiles, including those in “sensory organ morphogenesis,” “regulation of protein ubiquitination,” “blood circulation,” and “blood vessel development.” These results indicated different selection pressures imposed on the highland and subhighland lineages of the Schizothoracine subfamily, with a higher number of genes in the high-altitude species involved in adaptations such as sensory perception, blood circulation, and protein metabolism. Our study indicated divergent genetic adaptations in the aquatic species facing the phased uplifting of QTP.

Patterns of Diversity and Spatial Variability of β-Defensin Innate Immune Genes in a Declining Wild Population of Tree Swallows

Assessing the genetic variation and distribution of immune genes across heterogeneous environmental conditions in wild species is essential to further our understanding of the role of pathogen pressure and potential resistance or prevalence in hosts. Researchers have recently investigated β-defensin genes in the wild, because their variability suggests that they may play an important role in innate host defense. This study investigated the variation occurring at 6 innate immune genes of the β-defensin family in a declining population of tree swallows (Tachycineta bicolor) in southern Québec, Canada (N = 160). We found that all 6 genes showed synonymous and nonsynonymous single nucleotide polymorphisms (SNPs) within the exon coding for the mature peptide. These results indicated that this group of genes was diverse in tree swallows. Our results suggested a potential interaction of this group of genes with fluctuating pathogen diversity, however, we found no sign of positive or negative selection. We assessed whether or not the distribution of genetic diversity of β-defensin genes in our study population differed between 2 regions that strongly differ in their level of agricultural intensification. Adults are highly philopatric to their breeding sites and their immunological responses differ between these 2 regions. However, we found little evidence that the level and distribution of genetic variability differed between these heterogeneous environmental conditions. Further studies should aim to assess the link between genetic diversity of β-defensin genes and fitness-related traits in wild populations.

Evolution of the functionally conserved DCC gene in birds

Understanding the loss of conserved genes is critical for determining how phenotypic diversity is generated. Here we focus on the evolution of DCC, a gene that encodes a highly conserved neural guidance receptor. Disruption of DCC in animal models and humans results in major neurodevelopmental defects including commissural axon defects. Here we examine DCC evolution in birds, which is of particular interest as a major model system in neurodevelopmental research. We found the DCC containing locus was disrupted several times during evolution, resulting in both gene losses and faster evolution rate of salvaged genes. These data suggest that DCC had been lost independently twice during bird evolution, including in chicken and zebra finch, whereas it was preserved in many other closely related bird species, including ducks. Strikingly, we observed that commissural axon trajectory appeared similar regardless of whether DCC could be detected or not. We conclude that the DCC locus is susceptible to genomic instability leading to independent disruptions in different branches of birds and a significant influence on evolution rate. Overall, the phenomenon of loss or molecular evolution of a highly conserved gene without apparent phenotype change is of conceptual importance for understanding molecular evolution of key biological processes.

An ecological model organism flies into the genomics era

Despite the very rapid 'genomicization' of the field of Molecular Ecology in recent years, there have been relatively few annotated whole-genome assemblies of nonmodel organisms published. Instead, molecular ecologists have more frequently utilized next-generation sequencing technologies to develop genome-wide markers or to generate transcriptome data. Whole-genome assemblies are more expensive and require considerable computational resources and bioinformatic expertise. However, the availability of an annotated genome offers exciting opportunities to address fundamental questions in ecology and evolution that are difficult to address with moderate sets of markers or by transcriptome sequencing. Such questions include elucidating the roles of natural and sexual selection in shaping diversity, determining the roles of regulatory and protein-coding change in the evolution of traits, and determining the genomic architecture of sex-specific trait variation. Arguably, these questions are most tractable--and most interesting--in well-characterized species for which there is already some knowledge of natural and sexual selection, and of the traits that are most likely to link to fitness. In this issue, Mueller et al. (2016) present the assembly and annotation of the genome of the blue tit (Cyanistes caeruleus), a model ecological species. In addition, by sequencing the transcriptome of male and female blue tits, the authors identify and annotate sex-biased gene expression and conclude that noncoding RNA genes are likely to play a significant role in sex-biased expression. By making their assembly and annotation publically available and accessible via a genome browser, Mueller et al. (2016) offer exciting possibilities for further research into the genomic basis of adaptation, and investigation of the roles of natural and sexual selection, in this well-studied ecological model species.

Population Genomics Reveals Low Genetic Diversity and Adaptation to Hypoxia in Snub-Nosed Monkeys

Snub-nosed monkeys (genus Rhinopithecus) are a group of endangered colobines endemic to South Asia. Here, we re-sequenced the whole genomes of 38 snub-nosed monkeys representing four species within this genus. By conducting population genomic analyses, we observed a similar load of deleterious variation in snub-nosed monkeys living in both smaller and larger populations and found that genomic diversity was lower than that reported in other primates. Reconstruction of Rhinopithecus evolutionary history suggested that episodes of climatic variation over the past 2 million years, associated with glacial advances and retreats and population isolation, have shaped snub-nosed monkey demography and evolution. We further identified several hypoxia-related genes under selection in R. bieti (black snub-nosed monkey), a species that exploits habitats higher than any other nonhuman primate. These results provide the first detailed and comprehensive genomic insights into genetic diversity, demography, genetic burden, and adaptation in this radiation of endangered primates.

Genome-wide analysis reveals adaptation to high altitudes in Tibetan sheep

Tibetan sheep have lived on the Tibetan Plateau for thousands of years; however, the process and consequences of adaptation to this extreme environment have not been elucidated for important livestock such as sheep. Here, seven sheep breeds, representing both highland and lowland breeds from different areas of China, were genotyped for a genome-wide collection of single-nucleotide polymorphisms (SNPs). The FST and XP-EHH approaches were used to identify regions harbouring local positive selection between these highland and lowland breeds, and 236 genes were identified. We detected selection events spanning genes involved in angiogenesis, energy production and erythropoiesis. In particular, several candidate genes were associated with high-altitude hypoxia, including EPAS1, CRYAA, LONP1, NF1, DPP4, SOD1, PPARG and SOCS2. EPAS1 plays a crucial role in hypoxia adaption; therefore, we investigated the exon sequences of EPAS1 and identified 12 mutations. Analysis of the relationship between blood-related phenotypes and EPAS1 genotypes in additional highland sheep revealed that a homozygous mutation at a relatively conserved site in the EPAS1 3' untranslated region was associated with increased mean corpuscular haemoglobin concentration and mean corpuscular volume. Taken together, our results provide evidence of the genetic diversity of highland sheep and indicate potential high-altitude hypoxia adaptation mechanisms, including the role of EPAS1 in adaptation.