Biology subjects

Janke, A.

Publications and source records attributed to Janke, A..

At least 19 recordsLinked to original sources

bioRxiv2025

Species delimitation using genome-wide estimates of Dxy and Fst

Accurate and stable species delimitation is essential for effective nature conservation and management. Advances in genomics now offer the potential for consistent decision-making. We performed a meta-analysis of genomic data from hundreds of sister lineages of large mammals to test whether species boundaries can be identified using genome-wide sequence dissimilarity estimates. We find that a combined threshold of absolute (Dxy = 0.225% [0.20%-0.27%]) and relative genetic distance (Fst = 0.26 [0.19-0.54]) predicts current taxonomic status with over 90% accuracy. This predictive power indicates that mammalian taxonomists managed to maintain consistency across taxa despite having to rely on disparate morphological traits. Lineage pairs exhibiting Haldanes Rule exceed far higher thresholds (Dxy = 0.4%; Fst = 0.55), implying that mammalian taxonomists adhere to species concepts which allow for interbreeding. Our findings challenge the significance of fast-track bottleneck speciation and suggest instead that deep divergences of up to 100,000 generations are usually required for mammalian sister lineages to remain genetically isolated upon secondary contact. We discuss taxonomic revisions to improve temporal banding, including three potential cases of cryptic speciation: southern versus eastern aardwolves, Asiatic black bears versus Japanese black bears, and European versus Asian wild boar. In summary, our meta-analysis provides simple rules for species delimitation and offers new insights into the taxonomy and speciation dynamics of large mammals.

genomics↗

bioRxiv2025

DIST: Distance-based Inference of Species Trees

Inferring species trees from concatenated loci is often criticised for failing to account for gene tree discordance - particularly when using character-based methods. However, this criticism does not apply to distance-based concatenation trees, which can be shown to be statistically consistent even in anomaly zones. Building on this insight, we introduce DIST (Distance-based Inference of Species Trees), an intuitive and scalable method that infers species trees from population-level distance matrices containing multi-locus estimates of Dxy, FST or coalescence units ({tau}). DIST derives these values from between-individual sequence dissimilarity estimates, E(p), using basic equations from coalescence theory. Under certain conditions, DIST can also quantify gene tree discordance and distinguish whether it arises from gene flow or incomplete lineage sorting alone. While conceptually related to more sophisticated summary methods, DIST differs in that it does not seek the species tree which best explains a set of gene trees. Instead, it searches for the species tree which best explains an average gene tree, of which all branch lengths reflect mean coalescence time, E(t). Although this average gene tree is rarely observed empirically, it is approximated by an individual-level distance-based tree, traditionally referred to as a tree of individuals. The DIST algorithm is implemented in the R package SambaR, which now accepts input in the form of pairwise E(p) estimates.

bioinformatics↗

bioRxiv2025

Chromosome-level genome assembly of the lemon sole Microstomus kitt (Pleuronectiformes: Pleuronectidae)

BackgroundThe lemon sole (Microstomus kitt) is a culinary fish from the family of righteye flounders (Pleuronectidae) inhabiting sandy and shallow offshore grounds of the North Sea, the western Baltic Sea, the English Channel, the shallow waters of Great Britain and Ireland as well as the Bay of Biscay and the coastal waters of Norway. FindingsHere, we present the chromosome-level genome assembly of the lemon sole. We applied PacBio HiFi sequencing on the PacBio Revio system to generate a highly complete and contiguous reference genome. The resulting assembly has a contig N50 of 17.2 Mbp and a scaffold N50 of 27.2 Mbp. The total assembly length is 628 Mbp, of which 616 Mbp were scaffolded into 24 chromosome-length scaffolds. The identification of 99.7% complete BUSCO genes indicates a high assembly completeness. ConclusionsThe chromosome-level genome assembly of the lemon sole provides a high-quality reference genome for future population genomic analyses of a commercially valuable edible fish.

evolutionary biology↗

bioRxiv2024

Whole-genome re-sequencing of the Baikal seal and other phocid seals for a glimpse into their genetic diversity, demographic history, and phylogeny

BackgroundThe iconic Baikal seal (Pusa sibirica), the smallest true seal, is a freshwater seal that is endemic to Lake Baikal where it became landlocked some million years ago. It is a rather abundant species of least concern, despite the limited habitat. Until recently, research on its genetic diversity has only been done on mitochondrial genes, restriction fragment analyses, and microsatellites, before its reference genome has been published. FindingsHere we report the genome sequences of six Baikal seals, and one individual of the Caspian seal, ringed seal, and the harbor seal, re-sequenced from Illumina paired-end short read data. Heterozygosity calculations of the six newly sequenced individuals are like the previously reported genomes. In addition, the novel genome data of the other species contributed to a more complete phocid seal phylogeny based on whole-genome data. ConclusionsDespite the long isolation of the land-locked Baikal seal population, the genetic diversity of this species is in the same range as other seal species. The Baikal seal appears to form a single, diverse population. However, targeted genome studies are needed to explore the genomic diversity throughout their distribution.

evolutionary biology↗

bioRxiv2024

Calculating and interpreting FST in the genomics era

The relative genetic distance between populations is commonly measured using the fixation index (FST). Traditionally inferred from allele frequency differences, the question arises how FST can be estimated and interpreted when analysing genomic datasets with low sample sizes. Here, we advocate an elegant solution first put forward by Hudson et al. (1992): FST = (Dxy -{pi} xy)/Dxy, where Dxy and{pi} xy denote mean sequence dissimilarity between and within populations, respectively. This multi-locus FST-metric can be derived from allele frequency data, but also from sequence alignment data alone, even when sample sizes are low and/or unequal. As with other FST-metrices, the numerator denotes net divergence (Da), which is equivalent to the f2-statistic and Neis D (for realistic estimates of Dxy and{pi} xy). In terms of demographic inference, net divergence measures the difference in increase of Dxy and{pi} xy since the population split, owing to a reduction of coalescence times within populations as a result of genetic drift. Because different combinations of{Delta} Dxy and{Delta}{pi} xy can produce identical FST-estimates, no universal relationship exists between FST and population split time. Still, in case of recent population splits, when novel mutations are negligible, FST-estimates can be accurately converted into coalescent units ({tau}. i.e., split time in multiples of 2Ne). This then allows to quantify gene tree discordance, without the need for multispecies coalescent based analyses, using the formula: Pdiscordance = [2/3]{middle dot}(1 - FST). To facilitate the use of the Hudson FST-metric, we implemented new utilities in the R package SambaR.

genomics↗

bioRxiv2024

High-speed whole-genome sequencing of a Whippet: Rapid chromosome-level assembly and annotation of an extremely fast dog's genome

BackgroundThe time required for sequencing and de novo assembly of genomes is highly dependent on the interaction between laboratory work, sequencing capacity, and the bioinformatics workflow. As a result, genome projects are often not only limited by financial, computational and sequencing platform resources, but also delayed by second party sequencing service providers. By bringing together academic biodiversity institutes and a medical diagnostics company with extensive sequencing capabilities and know-how, we aimed at generating a high-quality mammalian de novo genome in the shortest possible time period. Therefore, we streamlined all processes involved and chose a very fast dog as a model: The Whippet. FindingsWe present the first chromosome-level genome assembly of the Whippet. We used PacBio long-read HiFi sequencing and reference-guided scaffolding to generate a high-quality genome assembly. The final assembly has a contig N50 of 55 Mbp and a scaffold N50 of 65.7 Mbp. The total assembly length is 2.47 Gbp, of which 2.43 Gpb were scaffolded into 39 chromosome-length scaffolds. In addition, we used available mammalian genomes and transcriptome data to annotate the genome assembly. The annotation resulted in 28,383 transcripts resembling a total of 90.9% complete BUSCO genes and identified a repeat content of 36.5%. ConclusionsSequencing, assembling, and scaffolding the chromosome-level genome of the Whippet took less than a week and adds a high-quality reference genome to the list of domestic dog breeds sequenced to date.

genomics↗

bioRxiv2023

Near chromosome-level and highly repetitive genome assembly of the snake pipefish Entelurus aequoreus (Syngnathiformes: Syngnathidae)

The snake pipefish, Entelurus aequoreus (Linnaeus, 1758), is a slender, up to 60 cm long, northern Atlantic fish that dwells in open seagrass habitats and has recently expanded its distribution range. The snake pipefish is part of the family Syngnathidae (seahorses and pipefish) that has undergone several characteristic morphological changes, such as loss of pelvic fins and elongated snout. Here, we present a highly contiguous, near chromosome-scale genome of the snake pipefish assembled as part of a university masters course. The final assembly has a length of 1.6 Gbp in 7,391 scaffolds, a scaffold and contig N50 of 62.3 Mbp and 45.0 Mbp and L50 of 12 and 14, respectively. The largest 28 scaffolds (>21 Mbp) span 89.7% of the assembly length. A BUSCO completeness score of 94.1% and a mapping rate above 98% suggest a high assembly completeness. Repetitive elements cover 74.93% of the genome, one of the highest proportions so far identified in vertebrate genomes. Demographic modeling using the PSMC framework indicates a peak in effective population size (50 - 100 kya) during the last interglacial period and suggests that the species might largely benefit from warmer water conditions, as seen today. Our updated snake pipefish assembly forms an important foundation for further analysis of the morphological and molecular changes unique to the family Syngnathidae.

genomics↗

bioRxiv2023

Genomic analysis reveals limited hybridization among three giraffe species in Kenya

BackgroundIn the speciation continuum the strength of reproductive isolation varies, and species boundaries are blurred by gene flow. Interbreeding among giraffe (Giraffa spp.) in captivity is known and anecdotal reports of natural hybrids exist. In Kenya, Nubian (G. camelopardalis camelopardalis), reticulated (G. reticulata), and Masai giraffe sensu stricto (G. tippelskirchi tippelskirchi) are parapatric, and thus the country might be a melting pot for these taxa. We analyzed 128 genomes of wild giraffe, 113 newly sequenced, representing these three taxa. ResultsWe found varying levels of Nubian ancestry in 13 reticulated giraffe sampled across the Laikipia Plateau most likely reflecting historical gene flow between these two lineages. Although comparatively weaker signs of ancestral gene flow and potential mitochondrial introgression from reticulated into Masai giraffe were also detected, estimated admixture levels between these two lineages are minimal. Importantly, contemporary gene flow between East African giraffe lineages was not statistically significant. Effective population sizes have declined since the Late Pleistocene, more severely for Nubian and reticulated giraffe. ConclusionsDespite historically hybridizing, these three giraffe lineages have maintained their overall genomic integrity suggesting effective reproductive isolation, consistent with the previous classification of giraffe into four species.

evolutionary biology↗

bioRxiv2021

Gene losses in the common vampire bat illuminate molecular adaptations to blood feeding

Feeding exclusively on blood, vampire bats represent the only obligate sanguivorous lineage among mammals. To uncover genomic changes associated with adaptations to this unique dietary specialization, we generated a new haplotype-resolved reference-quality genome of the common vampire bat (Desmodus rotundus) and screened 26 bat species for genes that were specifically lost in the vampire bat lineage. We discovered previously-unknown gene losses that relate to metabolic and physiological changes, such as reduced insulin secretion (FFAR1, SLC30A8), limited glycogen stores (PPP1R3E), and a distinct gastric physiology (CTSE). Other gene losses likely reflect the biased nutrient composition (ERN2, CTRL) and distinct pathogen diversity of blood (RNASE7). Interestingly, the loss of REP15 likely helped vampire bats to adapt to high dietary iron levels by enhancing iron excretion and the loss of the 24S-hydroxycholesterol metabolizing enzyme CYP39A1 could contribute to their exceptional cognitive abilities. Finally, losses of key cone phototransduction genes (PDE6H, PDE6C) suggest that these strictly-nocturnal bats completely lack cone-based vision. These findings enhance our understanding of vampire bat biology and the genomic underpinnings of adaptations to sanguivory.

evolutionary biology↗

bioRxiv2020

Chromosome-level genome assembly of a benthic associated Syngnathiformes species: the common dragonet, Callionymus lyra

BackgroundThe common dragonet, Callionymus lyra, is one of three Callionymus species inhabiting the North Sea. All three species show strong sexual dimorphism. The males show strong morphological differentiation, e.g., species-specific colouration and size relations, while the females of different species have few distinguishing characters. Callionymus belongs to the benthic associated clade of the order Syngnathiformes. The benthic associated clade so far is not represented by genome data and serves as an important outgroup to understand the morphological transformation in long-snouted syngnatiforms such as seahorses and pipefishes. FindingsHere, we present the chromosome-level genome assembly of C. lyra. We applied Oxford Nanopore Technologies long-read sequencing, short-read DNBseq, and proximity-ligation-based scaffolding to generate a high-quality genome assembly. The resulting assembly has a contig N50 of 2.2 Mbp, a scaffold N50 of 26.7 Mbp. The total assembly length is 568.7 Mbp, of which over 538 Mbp were scaffolded into 19 chromosome-length scaffolds. The identification of 94.5% of complete BUSCO genes indicates high assembly completeness. Additionally, we sequenced and assembled a multi-tissue transcriptome with a total length of 255.5 Mbp that was used to aid the annotation of the genome assembly. The annotation resulted in 19,849 annotated transcripts and identified a repeat content of 27.66%. ConclusionsThe chromosome-level assembly of C. lyra provides a high-quality reference genome for future population genomic, phylogenomic, and phylogeographic analyses.

genomics↗

bioRxiv2020

Biodiversity genomics of small metazoans: high quality de novo genomes from single specimens of field-collected and ethanol-preserved springtails

Genome sequencing of all known eukaryotes on Earth promises unprecedented advances in evolutionary sciences, ecology, systematics and in biodiversity-related applied fields such as environmental management and natural product research. Advances in DNA sequencing technologies make genome sequencing feasible for many non-genetic model species. However, genome sequencing today relies on large quantities of high quality, high molecular weight (HMW) DNA which is mostly obtained from fresh tissues. This is problematic for biodiversity genomics of Metazoa as most species are small and yield minute amounts of DNA. Furthermore, briging living specimens to the lab bench not realistic for the majority of species. Here we overcome those difficulties by sequencing two species of springtails (Collembola) from single specimens preserved in ethanol. We used a newly developed, genome-wide amplification-based protocol to generate PacBio libraries for HiFi long-read sequencing. The assembled genomes were highly continuous. They can be considered complete as we recovered over 95% of BUSCOs. Genome-wide amplification does not seem to bias genome recovery. Presence of almost complete copies of the mitochondrial genome in the nuclear genome were pitfalls for automatic assemblers. The genomes fit well into an existing phylogeny of springtails. A neotype is designated for one of the species, blending genome sequencing and creation of taxonomic references. Our study shows that it is possible to obtain high quality genomes from small, field-preserved sub-millimeter metazoans, thus making their vast diversity accessible to the fields of genomics.

genomics↗

bioRxiv2020

SambaR: an R package for fast, easy and reproducible population-genetic analyses of biallelic SNP datasets

BackgroundSNP datasets can be used to infer a wealth of information about natural populations, including information about their structure, genetic diversity, and the presence of loci under selection. However, SNP data analysis can be a time-consuming and challenging process, not in the least because at present many different software packages are needed to execute and depict the wide variety of mainstream population-genetic analyses. Here we present SambaR, an integrative and user-friendly R package which automates and simplifies quality control and population-genetic analyses of biallelic SNP datasets. SambaR allows users to perform mainstream population-genetic analyses and to generate a wide variety of ready to publish graphs with a minimum number of commands (less than ten). These wrapper commands call functions of existing packages (including adegenet, ape, LEA, poppr, pcadapt and StAMPP) as well as new tools uniquely implemented in SambaR. ResultsWe tested SambaR on online available SNP datasets and found that SambaR can process datasets of millions of SNPs and hundreds of individuals within hours, given sufficient computing power. Newly developed tools implemented in SambaR facilitate optimization of filter settings, objective interpretation of ordination analyses, enhance comparability of diversity estimates from reduced representation library SNP datasets, and generate reduced SNP panels and structure-like plots with Bayesian population assignment probabilities. ConclusionSambaR facilitates rapid population genetic analyses on biallelic SNP datasets by removing three major time sinks: file handling, software learning, and data plotting. In addition, SambaR provides a convenient platform for SNP data storage and management, as well as several new utilities, including guidance in setting appropriate data filters. Availability and implementationThe SambaR source script, manual and example datasets are distributed through GitHub: https://github.com/mennodejong1986/SambaR

genetics↗

bioRxiv2020

Improving the chromosome-level genome assembly of the Siamese fighting fish (Betta splendens) in a university Master's course.

BackgroundEver decreasing costs along with advances in sequencing and library preparation technologies enable even small research groups to generate chromosome-level assemblies today. Here we report the generation of an improved chromosome-level assembly for the Siamese fighting fish (Betta splendens) that was carried out during a practical university Masters course. The Siamese fighting fish is a popular aquarium fish and an emerging model species for research on aggressive behaviour. We updated the current genome assembly by generating a new long-read nanopore-based assembly with subsequent scaffolding to chromosome-level using previously published HiC data. FindingsThe use of nanopore-based long-read data sequenced on a MinION platform (Oxford Nanopore Technologies) allowed us to generate a baseline assembly of only 1,276 contigs with a contig N50 of 2.1 Mbp, and a total length of 441 Mbp. Scaffolding using previously published HiC data resulted in 109 scaffolds with a scaffold N50 of 20.7 Mbp. More than 99% of the assembly is comprised in 21 scaffolds. The assembly showed the presence of 95.8% complete BUSCO genes from the Actinopterygii dataset indicating a high quality of the assembly. ConclusionWe present an improved full chromosome-level assembly of the Siamese fighting fish generated during a university Masters course. The use of ~35x long-read nanopore data drastically improved the baseline assembly in terms of continuity. We show that relatively in-expensive high-throughput sequencing technologies such as the long-read MinION sequencing platform can be used in educational settings allowing the students to gain practical skills in modern genomics and generate high quality results that benefit downstream research projects.

evolutionary biology↗

bioRxiv2018

Limited Introgression Supports Division of Giraffe into Four Species

All giraffe (Giraffa) were previously assigned to a single species (G. Camelopardalis) and nine subspecies. However, multi-locus analyses of all subspecies have shown that there are four genetically distinct clades and suggest four giraffe species. This conclusion might not be fully accepted due to limited data and lack of explicit gene flow analyses. Here we present an extended study based on 21 independent nuclear loci from 137 individuals. Explicit gene flow analyses identify less than one migrant per generation, including between the closely related northern and reticulated giraffe. Thus, gene flow analyses and population genetics of the extended dataset confirm four genetically distinct giraffe clades and support four independent giraffe species. The new findings call for a revision of the IUCN classification of giraffe taxonomy. Three of the four species are threatened with extinction, mostly occurring in politically unstable regions, and as such, require the highest conservation support possible.

ecology↗

bioRxiv2018

DeepQSM - Using Deep Learning to Solve the Dipole Inversion for MRI Susceptibility Mapping

Quantitative susceptibility mapping (QSM) aims to extract the magnetic susceptibility of tissue from magnetic resonance imaging (MRI) phase measurements. The mapping of magnetic susceptibility in vivo has gained broad interest in several fields of science and medicine because it yields relevant information on biological tissue properties, predominantly myelin, iron and calcium. Thereby, QSM can also reveal pathological changes of these key components in devastating diseases such as Parkinsons disease, Multiple Sclerosis, or hepatic iron overload. As QSM requires the solution of an ill-posed field-to-source-inversion, current techniques utilize manual optimization of regularization parameters to balance between smoothing, artifacts and quantification accuracy. We trained a fully convolutional deep neural network - DeepQSM - to invert the magnetic dipole kernel convolution. This network is capable of solving the ill-posed field-to-source inversion on real-world in vivo MRI phase data without the need for manual parameter tuning, which proves that this network has generalized the underlying mathematical principle of the dipole inversion. We demonstrate that DeepQSMs susceptibility maps enable identification of deep brain substructures that are not visible in MRI phase data and provide information on their respective magnetic tissue properties. We illustrate DeepQSMs clinical relevance in a patient with multiple sclerosis showing its sensitivity to white matter lesions. In summary, DeepQSM can be used to determine the composition of myelin sheets of nerve fibers in the brain, and to assess quantitative information on iron homeostasis and its dysregulation, and will subsequently contribute to a better understanding of these biological processes in health and disease.

neuroscience↗

bioRxiv2017

Building a high-resolution in vivo minimum deformation average model of the human hippocampus

ObjectiveMinimum deformation averaging (MDA) procedures exploit the information contained in inter-individual variations to generate high-resolution, high-contrast models through iterative model building. However, MDA models built from different image contrasts reside in disparate spaces and their complementary information cannot be utilized easily. The aim of this work was to develop an algorithm for the non-linear alignment of two MDA models with different contrasts to create a high-resolution in vivo model of the human hippocampus with a spatial resolution of 300 m.\n\nMethodsA Turbo Spin Echo MDA model covering the hippocampus was contrast matched to a whole-brain MP2RAGE MDA model and aligned using cross-correlation and non-linear transformation. The contrast matching algorithm followed a global voxel location-based approach to estimate the relationship between intensity values of the two models. The performance of the algorithm was evaluated by comparing it to a non-linear registration obtained using mutual information without contrast matching. The complimentary information from both contrasts was then utilized in an automated hippocampal subfield segmentation pipeline.\n\nResultsThe contrast of the Turbo Spin Echo MDA model could successfully be matched to the MP2RAGE MDA model. Registration using cross correlation provided more accurate alignment of the models compared to a mutual information based approach. The segmentation using ASHS resulted in hippocampal subfield delineations that resembled the tissue boundaries observed in the Turbo Spin Echo MDA model.\n\nConclusionThe developed contrast matching algorithm facilitated the creation of a high-resolution multi-modal in vivo MDA model of the human hippocampus. This model can be used to improve algorithms for hippocampal subfield segmentation and could potentially support the early detection of neurodegenerative diseases.

neuroscience↗

bioRxiv2017

Phylogenetic Conflict In Bears Identified By Automated Discovery Of Transposable Element Insertions In Low Coverage Genomes

Compared to sequence analyses, phylogenetic reconstruction from transposable elements (TEs) offers an additional perspective to study evolutionary processes. However, detecting phylogenetically informative TE insertions requires tedious experimental work, limiting the power of phylogenetic inference. Here, we analyzed the genomes of seven bear species using high throughput sequencing data to detect thousands of TE insertions. The newly developed pipeline for TE detection called TeddyPi (TE detection and discovery for Phylogenetic Inference) obtained 150,513 high-quality TE insertions in the genomes of ursine and tremarctine bears. By integrating different TE insertion callers and using a stringent filtering approach, the TeddyPi pipeline produced highly reliable TE insertion calls, which were confirmed by extensive in vitro validation experiments. Screening for single nucleotide substitutions in the flanking regions of the TEs show that these substitutions correlate with the phylogenetic signal from the TE insertions. Our phylogenomic analyses show that TEs are a major driver of genomic variation in bears and enabled phylogenetic reconstruction of a well-resolved species tree, even with strong signals for incomplete lineage sorting and introgression. The analyses show that the Asiatic black, sun and sloth bear form a monophyletic clade. TeddyPi is open source and can be adapted to various TE and structural variation callers. The pipeline makes it easy to confidently extract thousands of TE insertions even from low coverage genomes of non-model organisms, opening new possibilities for biologists to study phylogenies, evolutionary processes as well as rates and patterns of (retro-)transposition and structural variation.

evolutionary biology↗

bioRxiv2016

Screening for the ancient polar bear mitochondrial genome reveals low integration of mitochondrial pseudogenes (numts) in bears

Phylogenetic analyses of nuclear and mitochondrial genomes have shown that polar bears captured the mitochondrial genome of brown bears some 160,00 years ago. This hybridization event likely led to an extinction of the original polar bear mitochondrial genome. However, parts of the mitochondrial DNA occasionally integrates into the nuclear genome, forming pseudogenes called numts (nuclear mitochondrial integrations). Screening the polar bear genome for numts, we identified only 13 such integrations. Analyses of whole-genome sequences from additional polar bears, brown and American black bears as well as the giant panda indicates that the discovered numts entered the bear lineage before the initial ursid radiation some 14 million years ago. Our findings suggests a low integration rate of numts in the bear lineage and a complete loss of the original polar bear mitochondrial genome.

evolutionary biology↗