Evolutionary history inferred from the de novo assembly of a nonmodel organism, the blue-eyed black lemur

A Pervasive History of Gene Flow in Madagascar's True Lemurs (Genus Eulemur)

In recent years, it has become widely accepted that interspecific gene flow is common across the Tree of Life. Questions remain about how species boundaries can be maintained in the face of high levels of gene flow and how phylogeneticists should account for reticulation in their analyses. The true lemurs of Madagascar (genus Eulemur, 12 species) provide a unique opportunity to explore these questions, as they form a recent radiation with at least five active hybrid zones. Here, we present new analyses of a mitochondrial dataset with hundreds of individuals in the genus Eulemur, as well as a nuclear dataset containing hundreds of genetic loci for a small number of individuals. Traditional coalescent-based phylogenetic analyses of both datasets reveal that not all recognized species are monophyletic. Using network-based approaches, we also find that a species tree containing between one and three ancient reticulations is supported by strong evidence. Together, these results suggest that hybridization has been a prominent feature of the genus Eulemur in both the past and present. We also recommend that greater taxonomic attention should be paid to this group so that geographic boundaries and conservation priorities can be better established.

Genetic characterization of Macaca arctoides: A highlight of key genes and pathways

When compared to the approximately 22 other macaque species, Macaca arctoides has many unique phenotypes. These traits fall into various phenotypic categories, including genitalia, coloration, mating, and olfactory traits. Here we used a previously identified whole genome set of 690 outlier genes to look for possible genetic explanations of these unique traits. Of these, 279 genes were annotated miRNAs, which are non-coding. Patterns within the remaining outliers in coding genes were investigated using GO (n = 370) and String (n = 383) analysis, which showed many interconnected immune-related genes. Further, we compared the outliers to candidate pathways associated with M. arcotides' unique phenotypes, revealing 10/690 outlier genes that overlapped these four pathways: hedgehog signaling, WNT signaling, olfactory, and melanogenesis. Of these, genes in all pathways except olfactory had higher F_ST values than the rest of the genes in the genome based on permutation tests. Overall, our results point to many genes each having a small impact on phenotype, working in tandem to cause large systemic changes. Additionally, these results may indicate pleiotropy. This seems to be especially true with the development and coloration of M. arctoides. Our results highlight that development, melanogenesis, immune function, and miRNAs may be heavily involved in M. arctoides' evolutionary history.

The contribution of historical processes to contemporary extinction risk in placental mammals

Species persistence can be influenced by the amount, type, and distribution of diversity across the genome, suggesting a potential relationship between historical demography and resilience. In this study, we surveyed genetic variation across single genomes of 240 mammals that compose the Zoonomia alignment to evaluate how historical effective population size (Ne) affects heterozygosity and deleterious genetic load and how these factors may contribute to extinction risk. We find that species with smaller historical Ne carry a proportionally larger burden of deleterious alleles owing to long-term accumulation and fixation of genetic load and have a higher risk of extinction. This suggests that historical demography can inform contemporary resilience. Models that included genomic data were predictive of species' conservation status, suggesting that, in the absence of adequate census or ecological data, genomic information may provide an initial risk assessment.

Functional genomics analysis reveals the evolutionary adaptation and demographic history of pygmy lorises

Lorises are a group of globally threatened strepsirrhine primates that exhibit many unusual physiological and behavioral features, including a low metabolic rate, slow movement, and hibernation. Here, we assembled a chromosome-level genome sequence of the pygmy loris (Xanthonycticebus pygmaeus) and resequenced whole genomes from 50 pygmy lorises and 6 Bengal slow lorises (Nycticebus bengalensis). We found that many gene families involved in detoxification have been specifically expanded in the pygmy loris, including the GSTA gene family, with many newly derived copies functioning specifically in the liver. We detected many genes displaying evolutionary convergence between pygmy loris and koala, including PITRM1. Significant decreases in PITRM1 enzymatic activity in these two species may have contributed to their characteristic low rate of metabolism. We also detected many evolutionarily convergent genes and positively selected genes in the pygmy loris that are involved in muscle development. Functional assays demonstrated the decreased ability of one positively selected gene, MYOF, to up-regulate the fast-type muscle fiber, consistent with the lower proportion of fast-twitch muscle fibers in the pygmy loris. The protein product of another positively selected gene in the pygmy loris, PER2, exhibited weaker binding to the key circadian core protein CRY, a finding that may be related to this species' unusual circadian rhythm. Finally, population genomics analysis revealed that these two extant loris species, which coexist in the same habitat, have exhibited an inverse relationship in terms of their demography over the past 1 million years, implying strong interspecies competition after speciation.

Impact of model assumptions on demographic inferences: the case study of two sympatric mouse lemurs in northwestern Madagascar

BACKGROUND

Quaternary climate fluctuations have been acknowledged as major drivers of the geographical distribution of the extraordinary biodiversity observed in tropical biomes, including Madagascar. The main existing framework for Pleistocene Malagasy diversification assumes that forest cover was strongly shaped by warmer Interglacials (leading to forest expansion) and by cooler and arid glacials (leading to forest contraction), but predictions derived from this scenario for forest-dwelling animals have rarely been tested with genomic datasets.

RESULTS

We generated genomic data and applied three complementary demographic approaches (Stairway Plot, PSMC and IICR-simulations) to infer population size and connectivity changes for two forest-dependent primate species (Microcebus murinus and M. ravelobensis) in northwestern Madagascar. The analyses suggested major demographic changes in both species that could be interpreted in two ways, depending on underlying model assumptions (i.e., panmixia or population structure). Under panmixia, the two species exhibited larger population sizes across the Last Glacial Maximum (LGM) and towards the African Humid Period (AHP). This peak was followed by a population decline in M. ravelobensis until the present, while M. murinus may have experienced a second population expansion that was followed by a sharp decline starting 3000 years ago. In contrast, simulations under population structure suggested decreasing population connectivity between the Last Interglacial and the LGM for both species, but increased connectivity during the AHP exclusively for M. murinus.

CONCLUSION

Our study shows that closely related species may differ in their responses to climatic events. Assuming that Pleistocene climatic conditions in the lowlands were similar to those in the Malagasy highlands, some demographic dynamics would be better explained by changes in population connectivity than in population size. However, changes in connectivity alone cannot be easily reconciled with a founder effect that was shown for M. murinus during its colonization of the northwestern Madagascar in the late Pleistocene. To decide between the two alternative models, more knowledge about historic forest dynamics in lowland habitats is necessary. Altogether, our study stresses that demographic inferences strongly depend on the underlying model assumptions. Final conclusions should therefore be based on a comparative evaluation of multiple approaches.

Molecular Adaptation to Folivory and the Conservation Implications for Madagascar’s Lemurs

The lemurs of Madagascar include numerous species characterized by folivory across several families. Many extant lemuriform folivores exist in sympatry in Madagascar’s remaining forests. These species avoid feeding competition by adopting different dietary strategies within folivory, reflected in behavioral, morphological, and microbiota diversity across species. These conditions make lemurs an ideal study system for understanding adaptation to leaf-eating. Most folivorous lemurs are also highly endangered. The significance of folivory for conservation outlook is complex. Though generalist folivores may be relatively well equipped to survive habitat disturbance, specialist folivores occupying narrow dietary niches may be less resilient. Characterizing the genetic bases of adaptation to folivory across species and lineages can provide insights into their differential physiology and potential to resist habitat change. We recently reported accelerated genetic change in RNASE1, a gene encoding an enzyme (RNase 1) involved in molecular adaptation in mammalian folivores, including various monkeys and sifakas (genus Propithecus; family Indriidae). Here, we sought to assess whether other lemurs, including phylogenetically and ecologically diverse folivores, might show parallel adaptive change in RNASE1 that could underlie a capacity for efficient folivory. We characterized RNASE1 in 21 lemur species representing all five families and members of the three extant folivorous lineages: (1) bamboo lemurs (family Lemuridae), (2) sportive lemurs (family Lepilemuridae), and (3) indriids (family Indriidae). We found pervasive sequence change in RNASE1 across all indriids, a dN/dS value > 3 in this clade, and evidence for shared change in isoelectric point, indicating altered enzymatic function. Sportive and bamboo lemurs, in contrast, showed more modest sequence change. The greater change in indriids may reflect a shared strategy emphasizing complex gut morphology and microbiota to facilitate folivory. This case study illustrates how genetic analysis may reveal differences in functional traits that could influence species’ ecology and, in turn, their resilience to habitat change. Moreover, our results support the body of work demonstrating that not all primate folivores are built the same and reiterate the need to avoid generalizations about dietary guild in considering conservation outlook, particularly in lemurs where such diversity in folivory has probably led to extensive specialization via niche partitioning.

A New World Monkey Resembles Human in Bitter Taste Receptor Evolution and Function via a Single Parallel Amino Acid Substitution

Bitter taste receptors serve as a vital component in the defense system against toxin intake by animals, and the family of genes encoding these receptors has been demonstrated, usually by family size variance, to correlate with dietary preference. However, few systematic studies of specific Tas2R to unveil their functional evolution have been conducted. Here, we surveyed Tas2R16 across all major clades of primates and reported a rare case of a convergent change to increase sensitivity to β-glucopyranosides in human and a New World monkey, the white-faced saki. Combining analyses at multiple levels, we demonstrate that a parallel amino acid substitution (K172N) shared by these two species is responsible for this functional convergence of Tas2R16. Considering the specialized feeding preference of the white-faced saki, the K172N change likely played an important adaptive role in its early evolution to avoid potentially toxic cyanogenic glycosides, as suggested for the human TAS2R16 gene.

Comparative genomic analysis of sifakas (Propithecus) reveals selection for folivory and high heterozygosity despite endangered status

Sifakas (genus Propithecus) are critically endangered, large-bodied diurnal lemurs that eat leaf-based diets and show corresponding anatomical and microbial adaptations to folivory. We report on the genome assembly of Coquerel's sifaka (P. coquereli) and the resequenced genomes of Verreaux's (P. verreauxi), the golden-crowned (P. tattersalli), and the diademed (P. diadema) sifakas. We find high heterozygosity in all sifakas compared with other primates and endangered mammals. Demographic reconstructions nevertheless suggest declines in effective population size beginning before human arrival on Madagascar. Comparative genomic analyses indicate pervasive accelerated evolution in the ancestral sifaka lineage affecting genes in several complementary pathways relevant to folivory, including nutrient absorption and xenobiotic and fatty acid metabolism. Sifakas show convergent evolution at the level of the pathway, gene family, gene, and amino acid substitution with other folivores. Although sifakas have relatively generalized diets, the physiological challenges of habitual folivory likely led to strong selection.

The Diversity of Primates: From Biomedicine to Conservation Genomics

Until now, the field of primate genomics has focused on two major themes: understanding human evolution and advancing biomedical research. We propose that it is now time for a third theme to receive attention: conservation genomics. As a result of anthropogenic effects, the majority of primate species have become threatened with extinction. A more robust primate conservation genomics will allow for genetically informed population management. Thanks to a steady decline in the cost of sequencing, it has now become feasible to sequence whole primate genomes at the population level. Furthermore, technological advances in noninvasive genomic methods have made it possible to acquire genome-scale data from noninvasive biomaterials. Here, we review recent advances in the analysis of primate diversity, with a focus on genomic data sets across the radiation.

Conservation genomic analysis reveals ancient introgression and declining levels of genetic diversity in Madagascar's hibernating dwarf lemurs

Madagascar's biodiversity is notoriously threatened by deforestation and climate change. Many of these organisms are rare, cryptic, and severely threatened, making population-level sampling unrealistic. Such is the case with Madagascar's dwarf lemurs (genus Cheirogaleus), the only obligate hibernating primate. We here apply comparative genomic approaches to generate the first genome-wide estimates of genetic diversity within dwarf lemurs. We generate a reference genome for the fat-tailed dwarf lemur, Cheirogaleus medius, and use this resource to facilitate analyses of high-coverage (~30×) genome sequences for wild-caught individuals representing species: C. sp. cf. medius, C. major, C. crossleyi, and C. sibreei. This study represents the largest contribution to date of novel genomic resources for Madagascar's lemurs. We find concordant phylogenetic relationships among the four lineages of Cheirogaleus across most of the genome, and yet detect a number of discordant genomic regions consistent with ancient admixture. We hypothesized that these regions could have resulted from adaptive introgression related to hibernation, indeed finding that genes associated with hibernation are present, though most significantly, that gene ontology categories relating to transcription are over-represented. We estimate levels of heterozygosity and find particularly low levels in an individual sampled from an isolated population of C. medius that we refer to as C. sp. cf. medius. Results are consistent with a recent decline in effective population size, which is evident across species. Our study highlights the power of comparative genomic analysis for identifying species and populations of conservation concern, as well as for illuminating possible mechanisms of adaptive phenotypic evolution.

Comparative Genomic Analysis of the Pheromone Receptor Class 1 Family (V1R) Reveals Extreme Complexity in Mouse Lemurs (Genus, Microcebus) and a Chromosomal Hotspot across Mammals

Sensory gene families are of special interest for both what they can tell us about molecular evolution and what they imply as mediators of social communication. The vomeronasal type-1 receptors (V1Rs) have often been hypothesized as playing a fundamental role in driving or maintaining species boundaries given their likely function as mediators of intraspecific mate choice, particularly in nocturnal mammals. Here, we employ a comparative genomic approach for revealing patterns of V1R evolution within primates, with a special focus on the small-bodied nocturnal mouse and dwarf lemurs of Madagascar (genera Microcebus and Cheirogaleus, respectively). By doubling the existing genomic resources for strepsirrhine primates (i.e. the lemurs and lorises), we find that the highly speciose and morphologically cryptic mouse lemurs have experienced an elaborate proliferation of V1Rs that we argue is functionally related to their capacity for rapid lineage diversification. Contrary to a previous study that found equivalent degrees of V1R diversity in diurnal and nocturnal lemurs, our study finds a strong correlation between nocturnality and V1R elaboration, with nocturnal lemurs showing elaborate V1R repertoires and diurnal lemurs showing less diverse repertoires. Recognized subfamilies among V1Rs show unique signatures of diversifying positive selection, as might be expected if they have each evolved to respond to specific stimuli. Furthermore, a detailed syntenic comparison of mouse lemurs with mouse (genus Mus) and other mammalian outgroups shows that orthologous mammalian subfamilies, predicted to be of ancient origin, tend to cluster in a densely populated region across syntenic chromosomes that we refer to as a V1R "hotspot."

A natural point mutation in the bitter taste receptor TAS2R16 causes inverse agonism of arbutin in lemur gustation

Bitter taste enables the detection of potentially harmful substances and is mediated by bitter taste receptors, TAS2Rs, in vertebrates. Few antagonists and inverse agonists of TAS2Rs have been identified, especially natural compounds. TAS2R16s in humans, apes and Old World monkeys (Catarrhini, Anthropoidea) recognize β-glucoside analogues as specific agonists. Here, we investigated responses of TAS2R16 to β-glucosides in non-anthropoid primates, namely lemurs (Lemuriformes, Strepsirrhini). Salicin acted as an agonist on lemur TAS2R16. Arbutin acted as an agonist in the ring-tailed lemur ( Lemur catta) but as an inverse agonist in black lemur ( Eulemur macaco) and black-and-white ruffed lemur ( Varecia variegata). We identified a strepsirrhine-specific amino acid substitution responsible for the inverse agonism of arbutin. In a food preference test, salicin bitterness was inhibited by arbutin in the black lemur. Structural modelling revealed this locus was important for a rearrangement of the intracellular end of transmembrane helix 7 (TM7). Accordingly, arbutin is the first known natural inverse agonist of TAS2Rs, contributing to our understanding of receptor-ligand interactions and the molecular basis of the unique feeding habit diversification in lemurs. Furthermore, the identification of a causal point mutation suggests that TAS2R can acquire functional changes according to feeding habits and environmental conditions.

IDP-denovo: de novo transcriptome assembly and isoform annotation by hybrid sequencing

Motivation

In the past years, the long read (LR) sequencing technologies, such as Pacific Biosciences and Oxford Nanopore Technologies, have been demonstrated to substantially improve the quality of genome assembly and transcriptome characterization. Compared to the high cost of genome assembly by LR sequencing, it is more affordable to generate LRs for transcriptome characterization. That is, when informative transcriptome LR data are available without a high-quality genome, a method for de novo transcriptome assembly and annotation is of high demand.

Results

Without a reference genome, IDP-denovo performs de novo transcriptome assembly, isoform annotation and quantification by integrating the strengths of LRs and short reads. Using the GM12878 human data as a gold standard, we demonstrated that IDP-denovo had superior sensitivity of transcript assembly and high accuracy of isoform annotation. In addition, IDP-denovo outputs two abundance indices to provide a comprehensive expression profile of genes/isoforms. IDP-denovo represents a robust approach for transcriptome assembly, isoform annotation and quantification for non-model organism studies. Applying IDP-denovo to a non-model organism, Dendrobium officinale, we discovered a number of novel genes and novel isoforms that were not reported by the existing annotation library. These results reveal the high diversity of gene isoforms in D.officinale, which was not reported in the existing annotation library.

Availability and implementation

The dataset of Dendrobium officinale used/analyzed during the current study has been deposited in SRA, with accession code SRP094520. IDP-denovo is available for download at www.healthcare.uiowa.edu/labs/au/IDP-denovo/.

Supplementary information

Supplementary data are available at Bioinformatics online.

Genome sequence and population declines in the critically endangered greater bamboo lemur (Prolemur simus) and implications for conservation

BACKGROUND

The greater bamboo lemur (Prolemur simus) is a member of the Family Lemuridae that is unique in their dependency on bamboo as a primary food source. This Critically Endangered species lives in small forest patches in eastern Madagascar, occupying a fraction of its historical range. Here we sequence the genome of the greater bamboo lemur for the first time, and provide genome resources for future studies of this species that can be applied across its distribution.

RESULTS

Following whole genome sequencing of five individuals we identified over 152,000 polymorphic single nucleotide variants (SNVs), and evaluated geographic structuring across nearly 19 k SNVs. We characterized a stronger signal associated with a north-south divide than across elevations for our limited samples. We also evaluated the demographic history of this species, and infer a dramatic population crash. This species had the largest effective population size (estimated between ~ 900,000 to one million individuals) between approximately 60,000-90,000 years before present (ybp), during a time in which global climate change affected terrestrial mammals worldwide. We also note the single sample from the northern portion of the extant range had the largest effective population size around 35,000 ybp.

CONCLUSIONS

From our whole genome sequencing we recovered an average genomic heterozygosity of 0.0037%, comparable to other lemurs. Our demographic history reconstructions recovered a probable climate-related decline (60-90,000 ybp), followed by a second population decrease following human colonization, which has reduced the species to a census size of approximately 1000 individuals. The historical distribution was likely a vast portion of Madagascar, minimally estimated at 44,259 km2, while the contemporary distribution is only ~ 1700 km2. The decline in effective population size of 89-99.9% corresponded to a vast range retraction. Conservation management of this species is crucial to retain genetic diversity across the remaining isolated populations.

angsd-wrapper: utilities for analysing next-generation sequencing data

High-throughput sequencing has changed many aspects of population genetics, molecular ecology and related fields, affecting both experimental design and data analysis. The software package angsd allows users to perform a number of population genetic analyses on high-throughput sequencing data. angsd uses probabilistic approaches which can directly make use of genotype likelihoods; thus, SNP calling is not required for comparative analyses. This takes advantage of all the sequencing data and produces more accurate results for samples with low sequencing depth. Here, we present angsd-wrapper, a set of wrapper scripts that provides a user-friendly interface for running angsd and visualizing results. angsd-wrapper supports multiple types of analyses including estimates of nucleotide sequence diversity neutrality tests, principal component analysis, estimation of admixture proportions for individual samples and calculation of statistics that quantify recent introgression. angsd-wrapper also provides interactive graphing of angsd results to enhance data exploration. We demonstrate the usefulness of angsd-wrapper by analysing resequencing data from populations of wild and domesticated Zea. angsd-wrapper is freely available from https://github.com/mojaveazure/angsd-wrapper.

Genome sequencing of Metrosideros polymorpha (Myrtaceae), a dominant species in various habitats in the Hawaiian Islands with remarkable phenotypic variations

Whole genome sequences, which can be provided even for non-model organisms owing to high-throughput sequencers, are valuable in enhancing the understanding of adaptive evolution. Metrosideros polymorpha, a tree species endemic to the Hawaiian Islands, occupies a wide range of ecological habitats and shows remarkable polymorphism in phenotypes among/within populations. The biological functions of genetic variations observed within this species could provide significant insights into the adaptive radiation found in a single species. Here de novo assembled genome sequences of M. polymorpha are presented to reveal basic genomic parameters about this species and to develop our knowledge of ecological divergences. The assembly yielded 304-Mbp genome sequences, half of which were covered by 19 scaffolds with >5 Mbp, and contained 30 K protein-coding genes. Demographic history inferred from the genome-wide heterozygosity indicated that this species experienced a dramatic rise and fall in the effective population size, possibly owing to past geographic or climatic changes in the Hawaiian Islands. This M. polymorpha genome assembly represents a high-quality genome resource useful for future functional analyses of both intra- and interspecies genetic variations or comparative genomics.