Towards complete and error-free genome assemblies of all vertebrate species

High-quality and complete reference genome assemblies are fundamental for the application of genomics to biology, disease, and biodiversity conservation. However, such assemblies are available for only a few non-microbial species1-4. To address this issue, the international Genome 10K (G10K) consortium5,6 has worked over a five-year period to evaluate and develop cost-effective methods for assembling highly accurate and nearly complete reference genomes. Here we present lessons learned from generating assemblies for 16 species that represent six major vertebrate lineages. We confirm that long-read sequencing technologies are essential for maximizing genome quality, and that unresolved complex repeats and haplotype heterozygosity are major sources of assembly error when not handled correctly. Our assemblies correct substantial errors, add missing sequence in some of the best historical reference genomes, and reveal biological discoveries. These include the identification of many false gene duplications, increases in gene sizes, chromosome rearrangements that are specific to lineages, a repeated independent chromosome breakpoint in bat genomes, and a canonical GC-rich pattern in protein-coding genes and their regulatory regions. Adopting these lessons, we have embarked on the Vertebrate Genomes Project (VGP), an international effort to generate high-quality, complete reference genomes for all of the roughly 70,000 extant vertebrate species and to help to enable a new era of discovery across the life sciences.

Using the 2020 global pandemic as a springboard to highlight the need for amphibian conservation in eastern Asia

Emerging infectious diseases are on the rise in many different taxa, including, among others, the amphibian batrachochytrids, the snake fungal disease and the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) virus, responsible for Coronavirus disease 2019 (COVID-19) in mammals. Following the onset of the pandemic linked to COVID-19, eastern Asia has shown strong leadership, taking actions to regulate the trade of potential vector species in several regions. These actions were taken in response to an increase in public awareness, and the need for a quick reaction to mitigate against further pandemics. However, trade restrictions rarely affect amphibians, despite the risk of pathogen transmission, directly, or indirectly through habitat destruction and the loss of vector consumption. Thus, species that help alleviate the risk of zoonoses or provide biological control are not protected. Hence, in view of the global amphibian decline and the risk of zoonoses, we support the current wildlife trade regulations and support measures to safeguard wildlife from overexploitation. The current period of regulation overhaul should be used as a springboard for amphibian conservation. To mitigate risks, we suggest the following stipulations specifically for amphibians. I) Restrictions to amphibian farming in eastern Asia, in relation to pathogen transmission and the establishment of invasive species. II) Regulation of the amphibian pet trade, with a focus on potential vector species. III) Expansion of the wildlife trade ban, to limit the wildlife-human-pet interface. The resulting actions will benefit both human and wildlife populations, as they will lead to a decrease in the risk of zoonoses and better protection of the environment.

SIGNIFICANCE STATEMENT

There is an increasing number of emerging infectious diseases impacting all species, including amphibians, reptiles and mammals. The latest threat to humans is the virus responsible for COVID-19, and the resulting pandemic. Countries in eastern Asia have taken steps to regulate wildlife trade and prevent further zoonoses thereby decreasing the risk of pathogens arising from wild species. However, as amphibians are generally excluded from regulations we support specific trade restrictions: I) Restrictions to amphibian farming; II) regulation of the amphibian pet trade; III) expansion of the wildlife trade ban. These restrictions will benefit both human and wildlife populations by decreasing the risks of zoonoses and better protecting the environment.

A new skink of the genus Scincella Mittleman, 1950 (Squamata: Scincidae) from southern Vietnam

A new skink of the genus Scincella Mittleman, 1950, from Binh Phuoc Province, southern Vietnam is described based on morphological data, including hemipenial characters, and nucleotide sequences from COI. The following morphological characters diagnose Scincella baraensis sp. nov.: relatively small size in adults (snout-vent length up to 49.2 mm); when limbs adpressed, toes do not or just reach fingers; 30 smooth midbody scale rows and dorsal scales not enlarged; 66-70 paravertebral scales; 64-66 ventral scale rows; 7 supralabials, the fifth and sixth below the center of the eye; enlarged temporal scales 1+2; nuchals present; ear with small auricular lobules; 18-20 smooth lamellae beneath toe IV; hemipenis smooth, short, and unforked; dorsum with faint black dots. The new species differs from its congeners by an uncorrected p-distance in COI sequences of at least 16.2%.

A New Species of Acanthosaura Gray, 1831 (Squamata: Agamidae) from Central Highlands, Vietnam

Herein, we describe a new agamid species of the genus Acanthosaura from Central Highlands of Vietnam: Gia Lai Province, Kon Chu Rang NR, and Kon Tum Province: Kon Plông and Ngoc Linh Mountain based on morphological and molecular data. Acanthosaura prasina sp. nov. is distinguished from all congeners by a combination of the following morphological characters. Acanthosaura prasina sp. nov. differs from A. capra, A. murphyi, and A. nataliae by the presence of a short spine on each side of the neck and a smaller body size. From the known species of «lepidogaster» complex and A. coronata it differs in the arrangement of dorsal crests with a distinct double row of vertebral scales, from A. brachypoda in a smaller body size, longer tail and limbs, fewer supra- and infralabials and coloration patterns with a white area on lips and shoulders; from A. lepidogaster by lacking a dark marking on the nape and the absence of a distinct diastema; from A. phongdienensis by lacking a dark marking on the nape. We provide a cyt b-based estimation of diversity of the genus Acanthosaura. A. prasina sp. nov. differs from A. phongdiensis, A. coronata, A. lepidogaster, A. armata, A. crucigera, A. nataliae, A. phuketensis, and Acanthosaura sp. SK in p-distances of 15.4, 24.5, 14.7, 14.6, 16.3, 14.6, 15.4, and 24.4%, respectively. The new species currently known from three localities from Central Highlands was recorded from 800 to 1700 m a.s.l. in the evergreen polydominant forests in the mountainous regions of Gia Lai and Kon Tum provinces. This is the 16th species of Acanthosaura and the ninth species of the genus from Vietnam.

Origin, clonal diversity, and evolution of the parthenogenetic lizard Darevskia unisexualis

BACKGROUND

The hybridization of female D. raddei and male D. valentini gave rise to the parthenogenetic Caucasian rock lizard Darevskia unisexualis. A previously identified genetic polymorphism in the species consisted of one common and two allozyme clones. Analysis of microsatellites and single nucleotide polymorphisms (SNPs) from the three species yields estimates of clonal diversity and tests the hypothesis of a single origin for D. unisexualis.

RESULTS

Genotyping and sequencing of four microsatellite-containing loci for 109 specimens of D. unisexualis, 17 D. valentini, and 45 D. raddei nairensis identified 12 presumptive clones, including one widespread and 11 rare clones. Most individuals in some localities had a rare clone. Clone-specific alleles in D. unisexualis were compared with those of the parental species. The results inferred a single hybridization event. Post-formation mutations best explain the less common clones.

CONCLUSIONS

Interspecific analyses identify alleles inherited by D. unisexualis from its bisexual ancestors. SNP analyses fail to reject the hypothesis of a single interspecific origin of D. unisexualis, followed by microsatellite mutations in this initial clone. Microsatellites detect higher clonal diversity in D. unisexualis compared to allozymes and identify the likely origins of clones. Our approach may be applicable to other unisexual species whose origins involve interspecific hybridization.

From asymmetrical to balanced genomic diversification during rediploidization: Subgenomic evolution in allotetraploid fish

A persistent enigma is the rarity of polyploidy in animals, compared to its prevalence in plants. Although animal polyploids are thought to experience deleterious genomic chaos during initial polyploidization and subsequent rediploidization processes, this hypothesis has not been tested. We provide an improved reference-quality de novo genome for allotetraploid goldfish whose origin dates to ~15 million years ago. Comprehensive analyses identify changes in subgenomic evolution from asymmetrical oscillation in goldfish and common carp to diverse stabilization and balanced gene expression during continuous rediploidization. The homoeologs are coexpressed in most pathways, and their expression dominance shifts temporally during embryogenesis. Homoeolog expression correlates negatively with alternation of DNA methylation. The results show that allotetraploid cyprinids have a unique strategy for balancing subgenomic stabilization and diversification. Rediploidization process in these fishes provides intriguing insights into genome evolution and function in allopolyploid vertebrates.

New country records for three species of frog from Myanmar including two genera (Nasutixalus and Oreolalax)

Myanmar, a biodiversity hotspot, harbors a striking diversity and endemism of species. Despite this, its herpetofauna remains one of the least explored in continental Asia due to restrictions of crossing political boundaries and infrastructure in remote regions. Many species in adjacent China and India are hypothesized to occur in Myanmar but records are wanting. Recent fieldwork found the frogs Polypedates braueri, Nasutixalus jerdonii and Oreolalax jingdongensis there, and the latter two species represent new generic records for Myanmar. All major morphological characters of these populations match the original descriptions. In addition, our matrilineal genealogy based on DNA barcoding confirms their identities. Overall, these findings confirm that the amphibian diversity is underestimated and this has important implications for conservation. Analyses indicate that northern Myanmar is a biogeographic corridor for the Himalayas, southern China, and northeastern India.

Multilocus phylogeny and cryptic diversity of white-toothed shrews (Mammalia, Eulipotyphla, Crocidura) in China

BACKGROUND

Crocidura, the most speciose mammalian genus, occurs across much of Asia, Europe and Africa. The taxonomy of Chinese representatives has been studied primarily based on cursory morphological comparisons and their molecular phylogenetic analyses remain unexplored. In order to understand the phylogeny of this group in China, we estimated the first multilocus phylogeny and conducted species delimitation, including taxon sampling throughout their distribution range.

RESULTS

We obtained one mitochondrial gene (cytb) (~ 1, 134 bp) and three nuclear genes (ApoB, BRCA1, RAG1) (~ 2, 170 bp) for 132 samples from 57 localities. Molecular analyses identified at least 14 putative species that occur within two major well-supported groups in China. Polyphyletic C. wuchihensis appears to be composed of two putative species. Two subspecies, C. rapax rapax and C. rapax kurodai should be elevated to full species status. A phylogenetic tree based on mitochondrial gene from Asian Crocidura species showed that the C. rapax rapax is embedded within C. attenuata, making the latter a paraphyletic group. Three strongly supported undescribed species (C. sp.1, C. sp.2 and C. sp.3) are revealed from Zada County of Tibet (Western China), Hongjiang County of Hunan Province (Central China) and Dongyang County of Zhejiang Province (Eastern China), Motuo County of Tibet, respectively. The divergence time estimation suggested that China's Crocidura species began to diversify during the late Pliocene (3.66 Ma) and the Early Pleistocene (2.29 Ma), followed by a series of diversifications through the Pleistocene.

CONCLUSIONS

The cryptic diversity found in this study indicated that the number of species is strongly underestimated under the current taxonomy. We propose that the three undescribed species should be evaluated using extensive taxon sampling and comprehensive morphological and morphometric approaches. Climate change since the late Pliocene and the uplift of the Qinghai-Tibet Plateau may result in the diversification and speciation of China's Crocidura species. In short, the underestimated diversity underlines the need for a taxonomic revision of Chinese Crocidura species.

Revalidation and resurrection of Panaspis massaiensis (Angel, 1924) and the description of a new species of Panaspis Cope (Squamata: Scincidae) from south-eastern Kenya

Historically Panaspis wahlbergi (Smith, 1849) has been the only assignable species present in Kenya. Recent studies have shown that it comprises multiple cryptic species and the nominal species is now restricted to southern Africa. Newly collected mitochondrial data (16S rRNA) helped to resolve the status of the Kenyan populations, which revealed the presence of two distant related species. Pairwise distances show average 5.87% differences between the two Kenyan species, and 3.58-5.27% and 8.62-9.15% to nominal P. wahlbergi and P. maculicollis Jacobsen Broadley, 2000 respectively. Ablepharus massaiensis Angel, 1924 was described from the Maasai plains near Nairobi, but has long been considered a junior synonym of P. wahlbergi. We herein resurrect Panaspis massaiensis comb. nov. as a valid species and describe a new species, Panaspis tsavoensis sp. nov. from the Tsavo Conservation Area in south-eastern Kenya. Morphological examinations of specimens reveal minor differences from each other as well as nominal forms of P. wahlbergi and P. maculicollis. Panaspis massaiensis comb. nov. shares with the P. wahlbergi group a white ventrolateral stripe but can be distinguished by the presence of 26 midbody scale rows versus 24. Panaspis tsavoensis sp. nov. on the other hand, lacks the white ventrolateral stripe, most similar to the P. maculicollis group but differs in that P. maculicollis breeding males have a black patch on the neck with diagonal rows of white spots. Panaspis massaiensis comb. nov. is widespread in the Kenyan and northern Tanzanian highlands, isolated dryland montane forests and rocky hills, while P. tsavoensis sp. nov. occur in the expansive arid lowlands of Tsavo Conservation Area and should be present in similar arid lowlands in northern Kenya as well as in adjacent Tanzania.

A new species of the genus Xenophrys Anura Megophryidae from northern Thailand

Species of Xenophrys are conserved morphologically and live primarily in forests. In Thailand, the genus harbors many cryptic species. Herein we report the collection of specimens from Doi Inthanon, Chiang Mai Province, northern Thailand, which were identified previously as X. minor. Molecular and morphological analyses find that these specimens differ significantly from other known congeners, and therefore we describe a new species. Further, our phylogenetic analyses indicate that X. latidactyla is a junior synonym of X. palpebralespinosa.

Conserved sequences identify the closest living relatives of primates

Elucidating the closest living relatives of extant primates is essential for fully understanding important biological processes related to the genomic and phenotypic evolution of primates, especially of humans. However, the phylogenetic placement of these primate relatives remains controversial, with three primary hypotheses currently espoused based on morphological and molecular evidence. In the present study, we used two algorithms to analyze differently partitioned genomic datasets consisting of 45.4 Mb of conserved non-coding elements and 393 kb of concatenated coding sequences to test these hypotheses. We assessed different genomic histories and compared with other molecular studies found solid support for colugos being the closest living relatives of primates. Our phylogeny showed Cercopithecinae to have low levels of nucleotide divergence, especially for Papionini, and gibbons to have a high rate of divergence. The MCMCtree comprehensively updated divergence dates of early evolution of Primatomorpha and Primates.

Interrogating Genomic-Scale Data for Squamata (Lizards, Snakes, and Amphisbaenians) Shows no Support for Key Traditional Morphological Relationships

Genomics is narrowing uncertainty in the phylogenetic structure for many amniote groups. For one of the most diverse and species-rich groups, the squamate reptiles (lizards, snakes, and amphisbaenians), an inverse correlation between the number of taxa and loci sampled still persists across all publications using DNA sequence data and reaching a consensus on the relationships among them has been highly problematic. In this study, we use high-throughput sequence data from 289 samples covering 75 families of squamates to address phylogenetic affinities, estimate divergence times, and characterize residual topological uncertainty in the presence of genome-scale data. Importantly, we address genomic support for the traditional taxonomic groupings Scleroglossa and Macrostomata using novel machine-learning techniques. We interrogate genes using various metrics inherent to these loci, including parsimony-informative sites (PIS), phylogenetic informativeness, length, gaps, number of substitutions, and site concordance to understand why certain loci fail to find previously well-supported molecular clades and how they fail to support species-tree estimates. We show that both incomplete lineage sorting and poor gene-tree estimation (due to a few undesirable gene properties, such as an insufficient number of PIS), may account for most gene and species-tree discordance. We find overwhelming signal for Toxicofera, and also show that none of the loci included in this study supports Scleroglossa or Macrostomata. We comment on the origins and diversification of Squamata throughout the Mesozoic and underscore remaining uncertainties that persist in both deeper parts of the tree (e.g., relationships between Dibamia, Gekkota, and remaining squamates; among the three toxicoferan clades Iguania, Serpentes, and Anguiformes) and within specific clades (e.g., affinities among gekkotan, pleurodont iguanians, and colubroid families).

Historical museum collections clarify the evolutionary history of cryptic species radiation in the world's largest amphibians

Inaccurate taxonomic assessment of threatened populations can hinder conservation prioritization and management, with human-mediated population movements obscuring biogeographic patterns and confounding reconstructions of evolutionary history. Giant salamanders were formerly distributed widely across China, and are interpreted as a single species, Andrias davidianus. Previous phylogenetic studies have identified distinct Chinese giant salamander lineages but were unable to associate these consistently with different landscapes, probably because population structure has been modified by human-mediated translocations for recent commercial farming. We investigated the evolutionary history and relationships of allopatric Chinese giant salamander populations with Next-Generation Sequencing methods, using historical museum specimens and late 20th-century samples, and retrieved partial or near-complete mitogenomes for 17 individuals. Samples from populations unlikely to have been affected by translocations form three clades from separate regions of China, spatially congruent with isolation by either major river drainages or mountain ranges. Pliocene-Pleistocene divergences for these clades are consistent with topographic modification of southern China associated with uplift of the Qinghai-Tibet Plateau. General Mixed Yule Coalescent model analysis indicates that these clades represent separate species: Andrias davidianus (Blanchard, 1871) (northern Yangtze/Sichuan), Andrias sligoi (Boulenger, 1924) (Pearl/Nanling), and an undescribed species (Huangshan). Andrias sligoi is possibly the world's largest amphibian. Inclusion of additional reportedly wild samples from areas of known giant salamander exploitation and movement leads to increasing loss of biogeographic signal. Wild Chinese giant salamander populations are now critically depleted or extirpated, and conservation actions should be updated to recognize the existence of multiple species.

A new skink of the genus Scincella Mittleman, 1950 (Squamata: Scincidae) from Ba Den Mountain, Tay Ninh Province, southern Vietnam

Ba Den is an isolated mountain in southern Vietnam and home to two endemic species of lizards. Herein, we describe another endemic species, a new skink of the genus Scincella Mittleman, 1950, from the area based on morphological data, including hemipenial characters and nucleotide sequences of COI. The following morphological characters diagnose Scincella badenensis sp. nov.: medium size in adults (snout-vent length up to 64.4 mm); toes reach to fingers when limbs adpressed; midbody scale rows 32-36, smooth; paravertebral scales 67-71; dorsal scales not enlarged; ventral scale rows 68-74; supraoculars four; prefrontals in broad contact with one another; loreal scales two; tympanum deeply sunk, without auricular lobules; two enlarged anterior temporal scales; smooth lamellae beneath toe IV 18-20; pair of enlarged precloacal scales; hemipenes short, smooth and forked near the tip with two short lobes and two small terminal papillae; no dorsal pattern in males; and females with black interruptive vertebral line. The new species differs from its congeners by at least 10.4% uncorrected p-distance in COI sequences.

A new species of Acanthosaura Gray 1831 (Reptilia: Agamidae) from central Vietnam

Herein, we describe the new agamid species Acanthosaura phongdienensis sp. nov. from central Vietnam based on morphological and genetic data. Males of the new medium-sized species have a snout-vent length of up to 77.4 mm and females up to 64.7 mm. In both genders, the tail is longer than the snout-vent length. A spine occurs on each side of the neck, the rostral scute is entire, and the nuchal and dorsal crests are continuous. A postorbital spine is about half as long as the diameter of the eye-ball, and small lateral scales intermix with large, keeled scales whose tips point backwards and upwards. The new species differs genetically from the closely related species A. brachypoda, A. coronata, and A. lepidogaster by uncorrected p-distances of 13.6%, 21.7%, and 12.8%, respectively. This is the 13th species of Acanthosaura and the eighth species in the genus from Vietnam.

Large-scale molecular phylogeny, morphology, divergence-time estimation, and the fossil record of advanced caenophidian snakes (Squamata: Serpentes)

Caenophidian snakes include the file snake genus Acrochordus and advanced colubroidean snakes that radiated mainly during the Neogene. Although caenophidian snakes are a well-supported clade, their inferred affinities, based either on molecular or morphological data, remain poorly known or controversial. Here, we provide an expanded molecular phylogenetic analysis of Caenophidia and use three non-parametric measures of support-Shimodaira-Hasegawa-Like test (SHL), Felsentein (FBP) and transfer (TBE) bootstrap measures-to evaluate the robustness of each clade in the molecular tree. That very different alternative support values are common suggests that results based on only one support value should be viewed with caution. Using a scheme to combine support values, we find 20.9% of the 1265 clades comprising the inferred caenophidian tree are unambiguously supported by both SHL and FBP values, while almost 37% are unsupported or ambiguously supported, revealing the substantial extent of phylogenetic problems within Caenophidia. Combined FBP/TBE support values show similar results, while SHL/TBE result in slightly higher combined values. We consider key morphological attributes of colubroidean cranial, vertebral and hemipenial anatomy and provide additional morphological evidence supporting the clades Colubroides, Colubriformes, and Endoglyptodonta. We review and revise the relevant caenophidian fossil record and provide a time-calibrated tree derived from our molecular data to discuss the main cladogenetic events that resulted in present-day patterns of caenophidian diversification. Our results suggest that all extant families of Colubroidea and Elapoidea composing the present-day endoglyptodont fauna originated rapidly within the early Oligocene-between approximately 33 and 28 Mya-following the major terrestrial faunal turnover known as the "Grande Coupure" and associated with the overall climate shift at the Eocene-Oligocene boundary. Our results further suggest that the caenophidian radiation originated within the Caenozoic, with the divergence between Colubroides and Acrochordidae occurring in the early Eocene, at ~ 56 Mya.

Genetic variation and cryptic lineage diversity of the Nigerian red-headed rock agama Agama agama associate with eco-geographic zones

Nigeria is an Afrotropical region with considerable ecological heterogeneity and levels of biotic endemism. Among its vertebrate fauna, reptiles have broad distributions, thus, they constitute a compelling system for assessing the impact of ecological variation and geographic isolation on species diversification. The red-headed rock agama, Agama agama, lives in a wide range of habitats and, thus, it may show genetic structuring and diversification. Herein, we tested the hypothesis that ecology affects its genetic structure and population divergence. Bayesian inference phylogenetic analysis of a mitochondrial DNA (mtDNA) gene recovered four well-supported matrilines with strong evidence of genetic structuring consistent with eco-geographic regions. Genetic differences among populations based on the mtDNA also correlated with geographic distance. The ecological niche model for the matrilines had a good fit and robust performance. Population divergence along the environmental axes was associated with climatic conditions, and temperature ranked highest among all environmental variables for forest specialists, while precipitation ranked highest for the forest/derived savanna, and savanna specialists. Our results cannot reject the hypothesis that niche conservatism promotes geographic isolation of the western populations of Nigerian A. agama. Thus, ecological gradients and geographic isolation impact the genetic structure and population divergence of the lizards. This species might be facing threats due to recent habitat fragmentation, especially in western Nigeria. Conservation actions appear necessary.